Neurosurgical forum Letters to the editor
Calcified meningiomas To The Editor: We read with great interest the article by Dr. Zhu and colleagues5 (Zhu Q, Qian M, Xiao J, et al: Myelopathy due to calcified meningiomas of the thoracic spine: minimum 3-year follow-up after surgical treatment. Clinical article. J Neurosurg Spine 18:436–442, May 2013). The authors reported on a series of 11 patients who had calcified meningiomas in the thoracic spine, 3 of whom had poor neurological outcomes. They concluded that calcified meningiomas had poorer surgical outcomes than noncalcified ones.5 The authors are commended for sharing their experience with the worldwide readership of the Journal of Neurosurgery. However, we respectfully point out that these calcified meningiomas are not necessarily hard in texture. Spinal meningiomas can have a soft consistency despite calcification, as demonstrated by CT. It was not clear what percentage of the calcified meningiomas in Dr. Zhu’s series was actually ossified. A recent patient of ours had a calcified spinal meningioma in T-5, as demonstrated on preoperative CT, causing severe cord compression (Fig. 1). The tumor was expected to be as hard as bone because it had a CT density similar to that of the neighboring vertebral body and lamina. Surprisingly, during the operation, we found that the tumor was very soft and could be removed using suction and microscissors (Fig. 2). The patient’s neurological function improved rapidly after surgery. Ossified spinal meningiomas are reported even more rarely than calcified spinal meningiomas.2 Occasional misuse of these two terms happens because the differences between them are seldom described in the literature. The term “calcified meningioma” is more of a radiographic description than a histopathological diagnosis. As in our case, most of these meningiomas with calcification on preoperative CTs are the psammomatous type according to histopathological studies (Fig. 3).3,4 The radiopaque calcification on the CT is probably attributable to the confluence of numerous densely packed psammoma bodies.1 On the other hand, “ossified meningioma” refers to a tumor with bony texture that is difficult to resect intraoperatively. However, both calcified and ossified meningiomas are not formal pathological nomenclature. For a pathological diagnosis, there is a metaplastic meningioma that has true lamellar bone formation (Fig. 4).1 This metaplastic lamellar bone can account for the stone-like texture of the ossified meningiomas. A calcified meningioma has no lamellar bone microscopically and is therefore actually gritty rather than stone-like in texture. This article contains some figures that are displayed in color online but in black-and-white in the print edition.
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Fig. 1. Preoperative sagittal (left) and axial (right) CT scans of the thoracic spine, demonstrating a high-density mass occupying the spinal canal. Both images revealed calcification of the tumor.
Fig. 2. Intraoperative pictures of a tumor, which was very soft and easy to remove piecemeal.
Fig. 3. Photomicrograph obtained in our patient, demonstrating a meningioma with abundant psammoma bodies, which could be accounted for by the calcification seen preoperatively. H & E, original magnification ×200.
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Neurosurgical forum 4. Solero CL, Fornari M, Giombini S, Lasio G, Oliveri G, Cimino C, et al: Spinal meningiomas: review of 174 operated cases. Neurosurgery 25:153–160, 1989 5. Zhu Q, Qian M, Xiao J, Wu Z, Wang Y, Zhang J: Myelopathy due to calcified meningiomas of the thoracic spine: minimum 3-year follow-up after surgical treatment. Clinical article. J Neurosurg Spine 18:436–442, 2013
Fig. 4. Photomicrograph demonstrating the pathology of an ossified meningioma surgically treated at our institute. There were true lamellar bone formations between the meningioma tumor tissues rich in psammoma bodies. The pathological diagnosis of this ossified tumor was metaplastic meningioma. H & E, original magnification ×40.
Outcomes following resection of a thoracic spinal meningioma are likely associated with the tumor’s location and texture. A ventrally located ossified meningioma is associated with the highest risk. A preoperative CT is helpful in detecting calcification in the tumor. However, the high density found on CT does not necessarily indicate a stone-like texture. Although the calcification can be soft intraoperatively, surgeons must always be cautious and prepared for a stone-like ossified meningioma when high density is seen preoperatively.
Hsuan-Kan Chang, M.D.1,2 Jau-Ching Wu, M.D., Ph.D.1–3 Diego Shih-Chieh Lin, M.D.4 Chih-Chang Chang, M.D.1,2 Tsung-Hsi Tu, M.D.1,2 Wen-Cheng Huang, M.D., Ph.D.1,2 Henrich Cheng, M.D., Ph.D.1–3 1 Neurological Institute Taipei Veterans General Hospital 2 School of Medicine National Yang-Ming University 3 Institute of Pharmacology National Yang-Ming University 4 Department of Pathology and Laboratory Medicine Taipei Veterans General Hospital Taipei, Taiwan
Response: First of all, we thank Dr. Wu for his interest in our article. We appreciate his comments. He showed us a perfect surgery for calcified meningioma. Different types of calcified meningiomas were discussed in his letter. To our knowledge, there are three types of calcified meningiomas: psammomatous, lamellar calcification, and total calcification.3 The psammomatous type is the most common of the three. In our opinion, the reason for the poorer outcome in calcified meningiomas, as compared with the noncalcified ones, is their hard texture and the adhesion with surrounding tissue (nerve and dura mater). On the other hand, location (ventral or dorsal tumor) is another important factor contributing to the prognosis of all types of meningiomas. For the patient mentioned by Dr. Wu, we found that a soft dorsal tumor without adhesion could be removed totally. And the patient’s neurological function improved rapidly after the surgery. Similar cases can be found at our institute. A 57-year-old woman had suffered weakness in both lower limbs for 5 months. A dorsal tumor was found in the thoracic spinal canal (Fig. 1). The tumor was removed totally, and the patient’s neurological function improved rapidly after the surgery. Unfortunately, not all of the tumors in our series were soft dorsal tumors without adhesion. For example, a 69-yearold woman in our series had suffered weakness in both lower limbs for 6 months. A ventral tumor was found in her thoracic spinal canal (Fig. 2). To remove a ventral tumor, piecemeal removal is often performed. During surgery, we often cut the denticulate ligament to release the spinal cord. After that, we have more space to remove the ventral tumor. Cerebrospinal fluid leakage and a transient
Disclosure The authors report no conflict of interest. References 1. Licci S, Limiti MR, Callovini GM, Bolognini A, Gammone V, Di Stefano D: Ossified spinal tumour in a 58-year-old wom an with increasing paraparesis. Neuropathology 30:194–196, 2010 2. Naderi S, Yilmaz M, Canda T, Acar U: Ossified thoracic spinal meningioma in childhood: a case report and review of the literature. Clin Neurol Neurosurg 103:247–249, 2001 3. Roux FX, Nataf F, Pinaudeau M, Borne G, Devaux B, Meder JF: Intraspinal meningiomas: review of 54 cases with discussion of poor prognosis factors and modern therapeutic management. Surg Neurol 46:458–464, 1996
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Fig. 1. A 57-year-old woman with a T4–5 calcified meningioma. A dorsal tumor was found on a sagittal MR image (A). An axial CT scan from CT 2D reconstruction (B) showing the mass was totally calcified. Photograph (C) of the removed tumor. Intraoperative photograph (D) of the tumor, which was very soft and easy to remove totally.
