Sporadic retromammary schwannoma

© BMJ Publishing Group Limited 2022. No commercial reuse. See rights and permissions. Published by BMJ. DESCRIPTION A male patient in his 70s with no relevant medical history presented to his primary care physician complaining of a painless lump on his left breast. On physical examination, a palpable and nontender breast mass was detected with no skin alterations or nipple retraction. Ultrasound (US) showed an oval, circumscribed, hypoechoic, noncalcified nodule with posterior enhancement, but no posterior shadowing, measuring 21 mm in the upperouter quadrant of the left breast immediately adjacent to the pectoralis major (figure 1). Breast MRI was performed for further characterisation. An ovalshaped mass with circumscribed margins was identified in a retromammary location with a partially intramuscular component. It was regularly encapsulated and had an isointense signal relative to skeletal muscle on T1weighted images and increased, slightly heterogeneous signal intensity on T2weighted images. It demonstrated intense enhancement after intravenous gadoliniumbased contrast material administration (figure 2). Two features present in this case are the peripheral rim of fat (split fat sign) and the central low T2signal (target sign), which probably represents fibrous tissue. These MRI features are typical of peripheral nerve sheath tumours. However, other typical signs of peripheral nerve sheath tumours were not recognised, such as the continuity of the lesion with a nearby nerve seen entering and exiting the mass and a fascicular appearance, known as the fascicular sign. A coreneedle biopsy was performed under US guidance. Histological evaluation of the tissue section was consistent with a schwannoma. Surgical resection was recommended to the patient, and he underwent a successful excision. The procedure was uneventful. A wellcircumscribed, xanthochromic and rubbery mass measuring 24 mm was removed and sent for anatomopathological analysis. Microscopic evaluation confirmed the diagnosis of a benign schwannoma, with S100 positivity. Postsurgical clinical assessment was unremarkable, and the patient was discharged. Schwannomas are the most common nerve sheath tumours. They are usually benign, wellencapsulated, slowgrowing tumours composed of Schwann cells. Although rare, malignant transformation may occur. The tumour can originate anywhere in the body. While the vast majority of cases are sporadic and solitary, multiple lesions should prompt investigation of related genetic diseases, such as neurofibromatosis type 2. It may present as an asymptomatic