Meningeal Sarcoma and Meningeal Hemangiopericytoma

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CHAPTER 132 Meningeal Sarcoma and Meningeal Hemangiopericytoma

Alim M. Ladha, Barton L. Guthrie, Matthew G. Ewend

Meningeal sarcoma and hemangiopericytoma are two disparate entities that have several things in common, including being a mimic for their more benign counterpart meningioma. They are locally aggressive central nervous system (CNS) lesions with true metastatic potential that are best treated by gross total resection followed by additional therapies. Diagnosis of either lesion should lead to an exhaustive systemic work-up because they are uncommon as primary intracranial lesions. Meningeal sarcoma and hemangiopericytoma do not have a unique constellation of symptoms but rather produce symptoms based on their intracranial location.

This chapter reviews the history, pathology, clinical significance, and typical treatment paradigms for meningeal sarcoma and meningeal hemangiopericytoma.

Meningeal Sarcoma

History

Sarcomas are tumors arising from mesenchymal tissue. Sarcoma is derived from the Greek word sar, which denotes a fleshy character related to the gross appearance of these tumors.¹ Sarcomatous tumors of the leptomeninges were described as early as 1929.² Although Virchow had reported CNS sarcomas before this, he actually may have been describing high-grade gliomas.³ In 1953, Christensen and Lara reported 24 cases of intracranial sarcoma, which they grouped into three distinct entities: fibrous sarcoma, spindle cell sarcoma, and polymorphocellular sarcoma.⁴ The distinctions were based on light microscopy findings. This system is not part of the 2007 World Health Organization (WHO) tumor classification scheme, but it did have prognostic significance. Median survival for these three subtypes is quite different: fibrous, 74 months; spindle cell, 27 months; and polymorphocellular, less than 1 year. The 2007 WHO classification of tumors of the CNS separates intracranial sarcomas according to their pattern of differentiation rather than their cell of origin (Table 132-1).⁵

TABLE 132-1 Tumors of the Meninges

Adapted from Louis DN, Ohgaki H, Wiestler OD, et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol. 2007;114:97-109.

Clinical Significance

Sarcoma progenitors cells are derived from mesenchymal tissue. The nervous system has multiple tissues of mesenchymal origin and thus may serve as the origin for sarcomas: dura, pia-arachnoid, stroma of the choroid plexus, adventitial fibroblasts associated with blood vessels, and tela choroidea.^3,⁶ Intracranial sarcomas may arise in continuity with the meninges or as intraparenchymal masses without a dural base when the origin is from blood vessels, the tela choroidea, or the choroid plexus stroma.

One can classify intracranial sarcomatous lesions into seven distinct groups ^7,⁸:

1 Primary sarcomas of the brain and meninges that arise de novo

2 Sarcoma arising in the context of meningioma

3 Sarcoma after treatment of the brain with radiotherapy

4 Gliosarcoma

5 Intracranial metastases from sarcomatous primary tumors outside the CNS

6 Sarcomas arising from the scalp and skull with intracranial extension

7 Nonmalignant tumors that may simulate sarcoma because of pleomorphism (pleomorphic xanthoastrocytoma, benign fibrous histiocytoma) or fascicular arrangement of the spindle cells with marked desmoplasia (superficial cerebral astrocytoma, desmoplastic infantile ganglioglioma)

Lesions in the last group are not true sarcomas but do share some common histologic findings. The first three entities are discussed in this chapter. Gliosarcoma is classified as a subtype of glioblastoma, an astrocytic tumor of neuroepithelial origin.⁵ The entity sarcoglioma, or the development of a glial neoplasm associated with a primary intracranial sarcoma, is discussed later. Sarcomatous metastases are similar in clinical behavior to other brain metastases and are discussed elsewhere. It is important to note that these metastases are histologically indistinguishable from primary CNS sarcomas, although new molecular techniques may enable us to elucidate the etiology of these lesions. Given the rarity of primary intracranial sarcomas, the finding of sarcomatous tissue in the brain should lead to a thorough search for a primary source outside the CNS. Scalp and skull tumors are discussed in separate chapters of this text.

