[Transcallosal and transcortical approaches for tumors at the anterior part of the lateral ventricle: relations between visualized and ventricular size].
The transcallosal approach has been widely used for tumors located near the midline of the anterior part of the lateral ventricle, while the transcortical approach is known to provide a wide surgical field in cases of hydrocephalus. However, it is not always easy to choose the appropriate approach in individual cases. The size of the visualized field obtained via the surgical approach is one of the most important factors determining the accessibility of the lesion. In this study, we investigated the difference in the sizes of the fields afforded by these two approaches on the basis of our clinical experience and simulation studies. We surgically treated intraventricular pathology located at the anterior part of the lateral ventricle in five patients with tumors and one with a cyst. Tumors with lateral extension of less than 20 mm were approached via the transcallosal route, and those with more than 20 mm of lateral extension via the transcortical route. In the simulation study, the size of the surgical field was measured through a 3-cm incision of either the cerebral cortex or the corpus callosum under various conditions of ventricular enlargement. Two patients treated via the transcortical approach underwent subtotal removal; one of them had a large bilaterally extending tumor measuring 50 mm in its greatest diameter, and the other had tumor involvement of the fornix. The other three tumors and the cyst were totally resected. While postoperative subcortical hematoma developed in two patients, one each treated via the transcortical and the transcallosal approach, no deficits remained at discharge. Since enucleation procedure was insufficient in patients with hard tumors, a wider surgical field than that in patients with soft tumors was considered necessary. When combined approaches are considered indispensable for a patient with a massive tumor, the transcortical approach may be indicated for priority of order to prevent bilaterally residual tumors. The simulation study disclosed that, in either approach, wider surgical field was obtained as the size of ventricle increased. However, the transcallosal approach afforded a wider field than did the transcortical approach not only in ventricules of normal size but also in mild hydrocephalus with cortical thickness of between 30 and 40 mm. The transcortical approach, on the other hand, produced a much wider field in more advanced hydrocephalus with a thickness of less than 30 mm. A wider surgical field can be obtained by certain tactics such as upward retraction of the incised corpus callosum, moving the cortical window, or oblique or transverse cortical incision.