Multimodality imaging features of parosteal lipomas

Objective To examine the multimodality imaging characteristics of parosteal lipomas. Materials and methods With IRB approval, our institutional imaging database and medical record were retrospectively reviewed from 1990–2020 for cases of pathologically-proven and/or imaging diagnosed parosteal lipomas. Results There were 22 patients (12 males, 10 females) with a mean age of 57.1 ± 12.7 years (range 31–80 years). 11/22 cases (50%) were pathologically-confirmed on biopsy or surgical resection and 11/22 (50%) had imaging features compatible with parosteal lipoma. Lesions occurred most commonly along the femur (8/22, 36%), followed by the forearm (3/22, 14%). All cases demonstrated a juxtacortical fatty mass containing an osseous excrescence that was firmly attached to the cortical surface. The osseous excrescences were characterized as pedunculated in 16/22 (73%) and sessile in 6/22 (27%). The average largest dimension of the osseus excrescences was 2.4 ± 1.6 cm (range 0.8–6.1 cm) and the lipomatous portions 7.8 ± 3.8 cm (range 2.0–19.5 cm). The excrescences contained mature bone in 12/22 (55%) cases and a mixture of mature bone and radiating bone spicules in 10/22 (45%). There were non-lipomatous elements in the fatty portion of the mass in 13/22 (59%) of cases. Most cases (19/22, 85%) had cortical thickening/periostitis near the base of the osseous stalk. Two patients had a bone scan that demonstrated uptake in the osseous excrescence, and two patients had an FDG PET/CT that demonstrated no uptake. Conclusion Parosteal lipomas are a rare benign lipomatous tumor with pathognomonic multimodality imaging features that may obviate the need for biopsy.