Neurosurgery

A laminectomy or osteoplastic laminotomy [20] is performed with a high-power drill using the craniotome attachment, round burr and rongeurs. The bone removal must always expose the solid tumor but not the rostral or caudal cysts. The cysts usually disappear after the neoplasm is resected, since the cyst walls of "capping" cysts are usually composed of non-neoplastic glial tissue.

Intraoperative sonography (Fig. 29.9) visualizes the full extent of the tumor and its relation to the bone removal, as well as cysts and displacement of the cord [21]. If the bone removal is not sufficient, the laminectomy is extended to expose the entire solid tumor prior to opening the dura.

The dura is then opened in the midline. The spinal cord is frequently expanded and it may even be rotated and distorted. The asymmetric expansion and rotation of the spinal cord may make identification of the midline raphe difficult. However, it is important to localize this raphe because this is the most frequent approach into the spinal cord. An alternative approach for extremely asymmetrical tumors is to enter the spinal cord through the dorsal root entry zone. This is an approach used sometimes when an asymmetric deficit is present; thus, it is essential to preserve the "good" arm and hand while the other upper extremity is already severely impaired, and deafferentation adds little morbidity.

If the tumor is not visible on the surface, the microsurgical laser is used to perform the myelotomy, with minimal neural injury. The various types of intramedullary tumors have different macroscopic appearances. Ependymomas (Fig. 29.6) are red or dark gray in color and have a clear margin from the spinal cord. This interface can be separated with the plated bayonet or the microsurgical laser. One pole of the tumor is identified and the cleavage plane separated in an axial direction. The ventral aspect of ependymomas is adherent to the anterior median raphe because the feeding vessels originate from the anterior spinal artery. It is essential to preserve this vessel. The majority of these tumors can be removed en bloc [6].

Astrocytomas or gangliogliomas have a gray-yellow glassy appearance. They must be removed from the inside out, until the glial-tumor interface is recognized by the change in color and consistency of the tissue. Rarely, a true plane between tumor and normal spinal cord exists, and futile efforts to define this interface result in hazardous manipulation of normal spinal cord tissue [18]. Their resection is usually started at the midportion rather than at the

Fig. 29.9. The intraoperative sonographic view of an intramedullary ependymoma allows for identification of the solid and cystic components.
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