Fibromatosis of the calf
Progressively increasing swelling in the left calf.
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A fairly well defined soft tissue mass lesion measuring approx 14.5 x 5.9 cms is seen involving the muscles of the posterior compartment of left leg (gastrocnemius, soleus and tibialis posterior). The lesion displays hypointense signal on T1 with a few areas of T1 hyperintensity, with low signal on GRE and heterogeneous signal on T2/STIR images . The lesion demonstrates heterogeneously intense post contrast enhancement. Perilesional edema is seen extending around the neurovascular bundle causing partial encasement of the posterior tibial artery at the mid calf level.
Underlying bones (tibia and fibula) appear normal with no sign of involvement by the mass. The overlying skin is unremarkable.
This lesion was histologically confirmed as fibromatosis.
Fibromatosis is relatively rare disease which is histologically defined by fibroblastic proliferations with spindle-shaped myofibroblastic cells, dense deposits of intercellular collagen with varying amounts of extracellular myxoid matrix. They show variable aggressiveness from benign to locally aggressive, but do not metastasize.