Rhabdomyosarcoma presenting as intramuscular haematoma due to brachioradialis tear after trauma

A man in his 40s with a history of neurofibromatosis type 1 presented to the emergency department with worsening anterior elbow pain and swelling after falling from a chair 2 months prior. An X-ray showed soft tissue swelling without fracture and the patient was diagnosed with a rupture of the biceps muscle. MRI of the right elbow showed a brachioradialis tear with a large haematoma along the humerus. This was initially thought to be a haematoma; therefore, wound evacuation was done twice. When the injury failed to resolve, a tissue biopsy was performed. This revealed a grade 3 pleomorphic rhabdomyosarcoma. It is important to consider malignancy in the differential diagnosis with rapidly growing masses even if the initial presentation is suggestive of a benign condition. Neurofibromatosis type 1 is also associated with a higher risk of malignancy than the general population.