The review, authored by a team of pediatric radiologists at Nemours Children’s Hospital in Florida, walks through the entire anatomy and engineering of shunt systems, from the proximal catheter threaded into a ventricle to the distal tubing that delivers fluid to an absorptive site in the body. Cerebrospinal fluid itself is produced mainly by the choroid plexus, specialized ependymal cells lining the ventricles, and it circulates continuously through the ventricular system and the subarachnoid spaces surrounding the brain and spinal cord before being cleared through arachnoid projections, meningeal lymphatic vessels, and the glymphatic system. When this elegant circulation breaks down, whether through obstruction, overproduction, or impaired absorption, the ventricles expand and compress the surrounding brain tissue, producing the constellation of symptoms that defines hydrocephalus.

A shunt system is deceptively simple in concept. A proximal catheter, typically made of silicone and measuring two to three millimeters in diameter, is placed within the fluid-filled space requiring diversion, most commonly a lateral ventricle. The fluid then passes through a valve that enforces one-way drainage and regulates flow according to the pressure gradient between the proximal brain compartment and the distal drainage site. Valves that respond purely to this pressure differential are called differential-pressure valves, and they may operate at a fixed preset pressure or at an adjustable setting that clinicians can reprogram noninvasively through the skin using magnetic tools. Raising the opening pressure reduces drainage and can allow the ventricles to enlarge, while lowering it increases flow, though the timing and magnitude of these changes vary considerably between patients. The review emphasizes a crucial safety point: magnetic resonance imaging can inadvertently alter programmable valve settings, so the valve must be checked promptly after every MRI scan, even though most modern designs are rated compatible up to 3 Tesla.

Where the distal catheter ends up matters enormously. The peritoneal cavity is the favored destination because its vast absorptive surface can soak up cerebrospinal fluid efficiently, making the ventriculoperitoneal shunt the workhorse of neurosurgery. But abdominal scarring, infections, necrotizing enterocolitis, or congenital gastrointestinal anomalies sometimes rule out the peritoneum. In those cases, surgeons may route the distal catheter into the right atrium of the heart, where the fluid enters the bloodstream, or into the pleural cavity surrounding the lungs. Recent meta-analyses cited in the review show that ventriculoatrial shunts, once largely abandoned in favor of the peritoneal route, now carry infection, revision, and mortality rates comparable to ventriculoperitoneal shunts. Even the gallbladder can serve as a destination in rare ventriculobiliary shunts, though the review cautions that a small pediatric gallbladder, sometimes only about 1.4 cubic centimeters in infants, limits storage capacity, and that mistaking this uncommon device for a truncated peritoneal shunt during surgery risks biliary leakage.

Imaging in the days after surgery reveals a predictable set of expected changes alongside genuine early complications. Mild pneumocephalus, air within the skull, is frequently seen and usually resolves on its own, though rarely it can progress to dangerous tension pneumocephalus. When markedly dilated ventricles collapse rapidly after shunting, fluid or blood can accumulate in the subdural compartment, and ventricular decompression may even shift the catheter tip out of the ventricle entirely. Intracranial hemorrhage, whether subarachnoid, intraventricular, or parenchymal, remains another recognized early risk that radiologists must actively exclude.

The stakes of getting imaging right are stark. Pediatric shunt failure rates reach 30 to 40 percent within the first year and approximately 50 percent by two years, according to figures compiled in the review. Non-contrast head CT is typically the first study ordered when malfunction is suspected, and low-dose protocols are preferred to limit radiation while preserving diagnostic accuracy. Increasingly, however, fast MRI protocols built around single-shot fast T2 sequences are replacing CT, offering a rapid assessment of ventricular size in minutes without sedation and without ionizing radiation, a particular advantage for children who require repeated follow-up imaging. Diffusion-weighted imaging adds another layer of power, detecting the restricted diffusion characteristic of purulent debris in ventriculitis or abscess. Still, the review stresses a humbling truth: ventricular size alone is not a reliable indicator of shunt function. Ventricles may remain stubbornly small despite malfunction in patients with poor brain compliance or slit ventricle syndrome, and changes in size may simply reflect valve reprogramming. Supporting clues include periventricular white matter edema, edema along the catheter track, and subgaleal fluid collections, though the authors warn that bright periventricular signal on T2 and FLAIR sequences must be distinguished from the normal incomplete myelination seen in very young children.

