Ensuring local control in meningiomas.

Meningiomas are mainly managed surgically and hence they are relatively rare to Radiation Oncologists. In reality, meningiomas are not uncommon: they represent nearly 20% of all intracranial tumors and approximately 25% of intraspinal neoplasms.” For the most part, intracranial meningiomas are benign, slow growing, well-circumscribed, extracerebral tumors which cause damage by compression rather than invasion of the brain parenchyma. Nevertheless, they commonly infiltrate mesodermal supportive tissues such as the dura and sinuses. l6 They are twice as common in females and tend to occur towards middle age with a peak incidence in the fifth decade. A universal feature of these tumors is their high tendency for post-surgical recurrences. These can manifest relatively early (within 2-3 years) with a mean interval for clinical detection around 4 years.‘2s’3 The recurrence incidence continues to rise with the passing of time. For example, after subtotal excision (SE), the average recurrence incidence for benign meningiomas is 35%, 60%, and 75% at 5, 10, and 15 years after initial surgery.‘9*24 Similarly, while there can be multiple recurrences along the course of ailment, the recurrence-free interval (RFI) tends to shorten after each recurrence.‘,’ I Also it is well-known that the less radical the operative procedure, the earlier the recurrence.13 To facilitate studying this, Simpson2’ identified five distinct grades of operation: Grades 1,2, and 3 represent total excision (TE) of the tumor with/without removal or coagulation of dural attachments and/or extensions; Grade 4 is SE and Grade 5 a simple biopsy and decompression. The higher the grade, the higher the incidence of recurrence and the shorter the RFI. Several factors, some highly interelated, seem to affect the recurrence incidence in these tumors: (a) tumor type and clinical behavior, (b) location and accessibility, (c) degree of resectability, and (d) prior recurrence. Histologically, meningiomas are divided into benign and malignant with the former being overwhelmingly commoner (90-97% of all meningiomas). Among benign meningiomas, the most common type is the syncytial (endotheliomatous or meningotheliomatous) accounting for at least 60% of all benign meningiomas. Other benign types include the fibroblastic (7%), transitional or mixed (23%) and the angioblastic ( 10%). Little prognostic value has been found among the different types of benign meningiomas with the sole exception of the angioblastic variety which exhibits high tendency towards malignant transformation and more aggressive behavior. There are three recognized subtypes of angioblastic meningiomas: (a) highly vascular meningiomas (7%) whose behavior resembles closely that of other benign types; (b) hemangioblastic (l%), and (c) hemangiopericytic (2%) both of which can show a high mitotic index. The hemangiopericytic type of angioblastic meningioma recurs with significantly higher frequency and shorter intervals than other benign types. In this respect, it is in a class by itself and exhibits an aggressive behavior closely resembling that of malignant meningiomas.“‘16 The latter, although rare (2-10% of all meningiomas), universally convey ominus prognosis. Any benign type of meningioma can become malignant, but the angioblastic type, particularly the hemangiopericytic subtype, has the highest incidence towards this feature.‘6.17 Multiple recurring meningiomas are at higher risk for malignant transformation. In a large Japanese series,25 3 of 14 recurrences (2 1%) were malignant at initial TE; however, at re-operation, 8 of 12 (67%) proved malignant indicating that five originally benign tumors (39%) became malignant at first recurrence. An “atypical” (malignant) meningioma is so called because the tumor shows atypical features indicative of rapid growth and aggressive behavior. These include high cellularity, cytologic pleo-