MR and CT findings in a case of hibernoma of the thigh extending into the pelvis

Pediatric cervicomediastinal hibernoma: a case report

Hibernoma is a rare lipomatous tumor of brown fat origin. Though uniformly benign in nature these tumors may cause symptoms secondary to extrinsic compression of neighboring structures. Hibernomas may be found anywhere that normal fetal brown fat may be located but are most commonly located in the thigh. We present a case of a hibernoma presenting as an unusual cervicomediastinal mass in a 6-year-old male. This mass was discovered during a diagnostic chest x-ray for pneumonia and treated by resection. Complete surgical resection is considered curative. Hibernoma should be considered in the differential diagnosis of any lipomatous tumor.

Imaging of hibernomas: A retrospective study on twelve cases

BACKGROUND

To analyze the imaging features of hibernomas on computed tomography (CT) and magnetic resonance (MRI).

METHODS

Twelve hibernomas were retrospectively assessed with CT and MR imaging and compared to the histology of the specimen

RESULTS

Nine females and three males with a mean age of 30 years were included. Ten tumors occurred in the thigh and two affected the subcutis of the periscapular and buttock regions. On eight CT scans, seven (87,5%) lesions were homogeneous and mildly to moderately hyperdense compared to subcutaneous fat while one lesion was heterogeneous with mixed hypo and hyperattenuating areas. On six T1W images, five (83,3%) lesions appeared homogeneous and hypointense relative to subcutaneous fat and one was heterogeneous. Incomplete fat suppression was depicted in all cases. All lesions displayed marked enhancement. Large intratumoral vessels were depicted in three of the 12 (25%) cases. Septations were depicted on four of the eight unenhanced CT and on all six MRI examinations.

CONCLUSIONS

Hibernoma usually appears hypodense and hypointense relative to subcutaneous fat on pre-contrast CT and MR T1W with variable enhancement patterns and incomplete fat suppression on STIR or fat-saturated sequences. These characteristics relate directly to the presence of brown fat. However, atypical findings such as heterogeneous patterns of mixed fatty and non fatty components on unenhanced CT and MR T1W can be also encountered. Absence of large intratumoral vessels should not exclude hibernomas from the differential diagnosis of regional lipomatous tumors.

Intraosseous hibernoma

We describe the imaging and pathological features of a rare case of sacral hibernoma that was discovered incidentally in a patient with low back pain. The benign-appearing, small intraosseous lesion in the sacrum was sclerotic on CT. MRI revealed that the lesion was heterogeneously hyperintense on T1W (lower in intensity than subcutaneous fat) and heterogeneously hypointense on fat-saturated T2W and STIR images. It showed mild heterogeneous enhancement on the post-contrast fat-saturated T1 MR images due to increased vascularity. A biopsy of the lesion was performed. The biopsy specimen demonstrated multivacuolated cells with immunohistochemical features of brown adipose tissue consistent with hibernoma.

[Hibernoma of the thigh]

Hibernoma is a rare benign tumour of brown fat. It presents as a voluminous slow-growing mass in the regions where remnants of brown fat can remain in adults. We report a case of a hibernoma on the thigh and present the diagnostic and therapeutic elements of this type of tumour, whose differential diagnosis of liposarcoma.

Subpleural Hibernoma

Here we report the case of a 41-year-old man with an asymptomatic, 5-cm, pleural-based mass excised by thoracoscopy. We also review the clinical, radiologic, and pathologic features of hibernomas.

Hibernoma: a case report demonstrating usefulness of MR angiography in characterizing the tumor

Hibernoma is a rare, benign soft-tissue tumor composed of brown fat. In the past, there has been an extensive discussion of the CT attenuation and MRI signal characteristics of hibernomas. However, recent reports have focused upon the tumor vascularity of hibernomas. We describe the only case in the literature which utilizes state of the art contrast enhanced MR angiography to clearly characterize the surface and intratumoral vessels to help confirm the diagnosis of a hibernoma and aid in the preoperative planning.

Hibernoma: MRI features in eight consecutive cases

AIM

To describe the preoperative magnetic resonance imaging findings of eight histologically-proven cases of hibernoma.

