Clinical significance of postdecompression facet joint effusion after minimally invasive decompression for degenerative lumbar spinal stenosis.

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ARTICLE

Clinical Significance of Postdecompression Facet Joint Effusion After Minimally Invasive Decompression for Degenerative Lumbar Spinal Stenosis Jwo-Luen Pao, MD,*wz Wen-Chih Chen, MD,z Chih-Hung Chang, MD, PhD,z Chiang-Sang Chen, MD,z and Jaw-Lin Wang, PhD*y

Study Design: A retrospective case series study. Objective: To investigate the clinical significance of postdecompression facet effusion (PDFE) after microendoscopic decompressive laminotomy (MEDL). Summary of Background Data: The facet joint effusion noted on magnetic resonance imaging was considered as an indicator of degeneration of the facet joints and segmental instability. PDFE occurring after MEDL might imply postdecompression segmental instability. Its clinical significance has not yet been clarified.

these 9 patients, the final outcomes were good. Progression of spondylolisthesis was noted in 2 patients without PDFE but no patients with PDFE during the follow-up period. Conclusions: The relatively high incidence of PDFE after MEDL suggests that injury to the integrity of facet joint is inevitable during decompression of the stenosis, even using minimally invasive techniques. However, the overall stability is well preserved with very rare progression of spondylolisthesis. Most patients with PDFE are asymptomatic. The prognosis of PDFE is very good. Spinal fusion is rarely indicated.

Materials and Methods: From 2005 to 2010, 165 patients with degenerative lumbar spinal stenosis (average age: 64.5, average follow-up: 25.8 mo) who received MEDL were reviewed. We investigated the incidence of PDFE with preoperative and repetitive magnetic resonance imaging at 6 months postoperatively. The clinical data and treatment courses were reviewed. The treatment outcomes were evaluated with Oswestry Disability Index and Japanese Orthopedic Association scores.

Key Words: postdecompression facet effusion, facet joint effusion, incidence, minimally invasive spine surgery, microendoscopic decompression, degenerative lumbar spinal stenosis, treatment outcomes, complication, magnetic resonance imaging, segmental instability

Results: The incidence of PDFE was 17.0% (n = 28), which was significantly higher in patients receiving multilevel decompression and patients with scoliosis or spondylolisthesis. The intensity of low back pain was similar between patients with and without PDFE, but “mechanical” low back pain was only noted in patients with PDFE. Of the 28 patients with PDFE, only 9 symptomatic patients required invasive treatment (5 facet joint steroid injection, 3 revision MEDL, and 1 spinal fusion). Although the postoperative Oswestry Disability Index and Japanese Orthopedic Association scores were significantly worse

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(J Spinal Disord Tech 2014;27:E318–E323)

Received for publication November 13, 2013; accepted May 19, 2014. From the *Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei; Departments of wMinimally Invasive Spine Surgery; zOrthopedic Surgery, Far-Eastern Memorial Hospital, New Taipei; and yDepartment of Mechanical Engineering, College of Engineering, National Taiwan University, Taipei, Taiwan. Supported by the Far-Eastern Memorial Hospital (FEMH-97-C-021) and National Health Research Institute, Taiwan (NHRI-EX999733EI). The authors declare no conflict of interest. Reprints: Jaw-Lin Wang, PhD, Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan (e-mail: [email protected]). Copyright r 2014 by Lippincott Williams & Wilkins

icroendoscopic decompressive laminotomy (MEDL) is a minimally invasive technique introduced in 2002, which enables effective decompression of degenerative lumbar spinal stenosis (DLSS) through a small endoscopic tubular retractor.1–7 With minimal injury to the paraspinal muscles and preservation of the posterior stabilizing structures, the segmental stability is maintained and spinal fusion or instrumentation is avoided.8–10 Facet joint effusion is a specific image finding readily detectable on routine lumbar spine magnetic resonance imaging (MRI) with widening of the joint space and excessive fluid accumulation. Excessive fluid found in the facet joint, just like excessive fluid in the knee or shoulder joints, indicates degeneration of the synovial joint. The clinical significance of facet joint effusion has not been carefully investigated in the past. Not until recently was it considered as an indicator of degeneration and segmental instability of the lumbar spine.11–17 The presence of facet joint effusion is suggestive of segmental instability12,14–16 and highly predictive of degenerative spondylolisthesis, even if not appreciated on the supine sagittal MRI.11,13,17 However, there were only few studies addressing the postdecompression facet effusion (PDFE) as a surgical complication after decompressive surgery for DLSS.18 As facet joint effusion may be considered as an

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indication for spinal fusion,16 the clinical significance of PDFE must be clarified. The purposes of this study are to investigate the incidence of PDFE after MEDL to examine if the segmental stability could be preserved after minimally invasive decompression, the influence of this complication on the treatment results, and the prognosis of this complication.

