When people hear the word hydrocephalus, they may think primarily of infants or children. But one form of hydrocephalus—idiopathic normal pressure hydrocephalus (iNPH)—is predominantly a condition of older adults. The available population-based research suggests that hydrocephalus becomes substantially more common with advancing age, particularly after 80.

The important point is that “hydrocephalus” is not one single condition. The studies discussed here specifically examine idiopathic normal pressure hydrocephalus, or iNPH. It is characterized by enlargement of the brain's ventricles and a clinical pattern that can include problems with walking, cognition, and bladder control. Because some of these symptoms can resemble ordinary aging, dementia, or other neurological disorders, iNPH can go unrecognized.

The two principal studies provide a particularly useful picture because one examined adults beginning at age 70, while the newer Shanghai study examined adults beginning at age 60 and provided additional age-specific data.

What happens after age 70?

The 2014 Swedish population-based study by Jaraj and colleagues examined 1,238 people aged 70 and older. The researchers used both clinical examinations and brain CT imaging and diagnosed probable iNPH according to established American-European guidelines.

The results were strikingly different between people in their 70s and those aged 80 and older.

Among people aged 70–79, the prevalence of probable iNPH was only 0.2%.

Among people aged 80 and older, however, the prevalence was 5.9%.

That represents an enormous increase with age. The researchers found that iNPH was strongly associated with being over 80, reporting an odds ratio of 35.5 compared with the younger age group.

In other words, based on this study, iNPH was relatively uncommon among people in their 70s but considerably more common among people in their 80s and beyond.

The newer Shanghai study adds an important age gradient

The 2025 Shanghai population-based observational study provides even more detailed information about how prevalence changes across older age groups.

Researchers examined 1,491 adults aged 60 and older and combined clinical information with brain imaging. Depending on the imaging criteria used, the overall prevalence of suboptimal probable iNPH was approximately 2.6%–3.1%.

But the overall number conceals an important fact: prevalence increased dramatically with age.

Using the study's DESH score ≥6 criterion, the observed prevalence was:

The progression is much more informative than the overall average.

The prevalence was less than 1% among people in their 70s, increased to more than 4% among people in their 80s, and exceeded 8% among people in their 90s.

This means that age 80 appears to be a particularly important dividing point in the available population-based evidence.

What about everyone over 70?

The Shanghai researchers also calculated prevalence for progressively older populations.

Using their primary DESH criterion, the estimated prevalence was:

• Age 70+: 3.30%
• Age 75+: 3.79%
• Age 80+: 4.82%
• Age 85+: 6.81%
• Age 90+: 7.99%

Using the alternative Radscale ≥7 criterion, the corresponding estimates were lower:

• Age 70+: 2.66%
• Age 75+: 3.03%
• Age 80+: 3.74%
• Age 85+: 4.88%
• Age 90+: 5.09%

These numbers demonstrate why it is difficult to give one definitive percentage for hydrocephalus in older adults. The prevalence depends partly on exactly how researchers define and identify iNPH.

Nevertheless, the age trend is remarkably consistent: prevalence increases as people get older.

The 70s versus the 80s is the critical distinction

If the question is specifically, “How common is hydrocephalus in people over 70?” the answer depends on what “over 70” means.

For people in their 70s, the evidence suggests that probable iNPH is uncommon—approximately 0.2% in the Swedish study and 0.75% in the Shanghai study using the latter study's stricter DESH criterion.

For people in their 80s, however, the numbers change substantially.

The Swedish study found 5.9% prevalence among people aged 80 and older. The Shanghai study found 4.15% among people aged 80–89 using its DESH ≥6 criterion. Another population-based study found an iNPH prevalence of 8.9% among people aged 80 and older, compared with 2.1% among those aged 65–79.

So a reasonable conclusion from these studies is that iNPH is not particularly common at 70–79, but becomes substantially more common beginning around age 80.

Why the numbers matter

One particularly important finding from the Swedish study was that only two of the people identified with iNPH had previously been treated for it. The authors therefore concluded that the number of people with iNPH was probably considerably higher than the number receiving treatment.

The study also found that 4.5% of participants had hydrocephalic ventricular enlargement on CT consistent with NPH. Other imaging abnormalities were even more common: 20.7% had an Evans Index greater than 0.3. Importantly, these imaging findings do not mean that everyone with the imaging abnormality has symptomatic iNPH.

That distinction is critical.

An enlarged ventricle on a brain scan is not synonymous with clinically significant hydrocephalus. The diagnosis of iNPH involves a combination of imaging and clinical findings.

Why hydrocephalus can be overlooked in older adults

The symptoms of iNPH can overlap with conditions commonly attributed to aging. Walking difficulties, cognitive changes, and bladder problems are all relatively common among older adults for many different reasons.

That makes iNPH particularly important to recognize because simply labeling these changes as “normal aging” could potentially miss an underlying neurological disorder.

The Swedish researchers specifically described iNPH as underdiagnosed and noted that it is one of the potentially reversible causes of cognitive impairment in older adults.

The newer Shanghai research likewise emphasizes the importance of considering iNPH when older adults present with cognitive impairment and gait disturbances.

So, how common is hydrocephalus after 70?

The best answer from these studies is that prevalence rises sharply with age.

For someone in their 70s, probable idiopathic normal pressure hydrocephalus appears to affect roughly 0.2%–0.8% of the population in the cited population-based studies.

After age 80, estimates generally rise into the several-percent range.

By age 90, the Shanghai study estimated approximately 8% prevalence using its DESH criterion, while its alternative diagnostic criterion produced an estimate of approximately 5%.

Thus, the phrase “hydrocephalus in older adults” can be misleading if it implies that the condition is equally common throughout the entire older population. The research instead shows a pronounced age relationship:

70s → relatively uncommon
80s → considerably more common
90s → common enough to affect roughly 1 in 12 to 1 in 20 people, depending on diagnostic criteria

The evidence therefore supports paying particular attention to iNPH in adults over 80, rather than treating hydrocephalus as primarily a pediatric condition.

One final caution is important: these percentages refer specifically to idiopathic normal pressure hydrocephalus or probable iNPH—not every form of hydrocephalus. They also come from different populations and diagnostic methods, so they should not be interpreted as a single universal prevalence rate for every older adult population.

Studies

Jaraj D, Rabiei K, Marlow T, Jensen C, Skoog I, Wikkelsø C. “Prevalence of idiopathic normal-pressure hydrocephalus.” Neurology. 2014;82(16):1449–1454.

Fang X, Xu X, Liu C, et al. “Prevalence of idiopathic normal pressure hydrocephalus in older adult population in Shanghai, China: A population-based observational study.” Alzheimer’s & Dementia. 2025;21(2):e14525.

2025 Shanghai study — full text

2014 Swedish study — PubMed

More Health Articles