A Rare Case of Anterior Cervical Triangle Soft Tissue Tumour: Hibernoma

Abstract

Hibernomas are infrequent brown adipose tissue neoplasms. The thighs, shoulder, neck, and back are the most common places they appear. These are benign lipomatous neoplasms. The clinical and radiological characteristics of hibernomas are described in this activity, along with the importance of the interprofessional team in the proper care of patients suffering from this illness. The clinical, radiological, and histologic characteristics of a patient with hibernoma resulting from swelling in the left lateral neck located in the anterior cervical triangle are discussed in this article.

Introduction

Brown adipose tissue hibernomas are rare and infrequent soft tissue neoplasms. The thigh, shoulder, neck, and back are the most commonly affected areas. Variants of myxoid and spindle cell hibernoma that are less prevalent are probably seen in the shoulder and posterior neck. Benign lipomatous neoplasms, hibernomas do not have the ability to turn malignant. Brown fat is seen in hibernating animals, which is how the term “hibernoma” was created. These tumors, which were initially reported by Merkel in 1906, resemble lipomas in terms of their clinical behavior but have distinct histologic and imaging characteristics [1]. The majority of hibernoma cases occur in young adults, with a mean age of 38.Brown fat makes up these benign neoplasms, which are often moderate in size, well-circumscribed, grow slowly, and histopathologically formed of brown fat cells.Most frequently include the thigh, trunk, and chest; Rare locations reported in fewer than 10% of cases include retroperitoneal, thoracic, and intraabdominal areas; fewer than 20% are intramuscular in place.Chief differential diagnosis includes well-differentiated liposarcomas (WDLS). Depending on which of the following histological classifications they belong to: (1) typical, (2) lipoma-like, (3) myxoid, and (4) spindle cell variations, hibernomas can have a varying histopathologic composition.(Table 1). 82% of instances are accounted for by the usual subtype [2]. These tumors might have a yellow, light brown, or grey hue upon physical examination. They could appear to be lobular. These neoplasms’ varying lipid content is the primary cause of their diverse appearance. These tumors appear as big, multi-vacuolated cells containing mature adipose tissue, frequently in huge quantities, under a microscope. Capillary vessels that branch out are also typical. White fat can be found in the lipoma-like subtype. Typically, the subtype has more than 70% dark fat. UCP1, a gene that marks brown fat, is highly expressed. In brief, these neoplasms have the following histopathologic features have a high concentration of cytochrome pigments; lack high mitotic activity and nuclear atypia; exhibit granular and multivacuolated cytoplasm of brown fat cells; exhibit eosinophilic and polygonal brown fat cells; contain a variable component of univacuolated white fat cells; have a variable percentage of brown fat cells; and show small multivacuolated brown fat cells on cytology. On cytologic examination, bland spherical nuclei and coarsely granular cytoplasm are characteristic characteristics.

Table 1.

Classification & histopathological characters of various types of hibernoma

Histological Type	Characteristic Features
Typical hibernoma	Eosionophilic, pale cell & mixed cell types
Myxoid variant	Loose basophilic matrix
Spindle cell hibernoma	Features of hibernoma & spindle cell lipoma
Lipoma like variant	Scattered hibernoma cell

Case Report

A 45 year old male with BMI of 23 came to ENT OPD in January 2024 with complaints of swelling in left side of neck since 13years with no signs of pain, tenderness (Figs. 1 and 2).patient apparently noticed swelling 13 years back which was small in size and gradually progressing to the present stage without any tenderness.patient is hypertensive, otherwise the patient is in good health & has no other significant past medical or surgical history.his physical examination revealed a large mobile mass about 18 × 12 × 10 cm in size was noted in left lateral region of anterior cervical triangle. Mass was not adherent & relatively mobile, non- pulsatile, no erythema or overlying skin changes were appreciated.no dysphagia or dyspnea was noted.

Fig. 1.

Preoperative image of mass

Fig. 2.

Preoperative image of Mass (side view)

On USG neck revealed a Well defined fatty lesion, measuring about 12.0 (craniocaudal) x 7.6 (AP) x 11.1 (Transverse) cm is seen deep to the clinical swelling. It is located in the subcutaneous plane. Left parotid and thyroid glands appear separate from the lesion. Left submandibular gland displaced superiorly. The lesion is superficial to left carotid and jugular vessels. No evidence of calcification/necrosis seen. No abnormal inter vascularity is seen. - These features are suggestive of lipoma.Patient was then subjected to routine haemtological& biochemical investigations.ECG, Chest, Abdomen xray were normal.