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Neurosurgical forum 3. Zhang J, Wang Z, Yu T: [Microsurgery for calcified spinal meningiomas (report of 24 cases).] Chin J Clin Neurosurg 17:460–462, 2012 (Chinese) Please include this information when citing this paper: published online November 1, 2013; DOI: 10.3171/2013.6.SPINE13512. ©AANS, 2014
Transpsoas approach
Fig. 2. A 69-year-old woman with a T-2 calcified meningioma. A ventral tumor was found on a sagittal MR image (A). An axial MR image (B) showing the same mass. The tumor was removed piecemeal (C).
deficit are most likely to occur in dorsal tumor cases. The psammomatous type of tumor can be removed piecemeal. But the total calcification type of tumor should sometimes be removed piecemeal to protect the spinal cord. In our case series, calcified meningiomas were pathologically diagnosed in all of the patients, or the tumor could not be confirmed as ossified meningiomas because the diagnosis of ossified meningioma is confirmed by observing bone trabecula. Ossified meningiomas were also diagnosed in some patients, who will be discussed in another case series in the future. In their report of 97 spinal meningiomas, Levy et al.1 found only 4 cases of calcification. Three of these 4 patients had a “disastrous surgical outcome.” Roux et al.2 reported on 3 ossified meningiomas among 54 spinal meningiomas, with an even worse outcome. In our series, the surgical outcome was much better. In conclusion, we believe that the preoperative diagnosis, location, and pathological type of calcified meningioma are important to patient outcome.
Qing Zhu, M.D. Jianru Xiao, M.D. Ming Qian, M.D. Zhipeng Wu, M.D. Spinal Tumor Center Shanghai Changzheng Hospital Second Military Medical University Lifei Wang, M.P.H. School of Public Health Fudan University Shanghai, China
References 1. Levy WJ Jr, Bay J, Dohn D: Spinal cord meningioma. J Neurosurg 57:804–812, 1982 2. Roux FX, Nataf F, Pinaudeau M, Borne O, Devaux B, Meder JF: Intraspinl meningiomas: review of 54 cases with discussion of poor prognosis factors and modern therapeutic management. Surg Neurol 46:458–464, 1996
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To The Editor: We read the article by Cahill and coauthors1 with interest (Cahill KS, Martinez JL, Wang MY, et al: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17:227–231, September 2012), but we have some points regarding the analysis and conclusions drawn by the article. In particular, 2 cases of femoral nerve injury with attendant quadriceps injury were reported upon. A rate of 4.8% quadriceps palsy was noted with lateral transpsoas approaches to the L4–5 level. The authors state that the injuries occurred “during dilation of the psoas muscle for the approach to the L4–5 disc space.” However, we are not certain how this conclusion can be drawn. First, the methods state that a posterior interbody procedure (transforaminal lumbar interbody fusion [TLIF] or posterior lumbar interbody fusion [PLIF]) would be performed in such cases, but it is not discussed in the actual case description. For both patients, what was done at L4– 5, a TLIF? Was the patient examined prior to performing the other procedure(s)? Is it possible that the TLIF caused an L-4 palsy? Generally, after new a neurological injury it is reasonable to obtain images in the patient to determine the cause. Was imaging performed? A critical analysis of the MRI sequences can show tracts through the psoas that lead to the L4–5 foramen, which could explain the palsy on the basis of technical error. Second, was the attending surgeon performing the procedure, or was the resident/fellow operating in these cases? Third, one case was a multilevel (L2–5) procedure. It is possible that the L3–4 transpsoas surgery caused an L-3 palsy and not the attempted L4–5 approach. Was a postoperative electromyography (EMG)/nerve conduction study performed at 6–12 weeks postoperatively to characterize the neural injury? In addition to the questions posed above, critical analysis of preoperative radiographs and MRI studies can reveal details that would have contributed to intraoperative difficulty. Transitional lumbosacral anatomy (hemisacralization of the sacrum, L-6 vertebrae, and so on) has been shown to be a risk factor for unsuccessful treatment of L4–5 performed using the transpsoas approach.4 Additionally, we disagree with the statement “In this retrospective analysis, we estimated that the overall rate of femoral nerve injury for the … L4–5 level was 4.8%....” Of the palsies, one surgery was a multilevel procedure (L2–5) with an aborted L4–5 and one was an aborted single-level L4–5. Of the successful L4–5 levels, the authors reported no femoral nerve palsies. It is very possible that the mul119
Neurosurgical forum tilevel (L2–5) case with a quadriceps palsy resulted from the L3–4 surgery due to L-3 neural injury. We would urge the authors to reconsider their published rate of palsies. One could consider the rate to be 1 of 41 L4–5 single-level procedures, or 2% in your series. Further clouding the conclusions that one can draw from the paper are omitted details such as: what neuromuscular agent was given for anesthesia? And at what time after induction was the approach to L4–5 made? If rocuronium was used, it is quite possible that residual agent could lead to fatigue and/or unreliable readings during neural injury. Houten et al.2 reported quadriceps palsy after transpsoas surgery without EMG changes. Perhaps further investigation of induction agents and neural agents after transpsoas surgery is indicated. In our center we always insist on the use of succinylcholine when performing transpsoas surgery. Additionally, what neuromonitoring system was used? Did the authors use directional nerveseeking probes when approaching L4–5? Directional neuromonitoring has been shown to decrease the rate of complications associated with the lateral transpsoas approach.5 Finally, in the discussion portion of the paper the authors point out that “the [femoral nerve] trunk [is] found in the center of the disc space in 15% of specimens in one cadaveric study.” This datum is used to support the assertion that one can “minimize this complication [femoral nerve palsies] through judicious use of the minimally invasive lateral fusion procedure at the L4–5 level….” We found that the nerves within the psoas move with limb range of motion in a recent study.3 They are lightly tethered within the psoas and the act of dissection moves the nerves significantly. Thus, the location of the neural elements after psoas dissection is probably even more variable. It is important to note that one may retract nerves in peripheral nerve surgery and in PLIF. Is there some inherent physiological difference between the nerves inside the canal and within the psoas that does not allow retraction during transpsoas surgery? Gentle, judicious dissection within the psoas with nerve mobilization if necessary, patient selection (avoid transitional lumbar anatomy), and directional neuromonitoring can probably avoid nerve palsy when treating L4–5 via the transpsoas approach. Joseph R. O’Brien, M.D., M.P.H. George Washington University Medical Center Washington, DC William D. Smith, M.D. University Medical Center Las Vegas, NV Disclosure Dr. O’Brien reports direct stock ownership in Spinicity and ownership in Stryker, and he is a consultant for Globus and NuVa sive. Dr. Smith reports no conflict of interest. References 1. Cahill KS, Martinez JL, Wang MY, Vanni S, Levi AD: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17: 227–231, 2012 2. Houten JK, Alexandre LC, Nasser RA, Wollowick AL: Nerve
