Spinal Extradural Meningeal Cyst: Correct Radiological and Histopathological Diagnosis

Kimiaki Sato, MD, Kensei Nagata, MD, Yasuo Sugita, MD

Disclosures

Neurosurg Focus. 2002;13(4) 

In This Article

Discussion

Spinal meningeal cysts are uncommon, accounting for 1 to 3% of all spinal tumors.[3,8] Spinal meningeal cysts occur most frequently in the thoracic spine (65%), followed by the lumbar and lumbosacral spine (13%), the thoracolumbar spine (12%), the sacral spine (6.6%), and the cervical spine (3.3%).[2] Most of the lesions are located posteriorly in the spinal canal. The present sex ratio of female to male (2:1) patients is the reverse of that in previous series.[7] Thoracic cysts typically occur in adolescents, and sacral cysts are more often found in adults.[2]

Intermittent exacerbation of symptoms may occur with postural changes and Valsalva maneuvers.[2] Intermittent episodes of remission are shown in more than 30% of patients, although in the majority episodes progress in severity over months.

Magnetic resonance imaging is very effective when diagnosing meningeal cysts and does not require intrathecal injection of contrast medium. It can correctly delineate the cyst, which has a CSF signal intensity, and define its anatomical relation to the surrounding structures. Many authors believe that MR imaging should completely replace myelography in cases involving spinal meningeal cysts. Once the cyst is identified, however, myelography and/or CT myelography may aid in demonstrating any connection between the cyst and the subarachnoid space.

Myelography or intraoperative inspection has demonstrated a subarachnoid space-cyst cavity connection in approximately half the cases.[2] In a recent study, however, the authors suggested that such a connection exists in nearly all cases of a meningeal cyst.[9] A subarachnoid space-cyst cavity connection was identified in all five cases in this series.

Computerized tomography myelography demonstrates partial or complete CSF block in the spinal canal. The extradural position of the meningeal cyst is verified by its displacement in the subarachnoid space and its common extension through several intervertebral foramina. The cyst itself usually spans several vertebral bodies in length.

It has been reported that, histopathologically, the cyst wall consists of fibrous connective tissue with or without an inner single-cell lining, which may represent an arachnoid membrane.[2,4,9] These findings have suggested that the cyst originates from the meninges because of the thick collagenous outer wall and a less consistent inner layer of arachnoid.[1] The primary origin of the extradural meningeal cyst, however, remains uncertain.

The differential diagnosis includes tumor, ependymal cysts, epi- or dermoid cysts, enterogenous cysts, and teratogenous cysts.[1] An ependymal cyst is typified by its lining of cuboidal-to-columnar, nonstratified, ciliated epithelium. It is usually situated anterior to the cervical cord and is found predominantly in children. Epidermoid and dermoid cysts occur most frequently in the lumbosacral area. Keratinizing squamous epithelium lines both cysts, but the wall of the dermoid contains sebaceous glands and hair follicles. Although rare, an enterogenous cyst most often affects the cervical and upper thoracic region. The cyst wall is only simple cuboidal or columnar epithelium, with or without cilia. The presence of an anterior osseous defect and/or goblet cells supports the diagnosis. A teratogenous cyst occurs at any level of the intradural compartment and is variably composed of neuroecto-, ecto-, endo-, and mesodermal derivative.

In previous reports, surgeons resected the cyst wall from the posterior aspect of the thecal sac and closed the dural defect to eradicate the valvelike mechanism.[4,5,10] Because the remaining cystic wall does not promote recurrence, total resection is unnecessary if the posterior wall of the thecal sac has been explored and the dural opening has been obstructed. In general, asymptomatic patients do not need surgery. Surgery is usually recommended in cases involving a large cyst with a mass effect and associated symptoms.[6]

Although a spinal meningeal cyst is rare, it should be kept in mind, especially when leakage of contrast medium is suspected during myelography and/or CT myelography. The diagnosis of a spinal extradural meningeal cyst is not made solely on histopathological findings. It is essential that the final characterization and diagnosis be based on combined intraoperative inspection, radiological findings, and histopathological results.

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