Not All Red Flags Indicate Malignancy: A Case Report of a Benign Lipoma Mimicking Soft-tissue Sarcoma

Soft-tissue sarcomas are uncommon malignant tumors that may present with enlarging, painful soft-tissue masses. However, certain benign lesions may occasionally demonstrate overlapping clinical features, creating diagnostic uncertainty. We report a case of a large lower limb lipoma that clinically mimicked soft-tissue sarcoma.

A 30-year-old woman presented with a progressively enlarging right calf swelling associated with nocturnal pain for 3 years. Physical examination demonstrated a large tender mass with poorly defined margins measuring approximately 20 cm × 15 cm. Due to concerning clinical features suggestive of malignancy, further evaluation was performed. Plain radiography showed no bony involvement, while ultrasound did not demonstrate a definite soft-tissue mass or vascular malformation. Magnetic resonance imaging revealed diffuse thickening of subcutaneous fat with homogeneous signal intensity similar to adjacent fat tissue, favoring a benign lipomatous lesion. The patient subsequently underwent surgical excision. Histopathological examination demonstrated mature adipocytes without atypia or lipoblasts, confirming a benign lipoma.

This case highlights the diagnostic challenges in differentiating benign lipomatous lesions from soft-tissue sarcomas based solely on clinical presentation. Appropriate imaging evaluation and histopathological confirmation remain essential for accurate diagnosis and optimal management of suspicious soft-tissue masses.