Before surgery, a careful examination of the MRI imaging is critical in reaching the goal of gross total resection. It helps to determine the surgical approach, to be prepared for surgical difficulties, and to anticipate a second staged surgery for large tumors.

The “crossbow incision” was first described by Cushing in 1905 and involved a midline sagittal skin incision in the suboccipital region, with a “T”-like horizontal incision at its superior extent. In 1928, Naffziger described the straight midline sagittal incision, which had been used by neurosurgeons up to date. At present, a midline incision is made from the inion down to the C3–C4 cervical lamina by splitting the nuchal ligament. In case of cerebellopontine involvement, an invert “L”-like incision is recommended.

The craniotomy should extend rostrally up to the level of the torcular, laterally (driven by size and tumor location, i.e., along the sigmoid sinus in case of cerebellopontine cisterns extension) and caudally down to the foramen magnum. A laminectomy of C1 at least may be necessary if the tumor has a spinal extension. A pedicle of muscle and fascia can be left attached to the external occipital protuberance in order to facilitate muscular closure at the end of the operation.

The dura matter may be opened in a “U-” or “Y”-shaped fashion. The authors use a U-shaped opening down to the occipito-C1 ligament, which facilitates the dura closure (Fig. 22.1b). In case of bulbar, cerebellopontine cisterns, or spinal involvement, a “Y”-shaped opening is necessary to better expose the structures (Fig. 22.1c).

If the patient is in a sitting position, the surgeon has to ask for jugular compression at each step of the opening to limit the risk of air embolism.

Some patients have a midline occipital sinus that can be a source of bleeding when the dura mater is opened. This bleeding can be controlled by clips that should be removed at the time of dura closure. Dura coagulation should be avoided as it generates its retraction and complicates the primary closure of the dura. The dura leaves are tacked to the margins of the muscle with sutures. The dura is covered with cottonoids and maintained wet throughout the surgery to reduce the degree of its retraction.

Often the ependymoma can be seen bulging out from underneath the arachnoid splaying of the cerebellar tonsils (Fig. 22.1c). The arachnoid is incised and opened over the cisterna magna for drainage of cerebrospinal fluid, except if it is filled by the ependymoma. The caudal portion of the tumor may be separated first from the medulla by using an arachnoid dissector, with care not to injure the spinal roots. In some cases with upper cervical spinal canal extension, the lower part of the tumor can be gently pulled from the spinal subarachnoid space and removed in one piece, avoiding extended laminectomy (Fig. 22.1d). In some other cases, it may stick to the spinal pia thus leading to tailored laminectomy and dissection along the medulla. Once the cisterna magna is free, a cottonoid is placed at its level to decrease the risk of drop metastases entering the spinal canal and reducing the amount of blood that escapes to subarachnoid space.

In case of midfloor-type ependymoma, the surgical steps are very similar to those used for medulloblastoma resection. A careful dissection of the telovelar fissure(s) is made depending on the tumor location. It can be done unilaterally or bilaterally avoiding the vermis incision. Involvement of one or both posterior inferior cerebellar artery(ies) (PICA) should be recognized on preoperative MRI and leads to a careful dissection of these arteries. The vascular supply to the tumor comes off of the PICA. Coagulation of large feeders to the tumor from the PICA will reduce the vascularity of the tumor and decrease preoperative bleeding. The tumor is then gradually removed using either the bipolar/suction technique or the ultrasonic aspirator, preferred by the authors. During excision of the tumor, cottonoids can be placed between the lateral capsule of the tumor and cerebellar tissue. In case of large tumors, internal debulking helps in reducing the need for cerebellar retraction during excision of the tumor. Moreover, when the interface between the normal tissue and the ependymoma is not so clear at the lower part, a superior and midline debulking to the aqueduct of Sylvius may help in the recognition of the normal fourth ventricle structures. The resection will then be made from back to front. Biopsy sampling for histology and genetic assessment is performed. If the ependymoma arises from the floor, a tiny portion of the tumor is left to avoid sequels. Also the tumor has been lifted off the floor of the fourth ventricle, and initially a cottonoid is placed between the tumor and the floor of the fourth ventricle for protection of the fourth ventricle floor structures. Ependymomas often stick to the obex, where their resection can be associated with cardio-rhythmic disorders. It is important to know that this complication may not be reproducible during a second step surgery for the same patient. The inferior pole is then dissected along its lateral margins, through the Luschka foramen, ideally controlled by endoscopy to avoid missing a small piece of tumor. After the tumor has been resected, careful inspection of the tumor bed can be assisted by the use of an endoscope, especially at the level of the roof of the fourth ventricle and the Luschka foramen.

In case of lateral-type ependymoma, the tumor often sticks to the lateral wall of the brainstem, at the junction of the pons and the medulla. In such cases, ependymoma may raise the cerebellum, distort the brainstem, and envelop the cranial nerves. Once the spinal portion has been removed, the vertebral artery can be traced. The tumor is then debulked laterally, until the lower cranial nerves are identified. They may be separated from the tumor in arachnoid folds or may strongly stick to it. Even with modern imaging, it is still difficult to preoperatively predict the attachment or invasion of these structures by the tumor. The authors recommend identifying the cranial nerves at the level of their foramen, dissecting them to the brainstem. The Luschka foramen is explored and tumor removed. In case of prepontine extension with basilar artery encasement, care must be taken not to injure perforating arteries, as the tumor can be developing in between these arteries and the brainstem. For this anterior portion, the use of an endoscope can be helpful to improve the quality of resection.