CSF shunts divert the excess of fluid from the ventricles (or other fluid-filled spaces, as subdural collections and intracranial cysts) to another body cavity. Basically, a shunt is composed of three components: a proximal (ventricular) catheter, the valve, and a distal catheter. These pieces can be manufactured in separated parts that are assembled at the time of insertion or be manufactured in a single kit called unishunt. Most shunts may also contain accessories such as integrated pumping devices or reservoirs, and they may also be supplied with an independent antisiphon device or with a siphon-controlling device integrated in the valve.

Most valves are of differential pressure type, flow regulated, or anti-gravitational. Valves may also be of fixed pressure (low, medium, or high pressure), or they may be externally adjustable (programmable valves). The internal mechanism that regulates CSF flow and pressure of the valve may consist of slits, diaphragm, ball and spring, or miter mechanisms. The components of the shunt are made up of silicone, complemented with other polypropylene or hardened plastic parts or with metallic connectors. Some silicone tubing is cured with silver for increasing resistance to stretching or kinking, while barium impregnation of the tubes is commonly utilized for radiologic identification of the integrity of the shunt.

The most popular type of shunting device is the ventriculoperitoneal shunt (VP), followed by ventriculopleural, ventriculoatrial (VA), lumboperitoneal (LP), and more rarely ventriculo-gallbladder (VGB) shunt. Other types of CSF shunt systems are presently considered only of historic interest. External ventricular drainage (EVD) consists of a temporary device endowed with a ventricular (or subdural) catheter that connects with a collecting bag. A variety of CSF drainage is the ventriculo-subgaleal shunt that drains the ventricular CSF to the subgaleal space and is commonly used as a temporizing measure for controlling ICP especially following ventricular hemorrhage or infection. In addition, ETV is a form of internal derivation of CSF that communicates the floor of the third ventricle with the basal cisterns. At present, ETV is more and more utilized for avoiding the innumerable complications of CSF shunting.

The term shunt failure is not well defined in the current literature. The most accepted view is that shunt failure consists of the inability to reach the goal of surgery. In CSF shunting, failure refers to the incapability of accomplishing an appropriate control of hydrocephalus (as opposed to success) indicated by revision, replacement, or removal of the shunt. The term complication refers to any adverse event that interferes with the expected success of the procedure including new insertions, revisions, or replacements of the valve. Complications may or may not be related with the surgical technique or the valve, and may or may not end with shunt revision or replacement. Complications may derive from problems related to the valve, the patient, or the surgery. In many occasions, the terms failure and complication are interchangeably used in the literature. The variety of devices and accessories employed for shunting of CSF attests for the lack of a rigorous knowledge of the mechanisms involved in the pathophysiology of hydrocephalus and the lack of established guidelines for its treatment. In addition, no CSF shunt has demonstrated its superiority over other shunt type.

Shunt failure can show up in several ways and may proceed with a rapid or slow onset and variable evolution. Shunt malfunction may appear acutely, with alarming signs of brain herniation, i.e., rapidly declining level of consciousness, pupillary changes, posturing, apneic spells, and bradycardia, indicating that we are facing an emergent situation [1, 25, 40]. Patients arriving in hospital in this way let little time for reflection and need emergent management. More often, subacute shunt failure appears in a less stressful scenario that permits calm assessment and allows time for planning the appropriate (medical or surgical) management. Shunt malfunction can also present with chronic manifestations such as mild psychomotor retardation, decreased vision, impaired ocular motility, unsteady gait and falls, mood changes, decreased school performance, increased tone and reflexes in the lower limbs, or symptoms and signs of brain stem involvement or of hydromyelia [51, 57]. In patients operated on for NPH, shunt failure is proclaimed by return to their presurgical situation. Patients show slow mental deterioration, urinary urgency or incontinence, and a worsening gait. Headaches, dizziness, and focal symptoms or signs appear exceptionally in NPH patients with shunt malfunction.

