Findings
There is a lesion of the calcaneus that demonstrates areas of fatty signal on MRI, fluid signal, and bone. The zero TE images highlight the bone within the lesion and the lower appearing density like process of the calcaneus. The CT is very analogous to the zero TE images with the fatty lesion containing bone (HU of the lesion demonstrated on the last CT sagittal image).
Diagnosis: Intraosseous Lipoma with Cystic Degeneration and Reactive Bone Formation
Lesions of the body of the calcaneus near the critical angle frequently fall into a differential diagnosis of a cystic lesion of bone or intraosseous lipoma. One caveat is a “pseudolesion” that can occur at this location related to a relative paucity of trabecular bone at this location. Intraosseous lipoma follow fat signal (more or less) on MRI and fat attenuation on CT. The lesions can be associated with a slight degree of surrounding edema as bone remodels and can be painful at times. Many as in this case, are found incidentally.
As seen in this case, the lipoma can undergo degeneration with areas of cystic change, dystrophic calcification, ossification, or necrosis. The lesions are benign and for the most part do not require intervention. Symptomatic lesions may require curettage and packing.
This case was a nice representation of the utility of zero TE imaging on MRI. One of the newer pulse sequences, it can generate CT like images from MR acquisition. Although still signal, the lesions can be seen to produce an “attenuation” like image which can be well correlated with a CT image. As in this case, the identification of bone for a lesion can be rendered much more easily than with traditional MR pulse sequences. The CT like images of MRI have also been employed for evaluation of anatomy in the shoulder to assess bone stock in the setting of instability and in the hip for the evaluation of impingement.