My mentor, Dr. Mark Souweidane, is a pediatric neurosurgeon specializing in minimally invasive techniques as well as convection enhanced drug delivery, also known as interstitial infusion.
On Tuesday, I got to see a brain biopsy on a human patient. The basic steps of the craniotomy were similar with how the rat surgeries in our lab are performed, i.e.
1. Creating an incision site
2. Removing the periosteum
3. Drilling a hole in the skull
4. Disrupting the dura.
The techniques involved, however, were much more refined in the clinical setting.
A special drill was used to create a 1.5 cm hole in the skull. The drill has an inner drill bit surrounded by an external cylinder. The drill bit is attached to a spring that determines whether the drill is switched on or not. Without any compression, the drill is in the OFF state. When the spring is compressed, the drill is in the ON state. Thus, when the drill bit is pressing against bone, the spring is compressed, and the drill starts penetrating the bone. Once the drill has penetrated the bone, there is no bone left to compress the spring attached to the drill bit, thus switching the drill off.
The biopsy itself was performed using a stereotactic system that first involved obtaining an MRI image of the patient's brain and then setting three external beacons fixed to the patient's skull to determine the x, y, and z coordinates. A biopsy probe, also with three external beacons, were then aligned with the MRI image's beacons. The biopsy probe has two cylinders, one over the other, with each having a small hole along the side that aligns with one another. After the probe is inserted into the brain and is in the region of interest based on the stereotactic system, a syringe is used to create a vacuum to suck brain tissue into the hole on the probe. This vacuum is maintained while the outer cylinder is rotated, cutting the brain tissue, and leaving a small biopsy sample int eh smaller cylinder.
A limitation of this technique is that the MRI image is not updated in real time, which means that any movement of the brain within the skull would not be reflected in the MRI image. The accuracy of this technique relies on the assumption that the brain does not shift within the skull after the MRI image is taken. That being said, any movement of the brain within the skull is likely to be minimal, which means that even if the x, y, and/or z coordinates are a little misaligned due to shifting, the biopsy location would still be close to the region of interest.
On Thursday afternoon, I joined Dr. Souweidane in his clinic as he met with some of his patients. While I had expected Dr. Souweidane to be an expert at diagnosing his patients' pathologies, which he was, I was pleasantly surprised by his adroit handing of his patients and their parents- from calming a frightened infant, to getting a parent to be forthcoming with their child's symptoms, and even calming and empathizing with an acrimonious parent whose son's surgery Dr. Souweidane refused to approve because the primary doctor did a terrible job of ordering the necessary tests to clear the boy for a surgical procedure.
On Friday, I shadowed Dr. Souweidane as he surgically corrected a sagittal craniosynostosis in a months-old infant. Even though the surgery was a minimally invasive procedure, It was a difficult procedure to watch.
The corrective procedure involved removing a strip of bone along the sagittal suture, as well as cutting the skull along the coronal and lambdoid sutures. All this was done using only two 1 1/2 inches long incisions- one anterior and one posterior- and with the aid of a endoscope.
Speaking briefly with the anesthesiologist, it appears that placing an infant under anesthesia requires more caution, because it is usually more difficult to wake the infant up after general anesthesia. Thus, potent but more transient anesthetics are used for infants and children with careful supervision to ensure the child does not awake prematurely.
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