Mechanical malfunction is the most frequent cause of CSF shunt failure. Its incidence may be as high as 50 % in children [4]. Shunt malfunction may be due to proximal catheter obstruction (the most common), valve obstruction, distal catheter occlusion, disconnections of shunt parts, fracture of the tubing, or migration of the proximal or distal catheters. Brain debris, choroid plexus, blood, or tissue reactions often occlude proximal catheters. Slit ventricles and faulty placement of the catheter within the ventricle may also interfere with the flow through the catheter.

On the contrary, the valve itself appears as the most dependable part of the shunt system. Obstruction of the valve is very rare and, in our experience, it happened in very few cases, and it was almost always produced by blood clots [42]. Breakage of the valve itself may occur without any apparent cause or may follow a cranial traumatism. Obstruction of the distal catheter generally occurs in systems with distal slit valves and very rarely in open-ended catheters [15]. In exceptional occasions, the distal tube may be occluded by fecal contents indicating bowel perforation. In the abdomen, distal catheters may be occluded by ingrowth of mesothelial cells and fibroblasts [17]. Kinking of the tube is also of very rare occurrence and is always due to a defective placement.

Detachment of ventricular catheters is almost exclusively due to a loose ligature or to using absorbable sutures. Separations of distal catheters generally occur at the site of connection to the valve, even in systems with soldered components. Stress rupture of the shunt tubing, in one or several pieces, usually takes place on the anterior neck or upper part of the chest wall and is favored by sustained or repeated stretching or friction. Notable deterioration of drainage systems usually occurs in shunts implanted for more than 5 years [20]. Rupture and disconnections mainly happen when there exist biodegradation and calcification of the outer surface of the tubes (Fig. 2.1) caused by aging of the device [6, 17, 20, 21, 76]. Resistance to rupture perhaps might be improved by incorporating tubes to the shunt device with a greater cross-sectional area [79].

Proximal catheters, reservoirs, and even the entire shunt may migrate into the brain, the ventricle, the scalp, or the subgaleal space. In occasions, catheter migration is accompanied by the valve (Fig. 2.2) or reservoir itself [12, 24, 42, 72]. Hydrogel-coated (BioGlide) catheters (devised to decrease cell adhesion aimed at reducing shunt obstruction and infection) seem to be more prone to disconnection and intracranial migration than standard devices [12]. In the same way, the proximal catheter (and its accompanying reservoir or valve) may be pulled out of the ventricle and be displaced down toward the subcutaneous tract. The distal catheter may be stretched out of the peritoneum too, migrating to the subcutaneous abdominal or thoracic tract or into the pleural space, or it may even follow an upward course and penetrate the skull, ventricle, etc. [43, 78]. Detached or broken distal catheters may totally migrate and lodge into the peritoneal cavity.

There are anecdotal reports on perforations and migrations of the distal tubing into the bowel, stomach, liver and gallbladder, scrotum, urinary bladder, pleural space, bronchi, and heart. Bowel perforation seems to be the most severe form of this complication [16]. Extrusion of shunts may take place through the anus, umbilicus, mouth, vagina, operation scars, midlumbar region, etc. [16, 19, 29].

Distal catheters of VA valves may also break or disconnect and stay in situ or migrate to the right heart ventricle, right atrium, pulmonary arteries, or cava vein [36]. All these mechanical complications habitually show the signs and symptoms reported above and are intimately related to the body cavity where the shunt drains (peritoneum, pleura, heart, lumbar spine, etc.).

Complications of CSF shunting are more prevalent in neonates and infants due to the special characteristics these patients possess [18, 19, 48]. There is an increased incidence of both shunt malfunction and shunt infection in this age group in comparison with older children and adults. This vulnerability is due to brain immaturity, skull flexibility, skin fragility (Fig. 2.3a), and compromised immunity. In neonates and infants, irritability, vomiting, decreased appetite, and lethargy, together with bradycardia and apneic episodes, indicate shunt malfunction. Bradycardia and apnea constitute a very reliable indication of shunt failure [40]. Clinical examination findings include abnormal growth of head circumference, bulging of the anterior fontanel (Fig. 2.3a), suture diastasis, sunsetting eyes, and dilated scalp veins (Table 2.3). Palpation of the anterior fontanel may give a reliable estimate of intracranial pressure and is a very dependable sign in children with open skull bones (Fig. 2.3b).

