Causes & Risk Factors

Subarachnoid hemorrhage (SAH)

Subarachnoid hemorrhage is bleeding into the space around the brain, which can cause hydrocephalus by impairing CSF flow and absorption.

In short: Subarachnoid hemorrhage (SAH)

It is bleeding into the subarachnoid space around the brain.
Blood can impair CSF flow and absorption.
It can cause acute or later (communicating) hydrocephalus.
It is an important cause of acquired hydrocephalus in adults.

What it is

Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space, the CSF-filled space surrounding the brain. It can result from a ruptured aneurysm, trauma, or other causes, and is an important cause of acquired hydrocephalus, especially in adults.

Understanding Subarachnoid hemorrhage (SAH)

Blood in the subarachnoid space can impair CSF flow over the brain and clog the absorption sites (arachnoid granulations), causing hydrocephalus. This can occur acutely (soon after the bleed, sometimes requiring an emergency external ventricular drain) or develop later as a communicating hydrocephalus that may need a shunt. Hydrocephalus is a recognized complication after subarachnoid hemorrhage, and patients are monitored for it during recovery. Both the acute and delayed forms are important to recognize and treat.

Why it matters

Understanding subarachnoid hemorrhage as a cause helps families see why bleeding around the brain can lead to hydrocephalus — both acutely and later — and why monitoring for hydrocephalus is part of recovery after such a bleed.

Common questions

What is subarachnoid hemorrhage?

Bleeding into the space around the brain.

How does it cause hydrocephalus?

Blood impairs CSF flow and absorption.

When can hydrocephalus occur?

Acutely or later, as a communicating form.

Bottom line

Subarachnoid hemorrhage is bleeding around the brain that can cause acute or delayed hydrocephalus by impairing CSF flow and absorption.

More terms in Causes & Risk Factors

Brain tumorA brain tumor can cause hydrocephalus by blocking the flow of cerebrospinal fluid through the ventricular system.
Posterior fossa tumorA posterior fossa tumor is a tumor at the back of the brain that commonly causes hydrocephalus by blocking the fourth ventricle.
Colloid cystA colloid cyst is a benign cyst that can block CSF flow at the foramen of Monro, causing hydrocephalus.
Arachnoid cystAn arachnoid cyst is a fluid-filled sac related to the arachnoid membrane that can sometimes obstruct CSF flow and cause hydrocephalus.
Chiari I malformationChiari I malformation is a condition where the lower cerebellum extends below the skull, sometimes affecting CSF flow.

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