You’re probably thinking, “I know someone who has a shunt.” Most people do or have at least heard the word “shunt” in passing.
What is a shunt? A shunt is a tube, akin to plumbing, that diverts cerebrospinal fluid (CSF) from the brain to an alternate compartment in the body (in most cases the abdominal or peritoneal cavity). A shunt is implanted to treat hydrocephalus or excess fluid in the brain (with resultant enlargement of the ventricles). This can occur in the context of high pressure (as is seen in the infant or young adult) or normal pressure (as is seen in the aged population). The etiology of the hydrocephalus is irrelevant however, as the procedure in both cases is identical.
- Dr. Osborn performs this procedure under general anesthesia utilizing a right frontal approach.
- The patient is positioned supine on the OR table.
- The head is shaved (partially) and an incision is marked in the right frontal region in the mid-pupillary line, 4 or so inches (10 cm) from the eyebrow.
- A second incision is then marked in the midline just inferior to the sternum.
- The skin is prepared and anesthetized. The incision (as marked) is made.
- A nickel-sized burr hole is then made in the right frontal region (with a perforating drill). The dura (leathery covering of the brain) is identified and cauterized.
- A second incision is then made in the subxyphoid region (below the sternum).
- Serial “shunt passers” are then utilized to create a subcutaneous tract for the shunt tubing. The shunt is passed through these hollow tubes (from top to bottom).
- The proximal catheter is then passed into the ventricles (utilizing standard landmarks and trajectory) and subsequently secured to the distal shunt hardware (unitized reservoir, valve* and distal catheter).
- CSF flow is then confirmed at the distal end of the catheter (at the subxyphoid site).
- The procedure is then turned over to a general surgeon who implants the shunt into the abdominal (peritoneal) cavity under direct laparoscopic vision. This allows for accurate placement of the catheter away from potentially obstructive abdominal fat. By virtue of the smaller caliber incisions, postoperative pain is lessened.
- The incisions are closed in anatomical layers.
- Surgical time is typically 45-60 minutes.
* To regulate spinal fluid flow, an interposed valve is positioned between the catheter that enters the brain and that which enters the abdominal cavity. The pressure in this valve (the “setting”) can be changed non-invasively (with an electromagnet) depending upon the needs of the patient. It is set to a standard pressure preoperatively.
WHAT YOU WANT TO KNOW
“What are the risks of a shunt operation?”
The major associated risks are hemorrhage (bleeding within the brain or on its surface), infection (necessitating hardware replacement after a thorough course of IV antibiotics) and malfunction. In children, malfunctions most often occur due to obstruction or blockage of the ventricular catheter (within the brain), while in adults the opposite is true: the catheter is obstructed in the abdomen. By far, the most often encountered complication is malfunction. The reported incidence varies but may be as high as 30% in 2 years.
Other complications may occur although these are related to the laparoscopic portion of the operation (bowel perforation, ileus, pneumothorax, for example) and general anesthesia. These are of extremely low incidence.
“I heard that Dr. Osborn utilizes a special technique to implant the catheter in the abdomen. Is that true?”
Dr. Osborn is assisted by a general surgeon who inserts the abdominal catheter laparoscopically. This is a well-described, time-tested technique. In a further attempt to reduce the incidence of malfunction, the general surgeon positions the catheter atop the liver, securing it in place with a small piece of synthetic mesh.
“How long does it take for a patient to see improvement in the wake of a shunt operation?”
Good question. And the answer is two-fold. In patients suffering from hydrocephalus with elevated intracranial pressure, the improvement is usually immediate (as the pressure is acutely lowered with shunting). In those with normal pressure hydrocephalus (NPH), the improvement occurs in a more delayed manner, typically over the course of weeks to months. During this period of time, patients will often require adjustments of their shunt valve pressure (to fine tune their response).
“My friend’s father had a shunt operation and thereafter developed bleeding on the brain. What happened?”
Likely he developed what is known as a “subdural hematoma.” Here’s what happens. As fluid is shunted from the cavities of the brain (ventricles) into the abdomen, the brain “deflates” and the cortex migrates inward, away from the inner aspect of the skull. This natural response to aggressive fluid drainage (from the center of the brain) puts veins coursing from the cortical surface to the leathery covering of the brain or “dura” on stretch. Sometimes in fact, the veins tear resulting in a subdural hemorrhage or hematoma.
Such bleeding may warrant emergent surgery. Often however, it can be managed non-operatively. How? By slowing down or in fact stopping drainage through the shunt system. In years past, this was accomplished by surgically tying off (ligating) the shunt. Nowadays, one simply reprograms the shunt and allows for brain expansion (barring any acute neurologic issues necessitating surgery). Of course during this recovery period, a patient’s gait problems (the primary indication for shunting) may return. A balance between these two entities (over and under-drainage) is the goal therefore, one obtained only through close interaction between surgeon and patient.
“How will I know if my shunt needs reprogramming? How is the shunt setting changed?”
Dr. Osborn will determine your need for a higher or lower valve pressure based upon your walking, in the context of other stigmata of under or over-drainage. For example, if walking has improved dramatically (in response to shunting) but you suffer from significant headache, Dr. Osborn will likely increase the valve opening pressure (increasing the internal resistance of the valve), thereby reducing flow through the system. This will be similarly performed in the event of development of a subdural hematoma.
Should you fail to improve postoperatively, Dr. Osborn will (serially) lower the shunt valve opening pressure, increasing flow through the system, in order to generate a response.
Keep in mind that everyone is different. CSF dynamics (and the need for drainage) vary from person to person. You may not respond to the same valve opening pressure as your friend or relative.
The shunt valve is reprogrammed during a routine office visit. An electromagnetic device is placed over the shunt valve (palpable bump in the right frontal region) and the attached programmer (set to the specific pressure) is cycled. The setting is acoustically confirmed (an intrinsic function of the programmer).