Australas Radio1 1992; 36: 262-264

Post-Laminectomy Pseudomeningocele: An Unusual Cause of Bone Erosion KENNETH K. LAU, M.B., B.S., MARK STEBNYCKYJ, M.B., B.S. AND ALLAN McKENZIE, M.B., B .S., F.R.A.C.R. Department of Radiology Repatriation General Hospital, Banksia Street, Heidelberg West, Victoria 3081 Australia.

ABSTRACT Pseudomeningocele is a rare complication of laminectomy, which can cause recurrent back pain with or without radicular signs. A case of bone erosion of the posterior vertebral elements by a pseudomeningocele is discussed. INTRODUCTION Pseudomeningocele is a rare complication of laminectomy. The incidence ranges from 0.07% in the series of 1700 laminectomies of Swanson and Fincher (1) to 2% in the series of 400 symptomatic post-laminectomy patients of Teplick et at (2). It is secondary to a dural tear during operation. It can also be a complication of lumbar puncture, closed spinal trauma, lumbar myelography, and surgical repair Of herniated lumbar bral discs (3)* Recurrent back pain with or without radicular signs is a constant feature in previously reported (4). post-~aminectomypseudomeningocele can be complicated by infection causing chronic meningitis (3), and by lumbar nerve root entrapment (4). Some cases can be asymptomatic (4). We present a case of postlaminectomy pseudomeningocele which caused unusual bone erosion of the posterior vertebral elements.

FIGURE 1A - Lumbar spine X-rays. A and B demonstrate degenerative changes and facet joint hypertrophy prior to laminectomy. C and D show recent bony destruction of inferior articular processes of L3 and L4 and left L4 lamina 9 months after L5 - S 1 laminectomy.

FIGURE 1C

FIGURE 1B

FIGURE 1D

CASE REPORT A 64 year old man complained of

several years’ history of increasing low back pain which radiated down the left leg. A diagnosis of spinal canal stenosis by lumbar myelogram

Key words: Pseudomeningocele Larninectorny Address for correspondence: K.K. Lau Department of Radiology Repatriation General Hospital Banksia Street Heidelberg West Victoria 3081 Australia Phone (03) 490 2 111

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was made elsewhere. A decompressive L5 - S 1 laminectomy with no ery was uneventful and he was able to

Accepted for publication on: 21st January, 1992 Australasian Radiology, Vol. 36, NO. 3 , August, 1992

POST-LAMINECTOMY PSEUDOMENINGOCELE mobilize without difficulty. Approximately 3 weeks later, he developed increasing right leg pain. He was managed with skin traction and lumbar epidural injections. His left leg pain recurred 9 months later. Clinical examination revealed some restriction of low back flexion and extension with unremarkable lower limb neurological signs. No abnormality was detected at the laminectomy scar site. He was referred to this hospital for neurosurgical assessment. Plain lumbosacral spine X-rays revealed moderate degenerative changes at intervertebral disc spaces and mild facet joint hypertrophic changes. There was scalloping of the posterior aspect of L3 and L4 vertebral bodies with recent destruction of the inferior half of the inferior articular processes of L3 and L4, and the left L4 lamina (Figure 1). Lumbar myelogram demonstrated several abnormalities: (i>a large pseudomeningocele filled with contrast posterior to the spinal theca at LA and was connected by a narrow stalk inferiorly, (ii) erosion of the L3 and L4 inferior articular processes and left L4 lamina by the pseudomeningocele, (iii) slight narrowing of the lumbar spinal theca adjacent to IA-5, and (iv) poor filling of L5 nerve root sheathes bilaterally (Figure 2). Post myelogram CT confirmed the presence of the pseudomeningocele eroding bone and the slightly thickened nerve roots of the cauda equina suggestive of mild arachnoiditis (Figure 3).

FIGURE 2A - Lumbar myelogram. A and B demonstrate pseudomeningocele posterolateral to the spinal theca on the left at L4 level with a narrow stalk inferiorly. It has caused bony erosion of inferior articular processes of L3 and L4 and left L4 lamina. The spinal theca is slightly narrowed at L4/5 level. L5 nerve root sheaths show poor filling bilaterally.

FIGURE2B

DISCUSSION Post-laminectomy pseudomeningocele results from a dural or arachnoid tear during spinal surgery. It has been described under different names in the literature, such as spinal extradural arachnoid pouch, meningocele spurius and meningeal pseudocyst (5).

The formation of the pseudomeningocele appears to be a mechanical process. The size of the pseudocyst is determined by the size of the defect in the dura-arachnoid layer, the pressure of the spinal fluid, and the resistance of the soft tissue. The pseudomeningocele is believed to be a true herniation of the arachnoid layer through a small tear in the dura forming a sac filled with cerebrospinal fluid (5). The outflow of the spinal fluid keeps the defect open and the pseudomeningocele tends to grow with the passage of time. A small herAustralasian Radiology. Vol. 36, No. 3 , August, 1992

FIGURE 3 - Post myelogram CT demonstrates the presence of the pseudomeningocele, thickened nerve roots of cauda equina suggestive of arachnoiditis, and the bone erosion due to the pseudomeningocele.

