This case demonstrates the plain film and MRI appearance of a histopathologically proven intraosseous lipoma within the right acetabulum, ischial tuberosity and inferior pubic ramus. Based on Milgram and co workers' proposed categories, this is a stage 3 heterogeneous lesion containing fluid equivalent cavities with ring-like enhancement on contrast administration and solid fatty components with septa. There is however no calcification or ossification. The broad differential diagnosis based on the plain film appearance includes a unicameral bone cyst in an adult patient, fibrous dysplasia, Langerhans cell histiocytosis, giant cell tumor of the hip/pelvis, and non-ossifying fibroma, and an aneurysmal bone cyst.

MRI dramatically reduces this differential diagnosis to fat-containing lesions.

Case courtesy of Dr Amaresh I. Ranchod