This case of a colloid cyst demonstrating thin peripheral calcification and thin enhancement with associated hydrocehpalus, is a little unusual, in that typically these cysts are more hyperdense on pre-contrast imaging. The presence of such florid hydrocephalus is also unusual as the majority of these lesions are found incidentally. Typical of lesions which cause hydrocephalus, is the larger size. 

This patient went on to have emergency surgery.