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K.K. LAU et a1 niation of a nerve filament into the dural opening may be another factor responsible for keeping the defect open. Other authors propose that continuous extravasation of cerebrospinal fluid through the dural and arachnoid tear into the retrolaminar space can eventually develop a surrounding fibrous capsule forming a sac (6,7). Teplick suggested that both types exist depending on the length of initial tear (2). In some cases, the pseudomeningocele can be missed on lumbar myelogram alone because there may be slow filling of the cyst through a narrow stalk or non-filling due to closure of the communication between the pseudomeningocele and the subarachnoid space (2). Pseudomeningoceles that are due to arachnoid herniation are more likely to maintain this communication. Hydrosoluble contrast medium may be more valuable in defining a sac communicating with the subarchnoid space because of its easy diffusibility in the cerebrospinal fluid (6). In this particular case, the communication between the subarachnoid space and the pseudomeningocele was readily detected on myelogram. If a pseudomeningocele is to be excluded after the normal introduction of contrast via a lumbar puncture, prone, supine and erect films should be performed in an attempt to fill the pseudomeningocele and outline its communication. This may not be possible if the communication is narrowed or closed. A post-myelogram CT examination of the lumbar spine will not only demonstrate if there is filling of the pseudomeningocele with contrast but may demonstrate other causal pathology

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which was not suspected. It will clearly delineate any sequelae of the pseudomeningocele such as bone erosion and vertebral body scalloping. A delayed CT examination may be helpful in demonstrating a slow filling pseudomeningocele with a narrow communication.

tion with the subarachnoid space. Post-myelography CT scanning with or without delay and ideally magnetic resonace imaging are helpful in detecting pseudomeningoceles and other pathology.

At present, CT scanning has been considered the most important noninvasive diagnostic procedure for detection of pseudomeningocele (8). If available, magnetic resonance imaging can delineate the location, extent and internal characteristics of pseudomeningocele, as well as giving a complete, non-invasive evaluation of the spinal cord, thecal sac, disc herniation, haematoma, and skeletal and para-spinal soft tissue abnormalities

We are grateful to Ms Kylie Chan for preparing the manuscript and Ms Danielle Edwards for the medical illustration.

(9). The case we have illustrated demonstrated unusual bone erosion caused by the pseudomeningocele. If plain spinal X-rays show scalloping of the posterior aspect of vertebral bodies, or erosion of laminae or articular processes in a post-laminectomy patient with recurrent back pain and lower limb neurological signs, the possibility of pseudomeningocele should be considered.

3.

SUMMARY Although uncommon, postlaminectomy pseudomeningoceles may occur more frequently than indicated by previous studies. If there is radiological evidence of bone erosion in a post-laminectomy patient, a pseudomeningocele should be excluded. Lumbar myelography alone may not detect a pseudomeningocele with a narrow or closed communica-

ACKNOWLEDGEMENTS

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Swanson HS, Fincher EF. Extradural arachnoidal cyst of traumatic origin. J Neurosurg 1947; 4: 530-538. Teplick GJ, Peyster RG, Teplick SK et al. CT identification of post laminectomy pseudomeningocele. AJR 1983; 140: 1203- 1206. Koo J, Adamson R, Wagner F et al. A new cause of chronic meningitis: infected lumbar pseudomeningocele. AM J Med 1989; 86: 103-104. Hadani M, Findler G , Knoler N et a l . Entrapped lumbar nerve root in pseudomeningocele after laminectomy: report of three cases. Neurosurg 1986; 19: 405-407. Miller P, Elder F. Meningeal pseudocysts (Meningocele spurius) following laminectomy. J Bone Joint Surg 1968; 50: 268-276. Pagni C, Cassinari V, Bernasconi V. Meningocele spurius following hemilaminectomy in a case of lumbar discal hernia. JNeurosurg 1961; 18: 709-710. Rinaldi I. Peach W. Postoperative lumbar meningocele. J Neurosurg 1970; 30: 504-507. Schumacher H, Wassmann H, Podlinski C. Pseudomeningocele of the lumbar spine. Surg Neurol 1988; 29: 77-78. Freedy R, Miller K, Eick J et al. Traumatic lumbosacral nerve root avulsion: evaluation by MR imaging. J Comput Assist Tomogr 1989; 13: 1052-1057.

Australasian Radiology, Vol. 36, No. 3, August, 1992

Post-laminectomy pseudomeningocele: an unusual cause of bone erosion.

Pseudomeningocele is a rare complication of laminectomy, which can cause recurrent back pain with or without radicular signs. A case of bone erosion o...
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