Chapter 119. Ventricular Shunt Evaluation and Aspiration

Pediatric and adult patients with ventricular shunts frequently seek medical attention in acute care settings with complaints that may or may not be caused by a malfunction and/or infection of these indwelling devices. The challenge for the Emergency Physician is to determine if the shunt system is functioning properly and if it is a direct cause of the patient's acute problem. This chapter will discuss the complications of ventricular shunt malfunction including infection.

Complications in children with ventricular shunts are common whereas those in adults occur less frequently. Approximately 30% to 40% of infants will experience shunt complications during their first year following shunt placement.1,2 Children who had shunts placed as infants will require two shunt revisions secondary to obstruction within their first 10 years.1 The overall shunt infection rate is 10% to 20%.1,3,4 Approximately 90% of these infections will present within 3 months of the shunt placement.1 These statistics apply to the population with conventionally treated hydrocephalus using indwelling ventricular shunt devices. It is significant to note that with the wide application and development of neuroendoscopic techniques, many of the complications discussed in this chapter may be significantly reduced or possibly eliminated.

Complications resulting from ventricular shunts take many forms.5 These include proximal obstruction (most common), distal obstruction, disconnection, wound and cerebrospinal fluid (CSF) infections, seizures, epidural hygromas, subdural hematomas, low (overdrainage) and high pressure (slit ventricle) syndromes, and cranial deformities. There are other unique complications experienced by the smaller number of patients who have ventriculoatrial (V-A) and ventriculopleural shunt systems and these will be discussed separately. Unless stated otherwise, the reader should assume that reference is being made to the more common ventriculoperitoneal (V-P) shunt device.

Patients with shunts may present with clinical entities as benign as a viral upper respiratory infection or with a life threat like hydrocephalus. The wide range of possibilities is a challenge to the Emergency Physician's diligence and clinical acumen. Common presenting symptoms include headache, fever, vomiting, decreased alertness, neck stiffness, visual changes, malaise, abdominal pain, abdominal distension, and surgical site problems.

Hydrocephalus, a condition defined by an excessive quantity of CSF, is the condition most frequently associated with the initial need for a ventricular shunt or a shunt revision if it malfunctions. Most abnormal accumulations of CSF are identified in the ventricles, although it may also occur in the subarachnoid or subdural spaces.

Several types of hydrocephalus are cited in the literature. Communicating hydrocephalus occurs when there is unobstructed flow of CSF between the ventricular system of the brain and the spinal cord. It frequently occurs in patients who have had a hemorrhage or infectious process whereby particulate matter interferes with the normal circulation and absorption of CSF. A congenital problem such as aqueductal stenosis or a mass lesion in the posterior fossa may obstruct the flow of CSF between the brain and spinal cord causing obstructive hydrocephalus or noncommunicating hydrocephalus. Normal pressure hydrocephalus is usually a diagnosis made in older people who present with the clinical triad of dementia, ataxic gait, and urinary incontinence. The CSF is found to flow within a normal pressure range, but the patient accumulates excess CSF due to decreased absorption. Hydrocephalus ex vacuo is the result of excessive CSF and ventricular enlargement due to brain atrophy. It presents a challenge to the acute care practitioner who may need to decide if a patient with large ventricles on head CT has a pathologic condition or has so much brain atrophy that the fluid-filled spaces appear excessively large.6

The clinical presentation of hydrocephalus will vary depending upon its acuity and the age of the patient. The individual who experiences shunt failure may present in the same way as one who is presenting with hydrocephalus initially. Infants may have an enlarged head circumference, a bulging anterior fontanel, separation of the cranial sutures, bilateral or unilateral palsy of the abducens nerve (medial eye deviation), or Parinaud's syndrome.7 Parinaud's syndrome is a paralysis of upward gaze (also known as “sunset eyes” or the setting sun sign), unequal pupils, and the loss of convergence.7

Within hours of an acute cause of hydrocephalus, the patient (past infancy) will commonly experience a headache with nausea and vomiting secondary to the quick increase in intracranial pressure (ICP). The patient may less commonly have a focal neurological deficit due to the pressure exerted by the brainstem from a dilated third ventricle. There may also be visual changes that include Parinaud's syndrome. A change in mental status may occur as the increase in ICP persists. Finally, the signs of herniation signify a terminal event. It will be observed with, for example, decorticate or decerebrate posturing, a third cranial nerve palsy, and the Cushing reflex (elevated blood pressure accompanied by bradycardia). The process of herniation is nearly completely reversible with immediate ventricular drainage through emergent revision of a malfunctioning shunt or the de novo placement of a ventricular drain.

