Hydrocephalus is broadly grouped into four types based on what is going wrong with cerebrospinal fluid (CSF) flow or absorption: obstructive (non-communicating) hydrocephalus, communicating hydrocephalus, normal pressure hydrocephalus, and hydrocephalus ex vacuo. Each type has different causes, behaves differently on brain scans, and often calls for a different treatment strategy. The boundaries between them are not always crisp, and some cases straddle categories, but the four-type framework remains the standard clinical starting point.
A Quick Word About Cerebrospinal Fluid
Your brain and spinal cord float in a thin cushion of clear fluid called cerebrospinal fluid. Most of it is produced by a network of blood vessels called the choroid plexus, which sits inside chambers (ventricles) deep in the brain.1PubMed Central. Cerebrospinal fluid circulation: What do we know and how do we know it? After circulating through and around the brain, CSF is normally reabsorbed back into the bloodstream. Hydrocephalus develops when something disrupts that cycle: too much fluid is made, too little is absorbed, or a blockage traps fluid inside the ventricles. The result is enlarged ventricles and, depending on the type, rising pressure that can damage brain tissue.
Obstructive (Non-Communicating) Hydrocephalus
This is the most mechanically straightforward type. Something physically blocks the narrow passages that connect the brain’s ventricles, so CSF gets trapped upstream of the blockage. The “non-communicating” label means the ventricles can no longer communicate freely with each other or with the space around the brain. Common causes include tumors pressing on the passages, congenital narrowing of the aqueduct of Sylvius (a tiny channel between the third and fourth ventricles), cysts, and scarring from infections or bleeding.
Because fluid backs up behind a dam, pressure can rise quickly. In infants whose skull bones have not yet fused, this often shows up as a rapidly enlarging head. In older children and adults, the skull cannot expand, so pressure builds against brain tissue instead, causing headaches, nausea, vision problems, and altered consciousness. Obstructive hydrocephalus is frequently the type that presents as a medical emergency, especially when a tumor or hemorrhage suddenly closes off a passageway.
Congenital forms deserve special mention. Genetic factors can disrupt normal brain development in ways that leave the fluid pathways malformed from birth. Research in animal models has shown that abnormal cellular signaling during early development can lead to structural defects that produce hydrocephalus before or shortly after delivery.2PubMed Central. Genetics of human hydrocephalus One well-known example is X-linked hydrocephalus, caused by mutations in a gene called L1CAM, which accounts for a meaningful share of congenital cases in boys. Other genetic syndromes, such as Dandy-Walker malformation, can also produce obstructive hydrocephalus through abnormal formation of the cerebellum and fourth ventricle.
Communicating Hydrocephalus
In communicating hydrocephalus, there is no physical blockage between the ventricles. Fluid flows freely through all the internal passages, but something prevents it from being reabsorbed once it reaches the brain’s surface. The classic explanation is that the arachnoid granulations, tiny one-way valves on the brain’s surface that drain CSF into the venous sinuses, are not working properly. Infections like meningitis, bleeding into the fluid spaces (subarachnoid hemorrhage), and inflammatory conditions can all scar or clog those granulations.3PubMed Central. Hydrocephalus: A Review of Etiology-Driven Treatment Strategies
That picture has gotten more interesting in recent years. Animal research has shown that CSF also drains through lymphatic vessels outside the skull, particularly in the region around the ethmoid bone (behind your nose). In rat models of communicating hydrocephalus, impaired lymphatic absorption had a measurable impact on overall CSF drainage and appeared to play a role in the enlargement of the ventricles.4PubMed Central. Elevated CSF outflow resistance associated with impaired lymphatic CSF absorption in a rat model of kaolin-induced communicating hydrocephalus This means the old textbook diagram, where all the absorption happens at the top of the brain, may be incomplete. The clinical implications of the lymphatic pathway are still being worked out, but it is a promising area of research.
Symptoms of communicating hydrocephalus depend on how quickly the absorption problem develops. A sudden bleed or severe meningitis can cause rapid pressure buildup with intense headaches, vomiting, and drowsiness. Slower-developing cases may present with gradually worsening balance, memory trouble, or bladder control issues, symptoms that shade into the territory of normal pressure hydrocephalus.
