Pleomorphic rhabdomyosarcoma of the calf

Case contributed by Dr Ashesh Ishwarlal Ranchod

Presentation

The patient presents with painful left knee masses.

Patient Data

Age: 50 years
Gender: Female

There are dual, superficial, subcutaneous, irregular, solid, left anterolateral and lateral periarticular (left knee) mass lesions as demonstrated. There is no intra-articular extension. There is perilesional edema. There is no aggressive vascularity.

MRI confirms dual, solid, heterogeneously enhancing periarticular mass lesions. The superior lesion is at the level of the left lateral collateral ligament and distal iliotibial band. The inferior lesion is adjacent to the tibialis anterior and extensor digitorum longus muscle. The lesions are extra-articular. Sagittal imaging confirms a dumbbell appearance with a linear connecting band of tissue. The distal femur, proximal tibia, and femur appear normal on all sequences.

Histology images

Pathology

1. H & E.

2. Excellent nuclear staining Myo D1 – indicating rhabdomyoblasts.

3. H & E routine section showing the tumor with severe nuclear pleomorphism and mitotic activity. Highly cellular.

4 and 5. Excellent cytoplasmic staining for muscle actin indicating muscle derivation.

Diagnosis: High-grade pleomorphic rhabdomyosarcoma.  

Histology report and images courtesy of Dr Jefferey A. Posen.

Case Discussion

Based on the imaging findings, suggesting an aggressive dual lesion, the patient underwent excision histology. There is histological confirmation of a high-grade pleomorphic rhabdomyosarcoma. Pleomorphic rhabdomyosarcoma is the least common type of rhabdomyosarcoma and accounts for only 5% of all rhabdomyosarcomas.

Based on the histological appearance, a spindle cell subtype is considered.

The anatomical site in this patient fits the incidence of these lesions mainly within the limbs and especially the thigh.

The patient's surgical margins were inadequate on initial excision and further surgical debridement was needed. On history, her follow-up has been unremarkable.

The radiological diagnosis offered was a likely malignant peripheral nerve sheath tumor especially of the superficial peroneal nerve in view of the lesions' anatomical location. Excision histology confirmed otherwise.

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