Chronic hydrocephalus can present with a variety of signs and symptoms. The patient may complain of an isolated bifrontal headache, a generalized headache, vomiting, a change in behavior, a change in mentation, or a change in cognition. Ocular findings include papilledema, unilateral or bilateral abducens nerve palsy, Parinaud's syndrome, or even a bitemporal hemianopsia. The extremities may be involved with spasticity in the legs that is more pronounced than that found in the arms.

Once the diagnosis of hydrocephalus is made, the Neurosurgeon will be responsible for treating the primary causes (e.g., tumor, bleed, congenital abnormality) along with placement of an indwelling ventricular shunt. The components of a standard shunt system include a ventricular catheter, a one-way valve, and distal tubing that enters the cavity into which the fluid is being shunted (Figure 119-1). It is standard practice to enter the right lateral ventricle and tunnel the valve system and distal tubing subcutaneously along the right temporoparietal region of the skull, the lateral neck, the anterolateral chest wall, and finally into the peritoneal space just superior or lateral (right side) to the umbilicus (Figure 119-2). The shunt system may occasionally be found on the left side in some patients.

Much of the shunt pathway is palpable on physical examination (Figure 119-2). The entire system may be visualized on plain radiographs. The system is impregnated with radiopaque material either entirely or with intermittent markings.

The ventricular catheter is inserted through a burr hole and into the lateral ventricle. The distal end of the ventricular catheter is connected to one of many different types of valves currently available. Functionally, there are two main types. The differential pressure valve allows the Neurosurgeon to select a low, medium, or high pressure system whereby the CSF will flow out of the ventricle through a one-way system when the CSF pressure or CSF flow rate builds to a specified level. A variable resistance constant flow valve keeps CSF rates constant and, therefore, provides a more physiologic system by varying the resistance in the valve as the individual changes position. Some of these valves, although palpable on physical examination, do not allow access to the CSF for aspiration nor do they allow for any noninvasive assessment of CSF flow. A bubble-like reservoir (may be single or two bubbles in tandem) for the draining of CSF is a common addition to the standard three-part shunt system. While they can be inserted anywhere in the system, they are most frequently located adjacent to the valve mechanism on the lateral aspect of the skull (Figure 119-2).

The distal tubing is made of a flexible and soft synthetic rubber material that is attached to the reservoir or valve system and tunneled subcutaneously through the lateral neck, chest, and abdominal wall. A small incision is made in the skin and the peritoneum where the tubing is brought from the subcutaneous tissue into the peritoneal cavity. After securing the tubing to the peritoneum, a generous portion of tubing is left free floating inside the peritoneal cavity. This allows for the distal end to lengthen as the patient grows and lends further stability to its place within the abdominal cavity.

The distal tubing in ventriculoatrial and ventriculopleural shunt systems will terminate in the right atria and right pleural cavity, respectively. However, these configurations are not used frequently. One may also come across a patient with a lumboperitoneal shunt that avoids any invasive procedures to the brain directly. This system is inserted into the lumbar subarachnoid space with the valve/reservoir system located above the iliac crest and the distal tubing tunneled subcutaneously in the abdominal wall and into the abdominal cavity.

The patient is subject to a host of complications due to mechanical malfunctioning that can occur anywhere along the path of the system. There is the risk of infection, as is the case with any indwelling medical device. The remainder of this chapter will guide the Emergency Physician through the process of identifying the various types of shunt problems.

The Emergency Physician is obliged to assess the patency, placement, and integrity of the shunt system when a patient presents with any symptoms even remotely related to hydrocephalus. The presence of systemic signs (e.g., fever, tachycardia, or hypotension) or local signs of infection (e.g., warmth, tenderness, bogginess, or redness along the shunt tract) is a reason to consider aspirating CSF from the system. This is not to say that every child with an upper respiratory infection requires that the shunt be tapped. It is not uncommon to have overlapping findings in that an infection may obstruct the system and therefore require both mechanical and infectious complications to be addressed. The withdrawal of CSF from the shunt can be lifesaving and sustain the patient who is herniating, in extremis, or deteriorating neurologically until a Neurosurgeon can repair the shunt.

