Hibernoma: comparing imaging appearance with more commonly encountered benign or low-grade lipomatous neoplasms

Hibernoma is a benign neoplasm comprised of brown fat and characteristic hibernoma cells often occurring in adults with proximal extremity/truncal predilection. Limited reports regarding imaging appearance and clinicopathological features of this rare tumor are available. Four histological subtypes have been described. We present nine patients with hibernoma evaluating preoperative imaging findings (eight MRI; one PET, CT), which may distinguish hibernoma from more common benign or low-grade lipomatous neoplasms and attempt to correlate imaging with histological subtype. Clinicopathological data of 14 patients are presented.

Following IRB approval, retrospective review identified 14 patients from our institution between 2000 and 2012. Preoperative imaging, pathology, and medical records were reviewed. We tested the reader's ability to distinguish hibernoma from lipoma and atypical lipomatous tumor (ALT) at preoperative MRI based on specific imaging criteria. In a separate test, another reader attempted to predict histological subtype. Diagnostic accuracy was recorded.

Six men and eight women with a mean age of 53 years were identified. Tumors involved the thigh (4), buttock (3), paraspinal muscles (3), retroperitoneum (2), shoulder (1), and knee (1). Eleven underwent margin negative resection; three excisional biopsy. When asked to differentiate hibernoma from lipoma and ALT, readers correctly identified 80 %, 80 %, and 100 % of hibernomas. Specific histological subtype was accurately predicted in most cases. Mean follow-up was 38 months with no local recurrences or metastases.

Hibernomas can be difficult to differentiate from other lipomatous neoplasms, but identification of certain imaging features, common location, and patient demographics can improve preoperative confidence. Given benignity, accurate prospective diagnosis may affect treatment planning and surveillance strategy.