Clinical: Recent trauma with heel pain. Lytic calcaneal lesion on radiograph without fracture.
1. Acute stress fracture of the posterior calcaneus with surrounding edema.
2. Intraosseous lipoma within the calcaneal body resulting in significant thinning of the lateral calcaneal body cortex and moderate thinning of the medial calcaneal body cortex. This could place the patient at risk for pathologic fracture given its size and extent of medullary involvement.
The main differential for a young person with a lytic lesion in the calcaneous is unicameral bone cyst (UBC) versus intraosseous lipoma. Intraosseous lipomas generally exist in three groups, as characterized by this paper: Radiology. 1988 Apr;167(1):155-60.:
Type 1 lesions show homogeneous hyperintense fat signal on T1- and T2-weighted MR images that will be entirely suppressed by STIR or fat saturated sequences. The trabecular cancellous bone pattern is typically absent within the lesion.
Type 2 lesions show hypointense inclusions on T1-weighted images, which may appear hyperintense on fat suppressed T2-weighted images (granulation tissue) or hypointense (calcifications or ossifications).
In addition to the signal characteristics of type 2 lesions, type 3 lesions may contain fluid-equivalent cavities and signal-void bony septae, and are surrounded by thickened, signal-void rims of sclerotic bone. Although there are typically no signs of aggressive behaviour, expansile intraosseous lipomas may outgrow the cortical border. This can be used to differentiate them from older bone infarcts, which may also develop cystic degeneration over time. Moreover, in intraosseous lipomas, T2-hyperintense granulation tissue of a central necrosis is surrounded by viable fat tissue. Conversely, in bone infarcts, fat tissue in the centre is surrounded by granulation tissue at the periphery. However, in cases with substantial secondary involution and necrosis, biopsy may be necessary to confirm the diagnosis.
This case seems to follow a type 3 pattern, especially the evidence of granulation tissue centrally.
1. Milgram J W. Radiology: April, 1998 – vol. 167, issue 1, pp. 155-160.
2. Propeck T, Bullard M A, Lin J, Doi K, Martel W. American Journal of Roentgenology: 2000 – vol. 175, pp. 673-678.