dilated

Dilated is an adjective used to describe something that has become enlarged or widened beyond its normal size. The word derives from the Latin dilatatus, dilatare, meaning to widen. In medical and biological contexts, dilation (or dilatation) refers to an increase in the diameter of a hollow structure or vessel.

In anatomy and physiology, dilation can affect any tubular or luminal structure. Common examples include dilated pupils in low light or during sympathetic activation, and pharmacologically induced mydriasis used in eye examinations. Radiological and clinical descriptions often note dilated ducts, vessels, or chambers, indicating that the lumen is wider than typical.

Specific medical conditions illustrate functional or pathologic dilation. Dilated cardiomyopathy is a disease in which the heart’s left ventricle enlarges and its pumping ability weakens. In the biliary and urinary systems, imaging may reveal dilated bile ducts or ureters, which can signal obstruction or disease. Dilation can be physiological, as in normal pupil response, or pathological, as when a structure enlarges due to injury, inflammation, or disease.

Usage notes distinguish dilation or dilatation as the noun form, and dilated as the past participle or adjective. American English typically uses dilation, while British English often uses dilatation. Varieties of English accept both spellings; the context usually clarifies whether one is describing the process (dilation) or the resulting state (dilated).