Intradural Tumors: Radiology - Surgery

Radiology

Magnetic resonance imaging (MRI) is the imaging study of choice to evaluate intradural neoplasms. MRI formidably shows anatomical details with minimal artifact from the surrounding osseous structures. It provides a triplanar view of the neoplasm which allows accurate differentiation between intramedullary and extramedullary tumors. Intravenous gadolinium contrast, and particularly with the recent advances in MR technology, such as faster pulse sequences, and cardiac gating, MRI has become increasingly accurate in predicting the histologic tumor type.

Surgery

Surgery is the most effective treatment for all intradural neoplasms. Long term control or cure can be achieved with total removal for the extramedullary tumors and the majority of intramedullary neoplasms. Thus, early diagnosis and aggressive initial surgery provide the best opportunity for long progression-free survival. The surgical exposure should encompass the tumor with some rostral and caudal margins to allow for adequate visualization. In children or young adults, osteoplastic laminoplasty may reduce the incidence of postoperative deformity.

Extramedullary Neoplasms

For resection of extramedullary tumors the bony removal must be wide on the ipsilateral side and may include the facets. After the bony exposure is achieved, the surgical principle is to remove the neoplasm with minimal traction on the spinal cord. The surgeon should also avoid injury to the nerve roots. In large tumors this may be accomplished by an intracapsular decompression before the tumor is removed. The ultrasonic surgical aspirator (CUSA) or the laser allow for rapid debulking without displacing the surrounding neural tissue.

In nerve sheath tumors which arise from the dorsal roots, the nerve root is intimately involved in the tumor. These tumors can rarely be separated from these roots. Therefore these dorsal roots may be sacrificed over a few segments in the thoracic region, however only very few dorsal rootlets should be sacrificed in the cervical region. These tumors rarely are adherent to the spinal cord and can easily be separated away from it.

Meningiomas which are located ventrally or ventrolaterally pose more of a surgical challenge. A wide laminectomy with debulking of the tumor permits the surgeon to maneuver it out from under the ventral area of the spinal cord. In most instances, the tumor attachment is at the dura while adhesions to the spinal cord are relatively minor.

Intramedullary Neoplasms

The exposure is similar to extramedullary tumors. The dura is then opened and secured with several tack-up sutures. It is important to emphasize that the swollen spinal cord is often rotated and distorted. It is essential to identify normal landmarks prior to performing a myelotomy. The myelotomy is performed over the center of the tumor using either bipolar cautery and an arachnoid knife or a laser (carbon dioxide or Nd:YAG).

Astrocytomas are gray in color, and they do not have a plane of dissection from normal spinal cord tissue. These neoplasms should be removed from "inside out" until a glial tumor interface is recognized by the change in color and consistency of the adjacent tissues. The excision of the astrocytoma is initiated in the mid-portion rather than the rostral or caudal pole of the neoplasm because the poles of the neoplasm have the least volume of tumor tissue, and removal of this part of the neoplasm may therefore be the most hazardous. The last fragments of the rostral and caudal segments of the tumor are removed by working within the myelotomy and distracting the residual neoplasm into the surgical cavity without extending the myelotomy.

Ependymomas are red or very dark gray and have a distinct cleavage plane between tumor and the adjacent neural tissue. Small tumors may be removed in one piece, whereas bulky ones must be excised in a piecemeal fashion. In these cases, it is hazardous to attempt an en bloc excision, as there will be excessive manipulation of adjacent neural tissue. In these cases, the center of the tumor must first be debulked, and only then should the cleavage plane between tumor and adjacent tissue be developed. This is accomplished by retracting the tumor tissue into the residual cavity, and not retracting the spinal cord from the tumor. There is usually an area of tumor tissue which is adherent to the anterior median raphe. These fragments must be removed in bits and pieces, and with sharp dissection to avoid injury to the anterior spinal artery.

Hemangioblastomas are most commonly located on the dorsal or dorsolateral surface of the cord. These lesions are, of course, vascular and therefore the surgeon should not enter the tumor because bleeding may be difficult to control. The dissection should proceed around the tumor surface with cauterization of the feeding vessels and tumor capsule. It is advisable to preserve at least one venous pedicle until all feeding arteries are divided.