If the tumor is determined to be a medulloblastoma, current treatment consists of surgically removing as much tumor as possible, followed by craniospinal (brain and spine) radiation and/or chemotherapy. Your doctor will suggest a treatment plan based on factors that indicate the risk of tumor recurrence — either “average-risk”
or “high-risk.” To determine risk, doctors look at the age of the patient; the amount of tumor remaining following surgery; and the amount of metastases, or tumor spread (also called M stage). Children are considered at “average-risk” of recurrence if they are diagnosed after age 3; if all, or nearly all, of the tumor is surgically removed; and if there is no evidence of metastases or tumor spread. All other pediatric medulloblastomas are considered to be at “high-risk” of recurrence. High-risk patients include those under age 3; if more than 1.5 cm (about 1/2 inch) of tumor volume remains following surgery; or if there is any evidence that the disease has spread. For adults, risk is generally determined by the amount of remaining tumor, and the presence or absence of tumor spread. The present staging system for medulloblastoma is of major importance. However, a variety of molecular changes were recently identified in childhood medulloblastoma tumors. Researchers are studying whether these findings will be helpful in determining whether children are of average or high-risk disease, or if the information might help to predict the chances of recurrence or spread. Researchers are also studying ways to obtain this biologic information in real-time (meaning within days after surgery).
“M stage” is a medical way of indicating the degree of metastasis (tumor spread), if any.
M0 means no evidence of metastasis has been found — the tumor appears to be limited to the area in which it grew.
M1 means there are tumor cells in the spinal fluid.
M2 means the tumor has spread within the brain.
M3 means the tumor has spread into the spine.
M4 means tumor spread away from the brain or spine (for example, in the rare situation in which the medulloblastoma spread to the chest or bones).
Removing as much tumor as possible is the most important step in treating medulloblastoma. The neurosurgeon has three goals for the surgery:
– To relieve cerebrospinal fluid buildup caused by tumor or swelling;
– To confirm the diagnosis by obtaining a tissue sample; and
– To remove as much tumor as possible with minimal neurological damage.
Several studies have shown the best chance for long-term tumor control is when all of the medulloblastoma visible to the neurosurgeon’s eye can be removed safely. Many technologically-advanced surgical tools are now available. MRI scanning combined with computer-aided navigation tools help the neurosurgeon map the exact tumor location before the operation, and track its removal during the procedure. High-powered microscopes provide visual enhancement. Ultrasound and gentle suction devices are used to remove tumor during the actual procedure. These techniques assist the surgeon in navigating around adjacent healthy structures.
While the goal is to eliminate the tumor, some medulloblastomas cannot be removed completely. In one-third of patients, the tumor grows into the brain stem, making total removal difficult because of potential neurological damage. If the tumor is determined to be inoperable, a biopsy may still be done to confirm the diagnosis. Steroids are drugs used before and after surgery to reduce swelling around the tumor.Occasionally, a ventriculostomy (an external drainage device) may be placed to divert excess cerebrospinal fluid from the brain. A permanent shunt, a long catheter-like tube that drains fluid from the brain to the abdomen, is sometimes necessary. In most cases, however, removing the tumor opens the cerebrospinal pathways, which restores both normal fluid flow and pressure. It also eliminates the need for a shunt or drainage device. Within two days following surgery, an MRI will be done to visualize the amount of remaining tumor. (If an MRI scanner is available in the operating room, the scan may be done during surgery.) The amount of “residual” or remaining tumor will be a strong factor in determining further treatment.