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injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:280–284, 2011 3. O’Brien J, Haines C, Dooley Z, Turner AL, Jackson D: Femoral nerve strain at L4-5 is minimized by hip flexion and increased by table break when performing lateral interbody fusion. Spine (Phila Pa 1976) [epub ahead of print], 2013 4. Smith WD, Youssef JA, Christian G, Serrano S, Hyde JA: Lumbarized sacrum as a relative contraindication for lateral transpsoas interbody fusion at L5-6. J Spinal Disord Tech 25:285–291, 2012 5. Uribe JS, Vale FL, Dakwar E: Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine (Phila Pa 1976) 35 (26 Suppl):S368–S374, 2010
Response: We thank the authors for raising several important points regarding our case series and results with the lateral interbody fusion procedure. Our group previously reviewed objective, patient-driven data, which demonstrated that the incidence of lumbosacral plexus sensory symptoms following the minimally invasive lateral approach was likely to be underreported.2 In this article we defined the incidence of postoperative abdominal flank bulge (4%), which appeared to be more common with approaches to upper lumbar vertebrae. We also report a higher incidence (4%) of femoral nerve injury with procedures that included the L4–5 level. This finding is entirely consistent with prior case reports and, more importantly, with the reported neuroanatomical location of the subcostal nerve within the abdominal muscle layers and the femoral nerve within the psoas muscle.1–5 We agree that there are numerous ways to injure a nerve during spine surgery. We considered all of the possible alternative explanations suggested by the authors for quadriceps weakness—including but not limited to TLIFrelated nerve injury, foraminal nerve injury via the lateral approach, injury to the femoral nerve from the lateral approach at a level other than L4–5, and transitional lumbosacral anatomy. We would like to reinforce the important finding that intraoperative real-time EMG monitoring indicated that the femoral nerve was activated during the transpsoas approach at the L4–5 level. In our multiplesurgeon series of lateral interbody fusions we have only had femoral nerve injury when the procedure involved the L4–5 level and when associated with positive activation. We would also like to address several of the other issues raised by the authors. At our institution the attending surgeon is present, responsible, and intimately involved for the duration of the procedure. Fluoroscopy and directional EMG probes are routinely used. We did not have postoperative MRI studies available for review, but the postoperative CT scan suggested the appropriate trajectory toward the midpoint of the disc space. We rely heavily on fluoroscopy to achieve this goal. In our institutional experience we have not seen an L-4 palsy at the level of the nerve root or dorsal root ganglion during an L3–4 or L4–5 PLIF procedure that resulted in significant quadriceps weakness. The femoral nerve is created primarily by contributions from the L-2, L-3, and L-4 roots, and it requires a more distal injury—such as the femoral nerve itself—to impact motor function to the extent seen in these cases. Regarding mobilization of the nerve, we would definitely agree that a technique that involves shallow docking of J Neurosurg: Spine / Volume 20 / January 2014
Neurosurgical forum the retractor and direct visualization and manipulation of the femoral nerve can be safely performed. Although not discussed in the manuscript, a shallow docking approach has been adopted as a technique when the neuromonitoring indicates that a safe corridor through the muscle is not present due to the anterior location of the femoral nerve. We do appreciate the feedback but believe that our interpretation of the results is the simplest, most realistic, and consistent with prior literature on femoral nerve injuries. Kevin S. Cahill, M.D., Ph.D., M.P.H. Joseph L. Martinez, M.D. Steven Vanni, D.O. Michael Y. Wang, M.D. Allan D. Levi, M.D., Ph.D. University of Miami Miller School of Medicine Miami, FL References 1. Benglis DM, Vanni S, Levi AD: An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. Laboratory investigation. J Neurosurg Spine 10:139–144, 2009 2. Cummock M, Vanni S, Levi AD, Yu Y, Wang MY: An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Clinical article. J Neurosurg Spine 15:11–18, 2011 3. Davis TT, Bae HW, Mok JM, Rasouli A, Delamarter RB: Lumbar plexus anatomy within the psoas muscle: implications for the transpsoas lateral approach to the L4-L5 disc. J Bone Joint Surg Am 93:1482–1487, 2011 4. Houten JK, Alexandre LC, Nasser R, Wollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:280–284, 2011 5. Uribe JS, Arredondo N, Dakwar E, Vale FL: Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. Laboratory investigation. J Neurosurg Spine 13:260–266, 2010 Please include this information when citing this paper: published online November 1, 2013; DOI: 10.3171/2012.11.SPINE12849. ©AANS, 2014
Reduction of atlantoaxial subluxation To The Editor: We read with great interest the article by Dr. Suh and colleagues7 (Suh BG, Padua MRA, Riew KD, et al: A new technique for reduction of atlantoaxial subluxation using a simple tool during posterior segmental screw fixation. Clinical article. J Neurosurg Spine 19:160–166, August 2013). They introduced a novel technique using a T-shaped rod tool to facilitate reduction after the placement of screws in C-1 and C-2. We found their surgical pearl of substantial value in practical use. However, a few questions need answering before the audience can safely apply the innovation. How was the reducibility determined preoperatively? Is there any caveat that the slipped atlantoaxial complex cannot be successfully reduced? As the authors describe in the introduction, any attempt at reduction might not always be easy. Solid purchase of each screw, including C-1 lateral mass screws and C-2 pedicle screws, is fundamental.4 The polyaxial screw head allows easy connection of the construct but might limit the power of reduction. Positioning the patient with a Mayfield head holder allows less manipulation of the atlantoaxial complex. Maintenance of a successfully reduced atlantoaxial subluxation might also be difficult.5 In some extreme cases, the highly mobile atlantoaxial complex requires a tremendous force of fixation to overcome the instability. Failure of fixation could happen within weeks after successful instrumentation and wiring (Fig. 1). Moreover, extension of the fixation construct to the occipital skull may raise the complication rate.6 What are the salvage strategies when there is pseudarthrosis and recurrence of subluxation? Reduction and fixation of the atlantoaxial complex is always challenging.1–3,8 Although the authors demonstrated a useful tool, each individual case requires a tailor-made preoperative plan and cautious execution when reduction is attempted. Peng-Yuan Chang, M.D. Jau-Ching Wu, M.D., Ph.D. Wen-Cheng Huang, M.D., Ph.D.
Fig. 1. A: Preoperative MR image. B: Three days postoperative radiograph demonstrating successful reduction of atlantoaxial subluxation. Fixation was made by C-1 lateral mass screws, C-2 pedicle screw, C-2 laminar screw, and wiring with autologous iliac bone graft. C: Six weeks postoperative radiograph demonstrating loss of reduction.
