Parosteal lipoma

Case contributed by Andrew Lawson
Diagnosis almost certain


Swelling over anterior thigh.

Patient Data

Age: 35 years
Gender: Female

Soft tissue ossification posterior to the mid to distal femoral diaphysis, which appears to be continuous with the bone. No periosteal reaction.  


Predominantly fatty lesion with parosteal ossifications.


A well-circumscribed, predominantly fat-containing lesion, arises within the muscle belly of vastus intermedius, measuring approximately 164 x 41 mm. The lesion originates at the level of the distal third of the femur and extends inferiorly, contained within the vastus, towards and into the suprapatellar recess of the knee. At the superior border, it breaches the intermuscular fascial plain and extends for a short distance into the lateral head of the biceps femoris muscle. No periosteal reaction is elicited along the cortical margin of the femur.

There are 2 discrete regions of focal ossification. The larger lesion lies posterior to the femur along the proximal margin of the fatty component and measures approximately 20 mm in diameter. A second intra-lesional focus is visible in the anterior component and measures approximately 5 mm. At the level of the origin of the quadriceps tendon, the vastus intermedius myotendinous junction is completely atrophied. The fat component demonstrates complete fat saturation and no contrast enhancement. No associated solid component. No bone marrow edema or neurovascular invasion.

Case Discussion

Primary parosteal fat-containing lesion within the mid-thigh within vastus intermedius, consistent with parosteal lipoma. The osseous component is mature and possibly from prior trauma. A small tongue of fat passes through septum into the origin of the short head of biceps femoris.

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