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:

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

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.

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

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.

FIGURE 132-4 Fibrosarcoma versus malignant fibrous histiocytoma in a young child. A, Oblique, coronal sonogram showing a large mass in the right hemisphere containing cystic (c) and solid (s) portions. B, An axial, contrast-enhanced computed tomographic scan confirms the complex appearance of the mass, its extra-axial location, a midline shift to the left, and dilation of the left lateral ventricle because of entrapment of its foramen. The mass was resected completely.

Treatment

Treatment options include surgery, radiotherapy, and chemotherapy. The goal of surgical therapy, as with all sarcomas, is complete surgical excision. Unfortunately, brain invasion is common with these lesions despite their circumscribed appearance on imaging studies. This often prevents obtaining a tumor-free margin. There are numerous case reports of long-term survivors after aggressive surgical resection with or without subsequent radiotherapy.¹⁰ The best outcome usually follows radical resection of a well-circumscribed tumor (fibrosarcoma or mesenchymal chondrosarcoma).³

Surgical technique focuses on careful resection of the tumor. Parenchymal invasion can make total excision difficult without the sacrifice of functioning brain and surface vessels. Frozen section pathologic margins may be useful when total excision is desired because microscopic invasion is not grossly apparent. After maximal possible resection, standard neurosurgical attention to hemostasis is imperative. Because these tumors often invade surrounding structures (dura, bone), care must be taken to confirm that the remaining dura or bone is free of tumor.

The exact role of radiotherapy and chemotherapy for CNS sarcomas is not yet established. Clearly, these modalities play a significant role in the treatment of sarcomas that occur elsewhere in the body. Because sarcomas of the CNS are histologically similar to those occurring elsewhere, it has been suggested that these therapies may have a role in treating CNS sarcomas as well, but supportive data for this hypothesis are lacking. However, current treatment strategies include radiation therapy for subtotal resection either in the form of conformal radiation therapy or stereotactic radiosurgery for residual or recurrent disease.³⁰

In general, patients with these tumors have short survival periods. Frequently, the tumors recur locally despite aggressive resection. Furthermore, metastatic disease is not uncommon. For determining prognosis, the histologic subtype of the tumor is a strong predictor. Patients with fibrosarcoma often have rapid progression of their disease and a median survival of 6 to 9 months. Local recurrence is common, and metastases can also be seen.^12,31,32 Local high-dose radiation therapy is used frequently in these patients. Subarachnoid spread can also occur. Treatment of patients with rhabdomyosarcoma is difficult. Despite aggressive chemotherapy and radiation therapy, most studies report median survival of less than 24 months.³² Children with meningeal sarcomatosis have a poor prognosis. Their clinical course can mimic that of meningoencephalitis.¹² Surgical resection is not possible because of the diffuse nature of the tumor, and the condition is usually fatal within a few weeks.³³

Discussion

Sarcomas arise from tissue of mesenchymal origin. In the brain, these tumors are most often in continuity with the dura. However, because of the mesenchymal origin of blood vessels and tela choroidea, intraparenchymal sarcomas can be seen. The pathologic classification of these tumors is based on the classification of soft tissue tumors arising outside the CNS. Sarcomas are organized according to the pattern of differentiation that they follow, which is determined by standard light microscopy, immunohistochemistry, and electron microscopy.

Because true intracranial sarcomas are rare, the differential diagnosis of these lesions includes metastatic sarcoma from a remote site. A thorough search for a primary sarcoma outside the CNS is recommended. The differential diagnosis also includes lesions from the leptomeninges (meningioma, malignant meningioma, hemangiopericytoma), gliosarcoma, and nonmalignant soft tissue tumors. MRI is the main imaging study for these lesions. Occasionally, angiography to define vessel involvement or CT to evaluate bony destruction may be valuable. Treatment generally involves an attempt at radical surgical excision, a common theme in case reports with long-term survival. Frequently, radiotherapy and chemotherapy are added, although data supporting their use are not yet available.

