[Surgical anatomy and surgical approaches of the third ventricle].

Careful analysis of MRI images is mandatory before any surgical procedure in the third ventricle. This analysis should take in account the relationship of the tumor itself, but also the grade of hydrocephalus and the main anatomical landmarks along the surgical approach. The first step is the access to the lateral ventricle, which may be achieved via transcortical or anterior transcallosal routes : these two operative procedures are detailed. The transforaminal entry to the third ventricle may be easy if hydrocephalus has widened the foramen of Monro. In other cases, a subchoroidal (or interthalamo-trigonal) approach is necessary, and the division of the thalamostriate vein is sometimes required. In this series, the transcortical route has been favoured by neurosurgeons. The advantages and drawbacks of both transcortical and anterior transcallosal routes are discussed. The anterior interhemispheric and pterional approaches are briefly evoked, as they were used in very few cases of this series. The management of hydrocephalus is discussed.