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Lipoma of Bone

Summary

Lipoma of bone (intra-osseous lipoma) is a rare benign bone tumor, similar to a soft tissue lipoma, but occurring within bone. The most common location is the calcaneus (heel bone).

This tumor presents in young to middle-aged adults, in their 30s, 40s and 50s.
Lipoma of bone is typically asymptomatic.
On x-ray, the lesion is well defined, lytic, and may have a central area of calcification.
For asymptomatic lesions, no treatment is necessary. Symptomatic lesions may be treated by curettage.
Complete Information on this Tumor
Introduction and Definition: 

This is a rare benign bone tumor. If present in adults, often as an incidental finding, and is rarely symptomatic. The most common site is the calcaneus, followed by the femur. This lesion has also been found in multiple bones, including the tibia, fibula ulna, skull.

Incidence and Demographics: 
This is a rare benign bone tumor. The true incidence is unknown. It is thought to represent 0.1% of bone tumors, but since these tumors do not create symptoms, most may be missed. The mean age at presentation is 43 years, males and females are equally affected.
Symptoms and Presentation: 

Most of these tumors are not symptomatic and are discovered as an incidental lesion. Some patients may present with pain, and pathological fracture can occur.

X-Ray Appearance and Advanced Imaging Findings: 
On x-rays, the lesion is well defined, has a latent, nonaggressive appearance, a narrow zone of transition, and typically forms a single rounded or roughly ovoid lytic lesion, rather than a loculated "soap bubble" appearance such as might be seen in aneurysmal bone cysts, or nonossifiying fibroma. In the calcaneus, lipoma of bone can be difficult to distinguish from unicameral bone cyst. Both occupy the same region of the calcaneus. Lipoma of bone is distinguished principally by the central calcific density and by MRI. The lesion may have a sclerotic rim, has a lucent lytic appearance, and may have central calcification. The calcification is amorphous and does not have any detectable patterns such as rings and arcs or popcorn (chondroid pattern) or ground glass ( fibrous dysplasia pattern). The calcification is typically relatively dense, central, and amorphous.
Laboratory Findings: 
No laboratory findings are useful in diagnosis
Differential Diagnosis: 
unicameral bone cyst, non-ossifying fibroma, aneurysmal bone cyst, chondrosarcoma, fibrous dysplasia
Preferred Biopsy Technique for this Tumor: 
open
Histopathology findings: 
Grossly, the tumor may be yellow or tan fatty material, soft or semi-liquid, with a gritty texture. Squeezing the tissue will cause oil droplets to be produced. There may be oily liquid within the tumor cavity. The tumor is comprised of mature fat cells and varying amounts of fibrous and vascular tissue.
Treatment Options for this Tumor: 
Many patients can be treated with observation and follow-up only. Since the lesion can be diagnosed with certainty based on imaging studies, biopsy is not always necessary. Curettage and bone grafting should be reserved for large, worrisome, or symptomatic lesions, or lesions where there has been documented radiographic change, or definite increase in symptomatology. Lesions in weight-bearing bones that require treatment may require additional bone stabilization procedures, such as internal fixation, or intramedullary rodding.
Preferred Margin for this Tumor: 
intra-lesional
Outcomes of Treatment and Prognosis: 
This lesion is not expected to recur following curettage. However, curettage does not always result in complete relief of symptoms related to the tumor.
Special and Unusual Features: 
Based on a large case series (Milgram), lipoma of bone has been divided into three stages, according to the histopathology findings, which also correspond with the radiologic findings. Stage I lesions are radiolucent with fine trabecular bone. Stage II lesions have partial fat necrosis and some fat calcification. Stage III lesions have a reactive ossified rim and more central calcification and ossification. Stage III lesions show more extensive necrosis on histologic examination. It is not clear whether this staging system has any value for either diagnosis, treatment, or prognosis.
Suggested Reading and Reference: 
Milgram, CORR 1988:231 277-302
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