MATERIALS AND METHODS

The site, size, and signal characteristics of eight consecutive hibernomas were retrospectively assessed on T1-weighted spin-echo and short T1 inversion recovery (STIR)/fat-saturated T2-weighted fast spin echo magnetic resonance images. Four patients also had gadolinium-enhanced fat-saturated T1-weighted spin echo imaging. Patient age and sex, and duration of symptoms were recorded.

RESULTS

Three female and five male patients with an average age 36 years (range 16-53 years) were included. Seven lesions occurred in the thigh, four in the anterior compartment and three in the posterior compartment. One lesion occurred superficial to the scapula. All cases demonstrated common magnetic resonance imaging findings of a well-defined, heterogeneous mass, slightly or clearly hypo-intense to subcutaneous fat on T1-weighted spin-echo images, with prominent thin low signal bands throughout the tumour. The lesions failed to fully suppress on STIR or fat-saturated T2-weighted images. Only one of the four contrast-enhanced studies demonstrated increased vascularity in the tumour.

CONCLUSION

The MRI findings of a lesion that is diffusely slightly hypointense to surrounding subcutaneous fat, should prompt the operator to consider hibernoma in the differential diagnosis.

Hibernoma--correlation of histopathology and magnetic-resonance-imaging features in 10 cases

OBJECTIVE, DESIGN AND PATIENTS: Hibernoma is an uncommon, slow-growing, benign soft-tissue tumour resembling brown adipose tissue. The histological appearances are well-documented, but there are relatively few descriptions of the magnetic resonance (MR) imaging features. We report a retrospective comparison of the histological and MR appearances of ten hibernomas of the extremities, classified histologically into lipoma-like [<70% multivacuolated adipocytes (MVAs)] and non-lipoma-like hibernomas (>70% MVAs).

RESULTS

The lipoma-like hibernomas measured 4-27 cm in maximum size. All were well-defined on MR imaging and histology except for one subcutaneous lesion that blended in with surrounding fat histologically. All lesions were isointense with subcutaneous fat on T1- and T2-weighting apart from one lesion that was predominantly slightly hypointense on T1-weighting and predominantly slightly hyperintense on T2-weighting and STIR. Two slightly inhomogeneous lesions contained thin (<5 mm thickness) tortuous vessels. One patient received intravenous contrast, but the lesion did not enhance. The six non-lipoma-like hibernomas measured 2.5-15.5 cm in maximum size and all were unencapsulated. Three were well-defined and three partly ill-defined on MR imaging. There were no significant differences in the MR characteristics of the non-lipoma-like variants. On T1-weighting, the non-lipoma-like hibernomas that contained >90% MVAs were predominantly slightly hypointense to subcutaneous fat. One lesion was isointense with subcutaneous fat, but this lesion only contained from 80-90% MVAs. All non-lipoma-like lesions were slightly hyperintense on STIR but so too were two of the four lipoma-like lesions. Four of the six non-lipoma-like lesions showed marked or moderate inhomogeneity due to thick septa and prominent vessels. Of the two cases that received intravenous contrast, both showed enhancement corresponding to regions of >90% MVAs or prominent vessels within fibrous septa.

CONCLUSIONS

MR imaging has shown some distinguishing features between lipoma-like and non-lipoma-like hibernomas. Lipoma-like hibernomas are usually isointense with subcutaneous fat on T1-weighting, are either homogeneous or slightly inhomogeneous and may contain thin tortuous vascular structures. Non-lipoma-like hibernomas are pre-dominantly slightly hypointense to subcutaneous fat on T1-weighting, often display marked or moderate inhomogeneity with prominent septa and vessels and enhancement is typical. The appearances of non-lipoma-like hibernomas are not diagnostic and may be mimicked by lipoma variants and by well-differentiated liposarcoma or atypical lipoma.

Hibernoma: Report emphasizing large intratumoral vessels and high T1 signal

We present the computed tomography (CT) and magnetic resonance (MR) imaging features of a gluteal hibernoma found incidentally at CT in an 80-year-old woman. Large, tortuous vessels were demonstrated within a high-T1-signal mass at MR imaging, a combination of findings in hibernomas that has been illustrated but not emphasized in the literature. Such a constellation of findings should strongly suggest the diagnosis of hibernoma (rather than well-differentiated liposarcoma or other soft tissue tumor).