Normal Pressure Hydrocephalus
Normal pressure hydrocephalus (NPH) is the sneakiest of the four types and the one most likely to be misdiagnosed. The ventricles enlarge, but CSF pressure, when measured with a lumbar puncture, reads as normal or only slightly elevated. NPH mainly affects older adults and typically announces itself with a triad of symptoms: gait disturbance (a shuffling, wide-based walk), cognitive decline, and urinary dysfunction.5PubMed. Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review All three do not have to appear at once. Walking problems usually come first, memory issues follow, and bladder trouble tends to show up last.
When NPH develops after meningitis, head trauma, or brain surgery, it is called secondary NPH. When no clear cause is found, it is labeled idiopathic (iNPH). The idiopathic form is the more common and the more controversial, because its symptoms overlap heavily with Alzheimer’s disease, Parkinson’s disease, and vascular dementia. A patient walking unsteadily with a foggy memory and some incontinence could have any of those conditions, or could have NPH, which is one of the very few causes of dementia that is potentially reversible with treatment.6PubMed Central. The Typical Triad of Idiopathic Normal Pressure Hydrocephalus in a 62-Year-Old Male
The reason “potentially reversible” matters so much is that shunt surgery can improve symptoms in a significant proportion of NPH patients. That makes getting the diagnosis right critical, and it also makes the distinguishing features between NPH and look-alike conditions a major focus of imaging research.
Hydrocephalus Ex Vacuo
Hydrocephalus ex vacuo is the odd one out. Technically, it is not hydrocephalus in the traditional sense because there is no problem with CSF production, flow, or absorption. Instead, brain tissue itself has shrunk, often from degenerative diseases like Alzheimer’s, stroke-related damage, or traumatic brain injury, and the ventricles passively expand to fill the space left behind. The total amount of fluid in the skull has not really increased; the brain has just become smaller.
This matters because treatment for true hydrocephalus (usually a shunt or surgery) would not help these patients and could actually harm them. Draining fluid from ventricles that are large only because the surrounding tissue has atrophied serves no purpose. Early CT studies distinguished the two conditions by looking at specific anatomical features: in true hydrocephalus with elevated pressure, the temporal horn tips of the ventricles widen and the surface grooves of the brain are compressed or invisible, while in hydrocephalus ex vacuo, the surface grooves are widened because the brain itself has shrunk.7PubMed. Ventricular differences between hydrostatic hydrocephalus and hydrocephalus ex vacuo by computed tomography
Getting the distinction right is harder than it sounds. A recent study found that patients with progressive supranuclear palsy, a movement disorder, can show ventriculomegaly on imaging that looks like NPH at first glance. Closer analysis, though, revealed that the pattern of brain changes was consistent with ex vacuo changes from central atrophy rather than true NPH, underscoring the risk of relying on simple measurements alone.8PubMed. High Evans Index in progressive supranuclear palsy may mimic normal pressure hydrocephalus: a retrospective cross-sectional study Specific radiological features, including the angle of a brain structure called the corpus callosum, the shape of the Sylvian fissure, and the pattern of sulcal (groove) narrowing at the top of the brain, can help clinicians separate the two conditions on MRI.9PubMed Central. Differences in Brain Morphology between Hydrocephalus Ex Vacuo and Idiopathic Normal Pressure Hydrocephalus
How Doctors Tell the Types Apart
Brain imaging is the first step. CT and MRI scans both work well for measuring ventricle size, and the two methods agree closely with each other when measuring the Evans Index (a ratio comparing the widest part of the frontal horns to the maximum width of the inner skull) and the width of the third ventricle.10PubMed Central. Ventricular Anatomy Across CT and MRI in Hydrocephalus: A Retrospective Study An Evans Index above 0.3 has long been used as a cutoff suggesting hydrocephalus, and large cross-population studies support that threshold.11PubMed Central. Normative parameters of the Evans Index using Computer Tomography in the Saudi population
But enlarged ventricles alone do not tell you which type of hydrocephalus you are dealing with. Obstructive hydrocephalus usually shows a clear pattern: the ventricles upstream of the blockage are ballooned, while those downstream are normal-sized. NPH has its own signature, known as DESH (disproportionately enlarged subarachnoid-space hydrocephalus), where the ventricles are large but the grooves at the top of the brain appear tight while the Sylvian fissures low on the brain’s sides are widened. Hydrocephalus ex vacuo, by contrast, shows ventricle enlargement accompanied by wide grooves everywhere, reflecting generalized brain shrinkage.
