Tell hydrocephalus from atrophy (dilated temporal horns and a small, sharp callosal angle versus widened sulci), find the level of obstruction by which ventricles are large, and look for signs that it is acute — transependymal oedema and effaced sulci.
Orient first
- Obstructive (non-communicating) hydrocephalus dilates the ventricles above a block — foramen of Monro, aqueduct, fourth ventricle outlets.
- Communicating hydrocephalus dilates all four ventricles (after haemorrhage or meningitis, or normal-pressure hydrocephalus).
- Atrophy enlarges ventricles AND sulci in proportion; hydrocephalus enlarges ventricles out of proportion, rounds the frontal horns and dilates the temporal horns early.
Acquire the study
- Non-contrast CT head with sagittal and coronal reformats.
The manoeuvre
- Temporal horns: dilated temporal horns are one of the earliest signs.
- Which ventricles are large: lateral and third only (aqueduct), all four (communicating or outlet obstruction).
- Periventricular low attenuation around the frontal horns (transependymal flow) and effaced sulci — acute.
- Coronal reformat: callosal angle at the posterior commissure (acute angle in normal-pressure hydrocephalus).
- The cause: a mass, haemorrhage in the ventricles or cisterns, a colloid cyst at the foramen of Monro.
What confirms it
- Ventricular enlargement out of proportion to the sulci, with a level of obstruction or a communicating pattern named.
What licenses you to exclude it
- Normal ventricular size for age excludes hydrocephalus at the time of the study.
The classic misread
- Calling ex-vacuo ventricular enlargement from atrophy hydrocephalus.