Review articleFailure of Cerebrospinal Fluid Shunts: Part I: Obstruction and Mechanical Failure
Introduction
Shunt dysfunction is an exceedingly common and frustrating problem observed in all neurosurgical practices. It has been estimated during recent prospective trials (Shunt Design Trial, Endoscopic Shunt Insertion Trial, Medos) that the failure rate for all implanted shunts is as high as 40% by 1 year and 50% by 2 years [1], [2]. These failure rates include infectious and noninfectious complications. The incidence of infection after shunt operation is approximately 8-10% in large trials and usually occurs within the first few months. This review will focus on noninfectious shunt failure and will not consider shunt infection in detail.
The noninfectious causes of shunt failure include obstruction (decreased or absent flow through the shunt because of occlusion of the shunt lumen), mechanical failure, overdrainage, loculation of the ventricles, and abdominal complications. Analysis of the different causes of shunt failure is an important step in reducing the overall failure rate. This two-part review will consider the noninfectious causes of shunt failure. The first part of the review describes the presentation of individuals with shunt failure and the timing and frequency of shunt failure. It will then focus on shunt obstruction and the mechanical causes of shunt failure. The second part of the review will consider shunt overdrainage, loculation of the ventricles, and abdominal complications of shunts.
Section snippets
Shunt Failure Presentation
Shunt failure presentations can take a variety of forms, based not only on the age of the patient but also on the type of shunt malfunction [3]. The patient history commonly includes the new onset of nausea, vomiting, irritability, fever, or an altered level of consciousness. Less commonly, shunt failure can present with increased seizure frequency, diplopia, weakness, or visual loss alone [4]. During the neurologic examination, it is possible to find evidence of papilledema, cranial nerve
Incidence
The overall incidence of shunt failure after initial insertion is approximately 40% at 1 year and 50% by the second year after insertion [5]. Long-term follow-up data from the Shunt Design Trial demonstrated overall shunt survival at 4 years of 41% [1]. Figure 1 demonstrates the mechanisms of shunt failure and the duration from implantation to failure [1]. Similar results have been obtained in other prospective studies (Endoscopic Shunt Insertion Trial, Medos) [2], and reports suggest failure
Causes and Timing
Noninfectious shunt failure may occur because of obstruction, mechanical failure of the shunt (which includes fracture of the tubing, disconnection of components, migration of the shunt, or misplacement), overdrainage, the development of loculations within the ventricular system, and abdominal causes. The varying types of shunt malfunction occur at different intervals after shunt surgery. Obstruction of the shunt system can occur at any time after shunt placement and at any point along the
Obstruction
Shunt obstruction can occur at any time after insertion, and all points along the shunt course are suspect when assessing for shunt malfunction. Shunt obstruction usually presents with clinical evidence of raised intracranial pressure. The presentation is age-dependent, with infants usually having nausea, vomiting, irritability, and a bulging fontanel. Older children and adults usually present with headache, nausea, vomiting, cranial nerve palsies, and ataxia among other neurologic findings.
Fracture
Shunt failure from a fracture of the distal tubing is a biomechanical component failure. The typical presentation of a fractured shunt system is usually quite late (often many years) after initial insertion and is related to both biomechanical stress as the subject grows and the inherent degradation of indwelling components because of host reactions. Inspection of the tubing indicates that it is often calcified with a buildup of proteinaceous material around the periphery. The tubing itself
Conclusions
Shunt dysfunction results from a broad spectrum of etiologies ranging from surgeon-related complications to isolated shunt materials failure to concurrent medical illnesses. Although the patient history and physical examination provide the initial suspicion of shunt failure, medical imaging often confirms the diagnosis and reveals the underlying cause. An understanding of the specific types of obstructive shunt malfunction, the potential causes of failure, and management options is important
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