Normal pressure hydrocephalus (NPH)

What it means

Hydrocephalus means an excess buildup of cerebrospinal fluid within the brain's ventricles, the natural fluid-filled cavities at its center. In normal pressure hydrocephalus, these ventricles enlarge over time, yet when the fluid pressure is measured directly — usually with a lumbar puncture — it comes back in the normal range, which is why the name sounds contradictory. The condition is thought to arise from a subtle problem with how cerebrospinal fluid is absorbed back into the bloodstream, allowing gradual ventricular enlargement without an obvious spike in pressure.

Why it appears on a CT or MRI report

NPH is usually first suspected because of a person's symptoms rather than an incidental scan finding: a slow, shuffling, wide-based gait; increasing forgetfulness or slowed thinking; and new difficulty controlling the bladder. A CT or MRI ordered to investigate these symptoms in someone over 60 will often show ventriculomegaly — enlarged ventricles — that looks disproportionately large compared to the amount of shrinkage (atrophy) elsewhere on the surface of the brain. Radiologists look for supporting features such as a narrowed angle between the top of the ventricles (the callosal angle) and crowding of the fluid spaces at the top of the brain alongside widened spaces lower down, a pattern sometimes summarized by the term DESH.

What it usually means

The classic combination of gait trouble, memory or thinking changes, and urinary urgency is sometimes called Hakim's triad, though not everyone has all three symptoms, and gait trouble is typically the earliest and most prominent. NPH can be primary, meaning no clear cause is found, or secondary to a prior brain bleed, meningitis, or head injury that disrupted normal fluid drainage. It is important because it is one of the few causes of dementia-like symptoms that can substantially improve with treatment, unlike most degenerative causes of cognitive decline.

When to follow up

If NPH is suspected, the usual next step is a referral to a neurologist or neurosurgeon, who may recommend a high-volume lumbar puncture or a period of temporary external drainage to see whether removing fluid measurably improves your gait and thinking — a positive response makes a good outcome from permanent treatment more likely. Treatment usually involves surgically placing a shunt, a thin tube that continuously drains excess fluid from the ventricles to another part of the body, and many people see meaningful improvement in walking within weeks of a working shunt, with memory and bladder symptoms sometimes improving more slowly or partially.

A plain-language way to picture it

Think of the ventricles as a sponge sitting inside the skull, kept a certain size by the balance of fluid flowing in and draining out. In NPH, drainage slows just enough that the sponge gradually swells over months or years, pressing gently outward on the surrounding brain tissue and mildly compressing the nerve pathways that control walking, thinking, and bladder control — even though the fluid pressure itself never spikes high enough to trigger the alarm bells of classic hydrocephalus. Draining some of that excess fluid, exactly like squeezing a swollen sponge, is often enough to let those pathways work normally again.