An unusual case of an intramuscular lipoma of the pectoralis major muscle simulating a malignant breast mass

Introduction: Intramuscular lipomas of the pectoralis major muscle are rare and may mimic malignant breast tumours. Clinical Picture: A 58-year-old Chinese woman presented with a 2-year history of an enlarging left breast mass. Clinical examination revealed a palpable hard mass in the left breast. Treatment: Standard mammographic views revealed a radiolucent mass deep in the left pectoralis major muscle. The mass was homogeneously hypoechoic with smooth margins on ultrasound. Outcome: Surgical excision of the mass was performed. Histological diagnosis was an intramuscular lipoma of the left pectoralis major muscle. Conclusions: Recognition of the radiolucent density and submammary location of a pectoralis major muscle lipoma is important as it allows the correct diagnosis to be made.