Researchers have started combining these traditional measurements with newer tools. A machine-learning model that combined ventricle shape measurements with cortical thickness data achieved about 90% accuracy in distinguishing iNPH from healthy brains, with the thickness of a specific region in the cingulate cortex turning out to be the most influential factor.12PubMed Central. Improve the diagnosis of idiopathic normal pressure hydrocephalus by combining abnormal cortical thickness and ventricular morphometry These automated approaches are still mainly in the research phase, but they hint at a future where imaging can make sharper distinctions between types, especially in borderline cases.
Beyond imaging, clinicians often use a “tap test,” draining a measured amount of CSF through a lumbar puncture, to see if symptoms improve temporarily. A patient with NPH who walks better after a tap test is considered a good candidate for a permanent shunt. This kind of functional testing adds a layer of information that imaging alone cannot provide.
Treatment Strategies
The treatment approach depends heavily on which type of hydrocephalus is present.
For obstructive hydrocephalus, the preferred option in many adults is endoscopic third ventriculostomy (ETV), a procedure where a surgeon uses a tiny camera to punch a small hole in the floor of the third ventricle, creating a bypass around the blockage so CSF can flow to the brain’s surface and be reabsorbed normally. In children, ETV is sometimes combined with cauterization of part of the choroid plexus to reduce CSF production at the same time.13High Yield Medical Reviews. Management of Pediatrics Hydrocephalus: A Systematic review and metanalysis; on Endoscopic third Ventriculostomy (ETV), vs. ventriculoperitoneal shunt (VPS), Treatments and Postoperative Outcomes ETV has the advantage of not requiring permanent implanted hardware.
For communicating hydrocephalus and NPH, the standard treatment is a ventriculoperitoneal (VP) shunt, a system of tubing that diverts excess CSF from the brain’s ventricles to the abdominal cavity, where it is absorbed. VP shunts have been the workhorse of hydrocephalus treatment for decades. They work, but they come with a meaningful complication burden. A large study following shunted patients for an average of about four years found that roughly one in four experienced at least one complication, and about one in five needed a shunt revision. Central nervous system infections occurred in about 6% of patients. Complication rates were highest in the first year and dropped substantially over time.14PubMed Central. The Rate of Complications after Ventriculoperitoneal Shunt Surgery
Children are hit particularly hard by shunt complications. Pediatric patients face higher rates of shunt failure than adults, with one study estimating the failure rate at around 46%.15Pakistan BioMedical Journal. Long-term outcomes of Ventriculoperitoneal Shunt Surgery in Patients with Hydrocephalus Growing bodies, smaller anatomy, and a longer lifetime of shunt dependence all increase the odds that the device will need to be revised at some point. Many children with hydrocephalus undergo multiple surgeries over their lifetime.
Hydrocephalus ex vacuo, again, is the exception. Because the ventricle enlargement reflects lost brain tissue rather than a CSF circulation problem, there is nothing to shunt. Treatment focuses on whatever is causing the underlying brain atrophy.
Living with Hydrocephalus Long-Term
Most discussions of hydrocephalus focus on diagnosis and surgery, but families and patients often want to know what life looks like years or decades later. The evidence here is cautiously encouraging for many patients, though not uniformly so.
