Background
Tissue-based pathological diagnosis is the criterion standard in the diagnosis of brain tumors. In situations in which surgical resection is not necessarily indicated but diagnosis of a brain lesion is needed to determine optimal treatment, a stereotactic brain biopsy offers a relatively safe and reliable method of obtaining diagnostic tissue. For over half a century, frame-based stereotactic methods have proven their use, and, more recently, frameless stereotaxy has emerged as a valuable alternative to this. Both framed and frameless stereotactic biopsy are discussed in this topic.
Indications
Brain biopsy should be considered when a tissue diagnosis from a suspicious brain lesion is needed to guide treatment and less-invasive methods of diagnosis are exhausted or inappropriate. Generally, brain biopsy is performed in 2 different scenarios. First, and most commonly, it is performed to confirm a suspected brain tumor. A typical situation occurs when diagnostic imaging demonstrates the classic appearance of a primary brain tumor and resection is not felt appropriate, as when the treating team suspects a high-grade glial tumor on the basis of imaging characteristics and does not feel that an aggressive resection is achievable. [1] Tissue diagnosis can confirm the suspected pathology and guide further non-operative treatments.
The second and fortunately less-common scenario occurs when a wide-ranging differential diagnosis has been cast, and a diagnosis remains elusive despite less invasive work-up.
Contraindications
Practically speaking, absolute contraindications to brain biopsy are limited to those lesions felt to be too small to accurately and safely target and to those patients who are coagulopathic or otherwise unable to safely tolerate intravenous sedation or general anesthesia. In patients whose mental status would not permit stereotactic frame placement while under local anesthetic, a general anesthetic could be considered.
In any patient considered for stereotactic brain biopsy, weighing the relative merits of biopsy, namely the ability to obtain a tissue diagnosis, against the potential risks is important. In making this decision, all less-invasive opportunities to obtain a diagnosis should be considered. These could potentially include imaging adjuncts such as MR spectroscopy, sampling of spinal fluid by lumbar puncture, or identification of alternative systemic lesions to biopsy, such as an accessible lung lesion in the setting of multiple intracranial metastases. Exercising caution is important when considering biopsy of lesions that are suspicious for vascular malformations or with highly vascular tumors such as metastatic melanoma. With intraventricular tumors, an endoscopic biopsy can be entertained in favor of a stereotactic biopsy.
-
Upper left: The Cosman-Roberts-Wells (CRW) unit is affixed to the skull using 4-point fixation of the base ring. The CRW frame is attached to the base ring by way of 3 ball-in-socket joints. Upper right: With adequate low placement of the base ring, direct posterior fossa trajectories are practicable. Lower left: Demonstration of a direct lateral entry point approach is possible with the frame. Lower right: Lateral placement of the base ring is feasible with the use of specially designed partial arcs.
-
The Leksell head ring.
-
Preoperative contrast-enhanced coronal T1-weighted MRI demonstrating a multifocal enhancing left fronto-temporo-insular tumor, suggestive of a high-grade glioma.
-
This illustrates the planned target, cortical entry point, and trajectory of the stereotactic biopsy of the lesion seen in the previous image. The trajectory is planned with an effort to obtain the most accessible enhancing portion of the lesion. Of note, the planning software reverses the conventional left-right orientation.
-
This is the 3-dimensional representation of the biopsy plan seen in the previous images as generated by the planning software. In the absence of a phantom base, generating this image in the operating room to confirm that the actual trajectory is consistent with this representation can be useful.
-
This is the postoperative noncontrast coronal CT scan of the same patient in the previous images, which clearly demonstrates the trephination and the biopsy tract, with a punctate hemorrhage at the biopsy site and scant hemorrhage along the tract.
-
This image illustrates a typical configuration of the targeting device. Knowing the distances from each point in the configuration to the target is important. From the bottom of the blue reducer, the target is 160 mm. The blue reducer measures 10 mm and thus places the target at 170 mm. Generally, an additional reducer, measuring 5 mm, is placed within the blue reducer, which leads to a final distance of 175 mm to target. Thus, the biopsy cannula can be set to that depth.
-
The distance to the target can be calculated, but direct measurement with a phantom base should be considered to confirm the calculation.
