CHAPTER 30 Tumors of the Meninges and Related Tissues: Meningiomas and Sarcomas Kimberly P. Cockerham, John S. Kennerdell, Joseph C. Maroon, and Ghassan K. Bejjani ANATOMY OFTHE MENINGES Associations Dura Mater Diagnosis Arachnoid Treatment Pia Mater Adjuvant Therapy MENINGIOMAS Clinical Characteristics by Location Histogenesis SARCOMAS OFTHE MENINGES AND BRAIN Incidence Chondrosarcoma Pathology Osteogenic Sarcoma Cytogenetics Primary Sarcoma of the Meninges and Brain Endocrinology Rhabdomyosarcoma ANATOMY OF THE MENINGES The meninges of the brain and spinal cord consist of three into several freely communicating compartments. They in- different layers: the dura mater, arachnoid (tela arach- clude the falx cerebri, the tentorium cerebelli, the falx cere- noidea), and pia mater. Considerable anatomic differences belli, and the diaphragma sellae. exist among these structures, and these differences influence The falx cerebri, so named because of its sickle-like form, the nature, location, and spread of tumors that arise from is a fixed, arched process that descends vertically in the them. longitudinal fissure between the cerebral hemispheres (Fig. 30.2). The tentorium cerebelli is an arched lamina that is DURA MATER elevated in its midportion and inclines downward toward its peripheral attachments on both sides. It covers the superior The dura mater, typically referred to as the dura, is a thick surface of the cerebellum and supports the occipital lobes membrane that is adjacent to the inner table of the skull and (Fig. 30.2). The falx cerebelli is a small triangular process acts both as the functional periosteum of the skull and the of dura mater that lies beneath the tentorium cerebelli in outermost membrane of the brain (Fig. 30.1). In the spinal the posterior cerebellar notch between the two cerebellar canal, this dura is separated from bone by a space that con- hemispheres. It is attached superiorly to the undersurface of tains epidural adipose and areolar tissue. At the orbital end the posterior portion of the tentorium cerebelli. Its posterior of the optic canal, the dura encloses the intracanalicular por- and inferior attachments are to the occipital bone and the tion of the optic nerve and splits into an inner layer that foramen magnum. becomes the dural sheath surrounding the orbital portion of The diaphragma sellae is a small horizontal fold of dura the optic nerve and an outer layer that becomes the perios- that roofs the sella turcica and almost completely covers teum of the walls of the orbit, the periorbita. the pituitary gland (Fig. 30.3). The infundibulum extends In several areas of the brain, dural processes extend in- through an opening in the diaphragma that varies consider- ward. These processes or infoldings divide the cranial cavity ably in size (1,2). 1483 1484 CLINICAL NEURO-OPHTHALMOLOGY Figure 30.1. The cerebral dura mater. The superior sagittal sinus has been opened, together with its lateral lacunae, to expose arachnoid granulations. (From Gluhbegovic N, Williams TH. The Human Brain: A Photographic Guide. Hagerstown, MD, Harper & Row, 1980.) Figure 30.2. The falx cerebri (FC). This sickle- shaped dural structure is attached superiorly to the inner surface of the skull in the midline as far posteriorly as the internal occipital protuberance. This attachment contains the superior sagittal sinus (SSS). The inferior border of the falx cerebri arches over the corpus callosum (CC) and contains the inferior sagittal sinus (ISS). This border is at- tached to the crista galli (CG) anteriorly and the tentorium cerebelli (TC) posteriorly. (From Gluh- begovic N, Williams TH. The Human Brain: A Photographic Guide. Hagerstown, MD, Harper & Row, 1980.) TUMORS OFTHE MENINGES AND RELATED TISSUES 1485 Figure 30.3. The diaphragma sellae. A, Schematic drawing of the pituitary gland showing its relationship to the intracranial portion of the optic nerve (ON) and the optic chiasm (C). The gland is surrounded by dura except at the site of exit of the pituitary stalk. The portion of dura covering the superior surface of the gland is the diaphragma sellae (arrowheads). B, Midsagittal section of the sellar region showing the pituitary gland and surrounding structures. The diaphragma sellae covers the entire superior surface of the gland except in the region of the stalk. (From Renn WH, Rhoton AL Jr. Microsurgical anatomy of the sellar region. J Neurosurg 1975;43Ϻ288–298.) ARACHNOID The arachnoid is a delicate membrane that consists of bundles of white fibrous and elastic tissue intimately blended together (Figs. 30.4 and 30.5). Its outer surface is covered with at least one, and often as many as ten, layers of flat, elongated cells (arachnoid cap cells). These cells are sepa- rated from the rest of the arachnoid layer by a thin basal lamina. In the region of the arachnoid villi, they serve as conduits for the cerebrospinal fluid (CSF) into the venous circulation of the dural sinuses. Figure 30.4. The cerebral arachnoid. On the