Bilateral telovelar approach: A safe route revisited for resections of various large fourth ventricle tumors
A 60-year-old male presented with progressive paraparesis and intractable headaches. The patient was known to suffer from neurofibromatosis type 2, and already had multiple meningiomas removed in the past. Magnetic resonance imaging (MRI) with I/V contrast revealed an oval shaped, partially cystic but homogeneously contrast enhancing, well demarcated tumor, which reached from the mid fourth ventricle to the aqueducts Sylvii mesencephali. The tumor extended also into the lateral recess []. To treat associated hydrocephalus, the patient first underwent an uncomplicated endoscopic third ventriculostomy from a right sided precoronal approach 3 days prior to definite open surgery.\nFor surgery, the patient underwent standard general endotracheal anesthesia and was placed into prone position in Mayfield 3-point skeletal fixation. He was resting on a Wilson frame with the neck in a highly flexed position. The Brain-LAB navigation system was used and fiducials were registered. Landmarks such as the superior sagittal sinus were marked and best trajectories were visualized. A standard bilateral suboccipital approach was chosen and the incision was carried out at the midline, starting about 3 cm above the inion and reaching down to the level of the C2 spinous process. A chiari-type bilateral suboccipital craniectomy was performed using a high-speed craniotome, thus achieving a bone window spanning high from near the inion to the foramen magnum. The margin of the bone flap was extended laterally to expose the sigmoid sinus. The posterior arch of C1 was resected bilaterally up to the sulcus arteriosus of the lateral mass. The best approach-angle was confirmed according to Brain-LAB criteria. A y-shaped durotomy was performed and the dural leaves where tagged up with 4-0 Nurolon (Ethicon) to expose the underlying cerebellum. The pia was transected and cerebrospinal fluid (CSF) was removed. Arachnoidal adhesions were lyzed. We then used a Greenberg retractor and both tonsils were gently retracted upwards and outwards under the microscope, after opening the bilateral cerebellomedullary fissures to gain access to the fourth ventricle. The floor of each cerebellomedullary fissure, composed by tela choroidea and inferior medullary velum, was exposed. Then the bilateral tela choroideae, lucent membranes covering the fourth ventricle around the foramen of Magendie, were opened with microinstruments to visualize and access the posterior-superior part of the fourth ventricle. Using this approach, an inferior vermian split was avoided and the caudal vermis could be easily elevated. Both the Posterior inferior cerebellar artery (PICAs) and the veins of each cerebellomedullary fissure were preserved. Tumorous tissue lodged in the fourth ventricle was immediately encountered and identified when looking from the obex superiorly. A small specimen was obtained upfront for intraoperative fresh frozen histopathological analysis.\nIn patient number 1, this revealed the diagnosis of a meningioma with some atypical features. Careful microscopic dissection in a circumferential plane and internal debulking were performed alternately. Cutting the margin of the inferior medullary velum on each side created a wide operative field allowing panoramic views superiorly toward the mesencephalic aqueduct as well as laterally toward the foramina Luschkae. At the end of the tumor dissection and its gross total removal, the caudal aqueductal opening and CSF egress via the bilateral foramina of Luschkae was seen. After absolute hemostasis was achieved, the ventricle was copiously irrigated until the irrigant remained clear and the durotomy was closed with a pericranial autograft. The latter was sutured in with a running 4-0 Nurolon stitch and augmented by a fibrin tissue sealant. The wound was closed in layers. The patient was kept intubated until imaging and the postoperative magnetic resonance image (MRI) revealed no residual tumor burden []. No new neurological deficit was noticed after the operation and the patient was successfully extubated POD#1. The patient had an unremarkable postoperative course and was discharged to rehab on POD #4.