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Neurosurgical forum Tsung-Hsi Tu, M.D. Henrich Cheng, M.D., Ph.D. Neurological Institute Taipei Veterans General Hospital Taipei, Taiwan School of Medicine National Yang-Ming University Taipei, Taiwan Disclosure The authors report no conflict of interest. References 1. Goel A: Editorial. Occipitocervical fixation: is it necessary? J Neurosurg Spine 13:1–2, 2010 2. Goel A, Shah A: Atlantoaxial facet locking: treatment by facet manipulation and fixation. Experience in 14 cases. Technical note. J Neurosurg Spine 14:3–9, 2011 3. Goel A, Shah A, Gupta SR: Craniovertebral instability due to degenerative osteoarthritis of the atlantoaxial joints: analysis of the management of 108 cases. Clinical article. J Neurosurg Spine 12:592–601, 2010 4. Hamilton DK, Smith JS, Sansur CA, Dumont AS, Shaffrey CI: C-2 neurectomy during atlantoaxial instrumented fusion in the elderly: patient satisfaction and surgical outcome. Clinical article. J Neurosurg Spine 15:3–8, 2011 5. Hood B, Hamilton DK, Smith JS, Dididze M, Shaffrey C, Levi AD: The use of allograft and recombinant human bone morphogenetic protein for instrumented atlantoaxial fusions. World Neurosurg [epub ahead of print], 2013 6. Mummaneni PV, Lu DC, Dhall SS, Mummaneni VP, Chou D: C1 lateral mass fixation: a comparison of constructs. Neurosurgery 66 (3 Suppl):153–160, 2010 7. Suh BG, Padua MRA, Riew KD, Kim HJ, Chang BS, Lee CK, et al: A new technique for reduction of atlantoaxial subluxation using a simple tool during posterior segmental screw fixation. Clinical article. J Neurosurg Spine 19:160–166, 2013 8. Wu JC, Tu TH, Mummaneni PV: Techniques of atlantoaxial fixation and the resection of C2 nerve root. World Neurosurg 78:603–604, 2012
Response: We thank Dr. Chang and colleagues for their interest in our paper and valuable comments. Reducibility can be determined preoperatively by using dynamic radiographs in many cases. If atlantoaxial subluxation seems to be irreducible on dynamic radiographs, we choose preoperative traction using Gardner-Wells tongs for fewer than 2 days. If at least partial reduction is demonstrated on traction lateral radiographs, we proceed with posterior surgery alone, because a greater reduction force can be applied with the reduction tools during surgery. In addition, intraoperative traction, release of the posterior soft tissues by capsulotomy (Fig. 5. in the original article), and intraoperative facet distraction will facilitate the reduction maneuver. Preoperative traction is helpful not only to confirm reducibility but also to stretch out the anterior soft tissue contracture, which normally cannot be resected during posterior surgery. Using our reduction tools is only a part of these combined reduction techniques. We do not utilize all of these procedures in simple cases, but neither do we use our tools alone in the challenging ones. We have not experienced a truly irreducible case without any evidence of even partial reduction during pre122
operative traction among several hundred surgical cases thus far. However, we think that a very small number of cases with extremely severe anterior tilt of the atlantoaxial facet joints caused by an old neglected congenital or early childhood–onset subluxation/dislocation along with extremely severe contracture of the anterior soft tissues may not show reducibility even with preoperative traction. In addition, if the patient has concomitant osteoporosis, excessive reduction force may lead to failure of the weak bone. In these cases, anterior release may be needed before posterior screw fixation.2 We agree that solid purchase of the screws is essential in barely reducible cases. In cases requiring excessive reduction force and/or with severe osteoporosis, we try our best to insert pedicle screws into C-2 rather than laminar screws and to insert C-1 lateral mass screws via the posterior arch rather than under the arch, to obtain greater fixation. In addition, we opt for bicortical purchase while taking care to avoid injury to the internal carotid arteries.1 We also consider using a transverse connector to improve pullout strength and rotational stability in selected cases. We agree that the polyaxial screw head might limit the power of reduction if conventional instruments are used. However, our tools make use of the advantages of polyaxial screw heads. As shown in Fig. 2 in the original article, the screw heads have to be polyaxial to allow for controlled manipulation using our tools. For example, the C-2 screw head is tilted cranially before reduction but will be less cranially tilted or even caudally tilted after reduction (Figs. 2 and 3 in the original article). We agree that a Mayfield head holder allows less manipulation of the atlantoaxial complex, particularly if multilevel fusion is to be done. While successful reduction can be easily achieved even with a Mayfield head holder in easy cases, we prefer to use Gardner-Wells tongs, particularly for challenging cases, since it allows for effective intraoperative traction, easier preparation of intraarticular fusion of the facet joints, and easier manipulation of the atlantoaxial complex. Note, however, that Gardner-Wells tongs may permit unwanted axial rotation of the patient’s head and neck during screw insertion. This may result in a decrease in the effective medial angulation of the screw trajectory, leading to violation of the C-1 vertebral artery foramen or C-2 vertebral artery groove.3 For better maintenance of reduction in selected cases, including for pseudarthrosis revision, we choose thicker (4.0 mm) screws, if feasible, bicortical fixation, and techniques described above. When the use of 2 pedicle screws is not feasible at C-2, we insert 3 or 4 screws at C-2 and/ or use a transverse connector. In addition, we always do intraarticular fusion of the facet joints as well as posterior fusion in these cases. We agree that each case requires a tailor-made preoperative plan and cautious execution when reduction is attempted. We appreciate your valuable comments. Bo-Gun Suh, M.D. Mary Ruth A. Padua, M.D. Ho-Joong Kim, M.D. Jin S. Yeom, M.D. Seoul National University College of Medicine Seoul National University Bundang Hospital Sungnam, Korea
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Neurosurgical forum K. Daniel Riew, M.D. Washington University in St. Louis St. Louis, MO Bong-Soon Chang, M.D. Choon-Ki Lee, M.D. Seoul National University College of Medicine Seoul National University Hospital Seoul, Korea
2. Wang C, Yan M, Zhou HT, Wang SL, Dang GT: Open reduction of irreducible atlantoaxial dislocation by transoral anterior atlantoaxial release and posterior internal fixation. Spine (Phila Pa 1976) 31:E306–E313, 2006 3. Yeom JS, Buchowski JM, Park KW, Chang BS, Lee CK, Riew KD: Undetected vertebral artery groove and foramen violations during C1 lateral mass and C2 pedicle screw placement. Spine (Phila Pa 1976) 33:E942–E949, 2008
References 1. Estillore RP, Buchowski JM, Minh DV, Park KW, Chang BS, Lee CK, et al: Risk of internal carotid artery injury during C1 screw placement: analysis of 160 computed tomography angiograms. Spine J 11:316–323, 2011