Hibernoma of the antero-lateral thigh

Hibernoma is a rare benign tumour of brown fat. In most cases it presents as a voluminous slow-growing mass in the regions where remnants of brown fat can remain in adults. We report a case of a hibernoma on the thigh and present the diagnostic and therapeutic elements of this type of tumour, whose differential diagnosis of liposarcoma.

Mediastinal hibernoma: a case report

Hibernomas are rare benign tumours that arise most often in adults from the remnants of fetal brown adipose tissue. They usually affect muscle and subcutaneous tissue and are asymptomatic and slow growing. The distribution of this tumour follows the sites of persistence of brown fat. Out of more then 100 cases described in the word literature only three hybernomas were mediastinal. A recent clinicopathological study of 170 cases from the Armed Forces Institute of Pathology confirmed the exceptionality of the intrathoracic location. This report describes a very rare case of mediastinal hibernoma in a young man.

Lipomatous tumors of soft tissue: MR appearance with histological correlation

There is a broad spectrum of lipomatous tumors that involve soft tissues including ordinary lipomas, variants of lipomas, heterotopic lipomas, lipomatosis, hibernomas and liposarcomas. The recognition of these tumors is important to avoid diagnostic pitfalls. The MR imaging appearance of the lesion, including location, shape and internal architecture, suggests the diagnosis of lipomatous tumors. The signal intensity on T1-, T2-, fat-suppressed T2-weighted (FS-T2) images or short tau inversion recovery (STIR), T1- and fat-suppressed T1-weighted images after Gd-DTPA administration can be a useful aid in distinguishing between biologically different types of lipomatous tumors. The imaging features are often characteristic and reflect the histological pattern of the tumors. We present an overview of the lipomatous tumors and we correlate MR imaging appearance with histological findings.

[Hibernoma: a rare case of massive weight loss]

Hibernoma is a rare soft tissue benign tumor composed of cells similar to those of brown fat observed in fetus and hibernating animals. Brown fat has thermogenous properties, by the way of carbohydrates and lipid catabolism, and can be of an important mean in thermoregulation. A massive weight loss is a rarely reported sign in patients with hibernoma. We report herein the case of a 47 man with a history of isolated weight loss, of 16 kg over 4 months. Clinical examination has shown a swelling of the right flank. Surgical resection has been made and histopathological examination has shown hibernoma. The post-operative weight gain confirmed the relationship between hibernoma and weight loss.

Fine-needle aspiration characteristics of hibernoma

BACKGROUND

Hibernoma is a rare, benign lipomatous tumor with features of brown fat. The preoperative diagnosis of hibernoma is difficult at times because its clinical, radiographic, and fine-needle aspiration (FNA) characteristics overlap with those of liposarcoma.

METHODS

The preoperative FNA findings of eight surgically excised hibernomas from seven patients (three men and four women, ages 24-60 years) were reviewed. The cytologic features were compared with the histologic features of the corresponding surgical specimens as well as lipomatous tumors and other lesions that may cause confusion in the differential diagnosis.

RESULTS

The FNA cytologic features of the hibernomas were found to correspond well with their histologic appearance. The FNA findings included small, round, brown fat-like cells with uniform, small cytoplasmic vacuoles and regular, small, round nuclei; delicate branching capillaries; and variable numbers of mature fat cells.

CONCLUSIONS

The FNA cytologic features of hibernoma are characteristic and useful in the preoperative investigation of lipomatous tumors, particularly with regard to excluding a diagnosis of liposarcoma.

Mediastinal hibernoma

A 46-year-old asymptomatic male was detected to have a posterior mediastinal mass on a routine check-up. He underwent thoracotomy to remove the mass, which was found to be a hibernoma. The mediastinum is an extremely rare site for an even rarer tumor like the hibernoma. An additional unique feature was the very large tumor size despite which the patient was asymptomatic. Imaging studies are not helpful in revealing its clinically indeterminate nature, hence a surgical specimen is necessary to establish the correct diagnosis. Total excision is advocated for cure, as there is no known malignant potential.