Suspicion of this tumor is occasioned by intermittent, severe bifrontal–bioccipital headaches, sometimes modified by posture (“ball valve” obstruction) or with crises of headache and obtundation, incontinence, unsteadiness of gait, bilateral paresthesias, dim vision, and weakness of the legs, with sudden falls but no loss of consciousness (“drop attacks”). Stooping may result in an increase or onset of headache and loss of balance. However, this intermittent obstructive syndrome has been infrequent in our experience. More often the patient has no headache and presents with the symptoms comparable to those of normal-pressure hydrocephalus or, as frequently, the tumor is found incidentally on CT or MRI. On CT and MRI, the lesion density depends on the hydration state of the mucopolysaccharides. These lesions do not restrict diffusion or enhance with contrast. Subtle behavioral changes are common and a few patients, as emphasized by Lobosky and colleagues, experience mild confusion and changes in personality that may reach the extreme of psychotic behavior. We have no experience with this constellation and find it difficult to understand from the location of the lesion or from hydrocephalus; in our experience, chronic headache or gait difficulty is usually present.
The treatment for many years has been surgical excision, which carries some risk, far less than in the past, but satisfactory results have also been obtained by ventriculoperitoneal shunting of the CSF, leaving the cyst untouched. Decompression of the cyst by aspiration under stereotactic control has also become a popular procedure.
Other tumors found in the third ventricle and giving rise mainly to obstructive symptoms are craniopharyngiomas (see later), papillomas of the choroid plexus, and ependymomas (discussed earlier).
This CSF-filled lesion, which is probably congenital, presents clinically at all ages but may become evident only in adult life, when it gives rise to symptoms of increased intracranial pressure and sometimes to focal cerebral or cerebellar signs, simulating intracranial neoplasm. Seizures may occur but are not characteristic. In infants and young children, macrocrania and extensive unilateral transillumination are characteristic features. Usually these cysts overlie the sylvian fissure or temporal pole; occasionally they are interhemispheric under the frontal lobes or lie in the pineal region or under the cerebellum. They may attain a large size, to the point of enlarging the middle cranial fossa and remodeling and elevating the lesser wing of the sphenoid, but they do not communicate with the ventricles. Rarely, one of these cysts may cover the entire surface of both cerebral hemispheres and create a so-called external hydrocephalus.
The cysts are readily recognized (often accidentally) on unenhanced CT or MRI, showing a circumscribed tissue defect filled with fluid that has the density of CSF (Gandy and Heier). If these cysts are completely asymptomatic, they should be left alone; if symptomatic, additional MRI studies are indicated, so as not to overlook a chronic subdural hematoma, which is often associated and may not be visualized on the unenhanced CT. Suprasellar arachnoid cysts are discussed further on, under “Empty Sella Syndrome.”
The treatment of enlarging and symptomatic cysts is marsupialization or, less preferably, by shunting from the cyst to the subarachnoid space.
Skull Base and Other Regional Intracranial Tumor Syndromes (Vestibular Schwannoma, Other Tumors of the Cerebellopontine Angle, Craniopharyngioma, Pituitary, Meningioma of the Sphenoid Ridge and Olfactory Groove, Glioma of the Optic Nerve, Pontine Glioma, Chordoma Chondrosarcoma, Glomus Jugulare and Carotid Body Tumors, Nasopharyngeal Carcinoma)