Hibernoma of the Neck: A Rare Cause of Neck Mass

JONATHAN WORSEY, MBBS, WILLIAM McGUIRT, MD, RICARDO L. CARRAU, MD, AND ANDREW B. PEITZMAN, MD

(Editorial Comment: A hibernoma is an uncom- mon benign tumor. Its origin in brown fat may cause confusion with a lipoma.)

Brown fat is found only in scattered foci in the adult human, commonest in the interscap- ular region, the mediastinum, and the neck. Tumors originating from these fat deposits are called hibernomas; approximately 100 are re- ported in the world literature with a small proportion occurring in the neck. A case of a hibernoma forming in the neck will be pre- sented and the clinical, radiologic, and patho- logic features of this unusual tumor dis- cussed.

CASE REPORT

A %-year-old man presented with a s-month his- tory of a painless mass in his right neck. On exam- ination a soft, smooth 7 x d-cm mass was palpable in the base of the posterior triangle of the left neck. The overlying skin moved freely over the mass, it was not tender, and there was no lymphadenopa- thy. Clinically it was believed to be a lipoma. A computed tomographic (CT) scan was performed to delineate the relations of this mass; it showed a large soft tissue mass in the base of the neck ex- tending backward toward the scapula, displacing but not invading adjacent structures (Fig 1). The mass enhanced with intravenous contrast and had several vessels running over and through it. The radiologic diagnosis was of a benign soft tissue tu- mor, possibly a plexiform neurofibroma, but un- likely to be a lipoma because of its vascularity.

The mass was approached through an oblique neck incision and easily mobilized anteriorly where it extended medially as far as the carotid sheath. The mass was red-brown in color, firm in consistency, and had several large veins coursing over its surface which were carefully divided. Pos-

From the Departments of Surgery and Otolaryngolo- gy, University of Pittsburgh Medical Center, Pitts- burgh, PA.

Address reprint requests to Andrew B. Peitzman, MD, Room AlOiO, Department of Surgery, Presbyterian Uni- versity Hospital, Pittsburgh, PA 15213.

Coovriaht 0 1994 bv W.B. Saunders Company 01&0709/94/1502-d011$5.00/0

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teriorly the mass was firmly adherent to the scap- ula and subscapularis muscle by fibrous bands that were sharply divided to completely excise the mass. On pathologic examination the mass re- vealed the classical features of a hibernoma. It was partly encapsulated and red-brown in color (Fig 2); the cut surface was tan-brown with occasional ar- eas of hemorrhage and a small amount of gray- white fibrous tissue [Fig 3). Histologically the mass was composed of lobules of predominantly round lipid-containing cells with multiloculated granular cytoplasm. The stroma between the cells contained many small vessels.

The patient remains well at a-month follow-up with no signs of recurrence of tumor.

DISCUSSION

Tumors of brown fat were first described at the beginning of this century1 and termed hi- bernomas a decade later because of their sim- ilarity to the “hibernating gland” of certain hibernating mammals2 Their distribution fol- lows that of the scattered brown fat deposits, being most commonly found in the subcuta- neous regions of the back, especially between the scapulae, also in the axilla, neck, and tho- raxa3 However, they have also been found in locations not known to be sites of brown fat

Fig 1. CT scan shows an 8 x IO-cm mass (HI extending from the skin anteriorly to the scapula posteriorly. Medial extant is to the carotid sheath. The mass enhanced with intravenous con- trast with several vessels shown (arrows).

152 American Journal of Otolaryngology, Vol 15, No 2 (March-April), 1994: pp 152-154

HIBERNOMA OF THE NECK 153

Fig 2. The gross specimen was 14 x 7 x 3.5 cm, partly en-

capsulated, and red-brown in color.

deposition such as the thigh or popliteal space. 4 They are rare tumors with no predom- inant sex distribution, but all reported cases in the neck are in males5,” The peak inci- dence is in the 20 to 40-year age group.

Presentation is usually as a painless mass, and those in subcutaneous locations are often thought to be a lipoma. If CT scanning is used a well-defined lesion with tissue attenuation between that of muscle and fat is seen which enhances on administration of contrast.7 Oc- casionally arteriography has been performed that shows hypervascularity but without neo- vascularization or arteriovenous shunting, which might be suggestive of a malignant le- sion.5 There are reports of the diagnosis of hi- bernoma being made by fine needle biopsy and cytologic examination,’ but the vascular- ity of these tumors is, perhaps, a potential drawback of this approach. Surgical removal

is the treatment of choice and is usually per- formed without difficulty because the encap- sulated tumor dissects out easily and does not invade adjacent structures, though, as in this case, there may be fibrous attachment to adja- cent muscle.g

The tumor usually has a brown capsule and the cut surface has a classical tan-brown ap- pearance (Fig 2). Microscopically the tumors have a lobular appearance with the predomi- nant cell type being a large multivacuolated cell with scant granular cytoplasm. Lesser numbers of univacuolated cells and smaller round cells with granular cytoplasm are also present. Numerous small vessels are present between the lobules, accounting for the en- hancement on CT and the angiographic fea- tures. Ultrastructural appearance reveals pleo- morphic mitochondria and abundant fat droplets, but scarce golgi apparatus and endo- plasmic reticu1um.l’ Most investigators would consider these to be essentially benign tumors although there is some controversy re- garding this. There are several reported cases11-13 of hibernomas that on microscopic evaluation had areas resembling a liposar- coma in an otherwise typical hibernoma. There was evidence of recurrence after exci- sion in two of these cases, but metastases have not been noted. It has been suggested that in the absence of frankly malignant behavior, which cellular pleomorphism, recurrence af- ter incomplete excision, and local infiltration do not necessarily confer, these should be per- haps considered highly atypical hiberno- mas.13

In conclusion, hibernomas are uncommon

Fig 3. The cut surface of the

specimen was tan-brown with occasional areas of hemorrhage and a smell amount of gray- white fibrous tissue.

154 WORSEY ET AL

tumors of brown fat that occasionally present as a neck mass and are often mistaken clini- cally for lipomas. A CT scan has a character- istic appearance but the correct diagnosis is rarely made with this modality. Removal is usually not difficult depending on the site, but fibrous attachments to adjacent muscle may require sharp division. Most investiga- tors agree that additional therapy is not needed after complete excision, although ra- diation therapy has been used in cases where some areas suspicious for well-differentiated liposarcoma were seen.13

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