21 Ventricular Shunt Malfunction

Introduction

A ventricular shunt (VS) malfunction is a common neurosurgical emergency. In fact, a shunt revision is one of the most common procedures a neurosurgeon may perform. It is estimated that up to 50% of shunts may fail within 2 years. Despite its apparent simplicity, a shunt revision requires meticulous attention to detail and vigilance in diagnosis and management to ensure the patient is treated in a timely and adequate manner. The workup and surgical treatment of a VS malfunction is fraught with risks and complications even in the most experienced hands. In the United States, shunt revision costs are high, perhaps over $1 billion a year. The human costs are staggering. Common causes of shunt malfunction include mechanical failure (obstruction, disconnection, or migration), hardware failure (valve), infection, functional (underdrainage or overdrainage), or a combination of these aforementioned issues. ¹ ^, ²

A typical clinical presentation of an acute VS malfunction includes drowsiness, severe headaches, and vomiting. ³ However, the presentation may be quite diverse, from rapid to slow/subtle and chronic. The common signs and symptoms may be as modest and inconspicuous as deterioration in school performance, irritability, increase in head circumference over the 95th percentile, increased lethargy or sleep, clumsiness, chronic malaise, chronic fever, abdominal pain, or swelling around the shunt tract. More impressive presentations include seizure, cranial nerve paresis (III, IV, or VI), decrease in visual acuity, paralysis of upward gaze, papilledema, weakness or paralysis, stupor, coma, or change in vital signs (decreased pulse or increased mean arterial pressure).

Obtaining meticulous information from a patient or his/her caregiver or the medical records about the type of shunt implanted and previous shunt failure presentation is important. Previous imaging, especially when done during symptom-free period, is vital in surgical decision making. Knowledge of the type of shunt and information about the setting, date, and specifics of previous operations may influence treatment strategy in complex cases. However, these details may often be incomplete. It is important to note that a shunt can malfunction without causing an obvious change in ventricular size, in part, due to poor compliance of the brain. However, the intracranial pressure (ICP) can be elevated and only the history from the patient or family member, symptoms, or exam may be helpful. In those patients whose scans may not change during a typical shunt malfunction, it is imperative to listen to the history provided by a knowledgeable caregiver who can accurately compare this presentation with that of a previous shunt malfunction. Failure to do so may be catastrophic.

The steps in working up a ventricular shunt malfunction:

Obtain information about the underlying etiology of hydrocephalus treated by initial shunt placement. In our experience, over 90% of patients have hydrocephalus from intraventricular hemorrhage (IVH) of prematurity, infection, trauma, tumor, normal pressure hydrocephalus (NPH), past hemorrhage, aqueductal stenosis, or congenital etiology (myelomeningocele, craniofacial, or genetic). In about 10% of patients the etiology is unclear. This history may be especially important in cases of aqueductal stenosis, in which a patient may undergo an endoscopic third ventriculostomy (ETV), instead of a shunt revision.
Determine the type of the VS. The most common are ventriculoperitoneal, ventriculoatrial, and ventriculopleural shunts; type of valve (maker, model, fixed pressure or adjustable [need to verify last pressure setting]); side of the shunt implantation; and date and type of recent interventions on shunt system. There are a variety of shunt valves currently available at the market (please refer http://www.pedsneurosurgery.org/education.asp for further information).

Indications

Clinical symptoms of shunt malfunction such as those listed in the introduction
Radiological symptoms of shunt malfunction with ventricular dilatation
Positive cerebrospinal fluid (CSF) cultures, positive evidence of microorganism or elevated white count consistent with infection, and other possible clinical scenarios described elsewhere ¹ ^, ²
Discontinuity in shunt tubing or dislodgement of tubing from ventricle or abdomen (VP), pleura (Vpleural), or heart (VA)
Exposure of shunt tubing
Shunt exploration without ventriculomegaly in patient who has poor compliance of brain, and presents with signs and symptoms of increased intracranial pressure
Slit-ventricle with intermittent shunt malfunction
Desire to convert shunt patient into a shunt-free patient by an ETV, in the face of a shunt obstruction

There is a simplified algorithm for decision making in ventricular shunt malfunction in Fig. 21.1 .

