Infratentorial supracerebellar approach to the colloid cysts of the third ventricle

OBJECTIVE: The transcallosal and the frontal transcortical approaches are t he most widely used methods in surgery of third ventricle colloid cysts. Ho wever, these approaches require traction of the frontal lobe and dissection of the corpus callosum or corticotomy and involve some postoperative conse quences. The rationale of the proposed method is to remove the colloid cyst by the infratentorial supracerebellar approach and the posterior wall of t he third ventricle without dissection of any neural structures. METHODS: Five patients with a colloid cyst of the third ventricle were oper ated on by the proposed method. The first patient presented with several mo nths' history of symptoms that included increased intracranial pressure and right-sided cerebellar signs, caused by a metastatic tumor of the right ce rebellar hemisphere. The other four patients had symptoms including intracr anial hypertension for an extended period of time without any other neurolo gical deficits. In all patients, magnetic resonance imaging revealed a coll oid 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 interpo situm is opened. Perforation of the inferior layer of the tela choroidea ju st above the suprapineal recess allows opening of the third ventricle cavit y. A foraminal region is exposed after a slight lateral displacement of med ial surfaces of the thalamus along the third ventricle roof. CONCLUSION: The proposed approach through the infratentorial supracerebella r space and the posterior wall of the third ventricle may be used for remov al of colloid cysts, especially in patients in whom the lateral ventricles are not enlarged.