Hibernoma: Don’t be caught out by a PET scan!

Cutaneous lesions and other non-endocrine manifestations of Multiple Endocrine Neoplasia type 1 syndrome

Background

Multiple Endocrine Neoplasia type 1 is a rare genetic syndrome mainly caused by mutations of MEN1 gene and characterized by a combination of several endocrine and non-endocrine manifestations. The objective of this study was to describe cutaneous lesions and other non-endocrine manifestations of MEN1 in a cohort of patients with familial (F) and sporadic (S) MEN1, compare the prevalence of these manifestations between the two cohorts, and investigate the correlation with MEN1 mutation status.

Methods

We collected phenotypic and genotypic data of 185 patients with F-MEN1 and S-MEN1 followed from 1997 to 2022. The associations between F-MEN1 and S-MEN1 or MEN1 mutation-positive and mutation-negative patients and non-endocrine manifestations were determined using chi-square or Fisher's exact tests or multivariate exact logistic regression analyses.

Results

The prevalence of angiofibromas was significantly higher in F-MEN1 than in S-MEN1 in both the whole (p < 0.001) and index case (p = 0.003) cohorts. The prevalence of lipomas was also significantly higher in F-MEN1 than in S-MEN1 (p = 0.009) and in MEN1 mutation-positive than in MEN1 mutation-negative (p = 0.01) index cases. In the whole cohort, the prevalence of lipomas was significantly higher in MEN1 mutation-positive compared to MEN1 mutation-negative patients (OR = 2.7, p = 0.02) and in F-MEN1 than in S-MEN1 (p = 0.03), only after adjustment for age. No significant differences were observed for the other non-endocrine manifestations between the two cohorts. Hibernoma and collagenoma were each present in one patient (0.5%) and meningioma and neuroblastoma in 2.7% and 0.5%, respectively. Gastric leiomyoma was present in 1.1% of the patients and uterine leiomyoma in 14% of women. Thyroid cancer, breast cancer, lung cancer, basal cell carcinoma, melanoma, and colorectal cancer were present in 4.9%, 2.7%, 1.6%, 1.6%, 2.2%, and 0.5% of the whole series, respectively.

Conclusions

We found a significantly higher prevalence of angiofibromas and lipomas in F-MEN1 compared with S-MEN1 and in MEN1 mutation-positive compared to MEN1 mutation-negative patients. In patients with one major endocrine manifestation of MEN1 , the presence of cutaneous lesions might suggest the diagnosis of MEN1 and a possible indication for genetic screening.

Beyond the "3 Ps": A critical appraisal of the non-endocrine manifestations of multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1), an autosomal-dominantly inherited tumor syndrome, is classically defined by tumors arising from the "3 Ps": Parathyroids, Pituitary, and the endocrine Pancreas. From its earliest descriptions, MEN1 has been associated with other endocrine and non-endocrine neoplastic manifestations. High quality evidence supports a direct association between pathogenic MEN1 variants and neoplasms of the skin (angiofibromas and collagenomas), adipose tissue (lipomas and hibernomas), and smooth muscle (leiomyomas). Although CNS tumors, melanoma, and, most recently, breast cancer have been reported as MEN1 clinical manifestations, the published evidence to date is not yet sufficient to establish causality. Well-designed, multicenter prospective studies will help us to understand better the relationship of these tumors to MEN1, in addition to verifying the true prevalence and penetrance of the well-documented neoplastic associations. Nevertheless, patients affected by MEN1 should be aware of these non-endocrine manifestations, and providers should be encouraged always to think beyond the "3 Ps" when treating an MEN1 patient.

CD10 (neprilysin) expression: a potential adjunct in the distinction of hibernoma from morphologic mimics