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Calcified meningiomas To The Editor: We read with great interest the article by Dr. Zhu and colleagues5 (Zhu Q, Qian M, Xiao J, et al: Myelopathy due to calcified meningiomas of the thoracic spine: minimum 3-year follow-up after surgical treatment. Clinical article. J Neurosurg Spine 18:436–442, May 2013). The authors reported on a series of 11 patients who had calcified meningiomas in the thoracic spine, 3 of whom had poor neurological outcomes. They concluded that calcified meningiomas had poorer surgical outcomes than noncalcified ones.5 The authors are commended for sharing their experience with the worldwide readership of the Journal of Neurosurgery. However, we respectfully point out that these calcified meningiomas are not necessarily hard in texture. Spinal meningiomas can have a soft consistency despite calcification, as demonstrated by CT. It was not clear what percentage of the calcified meningiomas in Dr. Zhu’s series was actually ossified. A recent patient of ours had a calcified spinal meningioma in T-5, as demonstrated on preoperative CT, causing severe cord compression (Fig. 1). The tumor was expected to be as hard as bone because it had a CT density similar to that of the neighboring vertebral body and lamina. Surprisingly, during the operation, we found that the tumor was very soft and could be removed using suction and microscissors (Fig. 2). The patient’s neurological function improved rapidly after surgery. Ossified spinal meningiomas are reported even more rarely than calcified spinal meningiomas.2 Occasional misuse of these two terms happens because the differences between them are seldom described in the literature. The term “calcified meningioma” is more of a radiographic description than a histopathological diagnosis. As in our case, most of these meningiomas with calcification on preoperative CTs are the psammomatous type according to histopathological studies (Fig. 3).3,4 The radiopaque calcification on the CT is probably attributable to the confluence of numerous densely packed psammoma bodies.1 On the other hand, “ossified meningioma” refers to a tumor with bony texture that is difficult to resect intraoperatively. However, both calcified and ossified meningiomas are not formal pathological nomenclature. For a pathological diagnosis, there is a metaplastic meningioma that has true lamellar bone formation (Fig. 4).1 This metaplastic lamellar bone can account for the stone-like texture of the ossified meningiomas. A calcified meningioma has no lamellar bone microscopically and is therefore actually gritty rather than stone-like in texture. This article contains some figures that are displayed in color online but in black-and-white in the print edition.
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Fig. 1. Preoperative sagittal (left) and axial (right) CT scans of the thoracic spine, demonstrating a high-density mass occupying the spinal canal. Both images revealed calcification of the tumor.
Fig. 2. Intraoperative pictures of a tumor, which was very soft and easy to remove piecemeal.
Fig. 3. Photomicrograph obtained in our patient, demonstrating a meningioma with abundant psammoma bodies, which could be accounted for by the calcification seen preoperatively. H & E, original magnification ×200.
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Neurosurgical forum 4. Solero CL, Fornari M, Giombini S, Lasio G, Oliveri G, Cimino C, et al: Spinal meningiomas: review of 174 operated cases. Neurosurgery 25:153–160, 1989 5. Zhu Q, Qian M, Xiao J, Wu Z, Wang Y, Zhang J: Myelopathy due to calcified meningiomas of the thoracic spine: minimum 3-year follow-up after surgical treatment. Clinical article. J Neurosurg Spine 18:436–442, 2013
Fig. 4. Photomicrograph demonstrating the pathology of an ossified meningioma surgically treated at our institute. There were true lamellar bone formations between the meningioma tumor tissues rich in psammoma bodies. The pathological diagnosis of this ossified tumor was metaplastic meningioma. H & E, original magnification ×40.
Outcomes following resection of a thoracic spinal meningioma are likely associated with the tumor’s location and texture. A ventrally located ossified meningioma is associated with the highest risk. A preoperative CT is helpful in detecting calcification in the tumor. However, the high density found on CT does not necessarily indicate a stone-like texture. Although the calcification can be soft intraoperatively, surgeons must always be cautious and prepared for a stone-like ossified meningioma when high density is seen preoperatively.
Hsuan-Kan Chang, M.D.1,2 Jau-Ching Wu, M.D., Ph.D.1–3 Diego Shih-Chieh Lin, M.D.4 Chih-Chang Chang, M.D.1,2 Tsung-Hsi Tu, M.D.1,2 Wen-Cheng Huang, M.D., Ph.D.1,2 Henrich Cheng, M.D., Ph.D.1–3 1 Neurological Institute Taipei Veterans General Hospital 2 School of Medicine National Yang-Ming University 3 Institute of Pharmacology National Yang-Ming University 4 Department of Pathology and Laboratory Medicine Taipei Veterans General Hospital Taipei, Taiwan
Response: First of all, we thank Dr. Wu for his interest in our article. We appreciate his comments. He showed us a perfect surgery for calcified meningioma. Different types of calcified meningiomas were discussed in his letter. To our knowledge, there are three types of calcified meningiomas: psammomatous, lamellar calcification, and total calcification.3 The psammomatous type is the most common of the three. In our opinion, the reason for the poorer outcome in calcified meningiomas, as compared with the noncalcified ones, is their hard texture and the adhesion with surrounding tissue (nerve and dura mater). On the other hand, location (ventral or dorsal tumor) is another important factor contributing to the prognosis of all types of meningiomas. For the patient mentioned by Dr. Wu, we found that a soft dorsal tumor without adhesion could be removed totally. And the patient’s neurological function improved rapidly after the surgery. Similar cases can be found at our institute. A 57-year-old woman had suffered weakness in both lower limbs for 5 months. A dorsal tumor was found in the thoracic spinal canal (Fig. 1). The tumor was removed totally, and the patient’s neurological function improved rapidly after the surgery. Unfortunately, not all of the tumors in our series were soft dorsal tumors without adhesion. For example, a 69-yearold woman in our series had suffered weakness in both lower limbs for 6 months. A ventral tumor was found in her thoracic spinal canal (Fig. 2). To remove a ventral tumor, piecemeal removal is often performed. During surgery, we often cut the denticulate ligament to release the spinal cord. After that, we have more space to remove the ventral tumor. Cerebrospinal fluid leakage and a transient
Disclosure The authors report no conflict of interest. References 1. Licci S, Limiti MR, Callovini GM, Bolognini A, Gammone V, Di Stefano D: Ossified spinal tumour in a 58-year-old wom an with increasing paraparesis. Neuropathology 30:194–196, 2010 2. Naderi S, Yilmaz M, Canda T, Acar U: Ossified thoracic spinal meningioma in childhood: a case report and review of the literature. Clin Neurol Neurosurg 103:247–249, 2001 3. Roux FX, Nataf F, Pinaudeau M, Borne G, Devaux B, Meder JF: Intraspinal meningiomas: review of 54 cases with discussion of poor prognosis factors and modern therapeutic management. Surg Neurol 46:458–464, 1996
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Fig. 1. A 57-year-old woman with a T4–5 calcified meningioma. A dorsal tumor was found on a sagittal MR image (A). An axial CT scan from CT 2D reconstruction (B) showing the mass was totally calcified. Photograph (C) of the removed tumor. Intraoperative photograph (D) of the tumor, which was very soft and easy to remove totally.