MATERIALS AND METHODS Our indications of MEDL were moderate to severe DLSS with persistent low back pain, radicular leg pain, neurological deficits, or neurogenic intermittent claudication refractory to conservative treatment for at least 3 months. We did not perform MEDL on patients with mechanical low back before the operation, translational instability with translation of >4 mm or angulation change of >10 degrees on dynamic radiographs, more than grade I spondylolisthesis, isthmic spondylolisthesis, or degenerative scoliosis with a Cobb angle of >15 degrees. After obtaining approval from the Research Ethics Review Committee of the hospital, 244 consecutive patients with DLSS who underwent MEDL between November 2005 and November 2010 were reviewed to determine study eligibility. Only those patients with complete image studies available for review were included in the study. The complete image studies included preoperative and postoperative MRI, and AP and weightbearing flexion-extension lateral lumbar radiographs. Patients who had prior surgeries on their lumbar spine were excluded. A total of 165 patients were included in this study. They were 65 males and 100 females with an average follow-up period of 28.0 months (range, 6–55 mo). The average age was 64.5 (range, 36–89 y). Of the 79 patients who were excluded, 59 did not have postoperative MRI, 12 had prior surgeries on their lumbar spines, 5 had died for reasons unrelated to spine pathology, 3 declined participation in the study. Chaput et al11 defined a facet joint effusion of >1 mm as “clinically measurable” because it was difficult to measure a facet joint effusion smaller than that size. They observed that the size of facet joint effusion was associated with clinical instability. Therefore, we defined the PDFE as

Facet Joint Effusion After MEDL

“new development” or “increase” of facet joint effusion of >1 mm in size after the operation, by comparing the postoperative with the preoperative axial T2-weighted MRI at the same level placing the patient in the neutral supine position without adjusting his/her posture (Fig. 1). Although we tried to follow a standard protocol to obtain the MRI, some of the preoperative MRI studies were performed at other hospitals that we had to accommodate with various imaging protocols to do all the measurements using our own software in the PACS system. MRI of the lumbar spine was performed preoperatively and at 6 months postoperatively to evaluate the incidence of PDFE at 6 months after the operation. Besides MRI, all patients had AP, lateral, and dynamic radiographs of the lumbar spine before the operation. Radiographic studies were repeated at 1, 6, 12 months, and then annually to check the segmental stability. We divided our patients into the Stable Group and the Unstable Group according to the preoperative radiographic findings. The Unstable Group consisted of 21 patients with spondylolisthesis, 10 patients with scoliosis, and 3 with both spondylolisthesis and scoliosis. The Stable Groups consisted of the remaining 131 patients who did not have such structural problems. Decompression of the stenosis was performed with techniques known as “unilateral laminotomy for bilateral decompression” using the endoscopic system manufactured by the Medtronic (METRx; Medtronic, Minneapolis, MN).1,4,5 Laminotomy and medial facetectomy were always started from the side of more severe neurological symptoms. Contralateral decompression was performed by undercutting the undersurface of the contralateral lamina and facet joint before removal of the ligamentum flavum. Finally, the ligamentum flavum was completely excised to check the adequacy of decompression. The treatment courses of all patients were retrieved from medical records and carefully reviewed. We used the 4-point categorical scale (none, mild, moderate, and severe) in the Japanese Orthopedic Association (JOA) scoring system5 to evaluate the intensity of low back pain. Specific complaints for posture-related low back pain, the “mechanical” low back pain, was specially recorded. The treatment results were evaluated using the Oswestry

FIGURE 1. Comparison of the 6-month magnetic resonance imaging (MRI) with the preoperative MRI to demonstrate the newly developed postdecompression facet effusion after MEDL. r

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FIGURE 2. Comparison of the 6-month magnetic resonance imaging (MRI) with the preoperative MRI to demonstrate the newly developed postdecompression facet effusion associated with an intraspinal facet cyst (arrow head) at the left facet joint.

