Parosteal lipoma mimicking a breast tumor.

Suyama L, Itoh A. BMJ Case Rep 2017. doi:10.1136/bcr-2017-220770 Description Parosteal lipoma is a rare benign tumour that is composed mainly of mature adipose tissue, and is contiguous to the periosteum of the underlying bone. Most parosteal lipomas are asymptomatic, but some may present motor and/or sensory deficits. A woman was seen in our office complaining a left breast tumour. The woman first noticed the tumour several years ago and underwent breast cancer screening annually but was never required for further evaluation. The tumour was slowly growing, and was associated with pain when lying in a prone position. On physical examination, a soft tumour measuring 9 cm could be felt in the lower-inner quadrant of the left breast, and was firmly fixed to the chest wall. Mammogram showed a well-circumscribed, smooth, lipomatous mass containing a coral-like calcification (figure 1). Breast ultrasonogram showed a large lipomatous nodule near the caudal end of the mammary gland. Although the lesion could not be detected clearly on a chest X-ray, a CT scan showed an osteoblastic portion arising from the fifth rib, and was surrounded by a capsulated lipoma. The lipoma was displacing the mammary gland upwards (figure 2). An MRI scan showed a parosteal lipoma, with no malignant findings. The patient wished to remove the tumour, and she underwent a tumour extirpation. The base of the ossified area was removed using a wire saw. A specimen mammography was taken to determine the adequacy of excision. On histological examination, the mass was composed of mature lipocytes containing a bony proliferation and was consistent with that of a parosteal lipoma. The patient’s pain relieved soon after the surgery and remains well at present.