Int J Clin Pediatr

International Journal of Clinical Pediatrics, ISSN 1927-1255 print, 1927-1263 online, Open Access

Article copyright, the authors; Journal compilation copyright, Int J Clin Pediatr and Elmer Press Inc

Journal website https://www.theijcp.org

Case Report

Volume 11, Number 3, October 2022, pages 92-97

A Hibernoma of the Neck Complicated With an Abscess

Figure 1. (a, b) Coronal T2-weighted DIXON fat-suppressed image and a coronal T1w image showing a T2 hyperintense and T1 homogeneously hypointense mass in level IV left with central cystic/necrotic formation on T2w. (c, d) Coronal 3DT1 fat-suppressed image after gadolinium showing enhancement of the walls of the central cyst and axial diffusion-weighted image (DWI) showing obvious diffusion restriction, all suggestive for abscess formation in the pre-existing mass.

Figure 2. Axial T2w image (a), axial T1w image (b) and axial T1w fat-suppressed image after gadolinium administration (c). Axial section at the upper level of the hibernoma without presence of abscess showing the mass to be T2 hyperintense, isointense to muscle on T1w images and showing a diffuse enhancement after gadolinium.

Figure 3. Hematoxylin and eosin stain. Microscopic examination shows multiple small brown fat cells with multiple small vacuoles on a slightly myxoid background (with courtesy from Department of Pathology).

**Table 1.** Characteristics of Hibernoma
Definition	Benign soft-tissue tumor which originates from the remnants of fetal brown adipose tissue
DD: differential diagnosis; MRI: magnetic resonance imaging; CT: computed tomography; PET: positron emission tomography.
Clinical findings	Mostly asymptomatic slow-growing, mobile, non-sensitive mass; Symptoms by compression of adjacent structures; Location: thigh, interscapular, mediastinum, back, head-and neck; Peak incidence: 30 - 50 years, female > male; DD liposarcoma, lipoma, angiolipoma
Imaging [9]	Ultrasonography: hyperechogenic mass with hypervascularity +/- arteriovenous shunts; MRI: imaging of choice: 1) Well-delineated mass, vascularized, enhancing after contrast injection; 2) T1/T2: high signal intensity but less than subcutaneous fat; 3) Fat saturation sequences: no removing signal; CT with contrast: hypervascularity and septae; Non-contrast CT: hypodense and well-delineate; difficult to distinguish from subcutaneous adipose tissue; PET: high metabolic activity - obsolete
Histology	Macroscopic: soft rubbery mass; Microscopic: 1) Multivacuolated brown adipocytes; 2) Small round central nucleus with large amount of eosinophilic cytoplasm; 3) Multiple small vacuoles; 4) Four subtypes: typical, spindle, lipoma-like and myxoid
Treatment	Surgical excision; No malignant transformations or metastasis

Table 1. Characteristics of Hibernoma

Definition

Benign soft-tissue tumor which originates from the remnants of fetal brown adipose tissue

DD: differential diagnosis; MRI: magnetic resonance imaging; CT: computed tomography; PET: positron emission tomography.

Clinical findings

Mostly asymptomatic slow-growing, mobile, non-sensitive mass; Symptoms by compression of adjacent structures; Location: thigh, interscapular, mediastinum, back, head-and neck; Peak incidence: 30 - 50 years, female > male; DD liposarcoma, lipoma, angiolipoma

Imaging [9]

Ultrasonography: hyperechogenic mass with hypervascularity +/- arteriovenous shunts; MRI: imaging of choice: 1) Well-delineated mass, vascularized, enhancing after contrast injection; 2) T1/T2: high signal intensity but less than subcutaneous fat; 3) Fat saturation sequences: no removing signal; CT with contrast: hypervascularity and septae; Non-contrast CT: hypodense and well-delineate; difficult to distinguish from subcutaneous adipose tissue; PET: high metabolic activity - obsolete

Histology

Macroscopic: soft rubbery mass; Microscopic: 1) Multivacuolated brown adipocytes; 2) Small round central nucleus with large amount of eosinophilic cytoplasm; 3) Multiple small vacuoles; 4) Four subtypes: typical, spindle, lipoma-like and myxoid

Treatment

Surgical excision; No malignant transformations or metastasis