The intraventricular approaches to craniopharyngiomas involving the lateral and third ventricles typically include the transcallosal and transcortical transventricular approaches. These approaches can be performed with minimal brain retraction and are excellent options for intraventricular tumors that extend into the anterior third ventricle and lateral ventricle. In cases in which the lateral ventricles are enlarged due to hydrocephalus or if the tumor presents itself to one lateral ventricle, the transcortical approach can be considered.
Alternatively, we prefer the interhemispheric transcallosal approach because it provides excellent midline access to both lateral ventricles and third ventricle without transgressing the cerebral cortex, thereby decreasing the risk of seizures. It also does not rely on large lateral ventricles to create the surgical corridor. However, these approaches are not useful for obtaining access and direct visual control of the suprasellar region, and can carry the risk of memory loss (forniceal injury), arterial stroke (injury to pericallosal arteries in transcallosal approach), venous infarct (injury to internal cerebral veins or bridging veins in transcallosal approach), and postoperative seizures (transcortical approach).
In summary, the intraventricular approaches can be used alone for purely intraventricular craniopharyngiomas, or they can be used in combination with other anterolateral and midline transcranial approaches to resect the intra- and extraventricular portions of the tumor.[11,46] The trans–lamina terminalis approach for third ventricular craniopharyngiomas has been discussed in the previous section on the transbasal approach, and will not be discussed here.
Transcortical Transventricular Approach: Technical Pearls
When performing the transcortical transventricular approach, the patient is positioned supine with the head elevated approximately 30° to facilitate venous drainage. A unilateral frontal craniotomy is performed on the side of the tumor extension or on the side of the surgeon's dominant hand. A ventricular catheter is placed into the lateral ventricle under stereotactic guidance and a small corticectomy is made at the catheter site. Under microscopic visualization, the catheter tract is followed and expanded until the lateral ventricle is exposed. At this point, it is essential to identify the choroid plexus, foramen of Monro, septum pellucidum, and thalamostriate vein to establish surgical orientation. Further access to the third ventricle can be performed using a subchoroidal approach, or in some cases, a transforaminal approach if the foramen of Monro is dilated. One disadvantage is the oblique viewing angle to the third ventricle that prevents the surgeon from adequately visualizing the ipsilateral wall of the third ventricle.
Interhemispheric Transcallosal Approach: Technical Pearls
The transcallosal approach, on the other hand, offers midline access so that both walls of the third ventricle are identified. The patient is positioned supine in the same manner and a unilateral frontal craniotomy is performed with extension of the bone flap across the midline. This allows mild retraction of the superior sagittal sinus when reflecting the dura medially to facilitate adequate access and visualization of the interhemispheric fissure. We prefer to position the patient in the lateral position so that the dependent ipsilateral frontal lobe falls away from the falx to facilitate gravity-assisted retractorless access to the interhemispheric fissure. The head of bed is elevated and the neck is flexed laterally so that the falx cerebri is roughly 30° from the horizontal plane. This provides a comfortable viewing trajectory to the interhemispheric fissure for the surgeon. In our experience, the arachnoid membranes over the interhemispheric fissure are very easy to dissect with gravity assistance in this lateral position. The pericallosal arteries are identified and separated to create a safe working corridor to the corpus callosum between the 2 vessels. After confirmation of the desired callosotomy target and working trajectory with image guidance, the corpus callosum is divided approximately 2–2.5 cm to access the lateral ventricle. Fenestration and partial resection of the septum pellucidum allows access to both lateral ventricles. For access to the third ventricle, an interforniceal approach can be performed when using the transcallosal approach. This can be performed by dividing the velum interpositum and working in between both fornices and internal cerebral veins. The fornices can be carefully separated by spreading the tips of the bipolar forceps or microbayonnetted forceps (bipolar spread technique). The arachnoid of the tela choroidea is identified and divided to drop into the third ventricle. This allows excellent midline visualization and control of both walls of the third ventricle. Alternatively, a subchoroidal or transforaminal corridor can be chosen as well to access the third ventricle. The most anterior portion of the third ventricle, including the supraoptic recess, remains a difficult area to visualize with the transcallosal interforniceal approach. One must use extreme caution not to cause inadvertent trauma to the fornices with microinstrumentation and suction devices.
Neurosurg Focus. 2016;41(6):e5 © 2016 American Association of Neurological Surgeons