Sarcomas can occur at any age. They account for just 0.1% to 3% of all intracranial tumors in both adult and pediatric series.^7,⁹ The less well-differentiated sarcomas (Christensen and Lara’s polymorphocellular sarcomas) usually occur in infants and young children. Meningeal sarcomatosis, or diffuse infiltration of the dura by sarcomatous cells in the absence of a clear mass, also tends to occur in very young children. Most authors have reported that the incidence is equal in males and females.^7,¹⁰ Sarcomas can occur at any site in the brain. In Paulus and coworkers’ series, 12 of 19 tumors (63%) were in direct contact with the dura.⁷ The remainder arose within the parenchyma of the brain, presumably from the mesenchymal tissue associated with blood vessels, the tela choroidea, or the choroid plexus. With the exception of rhabdomyosarcomas, which reportedly occur more frequently in the posterior fossa¹¹ and in the midline,¹² sarcomas occur with equal likelihood throughout the cranium.¹²

Pathology and Pathogenesis

The most recent revision of the WHO classification of brain tumors includes an expanded section on the wide range of mesenchymal tumors occurring in the CNS. The committee based this classification on the system for soft tissue tumors occurring outside the CNS.¹³ Differentiation of sarcomas by pathology is based on light microscopy (such as islands of cartilage in chondrosarcoma and osseous areas in osteosarcoma), immunohistochemistry (desmin and myoglobulin positivity in rhabdomyosarcoma), or ultrastructural features (Z bands in rhabdomyosarcoma).

The macroscopic appearance of these lesions is heterogeneous, but they tend to be large. Those arising from the dura are often firm, whereas those arising without clear dural attachment are often softer. In contrast to gliomas, sarcomas tend to be more distinct, with clearer macroscopic borders between the tumor and surrounding brain. They also tend to be firmer than gliomas. Hemorrhage, cysts, and necrosis can be seen within sarcomas.^11,^12,¹⁴

Angiosarcoma

These rare tumors constitute less than 1% of all sarcomas and usually arise in the skin or superficial soft tissues.¹¹ Occasionally, they arise from intracranial vessels. They typically have a spongy appearance because of abundant vessels. In more differentiated areas of the tumor, vascular channels may be seen. The basement membrane of the vessels can be demonstrated with a reticulum stain. Brain invasion is frequently seen with these lesions despite a circumscribed radiographic appearance.¹¹

Chondrosarcoma

These tumors arise from the dura, from the skull base, or rarely, from intraparenchymal sources.¹³ Chondrosarcomas arising in the fourth ventricle¹⁵ or in the falx¹⁶ have been reported. Some of these tumors exhibit a lower grade of malignancy than other sarcomas, but local recurrence and local aggressive behavior are still seen frequently.¹² Histologically, the cartilage component is less well developed, and the tumors are more cellular and pleomorphic than chondromas.¹⁴ Intracranial chondrosarcomas represent 0.15% of all primary intracranial lesions.¹⁴

Mesenchymal Chondrosarcoma

These lesions are usually attached to the dura and may occur in either the cranial vault or the spinal canal. They are often found in the first or second year of life. Mesenchymal chondrosarcomas exhibit a pattern of pale staining and atypical chondroid areas alternating with compact cellular aggregates.¹² Other histologic characteristics include thin-walled vascular spaces and limited areas of bone formation. These sarcomas have a moderate tendency to recur locally⁹ and may metastasize distantly.¹⁷

Rhabdomyosarcoma

These malignant tumors are composed of rhabdomyoblasts. They can arise either in the brain parenchyma or from the leptomeninges. They occur more frequently in children, often in the posterior fossa,^7,^11,¹³ where they can be difficult to differentiate from medullomyoblastoma. Rhabdomyosarcoma can also be seen as part of germ cell tumors of the pineal and suprasellar region.¹³ Histologically, these tumors are highly cellular and have myoblastic components. The diagnosis is aided by immunohistochemistry for myoglobin, myosin, muscle-specific actin, and desmin.¹³ Ultrastructure observations include the presence of Z bands and disorganized thick and thin filaments.¹³