When anatomy alone cannot settle the question, functional studies take over. The traditional radiographic shunt series, frontal and lateral views of the head, chest, and abdomen, is now known to have low sensitivity and a high false-negative rate, limiting its usefulness to suspected mechanical problems such as kinking or disconnection. Shuntograms, in which contrast or radiotracer is injected into the reservoir and followed through the system, assess both patency and physiological flow; one study of 107 contrast-enhanced shunt series found a higher negative predictive value than either CT or plain radiography. Radionuclide shuntograms are especially valuable when clinical suspicion of failure persists despite normal ventricular size, and combining nuclear medicine with CT outperforms CT alone. In one striking example from the review, tracer failed to spill into the peritoneum for two hours in a teenager with headaches and seizures, prompting positional maneuvers that restored free flow, revealing that constipation, of all things, had temporarily compressed the distal catheter and raised intra-abdominal pressure. Such false-positive obstructions, the authors note, can spare patients unnecessary revision surgery if recognized.

The catalog of long-term complications reads like a textbook of applied pathology. Obstruction, the most common malfunction, usually strikes at the ventricular catheter tip, where choroid plexus and ependymal tissue grow into the fenestrations, or at the valve, which can clog with blood or debris. Infections cluster within the first six months, typically from skin flora such as Staphylococcus epidermidis and Staphylococcus aureus, with the slow-growing Cutibacterium acnes capable of smoldering undetected for longer periods. Infected ventriculoatrial shunts are particularly dangerous because contaminated fluid drains directly into the bloodstream, and a distinctive late consequence, shunt nephritis, occurs in roughly 4 to 14 percent of infected cases through immune complex deposition in the kidneys, with only about half of affected patients regaining full renal function. Abdominal pseudocysts, fibrous-walled fluid collections that encase the distal catheter, can appear anywhere from three weeks to five years after surgery. Meanwhile, growing children stretch and calcify their tubing, and fractures most often occur in the mobile neck region roughly five years after calcifications first appear, prompting the authors to recommend closer surveillance once calcification is spotted on radiographs.

Perhaps the most conceptually fascinating complications arise from the physics of drainage itself. When an upright patient’s posture increases the vertical column of fluid between brain and abdomen, a siphoning effect can overdrain the system, collapsing the ventricles into slit-like spaces and, over years, producing the notorious slit ventricle syndrome, generally flagged radiologically by a fronto-occipital horn ratio of 0.2 or less. In this state the ventricle walls collapse around the catheter, functionally obstructing it even though the hardware is patent. Anti-siphon devices help, and their introduction has also reduced rates of trapped fourth ventricle, a condition in which inflammatory scarring isolates the fourth ventricle and progressive fluid accumulation there compresses the brainstem, sometimes producing a telltale keyhole shape as the ventricle herniates upward through the tentorial hiatus. The review’s overarching message is that no single test suffices: only a nuanced, multimodality approach, pairing anatomic imaging with functional studies and a deep understanding of each patient’s hardware, allows clinicians to catch these failures early and protect the children whose lives depend on these silent, tireless tubes.

Subject of Research: Multimodality imaging evaluation of cerebrospinal fluid shunt systems and their complications in hydrocephalus

Article Title: Multimodality imaging of cerebrospinal fluid shunts: system evaluation and complications

Article References: Hoodeshenase, S., Averill, L., Mody, T., & Johnson, C. (2026). Multimodality imaging of cerebrospinal fluid shunts: system evaluation and complications. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06759-z

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06759-z

Keywords: hydrocephalus, cerebrospinal fluid shunt, ventriculoperitoneal shunt, shunt malfunction, pediatric radiology, neuroimaging, shunt infection, slit ventricle syndrome, radionuclide shuntogram, MRI, shunt obstruction, trapped fourth ventricle