Fig. 32.4 (A,B) The 28-year-old male patient had a single epileptic seizure that led to the diagnosis. Magnetic resonance imaging was suspicious for ganglioglioma or tentorial meningioma. During a left pterional approach, there was no contact of the tumor to the dura. The tumor removal was uneventful, and the histology showed a fibrous type of meningioma. Postoperatively no neurological defects were found.
been reported by Levin and Rose and others.17,32,33,51 Similarly, Rhoton, after extensive anatomical investigations, has described an interhemispheric approach to the trigone.30 He advocates the transection of the posterior cingulum together with the most posterior part of the corpus callosum to enter the trigone of the ventricle medially. Tumor growth toward the corpus callosum facilitates all interhemispheric approaches (Fig. 32.5). To reach tumors of the posterior part of the third ventricle and the trigone, Yaşargil et al described another variant of an interhemispheric approach: the parietooccipital interhemispheric approach.14,33 In this approach, the cortical incision is performed at the precuneus to reach the medial aspect of the ventricular tumor. Yaşargil pointed out that the parietooccipital vein has to be handled with caution, not to risk venous infarction.52 This approach, like all interhemispheric approaches, does not compromise the temporoparietal association cortex and has the least risk of injury to the optic radiation. In interhemispheric approaches, contralateral approaches may be of significant advantage. For (small) tumors, McDermott described a very elegant contralateral transcallosal approach from the nondominant side to resect the tumor in the dominant side.6 However, it may be necessary to transect the lower part of the falx to have an optimal trajectory in these cases. The distance to the tumor is longer than in ipsilateral approaches, but the angle to reach the trigone is advantageous. The size of the tumor is a critical factor in considering this variant of interhemispheric approaches. Patients may be in a lateral position with the tumor side up, thereby reducing the need for brain retraction as gravity assists; sometimes retractors are not necessary at all.6,53 For this unorthodox positioning, like in any surgical approach that is less frequently used, neuronavigation is often very helpful.
32 Meningiomas of the Lateral and Fourth Ventricles
B
A
Fig. 32.5 Magnetic resonance imaging shows an incidental finding in a 37-year-old male harboring the smallest tumor in our series (2 cm). There is enlargement of the left temporal horn. This more medially localized tumor (type C) was resected uneventfully by an interhemispheric transcallosal approach (see also Fig. 32.2A,B).
Radiosurgery Radiosurgery has proven to be effective in meningiomas, with a high rate of tumor control and a low morbidity in areas along the skull base. Long-term follow-up has reported excellent results.8,9,54 Radiosurgery theoretically offers an ideal approach for intraventricular meningio-
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