Orbital histiocytosis on computed tomography.

Computed tomography (CT) findings in two patients with orbital histiocytosis are described. The main features are (a) replacement of bone by soft tissue, which has an absorption value of approximately 40 Hounsfield units (HU) and is not contrast-medium enhanced; (b) bone expansion at the rim of the lesion; (c) a large intraosseous component and a small extraosseous part; and (d) absence of calcification or periosteal reaction.