Brain Surgery Information:

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CHAPTER 13: DRAINS, SHUNTS, RESERVOIRS, AND NEEDLE BIOPSY WITH OR WITHOUT A HEAD FRAME

There are several procedures carried out by neurosurgeons referred to as “minor” procedures. Of course, for a patient undergoing such a procedure, this may not at all be minor. Further, although these procedures are generally regarded as being of low risk, they are not of zero risk. The following procedures are carried out relatively frequently among neurosurgical patients as a group.

Drains

·  External ventricular drain (EVD): An EVD allows CSF to be diverted temporarily from the ventricles to the outside world. Reasons for its placement include: (1) Hydrocephalus from any cause; (2) brain hemorrhage such as from an aneurysm or other lesion, particularly if the hemorrhage extends into the ventricles; (3) coma, particularly if associated with high ICP, in which case an EVD can be used to continually measure the ICP as well as to remove CSF periodically to lessen ICP; and (4) shunt infection, where the infected shunt is removed but CSF diversion is still required. An EVD consists of a ventricular catheter, which is a thin and flexible piece of tubing that will enter into the CSF-containing ventricle, in addition to tubing that will connect the ventricular end to a measuring column and collection bag kept at the patient’s bedside (Figure 23). Placement of an EVD usually occurs in the ER or ICU. It is typically done using a local anesthetic to numb the skin, and after the area of the forehead scalp has been shaved and then “prepped” with antiseptic solution. Many patients undergoing EVD placement are semiconscious or unconscious owing to their underlying brain injury or disease process. Those who are conscious are usually administered some form of IV sedation to assist. A scalpel is used to make two small stab incisions in the numbed frontal scalp and a hand-held twist drill is used to make a small opening in the frontal bone through which the ventricular catheter is carefully threaded. Once CSF flow is detected through the catheter, it is sutured to the skin surface and its components hooked up. The whole procedure takes about 30 minutes from start to finish. EVD placement is generally regarded as a low risk procedure, however, there is a 1-2% chance of brain hemorrhage during placement and a 1-2% chance of infection. Here, infection may be a superficial wound infection or deeper infections such as ventriculitis or meningoencephalitis. To prevent this, IV antibiotic may be administered around the time of EVD placement, or the EVD tubing may itself be pre-impregnated with antibiotic. Periodically, CSF is sent off from EVDs to the laboratory for analysis. With time, the EVD is either “weaned” and removed, or converted to a lumbar drain or a shunt (see below).

·  Lumbar drain: A lumbar drain is like a spinal tap or LP (Chapter 6), except that a thin and flexible piece of plastic tubing is intentionally left behind through the skin insertion point. The end of this tubing lies in the lumbar cistern. The tubing then runs on the surface of the back and is hooked up to a collection bag which is typically kept by the patient’s bedside affixed to a mobile stand. A lumbar drain allows for CSF diversion, especially in cases where an EVD has been removed, and the patient may still be dependent on CSF removal for an anticipated few or several more days. Such drains can be placed in the setting of: (1) Brain aneurysm rupture in order to continue removing blood from the ventricles and cisterns; (2) treatment of a postoperative or posttraumatic CSF leak from an incision or from the nose or ear, to allow pressure on the leak site to be reduced in order for it to heal; and (3) preoperative preparation, particularly for operations involving lesions located near the brainstem and cerebellum, where CSF removal from the drain will give good brain relaxation intraoperatively, and reduce the risk of CSF leak postoperatively. These drains are generally weaned and removed over three to four days after their placement. Lumbar drain insertion, like EVD placement, is a low risk procedure. There is a 1-2% chance of spinal hemorrhage or infection. The risk of hemorrhage is increased if the patient was recently on a blood thinner such as Plavix, or Coumadin/Warfarin. Once the drain is removed, there is a chance of a “low pressure headache” from ongoing CSF leak from the small pinhole in the spinal dura made during drain insertion. This can also occur following a regular LP, and can last several days. If it occurs, it is treated with bed rest for a few days, high oral fluid intake, and over-the-counter pain medications. If it persists for several days, an epidural blood patch may be recommended. This involves a second LP, this time injecting a certain volume of the patient’s own blood through the needle to form a local clot that seals off the pinhole. Another complication of LP and lumbar drain placement is numbness and tingling in the legs. If it occurs, it should settle within hours to a few days. It is highly unlikely that there will be any permanent leg weakness or sensory problem from lumbar drain placement or LP.

