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

Abstract and Introduction

Abstract

Object. Spinal extradural meningeal cysts are uncommon and rarely cause neural compression. The clinical, radiological, and histopathological characteristics of the lesions are discussed and previous reports reviewed.
Methods. The authors describe five cases of a spinal extradural meningeal cyst (three female and two male patients, with a mean age of 47 years (range 14-75 years). Four of the cysts were located at the thoracolumbar level, the fifth at the sacral level. Radiological and neuroimaging-based diagnosis was made using a combination of magnetic resonance imaging, myelography, and/or computerized tomography (CT) myelography.
A connection between the spinal subarachnoid space and the cyst cavity was demonstrated on myelography and/or CT myelography in all cases, and dural defects were confirmed visually intraoperatively. In all cases histopathological examination confirmed that the cyst wall was formed by nonspecific fibrous connective tissue without a single-cell layer of inner arachnoid lining.
Conclusions. A diagnosis of spinal extradural meningeal cyst is difficult to make based solely on histopathological examination. It is essential that the final characterization and diagnosis be based on intraoperative inspection combined with radiological and histopathological findings.

Introduction

Spinal extradural meningeal cysts are an uncommon cause of spinal cord or nerve root compression. The actual lining of the cyst cavity may or may not be shown to be arachnoidal tissue on histological examination. Therefore, the term "extradural arachnoid cyst" is used interchangeably with "extradural meningeal cyst." The classification of spinal meningeal cysts in the literature is indistinct and, in certain categories, histologically misleading. Goyal, et al.,[6] observed that extradural arachnoid cysts were synonymous with sacral meningoceles, arachnoid pouches, arachnoid diverticula, and meningeal cysts. Nabors, et al.,[9] have simplified the classification of spinal meningeal cysts into three major categories: extradural cysts without nerve root fibers (Type I); extradural cysts with nerve root fibers (Type II); and intradural cysts (Type III). Type IA is a so-called extradural meningeal cyst (extradural arachnoid cyst), Type IB is a sacral meningocele (occult sacral meningocele), Type II is a Tarlov perineural cyst or a spinal nerve root diverticulum, and Type III is an intradural arachnoid cyst.

Magnetic resonance imaging appears useful as an initial modality to identify the cystic mass. Myelography and/or CT myelography are essential to reveal any connection between the cyst and the subarachnoid space. Demonstration of this connection allows for an accurate diagnosis of a spinal meningeal cyst.

The final characterization is based on both the intraoperative inspection and the histopathological findings. A diagnosis of a spinal meningeal cyst should not be based solely on histopathological findings. In this study, we present five cases of a Type I spinal meningeal cyst, including one previously reported case.[11]

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