Mediastinal hibernoma: a case report

Abstract

Hibernomas are rare benign tumours that arise most often in adults from the remnants of fetal brown adipose tissue. They usually affect muscle and subcutaneous tissue and are asymptomatic and slow growing. The distribution of this tumour follows the sites of persistence of brown fat. Out of more then 100 cases described in the word literature only three hybernomas were mediastinal. A recent clinicopathological study of 170 cases from the Armed Forces Institute of Pathology confirmed the exceptionality of the intrathoracic location. This report describes a very rare case of mediastinal hibernoma in a young man.A 25 year old man was referred to the thoracic surgery department of the Second University of Naples (Italy) because of a left mediastinal mass, which was discovered on a routine pre-employment physical examination. The patient was completely asymptomatic. Physical examination and laboratory tests were non-contributory. A chest roentgenogram showed considerable enlargement of the mediastinum, involving particularly the left side of the chest ( fig 1A). Computed tomography showed a mixed density voluminous mass with well defined edges and nonhomogeneous density, involving predominantly the left part of the mediastinum (fig 1B). A thoracotomy was performed. A large, tan, lobulated, and encapsulated mass was found in the left mediastinum and was removed completely.The excised tumour specimen was fixed in 10% buffered formalin and paraffin wax embedded. Sections of 5 mm thickness were stained with haematoxylin and eosin, haematoxylin-van Gieson, and periodic acid Schiff-haematoxylin. Other sections were immunohistochemically stained using the standard avidin-biotin peroxidase complex method with S-100 antibody (Dako Corporation, Glostrup, Denmark). Diaminobenzidine was used as final chromogen and haematoxylin as nuclear counterstain. Negative controls were obtained by omitting the primary antibodies.Light microscopic examination revealed a tumour divided into numerous lobules by well vascularised connective tissue (fig 2A). The tumour cells were round or polygonal, multivacuolated with centrally placed nuclei resembling lipoblasts. Immunohistochemically, the cytoplasm of these cells was stained for S-100 protein ( fig 2B). Univacuolated cells with eccentrically placed nuclei resembling mature lipocytes were also present. A delicate fibrocollagenous and vascular capsule was present.These macroscopic and microscopic findings were suggestive of a mediastinal hibernoma. The patient made an uneventful recovery and after a five year follow up period there has been no recurrence.

Hibernoma of the Thigh: A Report of Four Cases

“…16 Signals vary depending on the cellular composition of each hibernoma. 17 The differential diagnosis includes lipoma, angiolipoma, malignant fibrous histiocytoma, and liposarcoma.…”

Subcutaneous fat in normal and diseased states

“…32,110,111 Hibernomas, rare and benign tumors thought to arise in adults from remnants of fetal BAT, express UCP-1, a finding that affirms the possibility that brown adipocytes can be reactivated in adult humans, at least under pathological conditions. [134][135][136] Consequently, pharmacological studies have been ongoing for many years. 2,5,137 The outcome of these studies, however, has so far been unsuccessful.…”

Functional Diagnosis of Hibernoma by FDG Imaging Under Propranolol Treatment: A Case Report

“…First, the CT scanning protocol that is used in hybrid PET/CT imaging is "low dose", for the sake of limiting the patients' exposure to ionizing radiations, therefore limiting our anatomic definition of the lesion and its changes in follow-up scans. However, the complete metabolic response after beta-blockade, the absence of macroscopic modifications and the lack of local invasion or distant localizations at follow-up scans strongly support the hypothesis of a benign lesion [17,18].…”