A 30-year-old male patient presented with pain in right heel region for the past 3 months. He was referred for CT to evaluate a possible lytic lesion within calcaneum detected on plain radiography. However, the patient was not able to present he radiographs for documentation at the time of scan.
A relatively well-defined lytic lesion was seen involving the right calcaneum. On the bone window images this lesion showed a few partial bony septae/thickned trabeculae with suggestion of subtle hyperdense areas within. Mild bony expansion was also seen. Soft tissue window images revealed predominant attenuation similar to subcutaneous fat in the periphery of the lesion with central hyperdense/calcific areas confirming a diagnosis of an intraosseous lipoma with areas of fat necrosis. No pathological fractures were seen involving the lesion.
Intraosseous lipomas (IL) are rare lesions constituting about 0.1% of bone tumours. They are commonly located in the proximal femur and calcaneum but can occur in other locations including pelvic bones and ribs [1, 2]. Although these lesions may be detected incidentally, up to 66% of patient report pain. Expansile bony remodelling and ischaemic changes have been postulated as probable causes for pain [2].
Based on radiological and pathological features Milgram classified IL into three stages [3].
Stage 1 – composed entirely of viable fat cells.
Stage 2 – composed of viable fat cells with interspersed areas of fat necrosis and calcification.
Stage 3 – composed of a large proportion of necrotic fat, calcification and cystic transformation.
The imaging appearance of IL varies depending on the stage of the lesion. Stage 1 lesions appear as well-defined lytic lesions with or without mild expansion on radiography and may mimic other lesions. CT and MRI are equally effective in demonstrating fat content within the lesion. CT demonstrates an intramedullary lesion with attenuation values ranging from – 60 to – 100 HU similar to subcutaneous fat. Attenuation values are usually slightly lower than normal marrow fat due to presence of cellular elements in yellow marrow. MRI classically shows T1 hyperintense signal with signal suppression on fat saturation sequences. Like CT the T1 signal of IL is slightly higher than marrow due to cellular elements in yellow marrow. Thickened trabecular ridges may be seen within the periphery of the lesion and are well demonstrated on CT [1, 2].
A well-defined lytic lesion in calcaneum with central calcification is pathognomonic of stage 2 IL. Calcification within IL may, however, add to confusion in other bones. Stage 2 lesions show fat attenuation with internal hyperdense areas and calcification on CT. Ischaemic changes within the lesion are thought to cause fat necrosis which appear hyperdense and may undergo calcification. The hyperdense areas may be subtle and may not be visualised on plain radiography. CT is the best modality to visualise these subtle areas. On MRI these lesions shows fat signal with internal hypointense areas corresponding to fat necrosis/calcification. Stage 3 lesions show varying degrees of calcification and cystic degeneration giving a confusing appearance on radiography. Even though cystic areas may predominate, identification of a peripheral rim of fat on CT/MRI aids in diagnosis. IL usually does not require treatment, but curettage and bone grafting may be done for symptomatic lesions [1, 2].
Intraosseous lipoma within the right calcaneum (Milgram's stage 2).
This case involves a 30-year-old male patient complaining of right heel pain for 3 months. Based on the CT images, the following findings are noted:
Based on the above imaging findings, as well as the patient’s age and clinical symptoms, the following diagnoses or differential diagnoses are considered:
Taking into account the patient’s age, clinical symptoms (intermittent pain), and the CT findings of clear fat density with local calcification, the most likely diagnosis is:
If further confirmation of the pathological nature is required, MRI or biopsy may be considered. However, for typical imaging findings, clinical correlation often suffices for diagnostic judgment.
An intraosseous lipoma is typically a benign lesion. If the lesion is small and symptoms are mild, conservative observation is an option; for symptomatic cases or those with structural risks, surgical intervention can be considered.
Rehabilitation/Exercise Prescription Recommendations:
This report is based on the currently available imaging and information for reference only and does not replace an in-person clinical diagnosis or treatment recommendation. If you have any concerns or your symptoms worsen, please seek prompt medical attention and follow the advice of a specialist.
Intraosseous lipoma within the right calcaneum (Milgram's stage 2).
