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Ann Thorac Surg 1997;64:1160-1162
© 1997 The Society of Thoracic Surgeons

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Case Report

Cervicomediastinal Hibernoma

Departments of General and Thoracic Surgery, General and Oncologic Surgery, and Pathology, Ospedale Maggiore Policlinico, IRCCS, University of Milan, Milan, Italy

Accepted for publication May 1, 1997.

	Abstract

Top Footnotes Abstract Introduction Comment References

 
Hibernoma is a benign soft-tissue tumor, derived from the brown fat, that often presents as a painless, slow-growing mass. About 100 cases of hibernomas have been reported in the world literature. Seven cases of intrathoracic hibernoma are reported, of which only 1 was located in the mediastinal region. That tumor was an intramediastinal hibernoma with a cervicomediastinal location, which was excised through an extended left supraclavicular incision without the necessity to perform a sternotomy. No recurrence was evident after 18 months.

	Introduction

Top Footnotes Abstract Introduction Comment References

 
Hibernoma is a rare, benign soft-tissue tumor derived from the remnants of fetal brown fat, which have persisted from embryonic life. It often presents as a painless, slowly enlarging mass and may be confused with a lipoma [1–3]. This tumor was first described by Merkl in 1906 [4]. The brown fat, described by Velch in 1670, is a specialized form of fat found in the hibernating and nonhibernating animals such as rats, monkeys, cats, rabbits, and humans.

In 1902 Shaw [5] demonstrated the presence of brown fat in the axillary region and subpleural space of the human fetus. Later on, Bonnot [6] reported the presence of brown fat in human adults in those locations described in the fetus.

About 100 cases of hibernomas have been reported in the world literature. Only 7 cases of intrathoracic hibernomas have been reported, 5 of which were confined to the subpleural space, 1 of which was intrapericardial, and 1 of which was located in the mediastinal region [2].

We present a case of intramediastinal hibernoma in a cervicomediastinal location.

A 33-year-old woman presented at our institution in 1995 for a voluminous neck mass located in the left supraclavicular region. The patient had first noted the presence of the mass in 1989 and denied pain or other symptoms.

Physical examination showed a voluminous, soft, and painless mass located in the left supraclavicular region. The overlying skin moved freely over the mass and there was no lymphadenopathy. The mass gave the impression that it continued into the mediastinum.

A chest radiograph (Fig 1) showed a dislocation of the trachea to the right. The ultrasound examination of the neck showed a large, solid mass measuring 10 x 4 cm with a homogeneous echo pattern. Color-Doppler ultrasound of the neck demonstrated the hypervascularity of the mass not infiltrating but displacing the left vascular structures of the neck. Fiberoptic tracheobronchoscopy confirmed the right dislocation of the trachea without infiltration of the tracheal wall by the mass. Computed tomography, performed to better delineate the relationship of the mass, showed a large soft lesion in the left supraclavicular region extending in the mediastinum measuring 11 x 5 cm, displacing but not invading the adjacent structures. The mass showed enhancement with intravenous contrast and had several vessels running over and through it.

View larger version (145K): [in this window] [in a new window]   Fig 1. . Preoperative chest radiograph showing dislocation of the trachea to the right (arrow).

View larger version (83K): [in this window] [in a new window]   Fig 2. . (A) T1-weighted magnetic resonance image showing a mass (M) in the anterior mediastinum extending to the left supraclavicular region, not infiltrating but displacing the trachea and the great vessels of the neck. (B) T2-weighted magnetic resonance image of the same mass (M).

The lesion was a tan-brown mass, encapsulated and lobulated, measuring 14 x 16 cm (Fig 3). Histologically, the lesion, intensely vascularized, had a lobular growth pattern and was predominantly characterized by roundish and oval cells, granular and eosinophilic in aspect, multivacuolated, with central regular nucleus. Rare univacuolated cells with eccentric nucleus, similar to mature adipocytes, were present (Fig 4). Ultrastructurally, both univacuolated and multivacuolated cells were characterized by cytoplasm filled with small or medium-sized lipid droplets and numerous mitochondria, with roundish and tubular parallel cristae, electron-dense matrix, and large matricial granules. All the tumor cells were invested by continuous basement membrane, and sometimes foci of plasmalemmal invagination were also noted.

