Meningiomas

The WHO classification schema is based on histopathologic morphology and correlates with prognosis. WHO grade I lesions are considered benign and by far comprise the majority of meningiomas. These are further subdivided based on their morphology into meningotheliomatous (including “psammomatous” tumors with characteristic whorl patterns of cells), fibromatous, and angioblastic types. Treatment approaches for all of these subtypes of benign meningiomas are the same. WHO grade II meningiomas are considered atypical meningiomas and constitute about 10% to 20% of cases. These are characterized by higher mitotic activity, defined as having greater than or equal to four mitoses per high-powered field, and three or more of the following features: increased cellularity, high nuclear to cytoplasmic ratio, prominent nucleoli, uninterrupted sheetlike growth, or areas of necrosis. The WHO grade III meningiomas are the least common but the most ominous. They are classified as “malignant” or “anaplastic.” These tumors exhibit loss of the typical meningioma growth patterns, infiltrative growth, abundant mitosis with atypia, and multiple areas of necrosis. Grade II or III meningiomas are significantly more likely to have invasive disease, local recurrence, and shorter overall survivals.

Clinical Manifestations. Presenting signs and symptoms depend on the location and growth rate of the tumor. Because most meningiomas are slow growing, patients are frequently asymptomatic, with the discovery of the tumor an incidental finding. Any signs or symptoms that do develop are usually secondary to compression of underlying structures.

Seizures are often presenting signs of meningiomas, especially those located near cerebral cortex. Focal weakness is another frequent complaint, with the pattern of weakness a potential clue as to the location of the tumor. For example, bilateral lower extremity weakness in the absence of a spinal cord lesion can often be seen with parasagittal lesions arising from the falx and compressing the adjacent motor strips of both hemispheres. A potential concern with these lesions is involvement of the sagittal sinus, which can lead to venous infarction. Spinal meningiomas can also cause bilateral leg weakness, but this is often accompanied by numbness. Foramen magnum meningiomas can present with insidious weakness of the arm and leg, which progresses to involve the contralateral limbs. This is accompanied by neck pain, worsened with neck flexion or Valsalva maneuvers. Because of the subtly progressive symptoms, this can be hard to diagnose and can be confused with multiple sclerosis.

Visual changes can be subtle but are commonly seen with meningiomas. Deficits may include visual loss, field deficits, and/or diplopia. Olfactory groove, medial sphenoid wing, and other parasellar tumors can compress the optic nerve (CN II), resulting in blindness with optic atrophy in one eye and papilledema in the other. This is otherwise known as the Foster-Kennedy syndrome. Parasellar lesions can also cause visual field deficits. When tumors involve the cavernous sinus, ocular palsies can be seen. This is frequently accompanied by facial numbness. Finally, meningiomas can arise from the optic sheath, resulting in slowly progressive loss of vision.

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