John - Week 3 - Myelomeningocele and Obstructive Hydrocephalus

On Friday, Dr. Souweidane operated on a 1-day-old neonate with myelomeningocele, which is the most common form of spina bifida. This is a neural tube defect in which the bones of the spinal column do not completely fuse around the spinal cord, resulting in an incomplete spinal canal from which the spinal cord and meninges protrude. The surgical intervention involved first removing any skin closely surrounding the exposed spinal cord, so as to prevent any dermoid cysts from forming after the spinal cord has been encased. The dura to the left and right of the exposed spinal cord was then cut and separated from the fascia, folded together over the spinal cord, and sutured with absorbable/biodegradable thread. The surrounding skin was similarly then separated from the remaining dura, pulled together, and sutured. 

Myelomeningocele is often accompanied by obstructive hydrocephalus, which was the case with this neonate. A ventriculoperitoneal (VP) shunt was chosen over an endoscopic third ventriculostomy (ETV) based on the patient's age. VP shunting involves creating a passage between the ventricles and the peritoneal cavity using tubes and a valve, while ETV involves creating a small hole at the bottom of the third ventricle. Both procedures aim to relieve pressure caused by the build up of CSF due to blockage of the aqueduct of Sylvius. ETV is usually performed if the patient is at least 6 months old, because the risk of blockage after ETV is significantly higher for patients younger than 6 months of age.

Unlike in older patients, the sutures of the neonatal skull have not fused, thus eliminating the need to drill a hole through the skull for the shunt to access the ventricles. Instead, the lambdoid suture can be gently separated for the tubing to access the ventricles. Because the neonate was so small, diagnostic ultrasound was used to visualize the ventricles to direct the placement of the shunt. Sufficient tubing was left in the peritoneal cavity of the neonate to allow for increases in his height during development. 

The benefit of an internalized shunt over an externalized one is that the excess cerebrospinal fluid directed from the ventricles to the peritoneal cavity is reabsorbed, preventing the loss of fluid, ions, and other components of the CSF in the patient. Potential problems with VP shunting include infection, dislodgment, and blockage, but become very rare six months after shunt implantation.

On a side note, unlike in last week's surgery, the analgesic administered on this day was given in intervals as opposed to a constant infusion rate. The interval was determined by the anesthesiologist based on factors including heart rate, and the time since the previous dose.