Figure 23 (above). EVD placement.

Shunts

A shunt is a piece of soft tubing that runs entirely under the skin surface from the ventricle or from the lumbar cistern to some other part of the body, most commonly the abdomen, but sometimes the lung or the neck. Shunts allow CSF to be continually diverted in patients who cannot absorb enough CSF for whatever reason. Shunts may be placed in patients who: (1) Are born with hydrocephalus; (2) develop hydrocephalus later in life following, say, brain aneurysm rupture, growth of an obstructive brain tumor, or some form of inflammation of the brain tissues such as in meningitis or ventriculitis; (3) cannot be successfully weaned from an EVD and/or lumbar drain; (4) have certain diseases such as NPH or BIHT. Shunt placement is carried out in the OR with the patient asleep. For the most common of shunt configurations referred to as the ventriculoperitoneal (VP) shunt, the shunt tubing runs from the ventricle to the abdomen’s peritoneal space or peritoneum. The tubing runs in a fatty tunnel between the two locations. There will be a small, curved skin incision somewhere in the scalp overlying a small burr hole drilled in the adjacent skull bone, a second tiny straight incision somewhere behind the ear, and a slightly longer third straight incision somewhere in the abdomen. The tubing is tunneled by the surgeon between these three incisions (Figure 24). There is typically a bump felt near the scalp incision, which arises from placement of a shunt valve that regulates the flow of CSF. This should be expected to be felt in this location. The tubing can also be felt, but is otherwise invisible to the naked eye. The tubing and the valve are left in permanently unless a need for their removal arises, say, if the system becomes infected or blocked. Other shunt configurations include: (1) The ventriculoatrial (VA) shunt which runs from the brain’s ventricle to the heart’s right atrium through a small incision made in the neck to allow access to the internal jugular vein; (2) the ventriculopleural shunt which runs from the brain’s ventricle to the lung’s surrounding pleural cavity; and (3) the lumboperitoneal shunt which runs from the lumbar cistern to the abdomen’s peritoneum. The concepts and tubing for these various shunt configurations are very similar. Shunt placement is generally regarded as a low-risk procedure. However, risks of shunt placement include a 10% chance of early or delayed infection requiring shunt hardware removal and replacement, a 10% chance of failure due to tubing disruption or blockage, and a 1-2% chance of hemorrhage in the brain or injury to the bowel during placement of a VP shunt. VA shunts have the added small risk of a significant heart rhythm disturbance, or arrhythmia, particularly at the time of VA shunt placement or very soon thereafter. Symptoms and signs of shunt infection usually manifest within the first few weeks of shunt placement, but may occur later. Symptoms can include unexplained fevers, redness along the shunt tubing site, headaches, nausea, vomiting, blurred vision, neck stiffness, increasing sleepiness, and sometimes increasing abdominal pain and tenderness.

Figure 24 (above). VP shunt placement.

Reservoirs

Reservoirs are small spaces enclosed by some form of plastic and buried under the skin surface. One end of a reservoir must end in a ventricle. The other end may be a dead end, as in the case of an Ommaya reservoir, or part of a shunt system’s tubing. Reservoirs are typically placed in the OR with the patient asleep, but sometimes just sleepy, so that CSF can collect in them in order to allow future access to the inside of a shunt system, or to the ventricular system itself. CSF can be removed from reservoirs to: (1) Allow for its analysis in the setting of suspected shunt infection; or (2) immediately reduce abnormally elevated brain pressure. Removal of CSF from a reservoir is referred to as a reservoir tap and is usually done under local anesthetic using a very fine needle at the patient’s bedside. In the case of an Ommaya reservoir, certain drugs such as chemotherapy and antibiotic agents can be injected through the reservoir directly into the ventricle in patients with certain brain tumors or infections. Placement of reservoirs is a very low-risk procedure, the main risks being a 1-2% chance of significant infection or hemorrhage during placement.