History

Meningeal hemangiopericytoma is a malignant neoplasm that occurs within the CNS and has the biologic capability to escape from the CNS and metastasize widely. The originating cells are thought to be meningeal capillary pericytes, Zimmerman pericytes, or precursor cells with angioblastic tendencies.^34,35 This lesion was dubbed hemangiopericytoma by Stout and Murray in 1942, although it was extracranial in location.³⁴ Information about this tumor comes from cases reported variably as angioblastic meningioma within large series of meningiomas^36–40 and series devoted to meningeal hemangiopericytomas.^41–51 Its biologic behavior, as well as molecular and genetic profile, suggests that this lesion may be accurately described as a dural-based sarcoma.⁵²

In 1938, Cushing and Eisenhardt identified a vascular form of meningioma and termed it angioblastic meningioma.⁵³ One variant behaved in a particularly malignant fashion, and it is to this tumor that the term angioblastic is generally applied.^53,54 Shortly thereafter, a soft tissue sarcoma called hemangiopericytoma was recognized to be histologically identical to angioblastic meningioma.^34,55,56 Begg and Garret, who gave the first report of a primary intracranial hemangiopericytoma in 1954, proposed that Cushing’s angioblastic meningioma was actually a primary meningeal hemangiopericytoma,⁵⁷ which was compatible with the known aggressive behavior of this tumor, and it was histologically identical to the tumor described by Stout and Murray.

The 2007 WHO classification differentiates meningeal hemangiopericytoma from meningioma and groups hemangiopericytoma in the category of mesenchymal tumors.⁵ Certainly, meningeal hemangiopericytoma must be recognized as a clinical entity distinct from meningioma, and management must reflect its much more aggressive behavior.

Clinical Significance

Hemangiopericytomas constitute 2% to 4% of large series of meningeal tumors.^{36,38,41,43,44,47,49,58,59} About 10% of meningeal hemangiopericytomas occur in children.⁶⁰ They can be misdiagnosed as meningioma and may be more common than reported.

Several studies have shown that unlike meningiomas, meningeal hemangiopericytomas are more common in males (56% to 75%) than females, even in the spinal location,^42,47,49,61 although a more recent study showed a slight female preponderance.⁵⁰ The average age at diagnosis is about 40 years.^48,60,61 Hemangiopericytomas are located similar to meningiomas, with 15% in the posterior fossa and 15% in the spine.^48,61,62 Of the spinal tumors, about half are in the cervical region.⁶¹ As with meningiomas, there is the occasional report of a nonmeningeal cerebral location for this tumor.^63–65 Primary multifocal meningeal hemangiopericytomas have not been reported.^49,61 These tumors are thought to account for approximately 1% of all CNS tumors.⁶⁶

Pathology and Pathogenesis

Grossly, meningeal hemangiopericytomas are firm and lobulated and vary from pink-gray to red in color. They are extremely vascular, are often adherent to the dura, but do not usually invade the brain.^47,49 They do not spread en plaque and rarely contain calcification.

The tumors are very cellular, with round to oval cells (Fig. 132-5A). The architecture varies from field to field, often resembling forms of ordinary meningioma.^35,49 The cells are arranged around thin-walled vascular spaces lined by a non-neoplastic endothelium. These “staghorn” capillaries are a distinguishing feature and can be quite numerous.^35,48

FIGURE 132-5 A, The characteristic histologic features are evident. Note the numerous thin-walled (arrowhead) capillaries (staghorn capillaries), the dense round to oval cells, and the mitotic figures. B, Reticulin stain showing reticulin encasing individual cells, which is diagnostic of hemangiopericytoma. Meningiomas have reticulin surrounding lobules of cells, not single cells.

Mitoses vary from one to several per high-powered field.^48,49 Microcysts, necrosis, and papillary architecture may be seen⁴⁹ and have been reported in up to 50% of the tumors.⁴⁸ Whorls and psammoma bodies are not seen.^48,49 Reticulin envelops individual cells (Fig. 132-5B) (thus differentiating it from meningioma, in which reticulin is scarcer and segregates the tumor into lobules). Hemangiopericytoma cells exhibit leiomyoblastic differentiation and secretion of basement membrane–like material, but surface membrane specializations (interdigitations, desmosomes, zonulae adherentes, and gap junctions) are absent.^51,52,67

Meningeal hemangiopericytomas usually contain subpopulations of cells that express factor XIIIa, which distinguishes them from meningioma and other soft tissue tumors, although this marker has been found to be positive in anaplastic meningioma as well.^52,68–70 Other markers include vimentin, HLA-DR, CD34, Leu-7, S-100 protein, CD99, and BCL-2.^52,68 Tumor cells are negative for the immunohistochemical markers factor VIII-RA and glial fibrillary acidic protein; EMA can be variable.^71,72

