Why is IV contrast used in cases like this?
This decision is usually made by the radiologists unless there is a clear history of malignancy for example. It is used for different reasons in body imaging, and in neuroimaging can be used to examine the arterial supply (angiogram, CTA), venous drainage (venogram, CTV) or differences in the parenchyma. In this case, the mass in the left cerebellum enhances (i.e. is denser) than the surrounding tissues, and denser than on the non-contrast scan. This suggests a richer blood supply and is found in a number of conditions which can be better investigated by MRI.
How are different types of hydrocephalus described?
This is of interest, but beyond undergraduate levels. Hydrocephalus is secondary to a disturbance in CSF flow - either due to blockges or impaired absorption. If there is no obstruction from the ventricles this is called "communicating hydrocephalus". This can occur in conditions like subarachnoid haemorrhage or meningitis with disturbed absorption, or other conditions like normal pressure hydrocephalus. In this case, this is "obstructive hydrocephalus" where the flow of CSF is structurally disturbed.
Large hyperdense and enhancing left cerebellar mass. with local oedema. Left cerebellar encephalocele into the occipital inner table.
Obstructive hydrocephalus with ventricular enlargement and periventricular low density (compatible with CSF shift).
No supratentorial masses or acute ischaemic areas. Right frontal encephalomalacia (presumed prior infarct). Normal calvarium and skull base.
For MR study.