View larger version (187K): [in this window] [in a new window]   Fig 3. . The mass, measuring 14 x 16 cm, was tan-brown and capsulated with a lobular aspect of the cut surface.

View larger version (152K): [in this window] [in a new window]   Fig 4. . Numerous small, round multivacuolated cells with granular aspect (A) and scattered larger univacuolated cells similar to mature adipocytes (B). (Hematoxylin and eosin; x25 before 49% reduction.)

	Comment

Top Footnotes Abstract Introduction Comment References

On computed tomography, hibernoma is a heterogeneously hypodense mass because of its lipid and fibrovascular content. On magnetic resonance imaging, the tumor appears bright on T1-weighted image and has a moderate signal intensity on T2-weighted images like subcutaneous fat. These may lead to confusion with liposarcoma [1].

Mertens and colleagues [7] reported 4 hibernomas with clonal chromosomal aberrations and rearrangements of chromosome bands 11q13-21. Meloni and colleagues [8] described a chromosomal involvement affecting 10q22 and 11q13 in hibernoma. Chromosome rearrangements involving 11q13 are not restricted to hibernomas but have been reported previously in some lipomas [7, 8].

Because these tumors are well encapsulated and do not show infiltrative growth, they can be totally removed without sacrificing vital structures. In our case, surgical excision was done through a supraclavicular incision extending to the sternal notch without the necessity to perform a sternotomy.

The tumor had a well-defined capsule and had a classic tan-brown cut surface, with lobular aspect. Microscopically the lesion was characterized by numerous small vessels and was constituted predominantly by round multivacuolated cells with granular aspect. In this case differential diagnosis with a variant of round cell liposarcoma must be considered, and electron microscopy gives a definitive resolution.

Although these tumors are considered benign, they tend to grow large, sometimes causing compression of the neighboring structures; therefore, surgical excision is always recommended.

	Footnotes

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Address reprint requests to Dr De Simone, via Mario Borsa 14, 20151 Milan, Italy.

	References

Top Footnotes Abstract Introduction Comment References

 

1. Cook MA, Stern M, de Silva R. MRI of a hibernoma. J Comput Assist Tomogr 1996;20:333–5.[Medline]
2. Ahn C, Harvey JC. Mediastinal hibernoma, a rare tumor. Ann Thorac Surg 1990;50:828–30.[Abstract]
3. Worsey J, McGuirt W, Carrau RL, Peitzman AB. Hibernoma of the neck: a rare cause of neck mass. Am J Otolaryngol 1994;15:152–4.[Medline]
4. Merkl H. Uber ein Pseudolipoma der Mamma (elgenartiger Fettzellentumor). Beitr Pathol Anat Allg Pathol 1906;39:152–7.
5. Shaw HB. Contribution to the morphology of adipose tissue. J Anat Physiol 1902;36:1–13.
6. Bonnot E. The interscapular gland. J Anat Physiol 1909;43:43–58.
7. Mertens F, Rydholm A, Brosjo O, Willen H, Mitelman F, Mandahl N. Hibernomas are characterized by rearrangements of chromosome bands 11q13-21. Int J Cancer 1994;58:503–5.[Medline]
8. Meloni AM, Spanier SS, Bush CH, Stone JF, Sandberg AA. Involvement of 10q22 and 11q13 in hibernoma. Cancer Genet Cytogenet 1994;72:59–64.[Medline]

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				Z.F. Udwadia, N. Kumar, and A. S. Bhaduri Mediastinal hibernoma Eur. J. Cardiothorac. Surg., April 1, 1999; 15(4): 533 - 535. [Abstract] [Full Text] [PDF]

This Article Abstract Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Luigi Santambrogio Mario Nosotti Luigi Bonavina Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Santambrogio, L. Articles by Bonavina, L. Search for Related Content PubMed PubMed Citation Articles by Santambrogio, L. Articles by Bonavina, L.