Hemangiopericytomas are genetically distinct from meningiomas.⁷³ Rearrangements of chromosome 12q13 are common in hemangiopericytoma, and several oncogenes are located in this region, including MDM2, CDK4, and CHOP/GADD153.^74,75 Cytogenic alterations in chromosomes 12q13, 19q13, 6p21, and 7p15 are not common in meningiomas.⁷⁶ Mutation of the NF2 tumor suppressor gene, which is frequently associated with meningiomas, is not found in hemangiopericytomas.⁷⁷ Loss of 1p32, 14q32, and 4.1B is also common in meningiomas but rarely seen in hemangiopericytoma.⁵² The biologic behavior of individual hemangiopericytomas cannot be correlated with histologic features such as mitoses, MIB-1, Ki-67, or DNA ploidy.^56,68,77

Recurrent tumors retain their histologic features, and metastatic hemangiopericytomas are histologically identical to the primary tumor.⁴⁹ Meningeal hemangiopericytomas are histologically and biologically distinct from atypical or malignant meningiomas.⁷⁸

Clinical Findings and Evaluation

Patients tend to be symptomatic for shorter periods before initial evaluation than is the case with meningioma patients, perhaps because of the more rapid growth rate of these tumors.¹⁶ The initial symptoms are related to tumor location.^47,49,61 The most frequent initial symptom is headache or focal signs related to tumor location (see Table 132-2).^42,50 Seizures are initially present in only about 16% of patients with supratentorial tumors,⁴⁹ which is compatible with the fact that they do not microscopically infiltrate the brain and grow rather rapidly. Intracranial hemorrhage as the initial symptom has also been described.⁷⁹

Imaging

Meningeal hemangiopericytomas may resemble meningiomas on imaging studies. CT typically shows a narrow or broad-based meningeal attachment. Most often the tumors appear hyperdense with focal areas of hypodensity on unenhanced CT scans and exhibit areas of heterogeneous enhancement with the administration of contrast material (Fig. 132-6).^50,80 They may have features suggesting malignancy, such as macroscopic brain invasion, or “mushrooming” inhomogeneous contrast enhancement and irregular borders.⁸¹ Bone erosion is seen in more than 50% of hemangiopericytomas,⁵⁰ and hyperostosis is not a feature of this tumor.^47,49,80,82

FIGURE 132-6 This lesion’s appearance is very similar to that of meningioma, with clearly delineated margins and a convexity location (A). Bone erosion (B) and lack of calcification, although not diagnostic, are seen. Hemangiopericytomas never show calcification or hyperostosis. The “mushroom” appearance is seen more commonly with hemangiopericytomas, but it is not diagnostic.

Hemangiopericytomas are usually isointense with gray matter and display prominent vascular flow voids on T1- and T2-weighted MRI (Fig. 132-7).⁵⁰ Heterogeneous enhancement is the most common appearance on T1-weighted gadolinium-enhanced images. About half the tumors have a dural tail sign. CT and MRI characteristics that may help differentiate hemangiopericytomas from meningiomas include a narrow-based dural attachment (seen more frequently in hemangiopericytomas) and hyperostosis of adjacent bone (seen in meningiomas but not in hemangiopericytomas).⁵⁰

FIGURE 132-7 A and B, Magnetic resonance images of the hemangiopericytoma in Figure 132-6 show that the tumor is arising from the convexity meninges and growing through the skull, as well as through the dura into the brain (arrow). Note the large vascular voids characteristic of these tumors (arrowhead). Homogeneous enhancement is not unusual.

The tumors frequently exhibit characteristic arteriographic features, including a corkscrew vascular configuration, shunting, and a long-lasting venous stain (Fig. 132-8).⁸³ As many as half have a significant internal carotid blood supply,^47,49,83 and few show early venous drainage, another factor that distinguishes them from ordinary meningiomas.^47,49 Hemangiopericytomas frequently have a dual blood supply from the internal carotid or vertebral arteries in addition to the external carotid supply.⁸⁰

FIGURE 132-8 A pre-embolization arteriogram of the lesion presented in Figures 132-6 and 132-7 shows very large meningeal feeders from the external carotid circulation along with rapid filling of the tumor (A). Selective embolization of the feeders resulted in marked devascularization (B), which greatly facilitated surgical hemostasis.