Shunt failure in older children and adults manifests itself with an almost constant triad that consists of headaches, vomiting, and somnolence [4]. Other complaints include blurred or failing vision, squint, loss of appetite, mood changes, and new onset or increase in the number of seizures. Table 2.4 shows some frequent (and less frequent) symptoms and signs of shunt malfunction in older children and adults. Differential diagnosis in children who present with vague symptoms must be made against common infantile diseases, especially gastrointestinal viral diseases or mild upper respiratory tract infections. Children are also prone to experience otitis media, and individuals with myelomeningocele often suffer from repeated urinary infections that may resemble (or mask) those of shunt failure.

Less often, shunt malfunction evolves with chronic and subtle clinical features as failing vision, mood and behavioral changes, gait clumsiness, frequent falls, regression or stagnation of developmental milestones, or even with deficient schooling progression. Clinical examination may show papilledema, spastic paraparesis, hypertonus, hyperreflexia, uni- or bilateral sixth cranial nerve palsy, cervical defense, spinal rigidity, erythema, palpable pseudotumors, or fluid collections along the shunt tract (Fig. 2.4a, b). Rupture or disconnection of the distal catheter can be diagnosed by palpating the entire shunt along the trajectory through the subcutaneous tissue. Partial calcification of distal catheters indicates tube degradation and should raise the suspicion of catheter breakage with or without intra-abdominal migration (Fig. 2.1). In peritoneal shunts, features of shunt malfunction referred to the abdominal cavity are usually the most striking (Table 2.4).

There is a group of pediatric patients who are admitted repeatedly to hospital with repeated shunt failure (“poor-shunt patients”) [81]. The main cause for recurring malfunction is proximal catheter obstruction. Known causative factors for this complication are a younger age at insertion, overdrainage, concurrent other surgeries, and certain causes of hydrocephalus [81].

Bergsneider et al. and Vinchon et al. [5, 84] reported several forms of shunt dysfunction in adults with pediatric-onset hydrocephalus and have also given an account of other related conditions such as adult slit ventricle syndrome, multi-compartmental hydrocephalus, newly diagnosed noncommunicating hydrocephalus, and non-NPH and NPH hydrocephalus [5]. Risk factors for shunt malfunction in adults has been especially described in VA shunts especially after previous multiple external drainages [32]. Adult NPH patients with shunt malfunction often return to hospital with the complaints of deterioration in comparison with the amelioration noted immediately after shunting. Clinical features in this group of patients consist of worsening gait, aggravation of urinary problems, and failing memory. Rarely these patients complain of headaches, mental dullness, dizziness, or seizures. Physical examination shows increased reflexes and Babinski sign, gait ataxia, parkinsonism, and signs of frontal release as sucking and grasping reflexes. Muscle strength is normal and there is no sensory loss. However, the appearance of focal signs, as hemiparesis, should raise the suspicion of a subdural hematoma. In an extensive series of chronic subdural hematomas, six instances (0.6 %) were associated with shunted hydrocephalus and presented with behavioral disturbances or headaches [26].

The majority of early complications occurs in the first year after shunt insertion and is in relation with patient age and condition, the surgical technique, and the function of the shunt itself. The most frequent reasons for early failure both in children and adults are proximal catheter obstruction and shunt infection [23]. In our experience, technical problems related to valve placement and inadequate selection of valve’s characteristics (pressure and size) may cause early shunt failure too. Late shunt dysfunction is almost exclusively due to proximal or distal catheter block or to fracture or disconnection in relation with problems pertaining to aging of the implanted material and to late infection. The hazard of shunt failure decreases as a function of time in both newly placed and revised shunts: “the longer a shunt functions, the less likely it is to fail” [53]. The rate of shunt infection decreases as a function of time too. Mc Girt reported a 14 % rate of failures for all shunts during the first month after shunt implant and only a 5 % rate beyond 4 years [53]. Obviously, shortening of the distal catheter due to the child’s growth is also a late age-related cause of shunt failure.