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Neurosurgical forum 3. Zhang J, Wang Z, Yu T: [Microsurgery for calcified spinal meningiomas (report of 24 cases).] Chin J Clin Neurosurg 17:460–462, 2012 (Chinese) Please include this information when citing this paper: published online November 1, 2013; DOI: 10.3171/2013.6.SPINE13512. ©AANS, 2014
Transpsoas approach
Fig. 2. A 69-year-old woman with a T-2 calcified meningioma. A ventral tumor was found on a sagittal MR image (A). An axial MR image (B) showing the same mass. The tumor was removed piecemeal (C).
deficit are most likely to occur in dorsal tumor cases. The psammomatous type of tumor can be removed piecemeal. But the total calcification type of tumor should sometimes be removed piecemeal to protect the spinal cord. In our case series, calcified meningiomas were pathologically diagnosed in all of the patients, or the tumor could not be confirmed as ossified meningiomas because the diagnosis of ossified meningioma is confirmed by observing bone trabecula. Ossified meningiomas were also diagnosed in some patients, who will be discussed in another case series in the future. In their report of 97 spinal meningiomas, Levy et al.1 found only 4 cases of calcification. Three of these 4 patients had a “disastrous surgical outcome.” Roux et al.2 reported on 3 ossified meningiomas among 54 spinal meningiomas, with an even worse outcome. In our series, the surgical outcome was much better. In conclusion, we believe that the preoperative diagnosis, location, and pathological type of calcified meningioma are important to patient outcome.
Qing Zhu, M.D. Jianru Xiao, M.D. Ming Qian, M.D. Zhipeng Wu, M.D. Spinal Tumor Center Shanghai Changzheng Hospital Second Military Medical University Lifei Wang, M.P.H. School of Public Health Fudan University Shanghai, China
References 1. Levy WJ Jr, Bay J, Dohn D: Spinal cord meningioma. J Neurosurg 57:804–812, 1982 2. Roux FX, Nataf F, Pinaudeau M, Borne O, Devaux B, Meder JF: Intraspinl meningiomas: review of 54 cases with discussion of poor prognosis factors and modern therapeutic management. Surg Neurol 46:458–464, 1996
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To The Editor: We read the article by Cahill and coauthors1 with interest (Cahill KS, Martinez JL, Wang MY, et al: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17:227–231, September 2012), but we have some points regarding the analysis and conclusions drawn by the article. In particular, 2 cases of femoral nerve injury with attendant quadriceps injury were reported upon. A rate of 4.8% quadriceps palsy was noted with lateral transpsoas approaches to the L4–5 level. The authors state that the injuries occurred “during dilation of the psoas muscle for the approach to the L4–5 disc space.” However, we are not certain how this conclusion can be drawn. First, the methods state that a posterior interbody procedure (transforaminal lumbar interbody fusion [TLIF] or posterior lumbar interbody fusion [PLIF]) would be performed in such cases, but it is not discussed in the actual case description. For both patients, what was done at L4– 5, a TLIF? Was the patient examined prior to performing the other procedure(s)? Is it possible that the TLIF caused an L-4 palsy? Generally, after new a neurological injury it is reasonable to obtain images in the patient to determine the cause. Was imaging performed? A critical analysis of the MRI sequences can show tracts through the psoas that lead to the L4–5 foramen, which could explain the palsy on the basis of technical error. Second, was the attending surgeon performing the procedure, or was the resident/fellow operating in these cases? Third, one case was a multilevel (L2–5) procedure. It is possible that the L3–4 transpsoas surgery caused an L-3 palsy and not the attempted L4–5 approach. Was a postoperative electromyography (EMG)/nerve conduction study performed at 6–12 weeks postoperatively to characterize the neural injury? In addition to the questions posed above, critical analysis of preoperative radiographs and MRI studies can reveal details that would have contributed to intraoperative difficulty. Transitional lumbosacral anatomy (hemisacralization of the sacrum, L-6 vertebrae, and so on) has been shown to be a risk factor for unsuccessful treatment of L4–5 performed using the transpsoas approach.4 Additionally, we disagree with the statement “In this retrospective analysis, we estimated that the overall rate of femoral nerve injury for the … L4–5 level was 4.8%....” Of the palsies, one surgery was a multilevel procedure (L2–5) with an aborted L4–5 and one was an aborted single-level L4–5. Of the successful L4–5 levels, the authors reported no femoral nerve palsies. It is very possible that the mul119
Neurosurgical forum tilevel (L2–5) case with a quadriceps palsy resulted from the L3–4 surgery due to L-3 neural injury. We would urge the authors to reconsider their published rate of palsies. One could consider the rate to be 1 of 41 L4–5 single-level procedures, or 2% in your series. Further clouding the conclusions that one can draw from the paper are omitted details such as: what neuromuscular agent was given for anesthesia? And at what time after induction was the approach to L4–5 made? If rocuronium was used, it is quite possible that residual agent could lead to fatigue and/or unreliable readings during neural injury. Houten et al.2 reported quadriceps palsy after transpsoas surgery without EMG changes. Perhaps further investigation of induction agents and neural agents after transpsoas surgery is indicated. In our center we always insist on the use of succinylcholine when performing transpsoas surgery. Additionally, what neuromonitoring system was used? Did the authors use directional nerveseeking probes when approaching L4–5? Directional neuromonitoring has been shown to decrease the rate of complications associated with the lateral transpsoas approach.5 Finally, in the discussion portion of the paper the authors point out that “the [femoral nerve] trunk [is] found in the center of the disc space in 15% of specimens in one cadaveric study.” This datum is used to support the assertion that one can “minimize this complication [femoral nerve palsies] through judicious use of the minimally invasive lateral fusion procedure at the L4–5 level….” We found that the nerves within the psoas move with limb range of motion in a recent study.3 They are lightly tethered within the psoas and the act of dissection moves the nerves significantly. Thus, the location of the neural elements after psoas dissection is probably even more variable. It is important to note that one may retract nerves in peripheral nerve surgery and in PLIF. Is there some inherent physiological difference between the nerves inside the canal and within the psoas that does not allow retraction during transpsoas surgery? Gentle, judicious dissection within the psoas with nerve mobilization if necessary, patient selection (avoid transitional lumbar anatomy), and directional neuromonitoring can probably avoid nerve palsy when treating L4–5 via the transpsoas approach. Joseph R. O’Brien, M.D., M.P.H. George Washington University Medical Center Washington, DC William D. Smith, M.D. University Medical Center Las Vegas, NV Disclosure Dr. O’Brien reports direct stock ownership in Spinicity and ownership in Stryker, and he is a consultant for Globus and NuVa sive. Dr. Smith reports no conflict of interest. References 1. Cahill KS, Martinez JL, Wang MY, Vanni S, Levi AD: Motor nerve injuries following the minimally invasive lateral transpsoas approach. Clinical article. J Neurosurg Spine 17: 227–231, 2012 2. Houten JK, Alexandre LC, Nasser RA, Wollowick AL: Nerve