Disability Index (ODI)19 for the overall disability and the JOA score for back pain, leg pain, and neurological symptoms. Patients were requested to complete the questionnaire survey before the operation, at 6 and 12 months after the operation, and then annually, which were conducted by the same assistant. All data were prospectively collected and retrospectively reviewed for analysis. Statistical analysis and comparison between groups were conducted using SPSS. Categorical data such as sex, preoperative diagnosis, decompression level, and intensity of low back pain were analyzed using w2 test. Numeral data were analyzed using independent t test or ANOVA. The level of significance was set to be 0.05.

RESULTS Before the operation, 42 patients already had facet joint effusion >1 mm thick. After MEDL, the size of facet joint effusion remained unchanged in 28 of the 42 patients. Progression of the preexisted facet joint effusion was noted in the other 14 patients. Newly developed facet joint effusion was noted in another 14 patients who had no facet joint effusion before the operation. By our definitions, the incidence of PDFE was 17.0% (28 in 165 patients). Associated intraspinal facet cyst formation was observed in 20 patients (Fig. 2). Comparison on the demographic data between patients with and without PDFE showed no statistically significant difference (Table 1).

All the patients received bilateral decompression through unilateral laminotomy. In the 28 patients with PDFE, 7 patients had PDFE only at the same side of laminotomy, 8 patients had PDFE only at the opposite side, and 13 patients had PDFE at both sides. w2 test revealed no significant difference between groups. Patients receiving 3-level decompression had the highest incidence of PDFE (37.5%, 6/16), followed by 2-level (16.7%, 11/66), and then 1-level decompression (13.3%, 11/83). The incidence of PDFE increased with the decompression levels. Statistically significant difference was noted between 1- and 3-level decompression (P = 0.019) (Table 2 and Fig. 3). The PDFE occurred most frequently at L4/5 (n = 23), followed by L3/4 (n = 3), L2/3 (n = 3), and L5/ S (n = 1). However, the highest incidence occurred at L2/ 3 (15.8%), followed by L4/5 (15.6%), L3/4 (4.5%), and L5/S (3.4%). It was noteworthy that all the patients with L2/3 PDFE also received 3-level decompression. The difference between levels did not reach the significant level (P = 0.05) (Table 2). The incidence of PDFE was significantly higher in the Unstable Group than in the Stable Group (29.4% vs. 13.7%, P = 0.030). Further comparison between subgroups revealed that the incidence was highest in patients with spondylolisthesis (33.3%), followed by patients with scoliosis (30.0%), patients with no structural problems (13.7%), and patients with spondylolisthesis and scoliosis (0%). However, significant difference was only noted between patients with no structural problems and patients

TABLE 1. Demographic Data Patient number MEDL levels Sex Male Female Age (y) Body weight (kg) Body height (cm) Follow-up (mo)

With PDFE

Without PDFE

Total

Incidence (%)

28 30

137 233

165 263

17.0 11.4

11 17 66.1 ± 9.1 66.1 ± 8.8 159.0 ± 7.7 28.0 ± 12.7

54 83 64.9 ± 12.1 63.3 ± 13.1 158.4 ± 8.4 25.1 ± 14.4

65 100 64.5 ± 11.8 63.8 ± 12.5 158.5 ± 8.2 25.8 ± 14.1

16.9 17.0

P

0.990* 0.605w 0.295w 0.769w 0.310w

*w2 test. wIndependent t test. MEDL indicates microendoscopic decompressive laminotomy; PDFE, postdecompression facet effusion.


