Meningothelial Tumors Meningiomas Grades

These generally benign tumors arising from the menin-gothelial cells of the arachnoidal cap cells occur in mid and late mid life, rarely in children. They constitute

figure 1 i.26b

Pineoblastoma in an adult male. A. Macrosection of the tumor (HE). B. The tumor fills the posterior part of the third ventricle (LFB-CV). C. Small seeding tumorous nodule in subarachnoid space consists of small cells with round-to-oval hyperchromatic nuclei (HE). D. The cells immunoreact for synaptophysin. E. Small tumorous nodules in the substantia nigra (HE).

figure 1 i.26b

Pineoblastoma in an adult male. A. Macrosection of the tumor (HE). B. The tumor fills the posterior part of the third ventricle (LFB-CV). C. Small seeding tumorous nodule in subarachnoid space consists of small cells with round-to-oval hyperchromatic nuclei (HE). D. The cells immunoreact for synaptophysin. E. Small tumorous nodules in the substantia nigra (HE).

15% to 25% of all intracranial tumors. A female predominance is attributed to the presence of progesterone receptors in the tumors. The majority of meningiomas are benign (80% to 90% are grade 1), a small number are atypical (5% to 15% are grade 2), and a smaller number are malignant (1% to 3% are grade 3). Preferential sites of meningiomas are the parasagittal region, the falx, and the lateral aspects of the hemispheres (plaque meningioma), and at the base the olfactory groove, the tuberculum sellae, and the sphenoid wing. They are less common in the posterior fossa and rare in the choroid plexus, pineal region, and orbit.

Head injury and therapeutic radiation to the head predispose to the growing of a meningioma. Solitary or multiple meningiomas occur in familial neurofibromatosis type 2 (NF2).

A number of cytogenetic and molecular genetic alterations have been identified in meningiomas. Mutations in NF2/merlin (schwannomin) gene protein on chromosome 22 and loss of DAL-1 gene protein on chromosome 18 occur in both benign and malignant meningiomas. Abnormalities of several chromosomes, including deletions of chromosomes 1, 10, 14, and loss of chromosome 9 have been implicated in meningiomas, particularly in malignant variants.

Clinical Features

Because meningiomas grow slowly and may become large before raising the ICP, partial or generalized seizures are often the presenting or only clinical manifestations for months or years. Focal neurologic symptoms and signs develop later and indicate the anatomic site. Bilateral parasagittal and falx meningiomas, by pressing on the leg area of the motor cortex, present with spastic paraparesis and urinary incontinence, mimicking a spinal cord lesion. On CT scan and MRI, meningiomas appear as extra-axial mass lesions compressing the brain substance. The surrounding edema and mass effect usually are not marked. CT scan readily identifies a calcified meningioma. On nonenhanced CT scan, a meningioma is iso- or hyperdense; it densely enhances with contrast media. It shows a dense homogenous enhancement on T1-weighted MR images, and is iso- or hyperintense on T2-weighted images.

Paraparesis Parasagittal

figure 1 1.27

Meningiomas. A. A small, round encapsulated parasagittal meningioma is loosely attached to the leptomeninges. It indents but does not invade the underlying cortex (HE). B. A large, lobulated falx meningioma slightly indents the corpus callosum. C. A huge olfactory groove meningioma presented with psychiatric symptoms in a 43-year-old woman. The olfactory nerves are embedded in the tumor, and the chiasma and hypothalamus are displaced caudally. D. A left medial sphenoid wing meningioma on sagittal noncontrast T1-weighted MR image appears as an extra-axial isointense mass lesion. It is presented in a 58-year-old man with progressive loss of vision in the left eye.

figure 1 1.27

Meningiomas. A. A small, round encapsulated parasagittal meningioma is loosely attached to the leptomeninges. It indents but does not invade the underlying cortex (HE). B. A large, lobulated falx meningioma slightly indents the corpus callosum. C. A huge olfactory groove meningioma presented with psychiatric symptoms in a 43-year-old woman. The olfactory nerves are embedded in the tumor, and the chiasma and hypothalamus are displaced caudally. D. A left medial sphenoid wing meningioma on sagittal noncontrast T1-weighted MR image appears as an extra-axial isointense mass lesion. It is presented in a 58-year-old man with progressive loss of vision in the left eye.

Benign meningiomas, particularly when favorably located, can be totally excised and have an excellent prognosis. Atypical and chiefly anaplastic meningiomas are more aggressive, become invasive, and are prone to recur. Postoperative survival averages 2 years.

Pathology

Grossly, the meningioma is extra-axial; encapsulated; round, oval, or lobulated; and firm or moderately soft. It slowly indents and displaces the underlying neural tissue (see Fig. 11.27). Its blood supply is from the men-ingeal branches of the external carotid arteries. The cut surfaces are pinkish-gray, granular, or gritty. The tumor may invade the bone, producing osteolytic or osteoblastic lesions (Fig. 11.28). Histologically, several types are distinguished. The great majority are benign (WHO grade 1), with a low rate of proliferation index. The tumor cells immunoreact for epithelial membrane antigen (EMA) and vimetin, and inconsistently for S-100 protein.

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