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injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:280–284, 2011 3. O’Brien J, Haines C, Dooley Z, Turner AL, Jackson D: Femoral nerve strain at L4-5 is minimized by hip flexion and increased by table break when performing lateral interbody fusion. Spine (Phila Pa 1976) [epub ahead of print], 2013 4. Smith WD, Youssef JA, Christian G, Serrano S, Hyde JA: Lumbarized sacrum as a relative contraindication for lateral transpsoas interbody fusion at L5-6. J Spinal Disord Tech 25:285–291, 2012 5. Uribe JS, Vale FL, Dakwar E: Electromyographic monitoring and its anatomical implications in minimally invasive spine surgery. Spine (Phila Pa 1976) 35 (26 Suppl):S368–S374, 2010
Response: We thank the authors for raising several important points regarding our case series and results with the lateral interbody fusion procedure. Our group previously reviewed objective, patient-driven data, which demonstrated that the incidence of lumbosacral plexus sensory symptoms following the minimally invasive lateral approach was likely to be underreported.2 In this article we defined the incidence of postoperative abdominal flank bulge (4%), which appeared to be more common with approaches to upper lumbar vertebrae. We also report a higher incidence (4%) of femoral nerve injury with procedures that included the L4–5 level. This finding is entirely consistent with prior case reports and, more importantly, with the reported neuroanatomical location of the subcostal nerve within the abdominal muscle layers and the femoral nerve within the psoas muscle.1–5 We agree that there are numerous ways to injure a nerve during spine surgery. We considered all of the possible alternative explanations suggested by the authors for quadriceps weakness—including but not limited to TLIFrelated nerve injury, foraminal nerve injury via the lateral approach, injury to the femoral nerve from the lateral approach at a level other than L4–5, and transitional lumbosacral anatomy. We would like to reinforce the important finding that intraoperative real-time EMG monitoring indicated that the femoral nerve was activated during the transpsoas approach at the L4–5 level. In our multiplesurgeon series of lateral interbody fusions we have only had femoral nerve injury when the procedure involved the L4–5 level and when associated with positive activation. We would also like to address several of the other issues raised by the authors. At our institution the attending surgeon is present, responsible, and intimately involved for the duration of the procedure. Fluoroscopy and directional EMG probes are routinely used. We did not have postoperative MRI studies available for review, but the postoperative CT scan suggested the appropriate trajectory toward the midpoint of the disc space. We rely heavily on fluoroscopy to achieve this goal. In our institutional experience we have not seen an L-4 palsy at the level of the nerve root or dorsal root ganglion during an L3–4 or L4–5 PLIF procedure that resulted in significant quadriceps weakness. The femoral nerve is created primarily by contributions from the L-2, L-3, and L-4 roots, and it requires a more distal injury—such as the femoral nerve itself—to impact motor function to the extent seen in these cases. Regarding mobilization of the nerve, we would definitely agree that a technique that involves shallow docking of J Neurosurg: Spine / Volume 20 / January 2014
Neurosurgical forum the retractor and direct visualization and manipulation of the femoral nerve can be safely performed. Although not discussed in the manuscript, a shallow docking approach has been adopted as a technique when the neuromonitoring indicates that a safe corridor through the muscle is not present due to the anterior location of the femoral nerve. We do appreciate the feedback but believe that our interpretation of the results is the simplest, most realistic, and consistent with prior literature on femoral nerve injuries. Kevin S. Cahill, M.D., Ph.D., M.P.H. Joseph L. Martinez, M.D. Steven Vanni, D.O. Michael Y. Wang, M.D. Allan D. Levi, M.D., Ph.D. University of Miami Miller School of Medicine Miami, FL References 1. Benglis DM, Vanni S, Levi AD: An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. Laboratory investigation. J Neurosurg Spine 10:139–144, 2009 2. Cummock M, Vanni S, Levi AD, Yu Y, Wang MY: An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Clinical article. J Neurosurg Spine 15:11–18, 2011 3. Davis TT, Bae HW, Mok JM, Rasouli A, Delamarter RB: Lumbar plexus anatomy within the psoas muscle: implications for the transpsoas lateral approach to the L4-L5 disc. J Bone Joint Surg Am 93:1482–1487, 2011 4. Houten JK, Alexandre LC, Nasser R, Wollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of 2 cases. J Neurosurg Spine 15:280–284, 2011 5. Uribe JS, Arredondo N, Dakwar E, Vale FL: Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. Laboratory investigation. J Neurosurg Spine 13:260–266, 2010 Please include this information when citing this paper: published online November 1, 2013; DOI: 10.3171/2012.11.SPINE12849. ©AANS, 2014
Reduction of atlantoaxial subluxation To The Editor: We read with great interest the article by Dr. Suh and colleagues7 (Suh BG, Padua MRA, Riew KD, et al: A new technique for reduction of atlantoaxial subluxation using a simple tool during posterior segmental screw fixation. Clinical article. J Neurosurg Spine 19:160–166, August 2013). They introduced a novel technique using a T-shaped rod tool to facilitate reduction after the placement of screws in C-1 and C-2. We found their surgical pearl of substantial value in practical use. However, a few questions need answering before the audience can safely apply the innovation. How was the reducibility determined preoperatively? Is there any caveat that the slipped atlantoaxial complex cannot be successfully reduced? As the authors describe in the introduction, any attempt at reduction might not always be easy. Solid purchase of each screw, including C-1 lateral mass screws and C-2 pedicle screws, is fundamental.4 The polyaxial screw head allows easy connection of the construct but might limit the power of reduction. Positioning the patient with a Mayfield head holder allows less manipulation of the atlantoaxial complex. Maintenance of a successfully reduced atlantoaxial subluxation might also be difficult.5 In some extreme cases, the highly mobile atlantoaxial complex requires a tremendous force of fixation to overcome the instability. Failure of fixation could happen within weeks after successful instrumentation and wiring (Fig. 1). Moreover, extension of the fixation construct to the occipital skull may raise the complication rate.6 What are the salvage strategies when there is pseudarthrosis and recurrence of subluxation? Reduction and fixation of the atlantoaxial complex is always challenging.1–3,8 Although the authors demonstrated a useful tool, each individual case requires a tailor-made preoperative plan and cautious execution when reduction is attempted. Peng-Yuan Chang, M.D. Jau-Ching Wu, M.D., Ph.D. Wen-Cheng Huang, M.D., Ph.D.
Fig. 1. A: Preoperative MR image. B: Three days postoperative radiograph demonstrating successful reduction of atlantoaxial subluxation. Fixation was made by C-1 lateral mass screws, C-2 pedicle screw, C-2 laminar screw, and wiring with autologous iliac bone graft. C: Six weeks postoperative radiograph demonstrating loss of reduction.
