Parosteal lipomas are rare benign fat containing tumours closely related to the periosteum of bone.
Parosteal lipomas are rare, making up just 0.3% of all lipomas. They typically occur in 40 to 60 year old patients.
Patients present with slowly enlarging, painless soft tissue mass closely related to bone. Another clinical manifestation is nerve palsy, the most commonly affected is the posterior interosseous nerve.
The tumor composed of mature adult fat similar to soft-tissue lipomas. There is often an osseous stalk with cortical thickening. It shows lobular growth with thin intervening septations. There is a lack of malignant potential.
The most common sites are the femoral, radial and humeral diaphysis. Cases have also been reported in the tibia, scapula, clavicle, ribs, pelvis, metacarpals, metatarsals, mandible and skull.
The major distinctive radiologic diagnostic feature is juxta-cortical fatty mass with variable septations and containing variable sizes of bony protuberances as well as adjacent cortical thickening.
- typically appears as a large, lucent mass
- diagnostic for fat density
- will also demonstrated lack of underlying medullary continuity (to differentiate from osteochondroma)
Will present as a T1/T2 hyperintense mass with loss of signal on fat suppression. MRI provides better contrast resolution for fibrovascular septa, which are seen as low-signal-intensity strands on T1-weighted images that become higher in signal intensity on long TR images (in particular fat suppression sequences).
MRI also allow for the best evaluation of adjacent nerve involvement and muscle atrophy.
Bone scintigraphy demonstrates increased radiotracer uptake limited to the site of the bony stalk.
Treatment and prognosis
Complete surgical resection may be performed, particularly in cases with nerve entrapment.
- 1. Murphey MD, Carroll JF, Flemming DJ et-al. From the archives of the AFIP: benign musculoskeletal lipomatous lesions. Radiographics. 2004;24 (5): 1433-66. Radiographics (full text) - doi:10.1148/rg.245045120 - Pubmed citation
- 2. Murphey MD, Johnson DL, Bhatia PS et-al. Parosteal lipoma: MR imaging characteristics. AJR Am J Roentgenol. 1994;162 (1): 105-10. doi:10.2214/ajr.162.1.8273646 - Pubmed citation