Surgical Procedures for Brain Tumors

Author: Patrick J Kelly M.D.
New York University School of Medicine
Copyright, 1994
Date: Sat, Jul 9, 1994

Sometimes physicians describe their operations in terms that are very foreign to the patient. The following is a primer for patients and their families in neurosurgical procedures which will help them better understand the surgical options for brain tumors.

Craniotomy

This means to make a trap-door in their skull to expose its contents. An incision must be made in the scalp and the scalp is peeled back to expose the bone of the skull. One or several holes (about 1/2 inch in diameter) are made in the skull using a special saw. Then the plate of bone is removed, exposing the outer membrane covering the brain -- or dura mater. The dura is cut and the surface of the brain is thus exposed. The operation to remove a brain tumor or perform some other task then proceeds. When this is completed, the dura is usually closed with sutures and the bone plate is replaced. This is held in place with wire or nylon sutures. The scalp is then closed.

Craniotomies are usually named for the part of the skull in which they take place: e.g. Frontal craniotomy, temporal craniotomy, etc.

Stereotactic Biopsy

Stereotactic (from Greek: Stereo-three dimensions; tactic-to probe) is a term to describe procedures done in precise and defined three dimensional space. These are ordinarily done with the patient's head held in a rigid frame (called a stereotactic frame). The frame is used to direct a probe into the brain through a small hole in the skull.

(39Kbytes) shows an axial CT of patient's head in a stereotactic frame. The white dots outside the patient's head are part of the internal calibration of the stereotactic frame.

Volumetric Stereotactic Procedures

Volumetric stereotaxis is a method for gathering, storing and reformatting imaging derived three dimensional volumetric information defining an intracranial lesion with respect to the surgical field. Most importantly, this information is displayed to the surgeon intraoperatively and scaled to the actual size and location of the surgical field. With this technique a surgeon can plan and simulate the surgical procedure beforehand, reach deep-seated or centrally located brain tumors employing the safest and lest invasive route possible.

Why is volumetric stereotaxis necessary?

Intracranial mass lesions are volumes in space. This is easily apparent on review of contiguous CT and MRI slice images of the lesion. However, translation of this three dimensional information from the imaging studies ( CT and MRI) to three dimensional surgical operating space within the patient's head is difficult and imprecise during an open operation. A surgeon may have difficulty in knowing where tumor ends and normal brain begins; in spite of the fact that this information is usually clear on the imaging studies. Indeed, there may even be difficulty in finding some subcortical tumors.

Without volumetric stereotaxis three things are possible:

A surgeon can get lost attempting to find the tumor. Brain tissue is damaged unnecessarily. This can result in neurologic deficit and prolonged and expensive rehabilitation efforts.
A surgeon can not tell where tumor ends and normal brain tissue begins. Thus there is some risk that the surgeon can resect normal brain tissue along with the tumor. In important brain areas, this will also result in neurologic deficit.
A surgeon performs a subtotal removal of the lesion. Much tumor remains behind, will recur sooner and require another operation or other treatments
Complete removal of the tumor.

What are the advantages of volumetric stereotaxis?

Volumetric stereotaxis provides the following major advantages to the surgeon in the management of intraaxial brain lesions:

It allows one to find the lesion.
It imparts a concept of the three dimensional shape of the lesion which is to be removed.
It allows preoperative surgical simulation and surgical approach or trajectory planning with respect to the configuration of the lesion and normal brain and vascular anatomy which must be preserved. Thus the safest and most effective surgical approach may be selected.
It indicates by means of a scaled real time display interactive software and stereotactic instrument where tumor ends and normal brain begins.

Volumetric stereotaxis has major advantages for the patient as well:

The smallest possible skin incision, craniotomy and brain incision. This minimizes injury to normal brain tissue.
Since the surgeon knows exactly where tumor ends and normal brain begins, a more complete tumor removal can be accomplished with much less risk to surrounding brain tissue.
The postoperative neurologic results are better than those associated with conventional (non-stereotactic, non-volumetric) surgical techniques.

Volumetric stereotaxis provides advantages to the insurance company since patients get out of the hospital faster, do better neurologically, and back to work earlier. In a practical sense, volumetric stereotaxis will save third party payors money because:

Volumetric procedures are less invasive than conventional intracranial neurosurgical procedures. Post-operative results are better and patients get out of the intensive care unit and out of the hospital faster. Less money is spent on ICU charges and post-op hospital days. In a study done at the MAYO Clinic total hospital charges including surgical fees for patients with astrocytic brain tumors undergoing Computer-assisted stereotactic volumetric resection procedures were approximately 67% of the total hospital charges for conventional surgical procedures in similar patients.
Volumetric stereotactic procedures require less time in the operating room ( 2-3 hours less in some cases) than patients undergoing conventional neurosurgical procedures for brain tumors. This is because the procedures are simulated on a computer system beforehand and can proceed efficiently as planned. This saves money on operating room charges.
"Inoperable" tumors (inoperable by conventional surgical techniques) can be resected with volumetric stereotactic resection procedures. Frequently, these are deep seated-relatively benign tumors in children and young adults. Many of these tumors can be cured with volumetric stereotaxis.
Neurologic results are better, less patients require rehabilitation programs and return to work sooner.

Instrumentation required for Volumetric stereotaxis:

A capacious computer and image processing system,
Systems for data acquisition,
Appropriate planning and real-time display software,
An interactive stereotactic surgical system.

(53.4Kbytes) An view of treatment planning for volumetric stereotaxis.

Point-in-space and Volumetric Stereotaxis

The difference between point-in-space and volumetric stereotactic procedures. What Volumetric stereotactic procedures provide that conventional point-in-space procedures do not.

Volumetric stereotactic procedures are not to be confused with simple point-in-space stereotactic procedures, which are employed for simple stereotactic biopsy, functional procedures, interstitional irradiation of brain tumors or to correctly position a bone flap over a superficial intracranial lesion or to find the superficial aspect of a deep-seated lesion.

Point-in-space procedures are simple; volumetric procedures are mathematically complex and require a computer system with specialized software to be done efficiently and safely.

Point in space procedures can be done without a computer. However, computer-assisted surgical planning with multimodality integration can be used in point-in-space stereotactic procedures to make them more time efficient, accurate and safer. Volumetric procedures cannot be performed without computer-assistance and intraoperative real-time interaction.