Presentation
Pain and numbness in the right ankle.
Patient Data
A lobulated, well-defined lesion - predominantly hyperintense with linear hypo-intense strands within on T1 and T2 images - is seen within the tarsal tunnel along the medial aspect of the foot.
The hyperintense areas within the lesion are suppressing on PD fat sat images, indicating a lipomatous component. Linear hypo-intense strands are persistently hypo-intense on all sequences, indicating fibrous component. This lesion characteristically gives a spaghetti-like appearance on coronal T2 images, and a coaxial cable-like appearance on axial T1 images.
The lesion is oriented along the medial plantar nerve with dimensions measuring 57 mm in length, 22 mm in width, and 42 mm in AP diameter.
Subchondral edema - hyperintense on T2, PD Fat sat, and hypo-intense on T1 images surrounded by thin sclerotic rim - is seen along the lateral aspect of the talar dome - suggestive of stage II osteochondral injury.
Multiple round to oval T1, T2 hyperintense lesions, partially suppressing on PD Fat sat images, are noted in the subcutaneous plane along the medial aspect of the ankle - likely subcutaneous lipomas.
Case Discussion
Fibrolipomatous hamartoma of the nerve, also known as lipomatosis of the nerve, is pathologically characterized by lipomatous and fibroblastic proliferation of these components within the epineurium of the nerve.
Upper limb nerves are more commonly involved, with the median nerve being the most common nerve of involvement. In the lower limb, the plantar nerve is involved, as in our case.
On MRI, the coaxial cable appearance on axial images and spaghetti-like appearance on coronal images are characteristic. This is due to fat components, which are hyperintense on T1, T2 images, intermixed with linear strands of hypo-intense fibrous components, giving this appearance.
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