727 Review Article Diseases of the Intracranial Meninges: MR Imaging Features Gordon Sze1 Although the meninges are often thought of simplistically as a connective tissue sac that contains the CSF and the contents of the CNS, they are far more complex. Anatomically, they com- prise several layers. Pathologically, numerous disease pro- cesses may affect the meninges; different processes may even involve different areas of the meninges. These factors all influ- ence the MR imaging characteristics of meningeal lesions. This review briefly discusses the anatomy of the meninges, the MR imaging technique when meningeal disease is suspected, and the appearance of the normal meninges. It then focuses on tumors, infections, cysts, and other lesions that primarily involve the meninges, excluding lesions that secondarily involve the meninges. Anatomy Anatomically, the cranial meninges comprise the dura mater, the arachnoid, and the pia mater. In the skull, the outer layer of the dura mater is closely applied to the inner table of the skull and corresponds to the periosteum [1]. It not only has connective and supportive functions but also may play a role in the formation of the cranial bones. This outer portion of the dura mater contains the meningeal arter- ies and veins, which form grooves in the inner table of the skull [2]. It is composed of elongated fibroblasts and con- tains large intercellular spaces. The inner layer of the dura mater consists of epithelial cells. Although the outer layer of the dura mater terminates at the foramen magnum, the inner layer continues into the spinal canal to form the spinal dura mater. The arachnoid is closely applied to the inner layer of the dura mater. Between the inner layer of the dura mater and the arachnoid is the potential subdural space, which is tra- versed by scattered trabeculae. Within the arachnoid is the CSF. The pia mater, finally, is applied closely to the surface of the brain and invests itself into the sulci. It is composed of collagenous fibers externally and vermicular and elastic fibers internally. The pia mater adheres to the adjacent neu- ral tissue. The pia mater and arachnoid together are referred to as the leptomeninges. Further details regarding anatomy can be found in standard texts [1]. MR Technique and Normal Appearance of the Meninges In the evaluation of suspected meningeal disease pro- cesses, MR imaging of the head is straightforward. A typical protocol consists of unenhanced short-TR and Iong-TR axial sequences, followed by contrast-enhanced short-TR axial sequences (e.g., 500/30 [TR/TE]). Other planes may pro- vide additional information. Contrast-enhanced short-TR coronal sequences can be particularly helpful. This protocol also permits evaluation of extraaxial cystic collections. Dif- ferentiation of true cysts from hematomas, whether acute or chronic, is generally straightforward. In the evaluation of meningeal processes, MR imaging is more sensitive than CT [3]. The inner table of the skull often obscures small lesions or subtle enhancement in the meninges on contrast-enhanced CT scans. With MR, even small lesions are easily detected. Received August 31, 1992; accepted after revision November 11, 1992. Presented in part at the annual meeting of the American Roentgen Ray Society, Orlando, FL, May 1992. of Diagnostic Radiology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510. Address correspondence to G. Sze. AJR 1993;160:727-733 0361-803X/93/1604-0727 © American Roentgen Ray Society Downloaded from www.ajronline.org by 14.165.91.109 on 07/24/23 from IP address 14.165.91.109. Copyright ARRS. For personal use only; all rights reserved
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