**Fig. 21.1** Simplified algorithm for decision making in ventricular shunt malfunction.

Preprocedure Considerations

Radiographic Imaging

Head computed tomography (CT; may be combined with fiducial markers for navigation) ( Fig. 21.2a ).
Rapid sequence brain magnetic resonance imaging (MRI; Haste T2 protocol) ⁴ ( Fig. 21.2b )—fast, generally no need for anesthesia/sedation. The rationale for using a fast T2- weighted abbreviated MRI exam is to avoid the radiation risk from cumulative CT scans.
Shunt series—X-ray: Head and neck anteroposterior (AP) and lateral ( Fig. 21.3a, b ), chest AP and lateral, abdomen and pelvis AP ( Fig. 21.3c ) and lateral. Abdomen and pelvis radiography is not necessary in case of ventriculoatrial or ventriculopleural shunt evaluation. ⁵
Shuntogram (radionuclide) provides some information regarding opening pressure and shunt flow. Radionuclide shuntogram should be considered in patients whose history, CT scan, or exam is not definitive and shunt flow characteristics need to be evaluated to decide whether or not to operate. A radionuclide study should not delay revision in the setting of an acute, obvious malfunction.

Diagnostic Procedures

Shunt tap—if the fever is greater than 101° F or there is a positive blood culture in last 48 hours and/or shunt system intervention within 6–12 months, proceed with shunt tap prior to revision. Over 95% of all shunt infections occur within 1 year of the last shunt instrumentation, with the majority of them occurring within 3 months.

**Fig. 21.2a, b** Preoperative imaging of shunt malfunction of the same patient. **(a)** Head CT and **(b)** brain MR (Haste T2 protocol).

**Fig. 21.3a–c** Shunt series. (a) Anteroposterior (AP) and (b) lateral skull showing ventricular catheter disconnection. (c) AP abdomen showing distal catheter disconnection (arrow).

Medication

Antibiotics

Any new shunt placement or revision: two doses of cefazolin or any late generation cephalosporin; first dose is administered during anesthesia induction (45 minutes to 1 hour prior to the incision) and the second dose after the surgery within 8 hours. Some surgeons cover the patients with antibiotics for 24 hours; however, the evidence mostly supports a single preoperative dose prior to skin incision. Consider vancomycin 1 hour in advance of surgery in methicillin-resistant Staphylococcus aureus–colonized patients.
Shunt infection: tap shunt, then immediately begin triple antibiotics (ceftriaxone, vancomycin, and metronidazole in community-acquired and imipenem/cilastin instead of ceftriaxone in hospital-acquired infection). ⁶

Operative Field Preparation

Preparation is done according to following the Hydrocephalus Clinical Research Network (HCRN) protocol adopted for Seattle Children’s Hospital ( Fig. 21.4 ). ⁷

Position the patient with the head away from the door. Wide exposure is important. Hair is removed with clippers. Preliminarily prepare the skin with chlorhexidine soap, then isopropyl alcohol, to remove any dirt or debris and allow to dry. Mark the incision.

Previous incisions on the scalp may be extended to get appropriate exposure of ventricular catheter and shunt valve (consider vascular supply to scalp so as not to devascularize the scalp flap). We use 2% chlorhexidine gluconate/70% isopropyl alcohol solution preparation for the surgical field and wait 3 minutes or longer to dry. Double gloves are advised. Drape with antimicrobial incise film and ensure isolation of potential infection sources (tracheostomy, gastrostomy tube, etc.).

**Fig. 21.4** HCRN protocol ⁷ /Seattle Children’s Hospital (SCH) protocol.

Operative Procedure

Shunt Revision

Positioning and Preparation (Fig. 21.5)

**Figure** Fig. 21.5 **Procedural Steps** The patient is placed supine with the head on a gel donut, head mildly rotated away from valve site for adequate exposure of operative field. A gel roll is placed under the shoulders to extend and maintain the appropriate plane for tunneling. Ensure appropriate foam or gel padding to reduce pressure sore risk at every pressure point. Always expose widely so that all parts of the shunt and tract (abdomen for the VPS, chest for ventriculoatrial or ventriculopleural shunt) are covered. In noninfected cases, incisions are infiltrated with 1% lidocaine with epinephrine 1:100,000. **Pearls** • Sometimes in complex patients wound preparation and draping may be challenging, such as those patients with chemotherapy catheters or gastrostomy tubes. • It is important to change gloves before making the incision.

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21 Ventricular Shunt Malfunction