Intraventricular tumors are often slow-growing and benign. These lesions frequently grow large before clinical manifestations and, ultimately, produce symptoms secondary to hydrocephalus, either by obstruction of the normal pathways of cerebrospinal fluid flow or by its overproduction. Most patients present with headaches . Colloid cysts, which typically occur anteriorly and superiorly within the third ventricle, have a tendency to intermittently obstruct the foramen of Monro, resulting in acute lateral ventricular hydrocephalus with symptoms of intracranial hypertension. Visual loss, impotence and diabetes insipidus may be caused by tumors invading the floor of the third ventricle. Asymmetric bitemporal hemianopia, starting with inferior temporal field loss, may occur due to dilatation of the third ventricle with pressure on the optic chiasm from above. The extension of the tumor may cause a variety of visual field defects, including homonymous hemianopia, binasal field defects, arcuate defects and central scotoma .
The standard preoperative imaging study is MRI. An MR scan provides information regarding the size of the tumor, its degree of invasion, its relationship with the surrounding anatomical structures and the extent of hydrocephalus. Information regarding the relationship of the tumor with surrounding venous structures is also critical in planning surgery. The exact location of the tumor, e.g. posterior third ventricle versus pineal or quadrigeminal, is of crucial importance in planning the surgical approach.
Neuroendocrinologic evaluation may be necessary, depending on the degree of hypothalamic involvement. Germ cell markers that will be detailed later in this chapter should be obtained if the tumor is suspected of being of germ cell origin. Visual field testing is obtained if the visual pathways are affected, and for patients undergoing a posterior approach to a tumor of the occipital horn or atrium.
Any lesion that appears to be highly vascular on MRI may be studied angiographically. Although not routine, angiography is important for large tumors and when the deep venous system should be visualized. Angiography will also provide information regarding the status of the bridging veins between the cerebral hemisphere and the sagittal sinus, useful for surgical
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