When a haematoma is not a haematoma

Cutaneous angiosarcoma (cAS) is a rare but highly aggressive vascular malignancy, often associated with chronic lymphoedema or previous radiotherapy. Its nonspecific clinical presentation can mimic benign conditions, leading to diagnostic delays. We report the case of a 70-year-old woman with chronic lymphoedema of the right arm following mastectomy and lymphadenectomy for breast cancer. She presented with a slowly enlarging haematoma-like lesion. Magnetic resonance imaging (MRI) performed externally suggested a benign haematoma. Due to progressive changes, the patient was referred to our department. High-resolution sonography revealed irregular dermal and subcutaneous vasculature with marked hyperperfusion. Deep skin biopsy demonstrated a vascular neoplasm composed of pleomorphic endothelial cells expressing ERG, CD31, D2-40 and c-Myc, with a high Ki-67 proliferation index, consistent with the diagnosis of cAS (Stewart-Treves syndrome). Computed tomography staging excluded metastatic disease, and systemic paclitaxel therapy was initiated. This case underlines the often inconspicuous clinical presentation of cAS and the limited diagnostic value of MRI for superficial lesions. High-resolution sonography may provide an important, noninvasive diagnostic clue by revealing marked hypervascularity, thereby prompting timely biopsy and improving early detection of this aggressive tumour.