Hibernomas are rare benign soft tissue tumors derived from brown fat. This case report describes an axillary hibernoma with intrathoracic extension, presenting as a thoracic outlet syndrome. A multimodality imaging series illustrates the classic radiologic features of hibernoma as well as its highly unusual pattern of growth. The latter resulted in TOS with vascular displacement and osseous remodeling, features that are generally absent in lipomatous masses. Detailed preoperative imaging allowed to plan a single surgical procedure in which an extrathoracic axillary approach was combined with intrathoracic video-assisted thoracic surgery.