From the Research
To check for third ventricle dilation on CT, look for widening of the third ventricle beyond its normal width of 2-7 mm, as a width exceeding 7 mm in adults generally indicates dilation, according to the most recent and highest quality study available 1. When evaluating third ventricle dilation, it is essential to consider the following key points:
- Measure the width at the mid-portion of the third ventricle on axial CT images, comparing it to age-appropriate normal values.
- The third ventricle appears as a slit-like CSF-filled space between the thalami on axial images.
- Assess other ventricular structures for proportional enlargement, as isolated third ventricle dilation is uncommon.
- Look for associated findings such as periventricular hypodensity, effacement of sulci, or other signs of increased intracranial pressure. Some common causes of third ventricle dilation include:
- Obstructive hydrocephalus from masses near the fourth ventricle or aqueduct of Sylvius
- Normal pressure hydrocephalus
- Cerebral atrophy The pattern of ventricular enlargement helps distinguish between obstructive hydrocephalus (disproportionate dilation) and cerebral atrophy (proportionate enlargement with prominent sulci) 1. It is also important to note that third ventricle dilation can be associated with poor prognosis, as seen in patients with spontaneous intracerebral hemorrhage 2. In addition, the use of 3D-construcive inference in steady state (3D CISS) MRI can provide accurate visualization of the third ventricle and help predict the technical challenge of puncturing the third ventricle floor in patients undergoing endoscopic third ventriculostomy (ETV) 3.