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Journal of Pediatric Surgery (2013) 48, 258–261

Pediatric cervicomediastinal hibernoma: A case report☆

Christopher A. Guidry⁎, Eugene D. McGahren, Bradley M. Rodgers, Bartholomew J. Kane⁎

Division of Pediatric Surgery, University of Virginia Department of Surgery

Received 3 July 2012; revised 23 September 2012; accepted 13 October 2012

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Key words:Hibernoma;Brown fat;Lipoma;Tumor;Pediatric;Thoracic mass

Abstract Hibernoma is a rare lipomatous tumor of brown fat origin. Though uniformly benign in naturethese tumors may cause symptoms secondary to extrinsic compression of neighboring structures.Hibernomas may be found anywhere that normal fetal brown fat may be located but are most commonlylocated in the thigh. We present a case of a hibernoma presenting as an unusual cervicomediastinal massin a 6-year-old male. This mass was discovered during a diagnostic chest x-ray for pneumonia andtreated by resection. Complete surgical resection is considered curative. Hibernoma should beconsidered in the differential diagnosis of any lipomatous tumor.Published by Elsevier Inc.

Hibernoma is a rare lipomatous tumor of brown fat origin.Though uniformly benign in nature, these tumors may causesymptoms secondary to extrinsic compression of neighbor-ing structures. This article outlines a case of a cervicome-diastinal hibernoma presenting in a 6-year-old male. Thecervicomediastinal mass was discovered during a diagnosticchest x-ray for pneumonia. In addition to a case history, thisarticle contains a brief discussion of the clinical featuresassociated with hibernoma, as well as a short review ofthe literature.

1. Case report

A 6-year-old male presented to his primary care physicianfor treatment of a left-sided pneumonia. The pneumonia wastreated appropriately with antibiotics and did not recur. The

☆ Reprints are not available from the authors.⁎ Corresponding authors. Christopher Guidry is to be contacted at

harlottesville, VA 22901, USA. Bartholomew Kane, UVA Surgeryepartment, PO Box 800679, Charlottesville, VA 22908, USA.

022-3468/$ – see front matter. Published by Elsevier Inc.ttp://dx.doi.org/10.1016/j.jpedsurg.2012.10.059

chest x-ray ordered to diagnose his pneumonia demonstrateda left apical thoracic mass (Fig. 1). The patient's motherreported that, in addition to his pneumonia symptoms, he hadexperienced anorexia and weight loss over the precedingseveral weeks. The child was referred to pediatric surgery atthat time. A thoracic and neck CT scan was obtained (Figs. 2and 3). This study demonstrated a 5.2 × 4.2 × 6.6 cm mass inthe left superior mediastinum, extending cranially to the levelof the left lobe of the thyroid. The lesion encased but did notcompress the left subclavian and vertebral arteries. It diddemonstrate 180-degree encasement of the left commoncarotid artery. Neuroendocrine tumor was considered on thediagnostic differential. Urinary VMA and HVA levels weremeasured and found to be undetectable.

The patient was taken to the operating room forthoracoscopic evaluation and biopsy of this lesion. A well-encapsulated mobile lesion with a fatty appearance wasfound underlying the posterior medial parietal pleura of theleft apex. Subcapsular bleeding was encountered uponmanipulation of the tumor. A biopsy was obtained. Frozensection histological evaluation revealed adipocytes withbenign epithelium. Resection was pursued via a modifiedsternotomy wherein the superior aspect of the incision was

Fig. 2 Computed Tomography with arterial phase contrast of the

259Pediatric cervicomediastinal hibernoma

extended laterally into the inferior left neck through a pre-existing skin fold. The tumor was successfully dissectedfrom all vital structures in two separate pieces. Care wastaken to identify and preserve the vagus nerve as well as itsrecurrent branch. Pathologic evaluation of the lesion showeda firm, multiloculated, fatty tumor with focal areas ofhemorrhage and no necrosis. Microscopically, the lesion wascomposed of mature adipocytes with multifocal areas ofvacuolated eosinophilic adipocytes, consistent with brownfat. These features were consistent with the diagnosis ofhibernoma. Following a brief hospital stay and recovery athome, the patient returned to normal activity. He does exhibitsymptoms of a mild left-sided Horner's syndrome charac-terized by minimal myosis and ptosis. To date, the patienthas shown no radiographic or clinical evidence of recurrence.

chest demonstrating left apical mass encasing the left subclavianand vertebral arteries.

