brain where cerebrospinal fluid (CSF) circulates. A small valve attached to tubing is placed under the scalp. The tubing is then threaded under the skin, down the neck, and into the abdominal cavity. Sometimes the shunt empties near the right atrium of the heart rather than the abdomen. In either SURGERY www.abta.org 11 location, the fluid drains out of the shunt and is absorbed by the body. The shunt filter catches small pieces of tissue and stray tumor cells that might be in the CSF as it drains away from the brain. Small incisions in the neck, chest and/or abdominal area are made to attach the tubing securely. The shunt has a valve that permits the CSF to only flow away from the brain, and controls the rate of flow. A shunt can be either temporary or permanent. Sometimes a tube is placed into one of the four cavities or ventricles in the brain and connected to a collecting bag outside of the body. This procedure is called a ventriculostomy and is a temporary way of draining the CSF. After the shunt is in place, most patients, especially children, experience dramatic improvement within days or weeks. It is fairly common that a shunt might need maintenance. Reasons for this include blockage of the Components of a typical ventriculoperitoneal (VP) shunt McGill University Health Centre, Montreal, Canada 12 AMERICAN BRAIN TUMOR ASSOCIATION catheter, an infection, a disconnection, or in the case of a child, the catheter may need to be lengthened due to the child’s growth. When these situations occur, a surgical procedure known as shunt revision may be done to correct the problem. Shunts may not be used if the pressure in the brain is too high. Abruptly changing the pressure may cause the brain to shift upward or downward toward the spine. In this situation, the doctor will use other methods to reduce the pressure before a shunt is inserted. OMMAYA RESERVOIR An Ommaya reservoir is a small container surgically implanted under the scalp and attached to a tube. The tubing may lead into a ventricle of the brain (where the CSF circulates) or into a fluid-filled cyst. This container can be used to: • Deliver chemotherapy to the brain and the CSF surrounding the brain without having to undergo spinal taps • Remove CSF from the reservoir to detect the presence of abnormal cells • Remove cystic fluid when it accumulates without having to undergo surgery Placement of a reservoir can be done in a 15–20 minute procedure. The Ommaya reservoir can be built into the catheter as part of a shunt, or as a stand-alone device. The reservoir can be removed if it is no longer needed. SKULL BASE SURGERY Skull base surgery refers both to the location of a tumor as well as a specialized technique used to remove a tumor in that area. The skull base is the delicate bony area that supports the bottom of the brain. Tumors located in this area often surround nerves and blood vessels involved in vision, smell, hearing, speech, SURGERY www.abta.org 13 swallowing, and eye and facial movements. Skull base surgery is challenging. It can involve removing the bone surrounding the brain and reassembling it again without disturbing the function of the crucial nerves or blood vessels in that area. This type of surgery can be very lengthy. TRANSPHENOIDAL SURGERY Transphenoidal surgery is an approach often used with pituitary adenomas and craniopharyngiomas. The term “trans” means through and “sphenoid” refers to the sphenoid bone located under the eyes and over the nose. The entry point for the neurosurgeon is through an incision made under the upper lip and over the teeth or directly through the nostril. These are sometimes the most direct routes to the pituitary gland. LASER INTERSTITIAL THERMAL THERAPY (LITT) LITT uses a laser to heat brain tumor tissue while monitoring the destruction of the tissue with an MRI that can measure the temperature of the tissues in real time. The laser probe is directed into the tumor through one or more small holes using stereotactic techniques. The availability of LITT is relatively new and may provide the benefit of surgical removal for some tumors that are difficult or impossible to access with a conventional craniotomy. WHAT TOOLS AND TECHNIQUES ARE AVAILABLE TO NEUROSURGEONS? BRAIN MAPPING While MRI and MRS scans give the neurosurgeon valuable information about the brain tumor, they don’t precisely identify sensitive areas of the brain that are responsible for speech, comprehension, sensation or movement. Brain mapping during surgery helps the neurosurgeon detect critical areas and distinguish the margin of the tumor from the rest of the brain tissue. 14 AMERICAN BRAIN TUMOR ASSOCIATION Brain mapping tools include: • Direct cortical stimulation • Somatosensory-evoked potentials • Functional MRI • Intraoperative ultrasound imaging • Intraoperative MRI Direct Cortical Stimulation This technique identifies sensitive areas of the brain through direct contact with the brain tissue. A probe is used to stimulate certain areas of the brain with a low dose of electrical current. As the probe touches an area of the brain, the electric current causes a visible movement of that related body part. If the patient is awake, this technique can also be used to locate critical areas in speech or sensation. This helps the neurosurgeon identify critical areas of the brain that must be carefully navigated.