Position

Most patients in our series were operated on in a semi-sitting position, with the head in mild flexion.1 The position assisted in having the shoulders out of the way of the surgical approach and provided a clear surgical view to the region. It also allowed for a relatively bloodless field, with the blood washing out by gravity during surgery. Apart from anesthesia-related precautions, all the safety norms necessary while operating in a sitting position are mandatory. There are large venous lakes in the extradural space around the foramen magnum, and generous packing of the region with Surgicel or Gelfoam is mandatory to avoid air embolism-related problems.

Incision, Surgical Exposure, and Steps

A straight midline incision is taken. The C2 spinous process forms the inferior landmark for exposure. The suboccipital bone, arch of the atlas, and C2 laminae are exposed in a subperiosteal plane. The exposure is widened on the side of the tumor using a self-retaining retractor. Such an approach allows wide lateral exposure up to the mastoid bone and to the condyle. Whenever necessary, the length of the incision can be increased to affect the lateral exposure. The incision and the subperiosteal bone exposure avoid the need for any muscle dissection or cutting into the muscles. The arch of the atlas is exposed widely. The subperiosteal dissection is done on the inferior aspect of the posterior surface of the arch of the atlas, and the exposure is extended laterally. The vertebral artery coursing over the posterior arch of the atlas is identified for proximal control. Large venous lakes inferior to the lateral aspect of the arch of the atlas in the region of the C2 ganglion may need packing with Surgicel. The bone exposure will depend on the nature and the extensions of the tumor. Usually a low suboccipital craniectomy on the side of the tumor that extends inferiorly up to the foramen magnum and laterally up to the occipital condyle is done. Whenever indicated, condylar drilling is possible for a more lateral and anterior exposure. The arch of the atlas is removed until the groove for the vertebral artery. Vertebral artery exposure and control are obtained in cases where the tumor encases the intracranial vertebral artery. The C2 spinous process and the ipsilateral half of the lamina are resected depending on the inferior extent of the tumor. The dural incision extends from the spinal dura to the cerebellar dura. The dural flap is everted laterally. After the dura is opened, the tumor, cranial nerves, and presumed site of the vertebral artery course are identified ( Fig. 40.1 ). The cerebellum is retracted superiorly to expose the tumor from a superior aspect. The cerebellar retraction is eased by arachnoidal sectioning that releases the vermis and tonsils from the medulla. On initial inspection, the tumor may appear formidable, with intimate relationships with blood vessels and nerves. However, as the dissection progresses, the tumor appears less complex, and resection becomes simpler. Dentate ligament is sectioned early in the operation to allow safer retraction of the cord. C1 and C2 roots must be differentiated from the spinal accessory nerve and other lower cranial nerves. Although sectioning of the C1 and C2 roots has almost negligible neurological sequelae, sectioning or even handling of the lower cranial nerves can result in devastating clinical deficits. Further dissection and tumor resection will depend on tumor-related factors. Consistency, vascularity, and the extent and nature of the dural attachment and relationship with the spinal cord, nerves, and blood vessels will ultimately determine the course of surgery. Most of the tumors are relatively soft and only moderately vascular. Tumors that encase the vertebral artery are usually softer in consistency. The tumor is first debulked progressively as much as possible. This procedure relaxes the region and allows more space to work around the tumor. Perforator injury is extremely dangerous for neural function and has to be prevented. After the initial tumor debulking, the site of tumor dural attachment is dealt with. The tumor is disconnected from its attachment, and bleeding sites are coagulated. In general, during surgery, coagulation is required only at the site of attachment. Coagulation within the confines or the bulk of the tumor is unnecessary. Coagulation outside the dome of the tumor is usually a technical error. The dissection of the tumor from the nerves and vessels is done in the subsequent stage of the surgery when the region is relaxed and the tumor is devascularized. This dissection is done with the use of meticulous and careful microsurgical techniques and appropriate angulation of the microscope. Resection of the part of the condyle can be done even during the tumor resection when an additional exposure is felt to be necessary. After resection of the tumor, the site of its attachment is coagulated, and the involved layer of dura is resected. No attempts were made in our series to resect the dura widely or to excise the involved bone.

Incomplete resection is usually due to wide tumor extensions, particularly when the tumor extends far beyond the midline. The portion of the tumor where dissection from perforators or nerve fibrils is diffcult or dangerous can be safely left behind. Tumors that have calcification and those with elastic consistency are more diffcult to resect. Recurrent tumors can sometimes be extremely diffcult for dissection. In situations where dissection of the tumor from the cervicomedullary cord is diffcult or where the pial plain is lost, it is safer to leave a large strip of the tumor in proximity of the cord. Any damage to the cord in this region can be extremely dangerous.