There are no contraindications to performing a thorough physical examination of the shunt system, obtaining a head CT, and obtaining plain radiographs to assess its integrity. There is some controversy, however, that surrounds the tapping of a shunt by personnel other than a Neurosurgeon.8–10 It is possible to disrupt the pressure and valve mechanism by the manipulation of the needle that is required to perform the tap. The reservoir may develop a leak if the correct technique is not employed or if the shunt is tapped too frequently. There is the risk that bacteria will be introduced into the system. Many patients have had multiple complications related to both a primary disease and the shunt, with some already having undergone a number of shunt revisions. It is prudent to assume a conservative approach with each of these patients and consult a Neurosurgeon prior to tapping the shunt.

The technique of shunt evaluation begins with taking a complete history and performing a thorough physical examination. Palpate the entire system starting with the cranium. Examine the surrounding scalp carefully for any bogginess (indicating that CSF may have extravasated from the system), redness, tenderness, or warmth. The suture line should be examined as well if the shunt has been placed recently. Examine the scalp on the right side for a burr hole. This is where you may palpate a shunt reservoir that is placed subcutaneously. The reservoir feels like a firm fluid-filled bubble. Compress the bubble gently to assess if there is brisk refilling of the CSF. Quick filling of the reservoir is an indication that the proximal portion of the system may be patent, but this is by no means a perfect test. Resistance to compression indicates a distal malfunction. Avoid pumping the reservoir repeatedly.

A double bubble (reservoir system) may be occasionally palpated. Compress the proximal reservoir to empty it and fill the distal reservoir. While still compressing the proximal reservoir, compress the distal reservoir. Any resistance to compression indicates a distal malfunction. With both reservoirs compressed, release the proximal reservoir. It should refill very quickly. Any delay in filling of the proximal reservoir indicates a proximal malfunction.

Move down and palpate the temporal region of the scalp and the neck. Note any gaps in the system that could indicate a disconnection. The individual components of the shunt system are commonly joined by small connectors that may come apart. Continue to palpate the tubing along the neck and chest until you reach the abdomen. Perform a thorough abdominal examination, specifically noting the presence of any tenderness, masses, distension, or erythema of the abdominal wall.

The distal end of the shunt may not function for several reasons. The tip may have withdrawn out of the peritoneal cavity and into the preperitoneal fat or subcutaneous tissue of the abdominal wall where the CSF cannot be resorbed. This may have occurred simply because the patient had grown and used up the extra length of catheter that was originally left in the peritoneal cavity just for this reason. Intraperitoneal infections, particularly those caused by anaerobic organisms, may cause loculations around the catheter tip forming a pseudocyst. It is important to note that these patients may not have any signs of a systemic infection. Additional causes of distal catheter obstruction include kinking of the intraabdominal tubing, debris collection around the tube openings, and compression secondary to pregnancy or other processes that increase the intraabdominal pressure.

After completing the history and physical examination, including an assessment of the shunt system, the differential diagnoses will help initiate an appropriate work-up. One or more of the following studies may be indicated: plain radiograph shunt series, computerized tomography (CT) of the head, shunt aspiration of CSF, or a radioisotope shunt scan. Stabilize the patient and arrange for an emergent head CT if any life-threatening signs of neurologic dysfunction appear.

There are several important points to note. Findings consistent with hydrocephalus include enlargement or effacement of the ventricles, particularly looking for fullness of the temporal horns of the lateral ventricles (Figure 119-3). It can be difficult to determine if there is a change in the ventricular system because congenital or chronic abnormalities can give the CT scan an abnormal appearance. The best way to approach this situation is to compare the current scan to a previous one, preferably by comparing the two scans side by side. Brain atrophy causes the ventricles to appear abnormally full when, in fact, they appear large because of the relative loss of brain tissue.