2. Discussion

Hibernoma is a rare tumor of brown fat origin initiallydescribed in 1906 by Merkel as a “pseudolipoma.” Gery firstused the term “hibernoma” in 1914 to characterize theresemblance of the tumor to brown fat in hibernating animals[1–4]. Brown fat serves a thermoregulatory role inhibernating animals as well as in human neonates andfetuses [5]. Largely a vestigial tissue in adults, it can befound in several locations, including the interscapular region,the axilla, the neck, the mediastinum, the periaortic area, theretroperitoneum, and as detached foci in the groin as well asperipherally in the limbs [6,7]. Histologically, brown fat ischaracterized by cells with eosinophilic, multivacuolatedgranular cytoplasm and centrally positioned nuclei [8,9] (Fig.4). The finding of such cells in a lipomatous tumor isdiagnostic for hibernoma.

Hibernomas usually present as a slow growing painlessmass, but may become symptomatic through compression ofadjacent structures, or torsion if pedunculated [3,4,10–14].These tumors have a variable gender distribution and

Fig. 1 Chest x-ray at presentation demonstrating left apical mass.

typically present between 20 and 40 years of age [3,11,15].The largest case series was described by Furlong, whocompiled a total of 170 cases of hibernoma. The average ageat presentation for that series was found to be 38 years oldwith a slight male predominance. The average size was 9.3cm with a range from 1 to 24 cm. Approximately 29.4%presented as a thigh mass, 10% in the back, 9.4% in the neck,6.4% in the chest, 6.4% in the arm, and 5.9% in the abdomenor retroperitoneum, followed by all other locations [11].Hibernomas most commonly present as solitary lesions,though there is one documented case of multiple hibernomasin a 1 month old female. In that case, histologicaldetermination was not obtained for all of the tumors [15].

A rare tumor in the general population, hibernoma is evenless common in children despite the increased amount ofnormal brown fat as compared to adults. In Furlong's series,only 9 (5.3%) occurred in patients less than 18 years of age[11]. Two of these patients were male. The anatomicdistribution was consistent with that of the previouslydescribed series. The most common location was still thethigh (3 cases) followed by a single case in each of thefollowing locations; back, chest, neck, breast, abdominalwall, and spine [11]. Other reports of pediatric hibernomahave occurred in the cervical area, the supraclavicular region,

Fig. 3 Re-demonstration of mass on Computed Tomography.

Fig. 4 Representative histopathology slide demonstrating multi-vacuolated eosinophilic cells consistent with hibernoma.

260 C.A. Guidry et al.

the nipple, the epidural space and the spermatic cord[7,8,15–18].

A review of the literature revealed 14 case reports ofhistologically proven hibernoma occurring within thethoracic cavity in both the adult and pediatric populations.Of these cases, 6 were sub-pleural in location, 5 were foundin the mediastinum, 2 were pericardial, and 1 was anteriorparavertebral [1,4–6,14,19–25]. Of the cases occurring inthe mediastinum, a single case was found to extend beyondthe thoracic cavity, into the cervical region. This hibernomapresented as a painlessly enlarging neck mass in a 33-year-old female [4]. Only a single case of a thoracic hibernomawas found in the pediatric population. That hibernomapresented as an asymptomatic left-sided mass confined to thethoracic cavity in a 16 year old male [1]. Multiple cases ofcervical hibernomas that did not extend into the thoraciccavity were found in the literature [8,12,15,16,26].

The diagnosis of hibernoma cannot be made usingradiographic information alone, though imaging studiescan help greatly with operative planning [22]. ComputedTomography generally reveals a well-defined mass thatenhances with intravenous contrast. MRI evaluation dem-onstrates T1 signal intensity between that of subcutaneous fatand muscle, depending upon the ratio of brown to mature fatpresent in the mass. The T2 signal profile is similar to that ofsubcutaneous fat [27]. Hibernomas are hypointense whencompared to subcutaneous fat on T1 images and do notcompletely suppress with STIR or fat-saturated T2 im-ages [23]. Hibernomas have been shown to have increasedFDG uptake on PET imaging, while lipomas typically havelow uptake. Liposarcomas, however, have variable FDGuptake, making it impossible to rule out sarcoma by imagingalone [22].

Complete surgical resection is considered the standard ofcare in the treatment of hibernoma. These tumors areuniformly benign. There have been no cases in the literatureof recurrence after complete resection. There have been tworeported cases of a questionably malignant hibernoma. One

was thought to have recurred after resection but was latershown to have been incompletely removed initially [26]. Inthe other case, the tumor was thought to be malignant basedupon possible local muscular invasion. However, the tumornever recurred after resection. No other cases havedemonstrated local invasion [11,26].

3. Conclusion

Based upon a thorough review of the current literature,this is thought to be the second reported case ofcervicomediastinal hibernoma, and the first such casedocumented in the pediatric population. Hibernoma shouldbe considered in the differential diagnosis of all lipomatoustumors in both the adult and pediatric populations.

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