On the Forefront: Frameless stereotactic CT-guided needle brain biopsy

Oct 01, 2004

Figure 1. The frameless stereotactic CT-guided needle brain biopsy apparatus. The apparatus is placed above the dog’s trunk, and a flexible arm holding the biopsy needle guide is mounted and fixed in position over the dog’s head to target the lesion. The biopsy needle guide is made of plastic to avoid image artifacts.
In animals suspected of having neurologic diseases, the diagnostic workup includes evaluating the animal's signalment and history and conducting thorough physical and neurologic examinations. Depending on the findings of these evaluations, a preliminary minimum database (i.e. a complete blood count, a serum chemistry profile with electrolytes, urinalysis, thoracic radiography, and abdominal ultrasonography) may also be needed. In animals suspected of having brain diseases, the diagnostic workup includes all of the evaluations mentioned above as well as specific tests such as computed tomography (CT) or magnetic resonance imaging (MRI) and cerebrospinal fluid analysis. With the development and adaptation of CT and, more recently, MRI for animals, it is now possible to identify and localize brain lesions. However, these imaging techniques are limited because they can only tell us whether there is a lesion in the brain. They cannot identify the cause of the lesion or whether it is treatable. Often, it is not possible to differentiate a brain tumor from an inflammatory or infectious disease.

Figure 2. The Sedan Side-Cutting Biopsy Needle.
As with many diseases, a biopsy is the only definitive way to diagnose a brain disease and determine whether treatment, excision, or both are possible. A biopsy may help to differentiate a tumor type or the type of infection or inflammation (i.e. fungal, bacterial, protozoal, viral, parasitic, immune-mediated). Until recently, performing a biopsy has required brain surgery with its complement of postoperative complications. Opening the skull is always risky, and with brain surgery, only superficial lesions may be accessible.

A new biopsy option

A stereotactic system uses three-dimensional coordinates to locate a site in the brain to be accessed surgically. Conventional stereotactic systems require the use of a stereotactic frame attached to a patient. Recently, a technique has been developed that allows veterinary neurosurgeons to obtain a biopsy sample of the brain: a frameless stereotactic CT-guided needle biopsy. This new technique does not require the complicated and expensive stereotactic frames used in previous studies.1-3 In this new procedure, the stereotactic frame is replaced by a biopsy needle guide inserted into a surgical arm, which, in turn, is attached to the apparatus (Figure 1). This technique is superior to surgical biopsies because it allows a surgeon to access places a scalpel cannot and do so without damaging surrounding tissues. The procedure is done in real time so that the clinician knows exactly where and how far to advance the needle. Adequate sample sizes (1.2 x 4 mm) are obtained for cytologic and histologic differentiation between infection, inflammation, and tumor.

How it works

Figure 3. Dr. Filippo Adamo, after performing a burr hole craniotomy with a hand drill, inserts the brain biopsy needle into the biopsy needle guide. The apparatus and the needle are prepositioned to target the lesion. The needle is advanced under CT guidance.
An animal is anesthetized in the CT suite, the hair on its head is clipped over the region of interest, and the skin is marked with indelible ink to correspond with the transverse plane. Several barium marks are applied along the ink line, and transverse contrast CT images are obtained. These images display the lesion in the brain as well as the barium lines over the skin. The barium line best aligned with the intracranial lesion is chosen as a reference point for the skin incision and the craniotomy. The target is localized on one transverse image, and the table position is noted.