STEREOTACTIC BRAIN BIOPSY
Everyone’s heard of a “biopsy,” right? Simply stated, a biopsy is a sort of surgical sampling. Neurosurgeons obtain biopsies of brain masses in order to establish a diagnosis (and therefore render proper treatment) in cases of unresectable lesions (those that are deeply-seated, very diffuse and those that are in so-called “eloquent” cortex). How does the neurosurgeon know where to guide the biopsy probe intraoperatively? By utilizing stereotaxis, a method for locating points within the brain using an external, three-dimensional frame of reference. It’s like GPS for the brain. Modern day computerized systems provide real-time intraoperative guidance and even calculate the distance and trajectory to the biopsy target.
- Dr. Osborn performs this procedure under general anesthesia (as it reduces the incidence of intraoperative seizures that may occur from the biopsy probe passing through the brain should one be kept awake).
- The patient is positioned on the table according to location of the biopsy target and more specifically the planned approach (i.e., where the burr hole will be placed in the skull). The head is affixed to the OR table with a vice-like device. This assures its stability as the probe is being passed into the brain (and therefore accuracy of the stereotactic guidance).
- The head is shaved (partially) and the stereotactic “coordinates” are registered into the software. The registration accuracy is then confirmed (by touching points on the patient’s skin and confirming correlation with the point seen on the computer-projected imaging study).
- The entry point and biopsy trajectory are then planned (based upon the shortest path to the target). An incision is marked at the planned entry point.
- The skin is prepared and anesthetized. The incision (as marked) is made.
- A nickel-sized burr hole is then made (with a perforating drill). The dura (leathery covering of the brain) is identified and opened.
- The biopsy apparatus is secured to the skull with small titanium bone screws. Ultimately the biopsy probe will be passed through this guide tube (fixed at a certain angle) until it reaches the biopsy target.
- Several calculations are made and the biopsy probe is readied, having been furnished with a “positive stop” at the calculated depth.
- The probe is then passed into the brain until the aforementioned “stop” is reached.
- Biopsy specimens are taken with a windowed probe using gentle suction.
- After obtaining the needed specimens, Dr. Osborn irrigates down the biopsy probe to assure that there has been no bleeding.
- The needle is withdrawn from the brain, and after the apparatus has been removed from the skull, the incision is closed in anatomical layers.
WHAT YOU WANT TO KNOW
“Why did my friend have a biopsy as opposed to a craniotomy? She wanted the mass taken out of her brain.”
One of several reasons. Either the lesion was deeply-seated (i.e., near the brainstem), too diffuse or located in “eloquent” cortex. The neurosurgeon may also have been considering diagnoses such as lymphoma (which is classically treated with radiation and/or chemotherapy, not surgical resection) or abscess (treated with biopsy/aspiration followed by antibiotics). Bottom line: If a mass is deemed too potentially risky to resect or resection will not alter the prognosis OR if the pathology may be amenable to medical therapy as opposed to open surgery, a biopsy is indicated.
“Someone told me that a stereotactic reference frame is drilled into your head prior to the procedure and removed thereafter. Is that true?”
Good question. Prior to advent of so-called “frameless” stereotactic systems, a reference frame was affixed to the skull in order to establish a three-dimensional coordinate system. The target coordinates were generated relative to this frame. Nowadays, due to the inherent accuracy of frameless systems (which establish a 3-D coordinate system using skin “surface matching” technology), it is unnecessary to apply a cumbersome stereotactic frame. They are used only for deep brain stimulation (DBS) and some forms of stereotactic radiosurgery (SRS).
“How long does it take for the biopsy results to come back?”
Typically, a specimen is sent for “frozen section” at time of surgery. This may prove diagnostic but permanent sections are still processed (with special stains) for final tissue diagnosis. Average turnaround time: 3-5 days. More complex cases may take 10-14 days.
“What are the risks of a stereotactic biopsy?”
Seems like a small procedure, right? It is. A biopsy probe is inserted into the brain under computer guidance through a nickle-sized burr hole. What could go wrong? The main risk of a biopsy, by virtue of the fact that it is performed through a nickel-sized hole, is bleeding within the brain, inaccessible bleeding. During open brain surgery, bleeding points are easily identified and addressed with cautery. This is not the case during a biopsy in which only the cortical (brain) surface is visible to the surgeon. That said, most hemorrhages are too small to have a clinical impact. Symptomatic hemorrhages (potentially requiring surgical intervention) occur in < 1% of those undergoing biopsies.
Other complications include infection and seizure (although this typically is a harbinger of an expanding hematoma within the brain). An “indeterminate” biopsy necessitating reoperation is a procedure risk as well.
“How long is the typical hospital stay for a stereotactic biopsy?”
Dr. Osborn maintains his patients in the ICU overnight post-procedure. A CT scan of the brain will be obtained on the morning after the biopsy to rule out bleeding. Barring any significant hemorrhage on the CT scan, patients are discharged home. Pathology and treatment options are discussed at time of the first postoperative office visit.