Although the morphologic diagnosis of hibernoma is usually straightforward, some hibernomas have atypical morphologic features, mimicking atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLs). In addition, the multivacuolated brown fat cells may be mistaken for lipoblasts by pathologists, especially those without significant soft tissue tumor exposure. Thus, we continue to receive in consultation cases of hibernoma sent for MDM2 fluorescence in situ hybridization testing to exclude ALT/WDL. Testing hibernomas for MDM2 amplification, however, adds cost and delays the final diagnosis. Recently, we have noted expression of neprilysin (CD10, CALLA), a zinc-dependent metalloproteinase involved in the inactivation of various peptide hormones, in brown fat cells, and wished to explore the potential utility of this widely available, inexpensive ancillary test in the differential diagnosis of hibernoma. Formalin-fixed, paraffin-embedded tissue sections from well-characterized cases of hibernoma (n = 48), brown fat (n = 21), ALTs/WDLs (n = 17), pleomorphic liposarcomas (PLPSs) (n = 6), lipomas (n = 5), and fat necrosis (n = 5) were immunostained for CD10, using a commercially available antibody and routine laboratory protocols. CD10 expression was evaluated in both adipocytes and in surrounding stromal cells. The hibernomas occurred in 28 men and 20 women, ranging from 11 to 76 years of age and involved the extremities (n = 25), pelvis (n = 7), abdomen/pelvis/retroperitoneum (n = 7), head and neck region (n = 6), back (n = 2), and chest (n = 1). All showed diffuse, strong CD10 expression in multivacuolated brown fat cells and in the majority of adjacent univacuolated fat cells. Brown adipose tissue from various anatomic structures showed an identical pattern of immunoreactivity. In contrast, CD10 expression was present in the adipocytes of only 3 of 17 (18%) ALTs/WDLs and was absent in lipomas and fat necrosis. Lipoblasts expressed CD10 in 3 PLPSs. Expression of CD10 by surrounding fibroblastic stromal cells was more widespread, present in 13 hibernomas, 10 ALTs/WDLs, 1 instance of fat necrosis, 6 PLPSs, and 4 examples of brown fat. We conclude that immunohistochemistry for CD10 may represent a useful, rapid and inexpensive ancillary test in the differential diagnosis of hibernoma from potential morphologic mimics, especially when morphologic features favor hibernoma. CD10 expression in adipocytes, however, should be rigorously distinguished from fibroblastic stromal cell CD10 expression, a nonspecific finding.

Hibernoma of the Upper Extremity: Complete Case of a Rare but Benign Soft Tissue Tumor

Hibernoma is a rare benign lipomatous tumor showing differentiation of brown fatty tissue. To the author's best knowledge, there is no known case of malignant transformation or metastasis. Due to their slow, noninfiltrating growth hibernomas are often an incidental finding in the third or fourth decade of life. The vast majority are located in the thigh, neck, and periscapular region. A diagnostic workup includes ultrasound and contrast-enhanced MRI. Differential diagnosis is benign lipoma, well-differentiated liposarcoma, and rhabdomyoma. An incisional biopsy followed by marginal resection of the tumor is the standard of care, and recurrence after complete resection is not reported. The current paper presents diagnostic and intraoperative findings of a hibernoma of the upper arm and reviews similar reports in the current literature.

[Increased glucose uptake by seborrheic keratosis on PET scan]

BACKGROUND

Positron emission tomography (PET) is an examination based upon the uptake of a radioactive tracer by hypermetabolic cells. It is primarily used in tandem with tomodensitometry (PET-TDM) for cancer staging because of its high sensitivity and specificity for the detection of metastases. However, unusually high uptake may occur with benign tumours, including skin tumours. Herein, we report an extremely rare case of pathological uptake levels resulting from seborrhoeic keratosis.

PATIENTS AND METHODS

A 55-year-old male patient with oesophageal squamous-cell carcinoma was referred to us following the discovery of an area of high marker uptake following PET-TDM and corresponding to a pigmented skin lesion. No other areas of suspect high uptake were seen. The lesion was surgically excised and histological examination indicated seborrhoeic keratosis. The histological appearance was that of standard seborrhoeic keratosis without any notable mitotic activity.

DISCUSSION

PET-TDM is an examination that enables diagnosis of malignancy. However, rare cases have been described of increased marker uptake by benign cutaneous tumours such as histiocytofibroma, pilomatricoma and condyloma. To date, there have only been only very few cases of increased uptake due to seborrhoeic keratosis.

CONCLUSION

This extremely unusual case of increased glucose uptake in PET-TDM due to seborrhoeic keratosis confirms that the hypermetabolic activity detected by this examination is not necessarily synonymous with malignancy and that confirmation by clinical and histological findings is essential. The reasons for increased metabolic activity within such benign tumours are not known.