There is no agreement in different studies as to the role played by etiology of hydrocephalus in the rate of subsequent shunt complications. Some find no differences between the diverse causes of hydrocephalus in the occurrence of shunt failures [28, 63]. However, others report an increased rate of shunt malfunction in patients with intraventricular hemorrhage, meningitis, or tumors [37, 39, 63]. Reported risk factors in tumoral hydrocephalus comprise age, tumor histology, and concurrent or prior surgical procedures (external ventricular drains, craniotomy, etc.) [66]. There is a higher rate of severe complications in myelomeningocele patients with the Chiari II malformation at the time of shunt malfunction. These patients may suffer early damage to the brain stem and upper cervical cord that causes breathing problems and quadriparesis [25, 51, 57].

Ventriculoperitoneal shunts may fail due to numerous causes as ascites (Fig. 2.5a), hernias, hydrocele, ileus, intussusception, torsion of omental cyst, peritonitis, peritoneal pseudocyst, volvulus, perforation of viscus, peritoneal pseudotumor, and catheter extrusion through several places (umbilicus, rectum, vagina, scrotum, mouth, gastrostomy wound, etc.). Most of these complications usually evolve with features of shunt malfunction and/or with those of infection [16]. An often overlooked cause of shunt malfunction is severe constipation (Fig. 2.5b) that causes increased intra-abdominal pressure thus impairing CSF drainage from the ventricles [49, 54, 71].

Malfunction of ventriculopleural valves is generally due to accumulation of fluid in the pleura (aseptic hydrothorax), pneumothorax, and rarely to pleural empyema or fibrothorax [45, 80]. Symptoms of thoracic involvement include chest pain, cough, shortness of breath, and tachypnea. On examination there may be decreased breath sounds, dullness on percussion, subcutaneous emphysema, pallor, sweating, tachypnea, and cyanosis.

Ventriculoatrial shunts are at present rarely implanted due to the severity of the problems that they may originate. VA valves in children require frequent catheter lengthening due to the patients’ growth. Specific complications of VA valves are often severe and include bland or septic pulmonary embolism, pulmonary hypertension, endocarditis, cor pulmonale, cardiac arrhythmias, and shunt nephritis. Clinical manifestations include chest pain, shortness of breath, low-grade fever, and, in the case of shunt nephritis sepsis, hepatosplenomegaly, arterial hypertension, hematuria, and proteinuria [61, 83].

Lumboperitoneal shunts are used in communicating hydrocephalus, NPH, pseudotumor cerebri, CSF fistulas, and postsurgical pseudomeningocele. LP valves have a high rate of complications [14, 85]. One of their main drawbacks of LP shunts is the difficulty they present for assessing their function. Morbidity of LP shunts may be due to mechanical complications (block, migration), overdrainage (subdural collections), infection, and development of acquired Chiari malformation. Acquired tonsillar herniation is the most feared complication, and it is thought to be more prevalent following the placement of valveless systems. Clinical features include back pain, back stiffness, sciatica, neurological involvement in the lower limbs, scoliosis, and those pertaining to symptomatic tonsillar herniation [14, 85].

Ventriculo-gallbladder shunts are indicated after failure of previously placed VP, VA, or ventriculopleural shunts. Complications comprise malfunction, disconnection, infection, gallbladder atony, gallbladder calculi, peritonitis, and bilious ventriculitis [27, 77].

Subdural-peritoneal shunts are used for draining subdural collections of fluid. Their main complications are blockage, infection, disconnection, migration (including intracranial migration of the entire system), CSF leakage, and skin ulceration, together with overdrainage that may produce cranioencephalic disproportion and proximal catheter adherence to brain surface at removal [22, 34].