This article was written for The Childhood Brain Tumor Foundation,Germantown, MD 20876

Clinical Update: Philip H. Cogen, M.D, Ph.D.

Brain tumors are the most common type of solid cancer in children, yet much remains to be learned concerning their origin and treatment. Although many children still succumb despite aggressive management, newer adjuncts in surgical resection have improved the outcome from these procedures. Several recent studies have confirmed that removal of as much of the tumor bulk as is possible leads to the best therapeutic response, even if the tumor is of the malignant type. This is especially true for ependymomas, where the outcome of treatment is directly related to the degree of tissue resection. To this end, newer instrumentation has been designed and implemented, tools that we use at the Children's National Medical Center, often on a routine basis, to maximize the surgical resection. For tumors in all parts of the brain, microsurgery, using a sophisticated scope on a universal mounting, allows for visualization of even small tumor remnants. It also allows the surgery to be performed through a small opening in the surrounding normal brain tissue, minimizing this trauma and decreasing post-operative neurologic deficits. The microscope also magnifies the blood supply to the tumor, so that feeding vessels can be ligated to decrease intraoperative blood loss, and blood vessels to the normal brain can be preserved.

A second useful adjunct that improves the capabilities of the surgeon to safely remove a tumor is intraoperative ultrasonography. A system such as the one we employ has probes that can be used even through a small burr (drill) hole in the skull to see the normal and abnormal structures, and guide the trajectory of the surgical approach. Ultrasonography can be used to look at the cerebrospinal fluid (CSF)-containing spaces in the brain-the ventricles-during surgery, and to identify cysts, entrapped fluid collections. After tumor removal, the ultrasound can be used to verify the degree of resection.

A different type of ultrasonic device is also a very valuable surgical adjunct, particularly for brain tumors. A high-speed, high-frequency type of ultrasound probe can actually break-up tumor tissue into small pieces that can be removed by suction. This device is especially beneficial in that it will not usually damage the surrounding normal brain, which has a different consistency from that of the tumor. We will employ a Cavitron Ultra-Sonic Aspirator (CUSA) newly re-designed with extra-small tips to gain access to even deeply-seated tumors without damaging the surrounding normal brain. The specimens obtained with the CUSA can also be saved and examined by the pathologist, so as to sample all of the different parts of the tumor.

Occasionally, we also use a laser to vaporize tumor tissue. The laser can be directly attached to the microscope to visualize the exact location to be treated. Although the laser is particularly useful for extremely firm tumors, and those with a high fat content, it does not control the degree of surrounding tissue injury as well as the CUSA.

Perhaps the most recent advance is the use of a frameless stereotaxic-type device for intraoperative localization and planning. Often referred to as an operative wand, we use this computerized device to integrate information from a CT or MRI scan with the patient's surface anatomy to locate precisely where the tumor lies. This can then be translated into the appropriate site for the craniotomy flap. During the procedure, the wand helps to localize the lesion as well. As these devices become more sophisticated, the size of the bone flap will decrease, and the ability to detect residual tumor during the procedure will increase.

Altogether, these and other surgical adjuncts have made resection of a childhood brain tumor far more successful in the hands of a skilled pediatric neurosurgeon with modern capabilities. Over time, newer modalities in surgery and adjunctive therapies will no doubt improve both quality of life and survival for the these children.

Philip H. Cogen, M.D.,Ph.D, Chairman, Department of Neurosurgery,

Children's National Medical Center.