Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) within the ventricles of the brain, causing them to enlarge and increasing pressure within the skull. It can affect people of all ages — from newborns to the elderly — and results from an imbalance between the production, circulation, and absorption of CSF. When untreated, progressive ventricular enlargement compresses the surrounding brain tissue and causes irreversible neurological damage.
Hydrocephalus can develop as a consequence of several other brain conditions covered at First Look MRI. Subarachnoid hemorrhage from a ruptured brain aneurysm, bleeding from an AVM, or subdural hematoma can all impair CSF absorption and trigger communicating hydrocephalus. Brain tumors are a leading cause of obstructive hydrocephalus by blocking CSF pathways. Normal pressure hydrocephalus in older adults is frequently mistaken for Alzheimer's disease or dementia — and unlike dementia, it is surgically treatable.
Causes
Obstruction of CSF flow (obstructive hydrocephalus)
The most common mechanism is a blockage that prevents CSF from flowing through the ventricular system. Brain tumors, cysts, and arachnoid cysts can physically obstruct CSF pathways. Aqueductal stenosis — narrowing of the cerebral aqueduct connecting the third and fourth ventricles — is a common congenital cause. Blood clots from intraventricular hemorrhage can acutely obstruct CSF flow, causing rapid ventricular enlargement and herniation risk.
Impaired CSF absorption and other causes
Communicating hydrocephalus occurs when CSF flow within the ventricles is patent but reabsorption at the arachnoid granulations is impaired. Common causes include meningitis (which scars the arachnoid granulations), subarachnoid hemorrhage from ruptured aneurysm, and head trauma. Normal pressure hydrocephalus (NPH) is a specific form affecting older adults in which ventricles enlarge progressively without a clearly elevated opening pressure — possibly from subtle reabsorption failure. Congenital hydrocephalus may result from genetic conditions, intrauterine infections (TORCH), or neural tube defects such as spina bifida with Chiari type II malformation.
Symptoms
Symptoms vary significantly by age and acuity of onset:
- Infants: Enlarging head circumference (crossing percentile lines), bulging anterior fontanelle, prominent scalp veins, downward deviation of the eyes ("sunset sign"), irritability, and poor feeding.
- Older children and adults (acute/subacute): Headache (worse in the morning and with Valsalva maneuver), nausea and vomiting, blurred or double vision, papilledema on fundoscopy, and progressive cognitive decline. Acute obstructive hydrocephalus is a neurological emergency.
- Normal pressure hydrocephalus (NPH) in older adults: The classic Hakim's triad — magnetic gait (shuffling, broad-based, difficulty initiating steps), urinary incontinence, and cognitive impairment. This triad is critically important to recognize because NPH is one of the few reversible causes of dementia-like symptoms. It is frequently misdiagnosed as Alzheimer's disease or Parkinson's disease.
Diagnosis
MRI is the preferred imaging modality, providing comprehensive evaluation of ventricular size, morphology, and the underlying cause. Key MRI findings in hydrocephalus include disproportionate ventricular enlargement (particularly the temporal horns), periventricular transependymal CSF signal — a sign of active CSF leakage under pressure into the surrounding white matter — and the specific cause of obstruction. In NPH, MRI shows a characteristic pattern of enlarged ventricles disproportionate to sulcal atrophy, and CSF flow voids through the aqueduct on phase-contrast sequences confirm preserved aqueductal flow.
CT scan is used in urgent settings to rapidly assess ventricular size and exclude acute hemorrhage. For NPH diagnosis and surgical planning, the large-volume lumbar puncture tap test is a critical clinical tool — removal of 30–50mL of CSF with neurological assessment before and after (gait speed, cognitive testing) identifies patients likely to respond to shunting. Patients with marked gait improvement after the tap test have the best surgical outcomes. Intracranial pressure monitoring over 24–48 hours may be used in ambiguous cases to document pressure waves consistent with NPH.
Classification
Hydrocephalus is classified by the mechanism of CSF accumulation:
- Obstructive (Non-communicating): CSF flow blocked within the ventricular system. Often acute and requiring urgent treatment. Caused by tumors, aqueductal stenosis, or intraventricular hemorrhage.
- Communicating: Impaired CSF reabsorption with patent ventricular pathways. Causes include post-hemorrhagic, post-meningitic, and post-traumatic. Typically more subacute in onset.
- Normal Pressure Hydrocephalus (NPH): Ventricular enlargement without clearly elevated pressure — a surgically treatable cause of gait disturbance, incontinence, and cognitive decline in older adults. Frequently misdiagnosed as dementia.
- Congenital: Present from birth — often diagnosed prenatally on ultrasound or in the newborn period. Associated with neural tube defects, genetic syndromes, or intrauterine infection.
Treatments
Treatment is surgical in the majority of symptomatic cases and aims to restore normal CSF dynamics, relieve intracranial pressure, and prevent further neurological injury. The underlying cause is treated simultaneously when possible — for example, resecting a tumor causing obstructive hydrocephalus.
Ventriculoperitoneal (VP) shunt:
The most widely used treatment — a catheter placed in the lateral ventricle drains excess CSF through a subcutaneous valve and tubing into the peritoneal cavity, where it is absorbed. Programmable shunt valves allow non-invasive adjustment of the drainage pressure after implantation. VP shunts are highly effective but require lifelong monitoring for mechanical failure, blockage, and infection — the most common complications. Shunt malfunction typically presents with recurrence of hydrocephalus symptoms and requires urgent imaging evaluation.
Endoscopic third ventriculostomy (ETV):
A minimally invasive endoscopic procedure that creates a new opening in the floor of the third ventricle, allowing CSF to bypass an obstruction and flow directly into the basal cisterns. ETV avoids the need for a permanent indwelling shunt and carries no long-term shunt malfunction risk. It is most effective in older children and adults with aqueductal stenosis or other clearly defined obstructive hydrocephalus, with success rates of 70–90% in optimal candidates. It is less effective in infants and in communicating hydrocephalus.
Treatment of underlying cause:
When hydrocephalus results from a surgically accessible brain tumor, cyst, or arachnoid cyst, resection of the obstructing lesion may resolve hydrocephalus without requiring a permanent shunt. Meningitis-related hydrocephalus is treated with appropriate antimicrobial therapy alongside CSF diversion.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Brain MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.