Stereotactic biopsy is an invasive technique that allows the physician to accurately localize and sample lesions within the brain, but is considered by some physicians to have significant morbidity and mortality rates with a high risk of sampling error. Initially performed freehand in the 1970s using computed tomographic (CT) scans as a guide, the technique changed after the development of the rigid head frame in the early 1980s. Guided by CT scan or by magnetic resonance imaging (MRI), the procedure is indicated when the pathology of the brain lesion is unknown or when future treatment decisions depend on the histologic nature of the lesion. Stereotactic biopsy can safely sample lesions deep within the brain, those in the eloquent cortex and those that are surgically unresectable. The technique is also indicated for use in patients who are too ill to undergo general anesthesia. Hall reports the results of stereotactic biopsies performed from February 1991 to December 1996 at the University of Minnesota Hospital and Clinic, Minneapolis.
A total of 134 stereotactic biopsies performed in 122 patients were reviewed. The patients participating in the study ranged from three to 83 years of age, with a mean age of 41 years. The medical and surgical records of all patients were analyzed to determine age, gender, location of lesion, frozen-section diagnosis, permanent pathologic diagnosis, diagnostic yield of the procedure and associated morbidity and mortality.
The majority of biopsies were performed using local anesthesia (1 percent lidocaine) and intravenous sedation. After a stereotactic head-frame was placed on the patient, CT or MRI was used to determine the biopsy target coordinates. MRI was preferred for brainstem lesions. During the procedure, a tissue sample was routinely sent for frozen section or, if infection with acquired immunodeficiency syndrome was suspected, either a touch or a smear preparation of a tissue specimen was obtained. After the biopsy, patients were observed overnight for any neurologic deterioration and were usually discharged the following morning.
Eighty-five lesions (63 percent) were biopsied with CT guidance and 49 lesions (37 percent) with MRI guidance. General anesthesia was used for biopsy of 28 lesions; seven of these were in children. The most frequently biopsied lesions were malignant brain tumors (62 lesions), followed by benign tumors (24 lesions) and neurologic disorders (23 lesions). Seven of the lesions biopsied did not demonstrate an intraoperative diagnosis; four of these were also found to be nondiagnostic on permanent pathology. Reasons for diagnostic failure included close proximity of the lesion to the cerebrospinal fluid pathways, inability to obtain diagnostic tissue despite multiple passes or inability of the needle to penetrate the mass.
Following biopsy, one patient who had a pontine anaplastic astrocytoma experienced temporary hemiparesis related to edema.A second patient sustained a fatal hemorrhage after a vascular pineal region mass was biopsied.
The author concludes that stereotactic brain biopsy is an extremely safe and effective procedure for determining the pathology of intracranial lesions. In this case series, the diagnostic yield was 96 percent, the morbidity rate was 0.7 percent and the mortality rate was 0.7 percent. A comparison of 7,471 similar procedures performed at other institutions yielded similar results: diagnostic yield of 91 percent, morbidity rate of 3.5 percent and mortality rate of 0.7 percent.