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Neurosurgical forum Tsung-Hsi Tu, M.D. Henrich Cheng, M.D., Ph.D. Neurological Institute Taipei Veterans General Hospital Taipei, Taiwan School of Medicine National Yang-Ming University Taipei, Taiwan Disclosure The authors report no conflict of interest. References 1. Goel A: Editorial. Occipitocervical fixation: is it necessary? J Neurosurg Spine 13:1–2, 2010 2. Goel A, Shah A: Atlantoaxial facet locking: treatment by facet manipulation and fixation. Experience in 14 cases. Technical note. J Neurosurg Spine 14:3–9, 2011 3. Goel A, Shah A, Gupta SR: Craniovertebral instability due to degenerative osteoarthritis of the atlantoaxial joints: analysis of the management of 108 cases. Clinical article. J Neurosurg Spine 12:592–601, 2010 4. Hamilton DK, Smith JS, Sansur CA, Dumont AS, Shaffrey CI: C-2 neurectomy during atlantoaxial instrumented fusion in the elderly: patient satisfaction and surgical outcome. Clinical article. J Neurosurg Spine 15:3–8, 2011 5. Hood B, Hamilton DK, Smith JS, Dididze M, Shaffrey C, Levi AD: The use of allograft and recombinant human bone morphogenetic protein for instrumented atlantoaxial fusions. World Neurosurg [epub ahead of print], 2013 6. Mummaneni PV, Lu DC, Dhall SS, Mummaneni VP, Chou D: C1 lateral mass fixation: a comparison of constructs. Neurosurgery 66 (3 Suppl):153–160, 2010 7. Suh BG, Padua MRA, Riew KD, Kim HJ, Chang BS, Lee CK, et al: A new technique for reduction of atlantoaxial subluxation using a simple tool during posterior segmental screw fixation. Clinical article. J Neurosurg Spine 19:160–166, 2013 8. Wu JC, Tu TH, Mummaneni PV: Techniques of atlantoaxial fixation and the resection of C2 nerve root. World Neurosurg 78:603–604, 2012
Response: We thank Dr. Chang and colleagues for their interest in our paper and valuable comments. Reducibility can be determined preoperatively by using dynamic radiographs in many cases. If atlantoaxial subluxation seems to be irreducible on dynamic radiographs, we choose preoperative traction using Gardner-Wells tongs for fewer than 2 days. If at least partial reduction is demonstrated on traction lateral radiographs, we proceed with posterior surgery alone, because a greater reduction force can be applied with the reduction tools during surgery. In addition, intraoperative traction, release of the posterior soft tissues by capsulotomy (Fig. 5. in the original article), and intraoperative facet distraction will facilitate the reduction maneuver. Preoperative traction is helpful not only to confirm reducibility but also to stretch out the anterior soft tissue contracture, which normally cannot be resected during posterior surgery. Using our reduction tools is only a part of these combined reduction techniques. We do not utilize all of these procedures in simple cases, but neither do we use our tools alone in the challenging ones. We have not experienced a truly irreducible case without any evidence of even partial reduction during pre122
operative traction among several hundred surgical cases thus far. However, we think that a very small number of cases with extremely severe anterior tilt of the atlantoaxial facet joints caused by an old neglected congenital or early childhood–onset subluxation/dislocation along with extremely severe contracture of the anterior soft tissues may not show reducibility even with preoperative traction. In addition, if the patient has concomitant osteoporosis, excessive reduction force may lead to failure of the weak bone. In these cases, anterior release may be needed before posterior screw fixation.2 We agree that solid purchase of the screws is essential in barely reducible cases. In cases requiring excessive reduction force and/or with severe osteoporosis, we try our best to insert pedicle screws into C-2 rather than laminar screws and to insert C-1 lateral mass screws via the posterior arch rather than under the arch, to obtain greater fixation. In addition, we opt for bicortical purchase while taking care to avoid injury to the internal carotid arteries.1 We also consider using a transverse connector to improve pullout strength and rotational stability in selected cases. We agree that the polyaxial screw head might limit the power of reduction if conventional instruments are used. However, our tools make use of the advantages of polyaxial screw heads. As shown in Fig. 2 in the original article, the screw heads have to be polyaxial to allow for controlled manipulation using our tools. For example, the C-2 screw head is tilted cranially before reduction but will be less cranially tilted or even caudally tilted after reduction (Figs. 2 and 3 in the original article). We agree that a Mayfield head holder allows less manipulation of the atlantoaxial complex, particularly if multilevel fusion is to be done. While successful reduction can be easily achieved even with a Mayfield head holder in easy cases, we prefer to use Gardner-Wells tongs, particularly for challenging cases, since it allows for effective intraoperative traction, easier preparation of intraarticular fusion of the facet joints, and easier manipulation of the atlantoaxial complex. Note, however, that Gardner-Wells tongs may permit unwanted axial rotation of the patient’s head and neck during screw insertion. This may result in a decrease in the effective medial angulation of the screw trajectory, leading to violation of the C-1 vertebral artery foramen or C-2 vertebral artery groove.3 For better maintenance of reduction in selected cases, including for pseudarthrosis revision, we choose thicker (4.0 mm) screws, if feasible, bicortical fixation, and techniques described above. When the use of 2 pedicle screws is not feasible at C-2, we insert 3 or 4 screws at C-2 and/ or use a transverse connector. In addition, we always do intraarticular fusion of the facet joints as well as posterior fusion in these cases. We agree that each case requires a tailor-made preoperative plan and cautious execution when reduction is attempted. We appreciate your valuable comments. Bo-Gun Suh, M.D. Mary Ruth A. Padua, M.D. Ho-Joong Kim, M.D. Jin S. Yeom, M.D. Seoul National University College of Medicine Seoul National University Bundang Hospital Sungnam, Korea
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Neurosurgical forum K. Daniel Riew, M.D. Washington University in St. Louis St. Louis, MO Bong-Soon Chang, M.D. Choon-Ki Lee, M.D. Seoul National University College of Medicine Seoul National University Hospital Seoul, Korea
2. Wang C, Yan M, Zhou HT, Wang SL, Dang GT: Open reduction of irreducible atlantoaxial dislocation by transoral anterior atlantoaxial release and posterior internal fixation. Spine (Phila Pa 1976) 31:E306–E313, 2006 3. Yeom JS, Buchowski JM, Park KW, Chang BS, Lee CK, Riew KD: Undetected vertebral artery groove and foramen violations during C1 lateral mass and C2 pedicle screw placement. Spine (Phila Pa 1976) 33:E942–E949, 2008
References 1. Estillore RP, Buchowski JM, Minh DV, Park KW, Chang BS, Lee CK, et al: Risk of internal carotid artery injury during C1 screw placement: analysis of 160 computed tomography angiograms. Spine J 11:316–323, 2011
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