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TABLE 2. Incidence Analysis

Decompression levels 1 level 2 levels 3 levels Decompression level L2/3 L3/4 L4/5 L5/S Preoperative stability Stable Group Unstable Group DLSS DLSS+olisthesis DLSS+scoliosis Olisthesis+scoliosis

With PDFE

Without PDFE

Total

Incidence (%)

11 11 6

72 55 10

83 66 16

13.3 16.7 37.5

0.061

3 3 23 1

16 63 124 28

19 66 147 29

15.8 4.5 15.6 3.4

0.050

18 10 18 7 3 0

113 24 113 14 7 3

131 34 131 21 10 3

13.7 29.4 13.7 33.3 30.0 0

0.030

*w2 test. DLSS indicates degenerative decompression facet effusion.

lumbar

spinal

stenosis;

PDFE,

P*

0.079


ed facet joint steroid injection. The remaining 1 patient required spinal fusion. Three patients had newly developed radicular leg pain as a result of intraspinal facet cyst and neural compression. Revision MEDL was required to excise the cysts. None of these patients had recurrence of symptoms after the above-mentioned treatments. In the functional outcomes evaluation, the overall ODI was improved from 57.0 ± 20.2 to 12.1 ± 17.1; the overall JOA score was improved from 11.9 ± 6.2 to 25.7 ± 5.0, good to excellent results were obtained in 90.3% patients (n = 149). The patients with symptomatic PDFE had the worst treatment results in both ODI and JOA score (P < 0.0005), as compared with the patients with asymptomatic PDFE or the patients without PDFE (Fig. 4).

DISCUSSION post-

with spondylolisthesis (13.7% vs. 33.3%, P = 0.025) (Table 2 and Fig. 3). Low back pain was significantly improved after MEDL as evaluated using the 4-point categorical scale. However, there was no significant difference in the pain intensity between the patients with facet joint effusions and those ones without, either before or after MEDL. After MEDL, this relation was also noted between the patients with PDFE and those ones without (Table 3). However, the “mechanical” low back pain was only noted in 6 patients with PDFE but in no patients without PDFE. Follow-up dynamic radiographs revealed progression of spondylolisthesis in 2 patients without PDFE but in no patients with PDFE. In the 28 patients with PDFE, 19 patients (70%) were asymptomatic and the other 9 patients (30%) had significant symptoms requiring invasive treatment. Six patients had mechanical low back pain. Five of them had good symptoms relief after a single-shot fluoroscopy-guid-

In our study, we evaluated the incidence of PDFE after MEDL by comparing the preoperative MRI with the repetitive MRI at 6 months after MEDL. We observed that 17% of patients had PDFE at the very shortterm follow-up. The results suggested that PDFE was a common complication after MEDL. Fortunately, the prognosis of this complication seemed to be quite good. In the 28 patients with PDFE, about 70% were asymptomatic and required no treatment. Secondary surgeries were required in only 4 patients, and only one of them required spinal fusion. Adequate decompression is the most determining factor for the surgical treatment of DLSS. On the contrary, excessive decompression may lead to postdecompression instability. Unilateral laminotomy for bilateral decompression is the most frequently used decompression technique in MEDL. Evidences from biomechanical as well as clinical studies suggested that this technique provides adequate decompression of stenosis while preserving the soft tissue and stabilizing bony structures, and therefore maintains the stability.1–3,8,9,20 A biomechanical cadaver study conducted by Hamasaki et al8 demonstrateed that unilateral laminotomy for

FIGURE 3. The incidence of postdecompression facet effusion (w2 test). LSS indicates lumbar spinal stenosis. r



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TABLE 3. Low Back Pain Versus Facet Effusion Patient Numbers With Different Pain Intensity Before MEDL After MEDL FE (+) before MEDL FE () before MEDL FE (+) after MEDL FE () after MEDL PDFE (+) PDFE ()

None

Mild

Moderate

Severe

P*

40 90 9 31 29 61 16 74

30 48 9 21 18 30 7 41

43 21 15 28 6 15 3 18

52 6 9 43 3 3 2 4

< 0.005 0.227 0.717 0.686

*w2 test. FE indicates facet joint effusion; MEDL, microendoscopic decompressive laminotomy; PDFE, postdecompression facet effusion.

bilateral decompression left the spine >80% as stiff as the intact spine and can preserve more of the facet joints than the other decompression techniques. Sasai et al9 observed no significant change in dynamic stability of the lumbar spine after decompression with this technique during a minimum 2 years of follow-up. However, they did notice a significant increase in the slip percentage in the subgroup of patients with spondylolisthesis. To achieve adequate decompression, the surgeon has to perform at least partial facetectomy to decompress the lateral recess and to free the entrapped nerve root. Therefore, no matter how minimally invasive it is, any decompression techniques will inevitably cause some injury to the integrity of the facet joint complex. That may explain the relatively high incidence of PDFE after MEDL. In the current study, we observed that PDFE was associated with the preoperative degeneration and the structural problems. The incidence of PDFE was higher in the patients receiving more levels of decompression, such condition usually occurred in the lumbar spines with more advanced degeneration. Although patients with significant radiographic instability were not included into our study, some of our patients still had structural problems such as low-grade spondylolisthesis or scoliosis.


