Intraventricular meningiomas account for 15%-17% of meningiomas in pediatric patients, but only 1.6% of meningiomas in adults. Only 50 reported cases of third ventricle meningioma exist in the literature, and most lesions are found within lateral ventricles. They commonly present as basal tumors with extension up into the floor of the third ventricle.
Most other lesions encroach on the third ventricle from the surrounding parenchyma. These are mostly glial tumors, including juvenile pilocytic astrocytoma, fibrillary astrocytoma, protoplasmic astrocytoma, subependymal giant cell astrocytoma, glioblastoma multiforme, and ependymoma. Metastatic neoplasms may involve the third ventricle via its roof, floor, lateral wall, or choroid plexus. Metastases from the lungs, colon, kidneys, and breasts are most common. In these cases, the prognosis is poor, and death is often due to progressive systemic disease. Suprasellar germinomas and craniopharyngiomas can invade the floor of the third ventricle from below. Suprasellar extension of pituitary macroadenomas may also involve the third ventricle. Decreased visual acuity or visual field, endocrinopathy, and headache are the main symptoms in these cases.
Other cystic lesions in the anterior third ventricular area include epidermoid cyst, dermoid cyst, and neurocysticercosis. Epidermoid and dermoid cysts are rarely found in the third ventricle, and neurocysticercosis is endemic to Mexico, Eastern Europe, Asia, Central and South America, and Africa. Fenestration into the third ventricle has occurred in 15%-25% of cases with ensuing hydrocephalus. Inflammatory lesions, such as pyogenic abscesses, and granulomatous diseases, such as tuberculosis or fungal infection, may rarely impinge on the third ventricle. Other lesions, such as sarcoidosis and histiocytosis, may involve the third ventricle via its floor and hypothalamus. Finally, vascular lesions, such as cavernous malformations and arteriovenous malformations, should be added to the differential diagnosis of third ventricular mass lesions.
The contents of the colloid cyst determine its appearance on imaging studies. The cyst may be found incidentally on CT scanning or when the patient presents with symptoms and signs of increased intracerebral pressure suggestive of acute obstructive hydrocephalus. It is generally a round homogeneous hyperdense mass within the third ventricle at the level of the foramina of Monro. Acute lateral hydrocephalus with periventricular edema might be seen due to the blockage of the cerebrospinal fluid pathway into the third ventricle. On T2-weighted MRI, the cyst might be either hypo- or hyperintense, and fluid-attenuated inversion recovery (FLAIR) shows periventricular edema in the acute stage of hydrocephalus as hyperintensity surrounding the lateral ventricle.
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