Impending herniation may be a concern if the brain appears to be under increased pressure with a loss of the sulcal markings, loss of the differentiation between the gray and white matter, or an inability to visualize the fourth ventricle. The ventricles can appear unusually small which may be an indication of a shunt system that is draining CSF too vigorously. Overdrainage may be the problem if the patient complains of a positional headache that is worse in the upright position and less severe when supine. If this is the case, it is important to carefully examine the CT scan for any subdural hematomas that can result from the brain shrinking away from the dura and tearing a bridging vein secondary to overdrainage of CSF.

The patient's scan may reveal small ventricles accompanied by signs of increased ICP in the slit ventricle syndrome.11,12 While the slit ventricle syndrome is poorly understood, it is theorized that ventricles with poor compliance (common in those with chronic hydrocephalus) will respond to small increases in CSF pressure with large increases in ICP. The management of the slit ventricle system can be medical, replacement of the valve with one of a higher resistance to flow, or the placement of a new shunt.12,13

Obtain a plain radiograph shunt series if there is the slightest suspicion of a shunt malfunction or infection. This study consists of anteroposterior and lateral plain radiographs of the skull, neck, chest, and abdomen. These films are useful for assessing placement and integrity of the connections within the shunt system.14 Shunt materials are impregnated with a radiopaque substance either completely or in regularly placed markings so that the entire device can be visualized on plain radiographs. It is important to obtain and review the lateral abdominal film as this view is frequently overlooked. It is impossible to determine if the shunt tubing lies within the peritoneal cavity or not if the lateral abdominal film is excluded. The entire path of the shunt system should be visualized. Particular findings to note on this study include placement of the ventricular catheter inside of the ventricle, the integrity of the connections around the valve and/or reservoir, and the identification of the distal catheter within the peritoneal cavity. Examine the chest radiographs closely for a pleural effusion or a pneumothorax in a patient with a ventriculopleural shunt.15

Tapping the ventricular shunt should be considered whenever there are signs of localized infection, systemic infection, or in some cases of suspected obstruction without an identifiable cause. It should also be performed if the patient is in extremis, deteriorating neurologically, or has signs of herniation on the CT scan. This can temporarily restore cerebral perfusion and sustain the patient until a Neurosurgeon can repair the shunt. It is recommended that a Neurosurgeon be consulted and given the first option to perform the procedure. The Neurosurgeon may have already manipulated the hardware multiple times and will ultimately be responsible for any shunt revisions and follow-up. Patients with ventriculoatrial shunts are a particular concern when there are any signs of an infection. The distal catheter sits at the intersection of the right atrium and the superior vena cava. This puts the patient at risk for life threats such as endocarditis and septic emboli. It may be possible to evaluate the majority of shunt malfunctions without tapping the device.8

Tapping a ventricular shunt is a quick and simple procedure. Palpate the lateral aspect of the skull (usually the right side of the patient) for the reservoir. Plain radiographs may be helpful if it is difficult to identify upon palpation. Prepare for the procedure by having the following equipment available: four sterile fluid specimen tubes with tight fitting tops (those supplied in the standard lumbar puncture kit are ideal), a 23 to 25 gauge butterfly needle, a 5 to 10 mL syringe, a shave-prep set, an antibacterial cleansing preparation (povidone iodine or chlorhexidine solution), a fenestrated drape, and personal protective equipment.

Local anesthetic is not required for this procedure. Place the patient in whatever position is mutually comfortable. Shave a small patch of hair overlying the reservoir. Clean the skin of any dirt and debris. Apply povidone iodine or chlorhexidine solution and allow it to dry. This procedure requires strict aseptic technique. The Emergency Physician should don full sterile and personal protective equipment at this point. This should include sterile gloves, a sterile gown, a face mask with an eye shield or goggles, and a cap. Place the drape over the patient's head so that the fenestration overlies the reservoir and prepped skin. Set up a bedside table with a sterile drape and all the supplies. A lumbar puncture tray supplemented with a butterfly needle is all that is required.

Insert the needle at approximately 45° from the vertex of the reservoir bubble with the tip pointed toward the center of the reservoir (Figure 119-4). This is where the greatest amount of CSF is located. Avoid inserting the needle into any of the connections or internal pressure mechanisms that may be at either end of the reservoir. Allow the CSF to passively drain from the butterfly tubing into sterile tubes. It may be necessary to very gently aspirate 4 to 5 mL of CSF with a sterile syringe. The ventricular end of the shunt is usually obstructed if CSF cannot be aspirated.10 Withdraw the needle from the shunt reservoir.

