Meningiomas invading the temporal bone with extension to the neck.

Meningiomas are the second largest group of brain tumors after gliomas. They account for 13 to 18 per cent of all primary intracranial neoplasms. The majority occur in the cerebral chamber; only 8 to 9 per cent are located in the cerebellar chamber. Meningiomas are hamartomatous, not truly neoplastic tumors, which arise from dural fibroblasts and particularly from arachnoid cells that tend to cluster around the tips of the arachnoid villi. Their preferential sites correspond closely with the locations where arachnoid villi are most frequently encountered, namely, along the major venous sinuses and their contributory veins, at the foramina of exit of the cranial nerves, and where arachnoid cell clusters are found within the trunk or the perineural sheaths of cranial nerves within or adjacent to the basal foramina. Of all intracranial meningiomas, 20 per cent eventually develop an extracranial extension. These extracranial extensions project, in order of decreasing frequency, to 1) the orbit, 2) the external table of the calvaria, 3) the nasal cavity and paranasal sinuses, and 4) the parapharyngeal (cervical) space. Once a meningioma has gained access to the temporal bone, its tendency to extend beyond the confinements of the skull increases to 43 per cent. The most frequent pathway is through the jugular and lacerate foramina into the parapharyngeal space, where it may manifest as a nasopharyngeal, oropharyngeal, retromaxillary, retromandibular, or cervical neck mass. A meningioma in the parapharyngeal area can represent 1) an extracranial extension of a primary intracranial tumor, 2) a neoplasm arising in the jugular foramen, 3) a neoplasm originating from an arachnoid cell cluster within the trunk of a cranial nerve or its perineural sheaths within or near a neural foramen, or 4) a metastasis to a cervical lymph node from a primary intracranial meningioma. Meningiomas extending to the neck are unique because of their tendency toward extracranial expansion, higher incidence of local recurrence, multicentric growth, and frequent combination with other neoplasms of the central nervous system. They are frequently an expression of the central form of neurofibromatosis (von Recklinghausen's disease).