Fourth ventricular meningioma in an adult: Case report and review of the literature

Meningiomas are one of the most common clinical entities in everyday neurosurgical practice. Most meningiomas are extra-axial dural-based lesions. They typically occur along intradural venous sinuses, at the confluences of multiple cranial sutures and also others sites where arachnoid granulations and arachnoid cell rests occur. Most of these tumors also do occur within the lateral ventricles than third ventricle but they are exceptional in fourth ventricle thought to arise from the choroid plexus without dural attachment. Here we present two cases of fourth ventricle meningiomas.

Extracranial, Extraspinal Meningiomas of the Head and Neck

The head and neck is the most frequent location for extraneuraxial meningiomas, be they wholly extracranial or extraspinal or extensions of central nervous system meningiomas. Regardless of anatomic site of origin, nearly all meningiomas arise from meningocytes of arachnoid granulations. Ectopic arachnoid cell clusters have a predilection for areas of dural penetration of cranial nerves, and it is in these areas that most extracranial meningiomas are found. Surgical excision is the mainstay of treatment and must be planned by radiologic studies to determine the extent of the tumor and the presence or absence of a companion central nervous system meningioma. The often locally invasive and aggressive behavior of the meningiomas belies their benign histologic appearance.

A light and electron microscopic and immunohistochemical study of human arachnoid villi

✓ The structure of human arachnoid villi was investigated by light and electron microscopy with the aid of immunohistochemical techniques. The human arachnoid villi examined were basically composed of four portions: a fibrous capsule, an arachnoid cell layer, a cap cell cluster, and a central core. The arachnoid cell layer encompassing the central core was mostly covered by the thin fibrous capsule with an endothelial investment. However, the fibrous capsule was often absent at the apical portion of the villus and a factor VIII-related antigen stain failed to confirm the investment of endothelial cells. Instead, the arachnoid cell layer abutted directly upon the lumen of a lateral lacuna or the sinus. The arachnoid cell layer was thickened in places, forming cap cell clusters; it usually consisted of outer and inner zones. On vimentin staining, the former was slightly positive while the latter was strongly positive. The central core contained a network of arachnoid cells intermingled with connective tissue fibers and was in continuity with the cranial subarachnoid space. Electron microscopy showed that the arachnoid cells contained a larger number of intermediate filaments in the inner zone than the outer zone. Ultrastructural immunohistochemical localization showed that vimentin was localized at the intermediate filaments and desmosomal plaques of the arachnoid cells. The arachnoid cells showed a marked variety in both the cell forms and the number of intermediate filaments or desmosomes, depending on their location.

Spontaneous Tumors of the Meninges in Rats

Histologic brain sections from 107 rats reported to have granular cell tumors or meningiomas in 2-year carcinogenicity studies conducted by the National Toxicology Program (NTP) or the National Cancer Institute (NCI) were reexamined microscopically. There were 62 rats with granular cell tumors, 26 with benign meningiomas, and 19 with meningeal sarcomas. Granular cell tumors were compatible with previous descriptions of this tumor. Meningeal sarcomas were subclassified into nine spindle cell sarcomas and ten fibrosarcomas. Among the rats with benign meningiomas, five were typical meningiomas (three fibroblastic meningiomas, and two meningothelial meningiomas) and 21 were meningothelial meningiomas containing cells with granules identical to those in granular cell tumors. There was a transition from epithelial-like cells of the meningothelial meningiomas to granular cells in these 21 cases. Based upon anatomic location, cytomorphologic similarities, and the occurrence of transitional or mixed forms of meningothelial meningiomas and granular cell tumors, it is suggested that these two tumors are related and may both originate from a common progenitor meningothelial arachnoid cell.