We observed that the incidence of PDFE was also significantly higher in patients with such structural problems than in patients without, especially in patients with spondylolisthesis. These observations might suggest the potential risks of MEDL in accelerating the facet joint degeneration and aggravation of the subtle segmental instability. Vague low back pain or low back soreness is a common complaint in patients with DLSS. This type of low back pain was usually treated by resting, bracing, or back exercise. Some patients may need NSAIDs or additional rehabilitation programs. We used the simplified 4-point categorical scale in the JOA system to evaluate the low back pain before and after treatment. Overall, the pain intensity was significantly reduced after MEDL. However, there was no significant difference in pain intensity between patients with or without facet joint effusion, either before or after MED. Furthermore, there was no significant difference in the pain intensity between the patients with PDFE and the patients without. Therefore, the association between facet joint effusion and this type of low back pain is very weak. On the contrary, the association between mechanical low back pain and PDFE is much stronger. Mechanical low back pain is posture related and usually associates with disk pathology, facet joint pathology, or segmental instability. In the current study, this specific type of low back pain only occurred in patients with PDFE. Fortunately, fluoroscopy-guide facet joint steroid injection was quite effective for symptoms relief. Only 1 patient with PDFE required spinal fusion because of persistent mechanical pain. Radicular leg pain resulting from neural compression by the associated intraspinal facet cyst is the other major reason for patients with PDFE to receive invasive treatment. The treatment for the facet cysts varied from observation, oral analgesics, orthopedic corset, needle puncture, facet joint steroid injection, or surgical excision with/without spinal fusion.21–24 Ikuta et al18 observed a benign clinical course of the postdecompression intraspinal facet cysts with spontaneous regression in 5 of 7 patients in 1 year. Our study

FIGURE 4. Comparison of treatment results between patients without postdecompression facet effusion (PDFE), patients with asymptomatic PDFE and symptomatic PDFE (ANOVA test). FE indicates facet joint effusion; JOA, Japanese Orthopedic Association; ODI, Oswestry Disability Index.


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also supported the conservative approach for the postdecompression intraspinal facet cysts. In our 20 patients with intraspinal facet cysts after MEDL, only 3 of them required secondary surgeries to relieve neural compression. Although the overall treatment results for our patients were quite good with significant improvement in ODI and JOA scores, the functional outcomes in those 9 patients with symptomatic PDFE were significantly worse than the others. However, after appropriate treatments, such as facet joint steroid injection, excision of the intraspinal facet cysts, or spinal fusion, they all had significant improvement with good results. No progression of spondylolisthesis was found in those patients with PDFE during the follow-up period. There are some limitations in this study. First, because this study was conducted in a homogenous patient population who received MEDL for DLSS, the results cannot be applied to patients who received traditional open surgery. A comparative study comparing minimally invasive surgery and traditional open surgery is required to realize the influence of soft tissue or structural damage on the development of PDFE. Second, a longer-term follow-up study with serial MRIs is helpful to understand the natural course of PDFE after MEDL and how long the good clinical results can maintain. In conclusion, the relatively high incidence of PDFE after MEDL suggests that even minimally invasive decompression cannot avoid injury to the facet joint complex and accelerate degeneration of the surrounding facet joints. However, the segmental stability was well preserved with good clinical results. If patients with DLSS do not have significant radiographic instability or mechanical low back pain, MEDL is a safe and effective minimally invasive procedure. Most patients with PDFE are asymptomatic. The prognosis of PDFE is very good. Spinal fusion is rarely indicated. REFERENCES 1. Guiot BH, Khoo LT, Fessler RG. A minimally invasive technique for decompression of the lumbar spine. Spine. 2002;27:432–438. 2. Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurg. 2002;51:S146–S154. 3. Palmer S, Turner R, Palmer R. Bilateral decompression of lumbar spinal stenosis involving a unilateral approach with microscope and tubular retractor system. J Neurosurg Spine. 2002;97:213–217. 4. Asgarzadie F, Khoo LT. Minimally invasive operative management for lumbar spinal stenosis: overview of early and long-term outcomes. Orthop Clin North Am. 2007;38:387–399. Abstract vi–vii. 5. Ikuta K, Arima J, Tanaka T, et al. Short-term results of microendoscopic posterior decompression for lumbar spinal stenosis. Technical note. J Neurosurg Spine. 2005;2:624–633.

