Infratentorial supracerebellar approach to the colloid cysts of the third ventricle.

OBJECTIVE: The transcallosal and the frontal transcortical approaches are the most widely used methods in surgery of third ventricle colloid cysts. However, these approaches require traction of the frontal lobe and dissection of the corpus callosum or corticotomy and involve some postoperative consequences. The rationale of the proposed method is to remove the colloid cyst by the infratentorial supracerebellar approach and the posterior wall of the third ventricle without dissection of any neural structures.
METHODS: Five patients with a colloid cyst of the third ventricle were operated on by the proposed method. The first patient presented with several months' history of symptoms that included increased intracranial pressure and right-sided cerebellar signs, caused by a metastatic tumor of the right cerebellar hemisphere. The other four patients had symptoms including intracranial hypertension for an extended period of time without any other neurological deficits. In all patients, magnetic resonance imaging revealed a colloid cyst of the third ventricle without hydrocephalus. TECHNIQUE: With the infratentorial supracerebellar approach, the arachnoid of the quadrigeminal cistern is dissected. The pineal body is separated and displaced from the internal vein medially, and the posterior velum interpositum is opened. Perforation of the inferior layer of the tela choroidea just above the suprapineal recess allows opening of the third ventricle cavity. A foraminal region is exposed after a slight lateral displacement of medial surfaces of the thalamus along the third ventricle roof.
CONCLUSION: The proposed approach through the infratentorial supracerebellar space and the posterior wall of the third ventricle may be used for removal of colloid cysts, especially in patients in whom the lateral ventricles are not enlarged.