Ventriculomegaly is NOT Characteristic of Pseudotumor Cerebri
Ventricle size in idiopathic intracranial hypertension (pseudotumor cerebri) is typically normal, and many reports consider the ventricles to be slit-like rather than enlarged. 1
Key Neuroimaging Features
The absence of ventriculomegaly is a defining characteristic that distinguishes pseudotumor cerebri from obstructive hydrocephalus:
- Normal or small ventricles are expected on imaging, with many cases showing slit-like ventricles due to the elevated intracranial pressure compressing the ventricular system 1
- Normal brain parenchyma without hydrocephalus is a diagnostic requirement for pseudotumor cerebri 2, 3
- The diagnosis specifically requires the absence of ventriculomegaly, mass lesion, or structural abnormality 4, 5
Why Ventricles Don't Dilate in Pseudotumor Cerebri
This is a critical distinction from obstructive hydrocephalus, despite both conditions involving elevated intracranial pressure:
- In pseudotumor cerebri, venous hypertension affects smooth blood flow but does not impair the pulsatile flow dynamics that would trigger compensatory ventricular dilation 6
- The CSF spaces remain patent and the cerebral windkessel mechanism remains effective, obviating the need for adaptive ventriculomegaly 6
- In contrast, obstructive hydrocephalus causes loss of CSF pathway volume and windkessel impairment, leading to compensatory ventricular enlargement 6
Typical Neuroimaging Findings Instead Include
When evaluating for pseudotumor cerebri, look for these secondary signs of elevated intracranial pressure rather than ventriculomegaly:
- Empty or partially empty sella (decreased pituitary height) 1, 2
- Posterior globe flattening (56% sensitivity, 100% specificity) 2
- Enlarged optic nerve sheaths (perioptic subarachnoid space dilatation) 1, 2
- Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 2
- Intraocular protrusion of the optic nerve head (40% sensitivity, 100% specificity) 2
- Transverse sinus stenosis on MR venography 2
Clinical Pitfall to Avoid
Do not exclude pseudotumor cerebri based on normal or small ventricle size—this is actually the expected finding. If ventriculomegaly is present, you must reconsider the diagnosis and evaluate for obstructive hydrocephalus, mass lesion, or other causes of elevated intracranial pressure 1, 7. The presence of ventriculomegaly with elevated intracranial pressure suggests a fundamentally different pathophysiologic process than pseudotumor cerebri 6, 5.