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6. Pao JL, Chen WC, Chen PQ. Clinical outcomes of microendoscopic decompressive laminotomy for degenerative lumbar spinal stenosis. Eur Spine J. 2009;18:672–678. 7. Rosen DS, O’Toole JE, Eichholz KM, et al. Minimally invasive lumbar spinal decompression in the elderly: outcomes of 50 patients aged 75 years and older. Neurosurg. 2007;60:503–509. 8. Hamasaki T, Tanaka N, Kim J, et al. Biomechanical assessment of minimally invasive decompression for lumbar spinal canal stenosis: a cadaver study. J Spinal Disord Tech. 2009;22:486–491. 9. Sasai K, Umeda M, Maruyama T, et al. Microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis including degenerative spondylolisthesis. J Neurosurg Spine. 2008;9:554–559. 10. Wong AP, Smith ZA, Lall RR, et al. The microendoscopic decompression of lumbar stenosis: a review of the current literature and clinical results. Minim Invasive Surg. 2012;2012:325095. 11. Chaput C, Padon D, Rush J, et al. The significance of increased fluid signal on magnetic resonance imaging in lumbar facets in relationship to degenerative spondylolisthesis. Spine. 2007;32: 1883–1887. 12. Rihn JA, Lee JY, Khan M, et al. Does lumbar facet fluid detected on magnetic resonance imaging correlate with radiographic instability in patients with degenerative lumbar disease? Spine. 2007;32:1555–1560. 13. Schinnerer KA, Katz LD, Grauer JN. MR findings of exaggerated fluid in facet joints predicts instability. J Spine Disord Tech. 2008;21: 468–472. 14. Oishi Y, Murase M, Hayashi Y, et al. Smaller facet effusion in association with restabilization at the time of operation in Japanese patients with lumbar degenerative spondylolisthesis. J Neurosurg Spine. 2010;12:88–95. 15. Hasegawa K, Shimoda H, Kitahara K, et al. What are the reliable radiological indicators of lumbar segmental instability? J Bone Joint Surg Br. 2011;93:650–657. 16. Lattig F, Fekete TF, Grob D, et al. Lumbar facet joint effusion in MRI: a sign of instability in degenerative spondylolisthesis? Eur Spine J. 2012;21:276–281. 17. Cho BY, Murovic JA, Park J. Imaging correlation of the degree of degenerative L4-5 spondylolisthesis with the corresponding amount of facet fluid. J Neurosurg Spine. 2009;11:614–619. 18. Ikuta K, Tono O, Oga M. Prevalence and clinical features of intraspinal facet cysts after decompression surgery for lumbar spinal stenosis. J Neurosurg Spine. 2009;10:617–622. 19. Fairbank JC, Pynsent PB. The Oswestry Disability Index. Spine. 2000;25:2940–2952; discussion 2952. 20. Hong S-W, Choi KY, Ahn Y, et al. A comparison of unilateral and bilateral laminotomies for decompression of L4-L5 spinal stenosis. Spine. 2011;36:E172–E178. 21. Khan AM, Girardi F. Spinal lumbar synovial cysts. Diagnosis and management challenge. Eur Spine J. 2006;15:1176–1182. 22. Martha JF, Swaim B, Wang DA, et al. Outcome of percutaneous rupture of lumbar synovial cysts: a case series of 101 patients. Spine J. 2009;9:899–904. 23. Hemminghytt S, Daniels DL, Williams AL, et al. Intraspinal synovial cysts: natural history and diagnosis by CT. Radiology. 1982;145:375–376. 24. Houten JK, Sanderson SP, Cooper PR. Spontaneous regression of symptomatic lumbar synovial cysts. Report of three cases. J Neurosurg. 2003;99:235–238.


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