In Case 15, A Ventriculoperitoneal shunt in a 6-year-old male, from Case Studies in Pediatric Emergency and Critical Care Ultrasound 2013, evaluation of VP shunt is discussed. The case discusses some novel uses of bedside ultrasound in evalution of VP shunt. However, I’m just using the case to review VP shunt evaluation.
The following is from the Case 15:
History of Present Illness
A 6-ear-old boy with spina bifida, type-2 Arnold Chiari malformation and a ventriculoperitoneal (VP) shunt presents with transient headache, confusion, and emesis, which began earlier in the day. After discussing his symptoms with neurosurgery resident on call, the family brought the child to the ED for further evaluation. He has had no fever and no diarrhea. He had one revision of his shunt at 6 months of age. Both parents agree that, at this time , he is back to his baseline.
The boy’s vital signs, physical exam and neurological exam in the emergency department were all completely normal.
The key to the case is that any patient with a VP shunt and symptoms suggestive of malfunction should probably have evaluation even if symptoms have completely resolved.
The following are excerpts from Reference (1)
More than 40,000 CSF shunts are placed annually in the United
States, the majority of which are for the treatment of hydrocephalus . Shunt failure occurs in 40–50% of patients
during the first 2 years after shunt surgery. The diagnosis is initially suspected on the basis of history and physical examination findings of increased intracranial pressure; however, imaging often confirms the diagnosis and reveals the underlying cause. Therefore, radiologists should be familiar with the radiologic manifestations of shunt
malfunction and complications.
Evaluation of Shunt Malfunction
The incidence of ventriculoperitoneal shunt
failure ranges from 25% to 40% at 1 year and 63% to 70% at 10 years . Failure rates with ventriculoatrial and ventriculopleural shunts are slightly higher . Patient presentation varies depending on patient age as well as the cause and acuity of failure . Symptoms with the highest positive predictive value include nausea and vomiting and decreased level of consciousness . Seizures, diplopia, and weakness are less frequent presentations . Neurologic examination may show papilledema, focal deficits, hyperactive
reflexes, and ataxia . In children, a bulging fontanelle or splaying of the cranial sutures may be observed .
The initial study for evaluating the size of the ventricles, shunt location, and integrity of the visualized components varies by institution. Unenhanced CT is a common choice but exposes the patient to ionizing radiation. Low-dose shunt protocols, which reduce tube current, result in suboptimal image quality
compared with standard-dose CT but are diagnostically
acceptable in the evaluation of shunt failure . Ventricular enlargement may be subtle and comparison with prior examinations is mandatory; however, the shunt
may fail without definite ventriculomegaly. Secondary signs of acute shunt failure that may be helpful in equivocal cases include transependymal flow of CSF, edema adjacent
to the catheter, and subgaleal fluid collections (Fig. 1).
MRI shows similar findings and is being increasingly used to minimize radiation exposure. In some institutions, single-shot T2-weighted MRI is the initial imaging modality
of choice in suspected shunt failure. Significant MRI-induced heating has not been shown to be an issue with modern shunt
valves. However, programmable shunt valves are adjusted with an external magnet. Changes in the valve-pressure setting have occurred after exposure of programmable valves to an
MRI magnetic field . Before performing MRI on a patient with a programmable shunt, the radiologist must confirm that theshunt is resistant to reprogramming at the magnetic field strength of the scanner. Newer valves such as the Polaris (Sophysa) and ProGAV (Aesculap) are resistant to reprogramming even at a 3-T magnetic field. If an unfamiliar
valve is encountered, the radiologistshould contact the manufacturer for specific MRI safety guidelines. After scanning, the neurosurgeon will frequently check whether the valve pressure setting has changed using a compass provided by the manufacturer .
Conventional radiography is primarily performed to evaluate for breaks, disconnections, or distal catheter migration. A typical series includes frontal and lateral radiography of the head and neck and frontal radiography of the chest and abdomen (Figs. 2 and 3). The goal is simply to include the entire
course of the shunt.
Radionuclide CSF shunt studies can evaluate shunt patency, differentiate proximal versus distal limb obstruction, and in some cases show the site of obstruction where activity
fails to progress through the system (Fig. 4). In fact, the combination of CT and radionuclide imaging is more sensitive than CT alone in diagnosing shunt malfunction .