Label the tubes of CSF and have them transported to the laboratory for a cell count and differential, Gram's stain, culture (bacterial, viral and fungal), and chemistry (protein and glucose). Obtain a sample of the patient's serum glucose at the same time so as to more accurately determine what level of glucose in the CSF to call abnormal. A normal level of CSF glucose should not be any lower than 50% to 66% of the serum level.

It is possible to attach the end of the butterfly tubing to a manometer so that an opening pressure can be measured. This must be done, however, with the patient in the lateral decubitus position, reservoir side up, and the head level with the heart.

Obtain a nuclear medicine scan (“shunt-o-gram”) if CSF cannot be aspirated to determine proximal patency of the system. A radioactive isotope (e.g., technetium) is injected into the reservoir after manually occluding the distal shunt tubing. The flow, or lack thereof, of the radioactive isotope is then imaged.4 The addition of a nuclear medicine scan to the CT scan can increase the sensitivity of diagnosing a shunt malfunction.16

A lumbar puncture should never be performed in lieu of tapping the shunt. Obstruction of the shunt system can result in obstructive hydrocephalus. Lumbar puncture in a patient with obstructive hydrocephalus can cause a significant pressure differential and precipitate brain herniation.

The CSF obtained from the shunt is interpreted in the same way as CSF from a lumbar puncture. A high white cell count with a large number of polymorphonuclear leukocytes, low glucose, and a high protein level indicates a high likelihood of bacterial infection. However, the positive Gram stain and culture make the definitive diagnosis. Unfortunately, there is no standard for the number of white cells that definitively indicates an infection. Some patients with indwelling shunts may have a chronically elevated CSF white blood cell count, albeit with more lymphocytes or eosinophils than polymorphonuclear leukocytes.3 Refer to Chapter 115 for a more detailed discussion regarding the evaluation of CSF. Antibiotic coverage should be initiated if a shunt is being tapped. Staphylococcus epidermidis causes the vast majority of infections with Staphylococcus aureus and gram-negative bacilli following in frequency.17,18 The current management of shunt-related infections has been reviewed by Stenehjem and Armstring.19 Empiric therapy includes vancomycin with either cefotaxime or ceftriaxone for children and vancomycin with rifampin for adults.20 Consider additional coverage for methicillin-resistant Staphylococcus aureus if indicated.

The ShuntCheckT (NeuroDx Development, Bensalem, PA) is a new device that allows the noninvasive detection of CSF flow through a shunt.21 The procedure requires placing an ice cube over the shunt. A single patient use and disposable sensor is placed on the skin of the neck overlying the shunt tubing. The sensor is attached to the ShuntCheckT device with a cable. The ShuntCheckT analyzes the temperature readings from the sensor and determines if CSF flow is present or not.

There are a few complications associated with the aspiration of a ventricular shunt. The introduction of bacteria into the reservoir can result in meningitis, peritonitis, brain abscesses, shunt occlusion, or infection anywhere along the course of the shunt tubing. It is of the utmost importance to maintain strict aseptic technique. The needle can damage the reservoir and result in a permanent hole necessitating its removal and replacement. A misplaced needle can damage the connections or valves of the shunt system.

Patients with indwelling ventricular shunt devices are subject to many complications throughout their lives. This most commonly includes obstruction, infection, and malfunction secondary to loss of placement or connection. Emergency Physicians will see patients of all ages with shunts and who present with headache, fever, nausea, vomiting, seizures, irritability, or a change in mental status. The challenge, frequently a formidable one, will be to determine whether or not the patient's complaint is related to the shunt. This chapter discussed some of the common shunt complications and an approach to their diagnosis. The head CT, the plain film shunt series, and the shunt tap will prove most useful. Of course, a careful history and a skilled physical examination will set the Emergency Physician on a path toward a good outcome for the patient. A Neurosurgeon should be consulted if available. A conservative approach to diagnosis, management, and patient disposition is strongly recommended due to the life-threatening nature of shunt complications.