Fibrosarcoma

Fibrosarcomas are the most common intracranial sarcomas (Fig. 132-1)¹¹^–¹³ and are more frequently seen in adults.⁷ They develop as a component of gliosarcoma, after radiotherapy (particularly treatment of the sella for pituitary adenoma), or as a primary intracranial sarcoma. These tumors arise from the dura or leptomeningeal infolds and can extend along the Virchow-Robin spaces.¹³ The tumors appear similar to fibrosarcomas occurring elsewhere in the body. Thus, a careful search for another primary site should be made if the diagnosis of intracranial fibrosarcoma is entertained. Given the higher frequency of gliosarcoma than fibrosarcoma, careful staining of the specimen with glial fibrillary acidic protein should be performed to exclude a glial component and the diagnosis of gliosarcoma.¹³

FIGURE 132-1 Dural-based fibrosarcoma in a child. A coronal, contrast-enhanced, T1-weighted magnetic resonance image shows a large and homogeneously enhancing mass in the left temporoparietal region. The mass does not invade the skull; it displaces the cortex inwardly but does not invade it radiographically.

It may be difficult to differentiate between a true fibrosarcoma and sarcomatous degeneration of a meningioma. Burger and Scheithauer identified the following as useful methods for making that distinction.¹³ First, the well-known herringbone appearance of fibrosarcoma is not usually seen after sarcomatous degeneration of a meningioma. Second, meningioma stains for epithelial membrane antigen (EMA), whereas fibrosarcoma does not. Unfortunately, not all malignant meningiomas stain for EMA. Thus, the presence of EMA immunostaining supports the diagnosis of a malignant meningioma, but its absence does not exclude it. Third, a past history of meningioma aids in the diagnosis, as does the presence of whorls or psammoma bodies.

Malignant Fibrous Histiocytoma

This rare intracranial tumor is histologically similar to its extracranial counterpart. Histologic findings include high cellularity, nuclear polymorphism, and varying inflammation.¹³ These tumors can arise in the dura¹⁸ or, less commonly, intraparenchymally.¹⁹ In Paulus and coworkers’ series, malignant fibrous histiocytomas were more common in adults.⁷

Primary Meningeal Osteosarcoma

Primary meningeal osteosarcoma is an extremely rare entity described in the literature only via case reports. Review of the literature demonstrates six cases. These tumors arise from the meninges and are within the differential diagnosis for dural-based lesions.²⁰ They are typically treated by aggressive resection and subsequent radiation therapy.

Other Sarcomas

Primary meningeal sarcomatosis refers to diffuse spread of sarcomatous tissue throughout the meninges without a focal mass.¹¹ Most cases are reported in young children. The tumor in the subarachnoid space covers the surface of the brain and may grow along penetrating vessels into the brain, as well as into the spinal and cranial nerves. Additionally, tumor can surround the spinal cord.⁹ Histologically, small, round tumor cells are usually seen.

Extraskeletal lesions with histologic findings identical to those of the bony lesions of Ewing’s sarcoma are rare but well described.²¹^–²⁵ The most frequent site involving the nervous system is the epidural space (particularly in the spine), but intraparenchymal lesions have also been described. Distant metastases from these lesions can subsequently be seen.¹² It has been suggested that these tumors are a type of the small, round cell tumor derived from neuroendocrine tissue¹² rather than from mesenchymal tissue. If so, they are not truly sarcomas. Recent evidence has classified these tumors as central and peripheral primitive neuroectodermal tumors, but they are still classified as mesenchymal tumors in the 2007 classification.

The cause of intracranial sarcomas is often unknown. Sarcoma develops in some patients after radiotherapy for a brain tumor ²⁶ and has developed in at least one patient after chemotherapy for a brain tumor.²⁷ Of the seven cases reported by Chang and colleagues, four were fibrosarcomas and three were malignant fibrous histiocytomas. Radiation doses ranged from 1600 to 6000 Gy.²⁶ The median time to diagnosis of the tumor was 8 years after radiation therapy. Sarcomas have been reported most frequently after irradiation of the sella for pituitary adenoma.^8,²⁸ The median time to development of sarcoma was 10 years, the minimum dose was 2000 Gy, and multiple courses of radiation increased the risk. Histologically, there may be evidence of recurrent adenoma within the sarcoma.^13,²³

Clinical Findings and Evaluation

The clinical features of patients with meningeal sarcomas are similar to those of other patients with malignant intracranial tumors. Symptoms are due to mass effect from the tumor or peritumoral edema (Fig. 132-2). Clinical symptoms include headaches, seizures, weakness, mental status changes, or symptoms of hydrocephalus (Table 132-2). Patients seen in this fashion are usually stabilized with therapy for increased intracranial pressure, such as steroids. If the tumor erodes through the skull into the soft tissues of the scalp, it may be manifested as a palpable mass (Fig. 132-3). Imaging should be obtained immediately.