A study of adults who had been treated with shunts for hydrocephalus in infancy found that their overall quality-of-life scores were close to population norms. The average health utility score (on a scale where 1.0 is perfect health) was 0.92 for the hydrocephalus group compared with 0.95 for controls. The difference was not statistically significant overall. However, the hydrocephalus group did score significantly lower on specific dimensions including vision, eating, daily activities, and mental function, and most of those differences were driven by a subgroup who also had cerebral palsy or epilepsy.16PubMed Central. Quality of life in adults treated in infancy for hydrocephalus
Adults with congenital hydrocephalus showed a similar pattern in another study. Their physical functioning, physical role functioning, and general health perception scores were lower than the general population, but their emotional, social, and mental health scores were not significantly different. The Mental Component Summary score was essentially equal to the comparison group.17PubMed. Adult long-term health-related quality of life of congenital hydrocephalus patients In other words, the physical effects of hydrocephalus and its treatment persist, but many patients develop emotional and social resilience that brings their mental health in line with the broader population.
The picture is more nuanced for children. When children with hydrocephalus assessed their own quality of life, they consistently rated it higher than their caregivers did. Cognitive health was the weakest area in both child and caregiver assessments, while social-emotional health fared better. Children who reported lower quality of life were more likely to also report symptoms of anxiety, depression, and fatigue.18PubMed Central. Hydrocephalus-Related Quality of Life as Assessed by Children and Their Caregivers The gap between child and parent ratings is worth noting: caregivers may be underestimating how well their children feel they are doing, or the children themselves may be adapting their expectations.
The Glymphatic Connection
One of the most active areas of hydrocephalus research involves the glymphatic system, a waste-clearance network discovered in the last decade that uses CSF flowing along the outsides of blood vessels to flush metabolic debris out of brain tissue. Emerging evidence suggests that disrupted glymphatic flow may play a role in the development of hydrocephalus after bleeding inside the ventricles.19PubMed Central. Therapeutic Hypothermia Alleviates Hydrocephalus and Neurological Dysfunction Post Intraventricular Hemorrhage by Enhancing Drainage of Glymphatic-Meningeal Lymphatic-Deep Cervical Lymphatic System
In iNPH specifically, altered CSF flow patterns may impair glymphatic transport, which could help explain why many NPH patients also develop deposits of abnormal proteins (amyloid and tau) more commonly seen in Alzheimer’s disease.20PubMed. Adult Hydrocephalus and the Glymphatic System If the brain’s waste disposal system is backed up because CSF is not flowing correctly, toxic proteins may accumulate faster. This overlap between hydrocephalus and neurodegeneration is an area where understanding is evolving rapidly, and it may eventually change how clinicians think about the relationship between NPH and Alzheimer’s.
Research into the meningeal lymphatic vessels, which drain fluid from around the brain into the body’s regular lymphatic system, has added another layer. One study found that after bleeding inside the ventricles, immune cells called neutrophils release web-like structures that physically damage lymphatic vessels and cause clots in them, obstructing drainage and worsening hydrocephalus. Targeting those immune structures could be a way to prevent secondary hydrocephalus from developing after a brain hemorrhage.21PubMed Central. Neutrophil extracellular trap-mediated impairment of meningeal lymphatic drainage exacerbates secondary hydrocephalus after intraventricular hemorrhage These findings are still preclinical, but they point toward therapies that go beyond diverting fluid mechanically and instead try to restore the brain’s own drainage infrastructure.
How Shunt Technology Has Changed Over Time
The modern VP shunt looks simple, a tube, a valve, and a catheter, but getting to this point took more than a century of trial and error. Ventricular puncture was first performed in the 1700s. Sterile technique arrived in the 1880s. Early shunts diverted CSF to the peritoneum, veins, pleural cavity, and even the ureters, but almost all failed because the materials were not up to the job.22PubMed. The scientific history of hydrocephalus and its treatment The real breakthrough came around 1960, when silicone tubing and reliable one-way valves converged. Since then, at least 127 distinct valve designs have been produced, though most are minor variations on a few basic principles. Second-generation valves added adjustability and anti-siphon features, allowing fine-tuning after implantation. Despite these advances, shunt failure and revision remain common problems, which is one reason endoscopic approaches have seen a resurgence since the 1990s.