Stereotactic brain biopsy using a needle or thin probe, with or without a head frame

A stereotactic brain biopsy is carried out if a small sample of brain and meningeal tissue is required in order to make a diagnosis of a specific brain disorder. Stereotactic implies needing specific image- and/or 3D coordinate guidance through the brain. Such biopsies are typically conducted because of the negative or “nondiagnostic” results of all other investigations (Chapter 6), and because the abnormality may be a small area deep within the brain. Unfortunately, not all stereotactic brain biopsies yield diagnostic results, but neurosurgeons will carry them out especially if they can define an appropriate “target” on the preoperative brain MRI. Usually, but not always, such a “preferred” target lights up abnormally on the MRI following administration of the IV contrast. If this target is successfully “hit” by the fine biopsy needle or probe, it is likely that some useful diagnostic tissue will be obtained. Many stereotactic brain biopsies involve the following, in this order:

·  Placement of a stereotactic head frame: A head frame (Chapter 14; Figure 25) is an MRI-compatible metal structure that is affixed to the head with a minimum of four pins after the scalp has been prepared with antiseptic and numbed with local anesthetic. Head frame placement is usually done with the patient sleepy. As the pins are turned in and pushed deeper, there may be a pressure sensation which is uncomfortable. If there is a sharp painful sensation, the physician will administer more local anesthetic to the pin site. The scalp rapidly gets used to the pressure sensation, and the vast majority of patients tolerate head frame placement very well. The head frame allows for a very accurate 3D map of the patient’s head and brain to be generated once the MRI is carried out. The head frame’s accuracy and coordinate system generally rely on a suitable OR table device called a “receiving yolk” to which the head frame is subsequently attached, and an advanced computer and software system to carry out the calculations for the appropriate probe-target trajectory and depth. Note: If the mass is very small and very deep, a frame-guided biopsy is probably more accurate.

·  Frameless stereotactic biopsy: Because of advances in neuronavigation ("GPS for the brain") technology, certain stereotactic biopsies can also be carried out safely and effectively without the need to place a head frame. The image below shows an intraoperative neuronavigation image acquired during a frameless stereotactic biopsy of a deeply located brain mass. The diagnosis from this particular biopsy was a specific type of brain cancer. The trajectory of the biopsy probe is shown in yellow. The skin entry point is at the green cross-hair, the biopsy target is at the red cross-hair. The images during the procedure update in real-time so the surgeon can constantly assess where the thin biopsy probe is passing as it is advanced through brain tissue. This enhances the safety and accuracy of the procedure.

·  Intubation of the patient: The anesthesiologist will intubate the patient after the head frame (if there is a head frame) is placed, and the patient is then taken to the MRI scanner asleep.

·  MRI head scanning with the head frame on: The MRI scan will generate the images required to visualize the probe’s trajectory prior to the procedure. Sometimes a CT scan is used instead. For frameless biopsy patients, the "frameless stereotactic protocol" MRI scan of the brain is carried out prior to the surgery.

·  Return to the OR asleep for needle biopsy: The patient returns to the OR and, with the head frame on (if the biopsy is a with-frame biopsy), is moved to the OR table. The head frame is attached to the receiving yolk. Several persons confirm the accuracy of the numbers and trajectory used for this procedure. The neurosurgeon makes a small incision in the scalp and carefully advances the biopsy needle along the chosen trajectory to the chosen depth. Usually a minimum of three small “core samples” are taken and sent to the OR pathologist for intraoperative confirmation that the tissue samples are indeed abnormal. The actual operating time for this procedure is usually only 30 minutes, however the procedure may take the good part of a day because of all of the steps involved, as indicated above.

·  Overnight ICU stay: The patient is returned to the ICU, and observed overnight, particularly for signs of significant brain bleeding or swelling. The risks of these are small, in the order of 1-2%. The biopsy needle’s small entry site in the scalp is usually closed with a self-dissolving suture, but this varies from surgeon to surgeon. The site may be covered by “skin glue” or a thin Steristrip or two. If present, Steristrips should be removed within one week of the procedure. Glue will dissolve with showering. Specifics of wound care should be discussed with the surgical team.

·  Await pathology and/or microbiology: Samples that were taken during the biopsy are processed by the various laboratories, and a result is usually available within a few working days of the procedure.

·  Dismissal with followup per a neurologist or neurosurgeon: The patient is dismissed from the ICU either to his or her home or to a general ward, depending mostly on the patient’s clinical state prior to the procedure. Followup will be arranged such that the patient meets with a physician after hospital dismissal to discuss the results of the biopsy and plan for appropriate treatment.