FIGURE 132-2 Undifferentiated sarcoma in a child. An axial, contrast-enhanced, computed tomographic scan shows a large enhancing mass in the right frontal region. It is an extra-axial mass with a large intracranial component that also extends through the skull into the overlying scalp. The involved bone is thick. There is a small amount of edema in the right frontal lobe, and the tumor is exerting a mass effect on the frontal lobe.

TABLE 132-2 Symptoms of Dural-Based Lesions Vary According to Location

LOCATION	SYMPTOMS
Frontal/parietal	Affective, hemiparesis, neglect, sensory disturbance, seizures; may be asymptomatic
Temporal	Seizures, speech disturbance
Frontal fossa	Behavioral disorder, olfactory loss
Sellar/parasellar	Visual loss, pituitary disturbance
Sphenoid wing	Visual disturbance, psychiatric disturbance, seizures, speech disorders
Cavernous sinus	Eye movement disturbance, facial pain or numbness
Posterior fossa	Ataxia, hydrocephalus, cranial nerve dysfunction

FIGURE 132-3 Undifferentiated sarcoma in an adult. A coronal, contrast-enhanced, T1-weighted magnetic resonance image shows a large mass in the right temporoparietal region. The mass is resulting in inferior displacement of the right lateral ventricle. The mass extends into the skull and overlying scalp.

Intracranial sarcomas have no typical imaging features. When they arise from the dura, they may simulate the more common meningioma (see Fig. 132-1). The presence of bone erosion overlying the mass suggests a more malignant tumor, but this finding may also be seen with typical and atypical meningioma. Extension into the scalp is more common with sarcoma than with meningioma. Underlying edema is also nearly universal with sarcomas but may also be seen in up to 50% of typical meningiomas. Invasion of the superficial venous structures may occur with both types of tumors. Although most adult CNS sarcomas are extra-axial masses, sarcomas and meningiomas in children commonly arise as intra-axial or intraventricular masses. Intraparenchymal sarcomas have no specific imaging features.

Imaging

Plain radiographs do not play a role in the diagnosis of these tumors. Computed tomography (CT) shows the tumors to be hypodense, isodense, or slightly hyperdense to brain tissue before the administration of contrast material. After the administration of iodinated contrast material, all CNS sarcomas enhance. This enhancement is most commonly solid and homogeneous, but it may be ring-like. CT is ideal to evaluate bone invasion or to help identify sarcomatous changes in patients with underlying fibrous dysplasia. CT provides limited evaluation of the subarachnoid space.

Magnetic resonance imaging (MRI) is probably the method of choice for the evaluation of CNS sarcomas, as it is for most brain tumors. The tumors are hypointense or isointense to brain tissue on unenhanced T1-weighted images. On T2-weighted images, they may be slightly hypointense, a finding that may reflect hypercellularity. All tumors show some enhancement after the intravenous administration of gadolinium, similar to that seen on CT. MRI is ideal to evaluate extension through the bone into the scalp, invasion of superficial venous structures, and extension into the soft tissues of the base of the skull. Direct evaluation of the bones in the base of the skull requires CT. Edema is better mapped with T2-weighted MRI.

Angiography plays a limited role in the evaluation of these tumors. It is no longer used for tumor localization but may be used to map blood supply to the lesion. In sarcomas, blood supply can be derived from the internal carotid artery, the external carotid artery, or both.¹ Hypervascular tumors may benefit from presurgical embolization to decrease their blood supply. Angiography may also show vessel encasement by tumor, but MRI is a better means of visualizing encasement. Sonography has a very limited role in the evaluation of these tumors. It may be used for diagnosis of tumors in utero,²⁹ for screening of newborns with enlarging heads (Fig. 132-4), and as an aid to intraoperative localization of sarcomas arising in the brain parenchyma.

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