Open excisional biopsy under GA was considered. Intraoperatively the mass was freed using blunt dissection (Figs. 3 and 4). Extreme care was taken not to disrupt the thin capsule. The mass was measured to be approximately 18 cm x 12 cm x10 cm. No obvious invasion into adjacent structures was noted. On pathological examination the specimen was found to have scattered brown fat cells amid white fat (Fig. 5). There were no areas of necrosis or mitotic figures identified. However, there were broad fibrous septae with entrapped skeletal muscle. Initially the specimen was identified as a lipoma; nonetheless because of the anatomical position, growth, and histologic findings, a well-differentiated liposarcoma remained in the differential diagnosis.

Fig. 3.

Intraoperative image of mass

Fig. 4.

Mass completely excised

Fig. 5.

Macroscopic image of mass. The mass is seen to have a yellow, greasy & lobulated surface

Microscopic examination demonstrated composition of yellowish brown adipose tissue mass, soft measuring 18 × 12 × 10 cm. Cross section shows lobulated appearance, separated by whitish fibrous bands.Histology shows a neoplasm, enclosed in a fibrous capsule, lobules of mature fat cells admixed with round to polygonal, multivacuolated cells They possess centrally located, bland, round nuclei. Lobules are separated by irregular collagenous bands and arborization of delicate blood vessels. Areas of myxomatous changes seen. No evidence of atypia malignancy found in any of the sections studied suggestive of Hibernoma (Fig. 6). The patient withstood the procedure very well. He was discharged home in good, stable condition after 3 days. The patient followed up in ent opd days later for post-operative discussion of surgery and findings.

Fig. 6.

Histopathological slides showing neoplasm, enclosed in a fibrous capsule, c/o lobules of mature fat cells admixed with round to polygonal, multivacuolated cells They possess centrally located, bland, round nuclei

Discussion

Hibernoma is a rare benign soft tissue tumor that arises from the remains of brown fat, similar to a tumor of certain dormant animal species. It is usually a small, benign, lobular, non-tender lesion arising in the mediastinum or scapula [3]. Merkel first described the tumor in 1906 [4]. The lesion was described as consisting of brown adipose tissue. In 1914, Gery described the similarity of morphological features between these tumors and hibernating glands in animals [5]. The function of this brown fat is to promote nonshivering thermogenesis. On thorough literature search, we found that < 20 cases of cervical hibernoma have been reported till date. Most cases occur in adult patients, and cervical hibernoma in children is extremely rare.

Hibernoma usually occurs in adults, with a peak incidence in the third decade and a preponderance in women. this report describes a case of hibernoma of a swelling on the left side of the anterior cervical triangle, initially diagnosed as a lipoma and later investigated for a suspected liposarcoma. the clinical presentation and imaging findings of hibernoma can mimic those of benign lipomas and malignant processes [6, 7].

Clinically, their consistency is multiple but usually harder than a regular lipoma.It is a mobile, slow-growing mass. It is usually asymptomatic but rarely may present with pain weight loss.Most common anatomical locations were the thigh shoulder, back, neck, chest, arm, and abdominal cavity [8–10].

Sonography is most effective in evaluating subcutaneous soft tissue hibernomas. The utility of sonography is somewhat limited in the evaluation of intramuscular hibernomas and deeper lesions. On sonographic imaging, these tumors are usually encapsulated and well circumscribed, and their echogenicity is similar to that of the surrounding fat. Occasionally, these tumors may exhibit mild hyperechogenicity or mild hypoechogenicity relative to the surrounding subcutaneous fat. The vessels or blood vessels seen in these tumors can often be seen with color Doppler imaging. Adjacent visible vasculature corresponding to a feeding vessel can also be identified. Both typical and atypical lipoma share these sonographic features.

The differential diagnosis of lipomatous soft tissue tumors is broad and includes benign (e.g., lipoma, hemangioma, angiolipoma) and malignant (e.g., liposarcoma) lesions. Lipomas are characterized by homogeneous adipose tissue, which may have thin septa. In a lipoma, contrast is not enhanced., although diagnosis can be hindered by infections, infarctions, and necrosis, as well as muscle fibers, intratumoral vessels, and fibrotic septa. Poorly differentiated liposarcoma is rarely confused with hibernomas due to the low fat content [11–13].

The treatment of choice for hibernoma is complete excision with preservation of vital structures.Hibernoma usually present as a well-circumscribed lesion; hence, the complete excision of the lesion is not a problem. Unlike lipomas, hibernomas have extensive vasculature, which must be carefully managed to avoid postoperative bleeding or hematoma.No recurrence or metastasis has been reported [10, 14].

Conclusion

Hibernoma is a rare benign soft-tissue tumor which arises from brown adipose tissue. It is very uncommon in the cervical region and is extremely rare in the pediatric age group. Their rarity -and lack of awareness make their diagnosis clinically challenging. The curative treatment is a complete excision. All neck masses excised should be subjected for HPE for adequate treatment.

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