Slide 1: Which patient has pathologic ventriculomegaly? Two CT scans of the head are shown.

Slide 2: CT scan on the left: Chronic ventriculomegaly. The third ventricle is enlarged but the walls are fairly parallel. Here the ventricles are enlarged, but the CSF-filled grooves along the brain surface, the sulci, are also very prominent.

CT scan on the right: Pathologic ventriculomegaly. There is blurring of the parenchyma along the walls of the ventricles, which signifies fluid, periventricular edema. The walls of the third ventricle are bowed outwards (blue arc). The ventricles are enlarged, but the sulci are “pressed out.”

Slide 3: Hydrocephalus (pathologic) versus chronic ventriculomegaly.

Here is a normal brain. Notice the balance between the size of the ventricles and the width of the CSF-containing grooves in brain parenchyma, the sulci.

In hydrocephalus, the ventricles are very dilated and often have convex borders from bring “overfilled.” The sulci are disproportionately smaller, as they are being squeezed out, or “effaced.” There is also edema along the ventricles. Think of it as intra-ventricular CSF under high pressure leaking through the ventricular walls.

This brain has undergone chronic volume loss. The ventricles appear large from compensatory ex vacuo dilation from the volume loss. Notice here that the sulci are also proportionately enlarged, as the parenchyma takes up less room inside the skill (see our prior post on cerebral atrophy).

Slide 4: Overview of cerebrospinal fluid (CSF) flow. Graphic of brain ventricles depicting the flow of CSF. Recall that CSF is produced in the choroid plexus (CP) in the ventricles. Starting in the lateral ventricles (LV), it flows into the third ventricle and through the thin cerebral aqueduct into the fourth ventricle. From there, it exists the ventricular system and fills the inside of the skull. It is resorbed into the venous system through the arachnoid granulations.

Slide 5: Categories of pathologic hydrocephalus. When considering the etiology and appropriate management for pathologic hydrocephalus, consider if the hydrocephalus is communicating or non-communicating to evaluate the underlying cause. Lesions near this part (cerebral aqueduct) of the CSF system result in non-communicating hydrocephalus; which results in ventriculomegaly upstream from the area of obstruction. Lesions here (arachnoid granulations) cause communicating hydrocephalus which results in enlargement of all ventricles.

Slide 6: Categories of pathologic hydrocephalus: differential diagnosis. At last, by tying together radiographic findings with anatomy and physiology you locate the level of the lesion, thus allowing you to narrow your clinical differential diagnosis.

Hydrocephalus type. Non-communicating. Ventricles upstream of obstruction will be enlarged. Pathophysiology. Ventricular flow is obstructed. Examples. Tumor compressing cerebral aqueduct. Intra-ventricular blood products clogging flow.

Hydrocephalus type. Communicating. All ventricles will be enlarged. Pathophysiology. Overproduction or under-resorption of CSF. Examples. Overproduction: choroid plexus papilloma. Under-resorption: damage to arachnoid granulations (meningitis, radiation).