is usually obstructed by choroid plexus, but floating debris or hypercellular CSF can result in the same obstruction; the distal catheter can be obstructed by the surrounding omentum or can be kinked or coiled Both proximal and distal portions can be occluded by the products of infection or by migration of the catheter tip into the brain parenchyma or intra-abdominal structures Poor absorption of excess fluid in the peritoneum due to decreased surface area can create the appearance of luminal obstruction, particularly in neonates In addition, as the child grows, the tension on the shunt system can lead to disconnection of the distal tubing Up to 60% of patients with CSF shunts experience a shunt malfunction in their lifetime, most commonly within the first months of initial shunt placement Parental history is paramount in deciding whether a child is experiencing symptoms of shunt malfunction The parent often notices that the child “just isn’t acting right” or is less active or thinking less clearly than usual The statement, “This is exactly how he acted the last time his shunt was obstructed,” is suggestive of another malfunction, regardless of the presence or absence of the symptoms listed in the following section Common signs and symptoms of mechanical shunt failure include headache, visual disturbances, vomiting, lethargy, and irritability ( Table 135.2 ) The astute parent or clinician may note mild ataxia, increased head circumference or bulging fontanel in an infant, swelling at the reservoir site, poor cognition, or abnormal behaviors A classic sign is “sunsetting eyes,” which is really an upgaze paresis and eyelid retraction associated with Parinaud syndrome from pressure on the quadrigeminal plate by a dilated suprapineal recess in direct communication with the third ventricle Increased tone, hyperreflexia, or Babinski reflex represents stretching and disruption of the corticospinal fibers originating from the motor cortex and can suggest shunt malfunction in a patient with a previously normal examination, although these symptoms are rarely present in a child without a severe alteration of consciousness Patients with Cushing triad (hypertension, bradycardia, and abnormal respiratory pattern) require immediate maneuvers to decrease ICP and guide them quickly toward operative repair of the shunt Seizures are uncommon as the sole manifestation of CSF shunt malfunction However, seizures can occur in children who have predisposing brain lesions, and many patients with CSF shunts have epilepsy Shunt infection must be considered in the child with symptoms of shunt malfunction, especially if the child has a history of recent shunt revision Ronan et al reported that more than one-third of patients with shunt infection presented with symptoms of malfunction If the history and physical examination of the ill child with a CSF shunt suggests a possible shunt malfunction, further evaluation includes urgent neuroimaging with either noncontrast computed tomographic (CT) scan or MRI, with comparison to the most recent prior study, if available Some MRIs may miss the location of the shunt tip, and will likely reset a programmable shunt, so one should have access to a programming magnet if MRI is used in a patient with this type of device The choice of imaging is based on institutional preference and techniques used Ultra low-dose helical CT protocols can be used to lower the radiation risk to the patient, and scout lateral radiographs that include entire neck to clavicles can reduce the need for plain radiographs or “shunt series,” which is most helpful in assessing the integrity of the shunt connection and in identifying the components of the working system A formal shunt series radiograph study should also be considered if there is localized swelling or pain along the shunt tubing, distal erosions (rare) with shunt tubing present outside the body, or at request of neurosurgery team to assist with shunt revision Abdominal ultrasound can help evaluate for pseudocyst in patients with abdominal symptoms, particularly in those patients who may have an unreliable abdominal examination due to sensory deficit or neurologic disease TABLE 135.2 CONCERNING FINDINGS IN PATIENTS WITH CEREBROSPINAL FLUID SHUNT MALFUNCTION Symptoms Fever Headache Altered mental status Irritability Lethargy/difficult arousal Confusion Vomiting Visual disturbances Seizures (rare to be the only manifestation) Signs Papilledema Bulging fontanel/enlarged head Engorged head veins Macewen sign (cracked pot sound during percussion) Abnormal neurologic examination Increased deep tendon reflexes or lower-extremity tone Positive Babinski sign Cranial nerve palsy—lateral (sixth) or upward (fourth) gaze (sunsetting) Respiratory compromise The clinical suspicion of a shunt malfunction based on history and physical examination may outweigh the data obtained from radiographic studies because shunt failure may occur without radiographic signs Pumping the shunt to test for obstruction is not always reliable In addition, pumping of the shunt can cause entrapment of choroid plexus in the proximal shunt tubing and lead to proximal catheter obstruction where none previously existed A new technique (ShuntCheck) that measures a reduction in distal neck temperature over the shunt after placing an ice bag proximally on the neck shows promise for confirming shunt flow but has not yet been published in the peer-reviewed literature FIGURE 135.4 Tapping the cerebrospinal fluid shunt If subsequent evaluation is still necessary to diagnose malfunction, a neurosurgeon should be consulted It may be necessary to “tap” the shunt ( Fig 135.4 ) The patient’s hair is either shaved or trimmed The scalp is cleansed first with alcohol and then with three applications of Betadine that are allowed to dry