Treatment

Treatment of meningeal hemangiopericytoma requires consideration of a multimodality approach, close follow-up, and aggressive treatment of recurrence. These patients are initially seen with lesions that at first are often mistaken for meningiomas. Once the diagnosis of hemangiopericytoma has been made, it is incumbent on the treating physician to recognize the malignant character of these lesions and proceed accordingly.

The principles of surgical resection are similar to those for meningioma. Surgery with the aim of gross total resection, Simpson grade I, is the primary modality for treatment of hemangiopericytoma. This entails resection of dura, bone, and if required, brain or vascular structures if able to do so without producing an unacceptable neurological deficit. Every effort should be made to achieve complete removal at the initial resection because surgery for recurrence is often more difficult and is less effective. In large series reporting surgery for these tumors, complete resection was possible in only 50% to 67% of cases.^47,49,61 If complete removal is not possible, adjuvant radiation therapy is recommended. Disease-free survival is demonstrably longer after complete resection, and recurrence is higher after subtotal resection.^66,84,85

Preoperative embolization can be effective in reducing the vascularity of these tumors. In cases in which hemangiopericytoma is highly suspected or known, preoperative angiography and embolization can reduce blood loss and facilitate tumor removal by significantly reducing the blood supply to the lesion.⁶⁶ Fountas and coauthors reported 50% lower average blood loss with embolization.⁶⁶

Radiosurgery

Radiosurgery is reportedly effective in controlling meningioma,⁸⁶ so it would seem to be a reasonable therapeutic option for meningeal hemangiopericytoma as well. Multiple series have described the experience of stereotactic radiosurgery for residual or recurrent disease.^85,87–89 Lunsford’s group reported a series in which stereotactic radiosurgery provided local control of 80% of lesions.⁸⁸ Galanis and coworkers reported that 17 of 20 lesions in 20 patients responded favorably.⁸⁷ Chang and Sakamoto reported a good response in 75% of patients.⁸⁹ Even though all these studies had a small sample size, the evidence clearly supports the use of stereotactic radiosurgery for the treatment of recurrence or residual disease, and variable numbers of these patients also received conventional radiotherapy. Disease progression and recurrence are assessed radiographically, and response to treatment can be quite dramatic (Fig. 132-9).

FIGURE 132-9 Meningeal hemangiopericytoma can respond well to radiosurgery. This patient received a radiosurgical dose of 1500 cGy to the recurrent tumor margins (A). Magnetic resonance imaging performed 3 months later (B) shows an excellent response.

Recurrence

Meningeal hemangiopericytoma has a relentless tendency to recur, even after what is considered complete surgical resection. Allowing for variable definitions of “extent of resection” and “recurrence,” median recurrence-free intervals after resection have ranged from 40 to 78 months.^47,49,61 Many years of recurrence-free survival are not uncommon.⁴⁹ After reviewing the literature, Schroder and colleagues found the 5-year recurrence rate to be around 60%.⁶¹ From an actuarial standpoint, Guthrie and coworkers calculated 5-, 10-, and 15-year recurrence rates of 65%, 76%, and 87%, respectively (Table 132-3).⁴⁹ Kim and coauthors reported a 5-year recurrence-free rate of 59.2%, 72.7% in the total excision group and 20% in the incomplete excision group.⁸⁴ From these data it is obvious that meningeal hemangiopericytomas are much more aggressive than meningiomas and that recurrence is likely if a patient survives for 5 years; it becomes more likely with extended survival. The fact is that if the patient lives long enough, the tumor will probably recur, thus requiring close follow-up and aggressive treatment at the initial appearance of signs and symptoms.

After the first recurrence, meningeal hemangiopericytomas tend to recur at shorter intervals. In a review of 44 patients operated on 79 times, the average interval to subsequent recurrence tended to shorten.⁴⁹ The average time to a second, third, and fourth operation for recurrence was 38, 35, and 17 months, respectively. In addition, 53% of patients improved and 3% worsened after the first operation, whereas only 33% improved and 13% worsened after subsequent operations, thus again suggesting that the time for optimal patient benefit is at the first operation.