superolateral surfaces of both cerebral hemispheres, the arachnoid appears as a delicate, transparent membrane through which the contours of the cerebral gyri can be seen, along with the venous and arterial channels that traverse the subarachnoid Figure 30.5. Schematic diagram of a coronal section of the meninges and space. Note the clusters of arachnoid granulations along the margins of the the cerebral cortex, showing the relation of the dura mater, arachnoid, and longitudinal cerebral fissure. (From Gluhbegovic N, Williams TH. The pia mater. Note the presence of an arachnoid villus and its relationship Human Brain: A Photographic Guide. Hagerstown, MD: Harper & Row, to a dural venous sinus. (From Weed LH. The formation of the cranial 1980.) subarachnoid spaces. Am J Anat 1923;31Ϻ191–221.) 1486 CLINICAL NEURO-OPHTHALMOLOGY The arachnoid is tightly adherent to the dura so that there of age and increase in number throughout life. Large granu- is only a potential space between them, the subdural space. lations are called pacchionian bodies. The arachnoid villi The cap cells that form the outer barrier layer of the arach- and granulations are responsible for transport of CSFfrom noid and the border cells of the inner layer of the dura are the subarachnoid space to the cerebral dural sinuses. tightly fused together, forming the interface layer (3–5). In contrast, the arachnoid is separated from the pia mater by PIA MATER the CSF-filled subarachnoid space. Although the arachnoid The innermost of the three layers of the meninges, the pia is rather closely apposed to the pia mater on the surface of mater, consists of a delicate, flat sheet of cells that is re- the brain, it does not extend into cerebral or cerebellar sulci. flected from the surface of the brain to form the outer coating The arachnoid villi invaginate the dura to project into the of the meningeal vessels in the subarachnoid space (Fig. venous sinuses (Fig. 30.5). Collections of these villi, forming 30.5). The pia mater of the brain is generally thinner than cauliflower-like clumps, are called arachnoid granulations that of the spinal cord. In most areas, it is connected with (6) (Fig. 30.1). They begin to develop at about 18 months the arachnoid by fine trabeculae lined by mesothelial cells. MENINGIOMAS In the past, these tumors were called ‘‘dural endothelio- Intracranial meningiomas are most commonly detected in mas,’’ ‘‘arachnoid fibroblastomas,’’ or ‘‘meningeal fibro- the middle and late decades of life (18). Meningiomas ac- blastomas.’’ These terms implied an understanding of the count for only 2–4% of primary intracranial tumors in pa- basic histogenesis of the tumor; however, it eventually be- tients less than 20 years of age (22–24). came evident that the embryologic derivation of the tumor Some of the meningiomas that occur in childhood appear cells was far from clear. Accordingly, Cushing introduced to be congenital, producing symptoms in the first few months the term ‘‘meningioma’’ to identify tumors that originate of life (25–28). These tumors tend to be of the convexity from cells of the meninges but without specifying their pre- type and are often associated with large peritumoral cysts. cise histogenesis (7–12). Most meningiomas in children, however, occur later, in the HISTOGENESIS first and second decades of life. Neurofibromatosis and pre- vious head irradiation are both significant risk factors. One Meningiomas may be attached to any of the three layers quarter of childhood meningiomas are associated with neu- of the meninges. They originate from the arachnoid cap cells rofibromatosis. In a large series of children who had received that line the outer surface of the arachnoid and are fused with the dural border cells to produce the interface layer radiation for tinea capitis, the relative risk of developing an between the dura and the arachnoid. Although some authors intracranial meningioma was increased fourfold (24). believe that these cells are derived from the neural crest and Meningiomas that occur in childhood tend to be more are thus of neuroectodermal origin, it appears more likely aggressive than their adult counterparts (21,22). In addition, that they are of mesenchymal origin (13,14). Nevertheless, malignant degeneration, often associated with necrosis, oc- the possibility remains that neural crest elements contribute curs in 50% of pediatric meningiomas (24). There are, never- to the development of the meninges (11,15). theless, many cases of benign childhood meningiomas Cap cells are not confined to the outer layer of the arach- (29,30). Both cyst formation and intraventricular location are noid. They are also found in the stroma of the normal choroid more characteristic of meningiomas presenting in childhood plexus, particularly in the heavy tufts of the glomus portion (24,31,32). In contrast, symptomatic intracranial meningio- in the region of the trigone of the lateral ventricles. These mas are not uncommon in older patients (18,21).