Obstructing isodense colloid cyst

Q: What is the main emergency finding? show answer

A: There is hydrocephalus of the lateral ventricles. (Note - don't be fooled looking at the axials alone which suggests third ventricle enlargement. This is just expansion of the lateral ventricle bodies, with actual effacement of the third ventricle as you can see in the other planes).

Q: With this finding - where should you concentrate on looking at? show answer

A: For lateral ventricle hydrocephalus, you should closely inspect the foramen of Monro for an obstructing lesion.

Q: What does this patient now need? show answer

A: If you have answered MRI, think about what is happening to the patient here. They are in a catastrophic state which will only get worse without decompression. You could wait for the pathology report instead of MRI at this rate! Ventricular access and drainage is required on an emergency neurosurgical list (given the findings and symptoms).

Q: Following decompression of the lateral ventricles, what does this MRI show? show answer

A: There is a colloid cyst in the roof of the third ventricle.

Q: Does the signal of the cyst change your opinion? show answer

A: It shouldn't too much - this is usually a diagnosis by virtue of anatomical location. T1w and T2w appearances can be variable, and when there is low T2w these typically completely suppress on FLAIR making them difficult to identify. The posterior low T2w/high T1w component in this case is likely the "motor oil" appearance typically used to describe cyst content.