Surgery

How is an intramedullary tumor actually removed from the spinal cord?

Many critical factors come together to provide the optimal environment for successful resection of such a tumor.

First of all: it is a team effort
While the experience of the neurosurgeon is a critical factor, so is the availability of sophisticated intraoperative neurophysiological monitoring, the availability of specialized instruments, such as the microsurgical laser, the availability of expert postoperative intensive care, nursing, physiotherapy, and so forth. It is also important that the child and adult convalesces in an environment sensitive to their needs.

Surgical experience in resection intramedullary spinal cord tumors is difficult to acquire because these tumors are quite rare. There are approximately 100 children and 250 adults who are diagnosed with this kind of tumor every year in North America. It is easy to understand that most members of the neurosurgical community have little or no experience with managing these tumors. Consequently it is essential that patients seek treatment in one of the few centers who have the surgical expertise, and where the material and intellectual "infrastructure" is available to successfully carry out these operations.

Operative Technique
Patients are operated on in prone position (laying face down). The skin incision is centered on the tumor level vis-à-vis the vertebrae of the spine. Sometimes an X-ray is necessary in the operating room to identify the correct level. In order to access the spinal cord the spinal canal must be opened from the back. That means some of the bone must be removed. These parts are called the laminae of the vertebrae; therefore we call this first part of the operation laminectomy. These laminae are cut out with a bone saw, and we make every attempt to replace them at the end of the operation, a maneuver, which is called an osteoplastic laminotomy. This restores more of the original bony structure of the spine, and, we believe, helps to prevent future spinal curvature.

Using an ultrasound-imaging device the tumor is then actually visualized. This helps confirm that the opening is large enough, and it distinguishes solid tumor portions from cystic (i.e. fluid-filled) components. As a next step electrodes for the intraoperative monitoring of the motor and sensory pathways of the spinal cord are inserted above and below the tumor level. Then the dura, the firm membrane that covers brain and spinal cord, is then opened.

The spinal cord is most often opened in the midline between the fiber pathways that carry sensory information from the periphery of the body to the brain. This is done with the microsurgical laser, as this instrument allows most precise cutting with minimal tissue manipulation. Using gentle movements with specialized microinstruments the tumor is separated from the normal surrounding spinal cord.

Depending on the tumor type the surgical technique may vary: for astrocytomas, the most common intramedullary tumors in children, the resection usually proceeds from the inside out. This means that the tumor is basically hollowed out by removing it in many small pieces. This can be done using the laser, the CUSA or cavitron (an ultrasonic aspirator that vaporizes tumor tissue and suctions it away at the same time), or it can be done using a small suction device. The rationale for this inside-out piecemeal technique is that astrocytomas do not have a clear-cut interface to the normal spinal cord. A small rim of tumor tissue therefore often remains, as taking too much at the end of the resection carries a very high risk of inflicting damage to the cord. Ependymomas, the most common spinal cord tumor in adults, have a clear-cut interface with the normal spinal cord. In this case it is most often possible to dissect the tumor away from the cord and remove it practically intact, with its capsule. The critical part here is the cutting of the blood vessels that supply this tumor. These always come from a larger vessel in the front of the spinal cord. Bleeding from these small vessels can be a problem. Coagulating the bleeding vessels with bipolar forceps carries a risk of coagulating the larger vessel, the anterior spinal artery, and thus compromising blood supply to the normal spinal cord.

It is quite clear that resection of a tumor out of the spinal cord is different from surgery elsewhere in the body where a surgeon may remove tissue widely beyond a tumor's borders. There are almost always small fragments of tumor which escape detection. This, what we call "microscopic disease" however seems not to influence the rate of recurrence that much: once 80% of an astrocytoma is removed, the likelihood of recurrence is about the same as for a resection of 99 %!

During resection of tumor, whether the "inside out" technique or the "en bloc" technique the motor evoked potentials are closely observed and any deterioration of recordings or loss of recordings is reported by the neurophysiologist to the surgeon. Most of the time any change is reversible by just pausing and irrigating the resection cavity. If monitoring indicates a critical injury is threatened surgery is stopped and the patient is allowed to recover. A second operation to remove the remaining tumor can be considered.

Cheryl Fried, RN