"Dilation should be used for situations in which there has been an active process by which a structure is enlarged, e.g. dilation of pupils by an ophthalmologist."
"Dilatation when the stretching has occurred pathologically, e.g. dilatation of the bowel proximal to an obstruction."
"Dilation and dilatation are commonly used in radiology, and medicine more generally. Both terms refer to the expansion of a 'hollow' anatomical or pathological structure, including vessels, cardiac chambers, cerebral ventricles, urinary tract, cysts, and also prostheses, e.g. stents and angioplasty balloons."