Aakriti Jain et al report the clinico radiological presentation of an unusual case of an ossified soft tissue mass in the leg in a 74-year-old man. Calcific myonecrosis is a rare soft tissue condition characterized by calcified mass within a compartment. Differential diagnosis of myonecrosis include myositis ossifcans and sarcomas with propensity for extra-osseous calcification like extra skeletal osteosarcoma, Ewing's sarcoma and epithelioid sarcoma. This entity is a late complication to trauma and prolonged high pressure state within the leg compartments. With imaging alone, the differential of soft tissue sarcoma could be ruled out but typical natural history of disease and radiopathological features aided in the diagnosis.
A 74-year-old male presented to the institute with gradually enlarging mass in right leg since 2 years with sudden increase in size over last 2 months. On examination, a large fusiform swelling over lateral aspect of leg was observed with fungating skin, local scarring of skin and serous discharge. Knee range of motion was within normal limits, although ankle was fixed in 35 degree of plantar flexion and there was clawing of toes.
The patient had history of fracture femur 50 years back managed conservatively with plaster cast following which he developed weakness in ipsilateral foot with toe deformity. 7 years back, patient sustained fracture distal femur following a fall for which he was operated and fracture fixed with plate. Following a latent period of 4 years, patient noticed swelling over the outer aspect of the leg.
Plain radiograph showed large soft tissue swelling in anterolateral aspect of leg eroding fibula and encroaching over lateral cortex with extensive calcification. CT scan showed a mass in anterior and lateral compartment of leg with prominent focculent calcification in periphery and subcutaneous area. On MRI, there was a 22×12×7 cm heterogeneously enhancing mass epicentered in the lateral compartment of leg eroding the middle third of lateral fibular cortex and marked scalloping of tibial cortex without any evidence of muscle edema, hypertrophy or fasciitis.
Patient underwent biopsy through the fungating swelling which yielded necrotic material. Radiographic imaging was subjected to thorough expert review for any heterogenous areas and CT-guided biopsy was done, reported as necrotic tissue with no atypical cells. Marginal excision was done with complete excision of necrotic muscles of anterior and peroneal compartment with removal of affected skin and bony tissue. There were no heterogenous areas but a few pus filled spaces were seen.
Histological examination showed fibrinoid necrosis, leukocytic debris with areas of calcification without evidence of neoplasia or granuloma. The post-operative period was uneventful. Final histopathology revealed irregular fibromuscular pieces measuring 30×15×6 cm with ulcerated overlying skin superficially and irregular grey white congested area on the deeper surface. No definite tumor could be identified on gross with microscopic assessment revealing extensive necrosis and hemorrhage. The patient has been in follow-up for 18 months with unrestricted limb usage at the last follow up. The surgical wound had healed with a sinus remaining on the scar with on and of serous discharge requiring dressing.
The diagnosis is calcific myonecrosis: a rare soft tissue condition characterized by calcified mass within a compartment. It is characterized by progressive dystrophic calcification of muscles occurring decades after the original injury. Although the pathophysiology is open to question, the disease mainly arises from compartment syndrome in a closed space leading to necrosis and fibrosis based on clinical presentations and histology of previous reported cases. Etiology is mainly attributed to muscle injury due to vascular compromise resulting in repetitive hemorrhage formation and calcification. This is followed by focal enlargement of the mass and herniation through the muscle to reach the subcutaneous planes.
The authors concluded that - calcific myonecrosis is a rare disorder mostly involving anterior and lateral compartment of lower limb occur ring as a late complication to trauma and prolonged high pressure state within the leg compartments. Although the diagnosis may often be confused with malignancies due to its rapid growth in few cases with necrotic areas encountered on biopsy, typical clinical presentation and imaging may provide aid in making the final diagnosis and initiating treatment.

Further reading:
Calcific Myonecrosis: Solving the Diagnostic Dilemma
Aakriti Jain, Amit K. Sahu, Sudhir B. Kulkarni, Akshay Tiwari.
Indian Journal of Orthopaedics (2022) 56:1474–1477
https://doi.org/10.1007/s43465-022-00674-9