Metastasis

Meningeal hemangiopericytomas are unique in that they frequently metastasize outside the CNS. The most common sites of metastasis in descending frequency are bone, lung, and liver.^{35,36,39,41,45,47,49,61,90} The rate of metastasis of meningeal hemangiopericytoma at 5, 10, and 15 years is 13%, 33%, and 64%, respectively (see Table 132-3),⁸⁴ thus making metastasis likely with prolonged survival. Realization that extraneural metastasis can occur after years of apparent tumor-free survival is critical for the long-term management of these patients. Intra-axial seeding of meningeal hemangiopericytomas is extremely rare. Treatment of metastasis usually requires a similar multimodality approach tailored to the location of the disease.

Survival

Guthrie and coworkers found that the median survival after the first operation was 60 months, with actuarial 5-, 10-, and 15-year survival rates of 67%, 40%, and 23%, respectively (see Table 132-3).⁴⁹ This is comparable to the cumulative survival rates of approximately 65%, 45%, and 15%, respectively, compiled by Schroder and colleagues from a review of 118 cases in the literature up to 1985.⁶¹ Fountas and coauthors reported a mean survival of 5.5 years.⁶⁶

Extraneural metastasis is a devastating occurrence and significantly shortens survival. In the Mayo Clinic series, 10 of 44 patients experienced extraneural metastasis at an average time of 99 months. The average length of survival after metastasis was 24 months. Five patients alive at 99 months in whom metastasis did not develop survived an additional 76 months.⁴⁹

Other than extraneural metastasis, the factor most clearly related to survival is postoperative radiotherapy. Guthrie and coworkers found that patients who underwent radiotherapy after the first operation experienced recurrence at an average of 74 months, with 5- and 10-year recurrence rates of 38% and 64%, respectively (see Table 132-3).⁴⁹ Patients not irradiated suffered recurrence at an average of 29 months, with 5- and 10-year recurrence rates of 90% (Table 132-3).⁴⁹ These authors found a dose effect in that patients receiving less than 4500 cGy tended to experience recurrence sooner than did those receiving 5000 cGy or more. In this same series, patients who underwent radiotherapy after the first operation survived an average of 92 months, and those who did not lived 62 months. Others have observed this response for meningeal as well as extraneural locations of this tumor.^61,91–94

Discussion

Meningeal hemangiopericytoma is a malignant primary neoplasm of the meninges that has the biologic behavior and characteristics of a sarcoma and is far more aggressive than its common counterpart meningioma. These tumors have a slight male preponderance, with an average age at diagnosis of about 40 years.^{37,38,58,59,95} Symptoms are usually present for a shorter time before initial evaluation than with meningioma, and seizures are less common than with meningioma.

These aggressive tumors have 5- and 10-year recurrence rates of 65% and 76%, respectively,⁴⁹ as compared with 20% and 30%, respectively, for meningioma.^59,95 Hemangiopericytomas are relatively responsive to radiation.^49,96,97 Perhaps the most striking difference from meningioma is the tendency for meningeal hemangiopericytoma to metastasize. Kepes found very few metastatic ordinary meningiomas.³⁹ In contrast, the rate of metastasis of meningeal hemangiopericytomas at 5, 10, and 15 years was 13%, 33%, and 64%, respectively,⁴⁹ thus making metastasis likely with prolonged survival (see Table 132-3).

Meningeal hemangiopericytoma should not be equated with atypical or malignant meningioma. The latter tumor shows loss of architecture, increased cellularity, nuclear atypia, and mitoses but remains recognizable as meningioma. Jaaskelainen and associates studied a series of atypical and anaplastic meningiomas and found them to be more aggressive than ordinary meningiomas, but less so than meningeal hemangiopericytomas.⁷⁸ Malignant meningiomas have little or no tendency to metastasize.

Meningeal hemangiopericytoma is an aggressive extra-axial CNS tumor that behaves like a soft tissue sarcoma. It has a relentless tendency for local recurrence, and distant metastasis remains a threat. The best opportunity to help the patient is at the first surgery, where every effort should be made to achieve complete removal. If there is any doubt about residual tumor, surgery should be followed by radiotherapy, radiosurgery, or both. Diligent long-term observation, along with periodic chest radiographs and work-up for bone pain and abnormal liver function test results to rule out metastasis, is required for all patients.