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Case Report Sonographic Findings of Hibernoma. A Report of Two Cases Jendrik Hardes, MD, 1 Stefanie Scheil-Bertram, MD, 2 Erich Hartwig, MD, 3 Carsten Gebert, MD, 1 Georg Gosheger, MD, 1 Michael Schulte, MD 4 1 Department of Orthopedics, Westfa ¨lische Wilhelms-Universita ¨t, Albert-Schweitzer-Str. 33, 48149 Mu ¨nster, Germany 2 Institute of Pathology, University of Ulm, Germany 3 Department of Trauma, Hand- and Recontructive Surgery, University of Ulm, Germany 4 Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Rotenburg (Wu ¨mme), Germany Received 8 January 2004; accepted 2 February 2005. ABSTRACT: We present 2 cases of hibernoma, a rare lipomatous tumor arising from brown fat tissue. In each case, a hyperechoic mass in comparison to sur- rounding musculature combined with elevated vascu- larization was highly suggestive of a liposarcoma. As a rule, malignancy cannot be excluded safely by imag- ing modalities, and a preoperative biopsy should be performed. Although rare, hibernomas should be considered in the differential diagnosis of lipomatous soft-tissue tumors. ª 2005 Wiley Periodicals, Inc. J clin Ultrasound 33:298–301, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jcu.20126 Keywords: hibernoma; lipoma; liposarcoma; color Dop- pler sonography; brown fat tumor; soft-tissue tumor H ibernomas are rare tumors originating from brown fat, a special form of fetal adipose tis- sue. Brown adipose tissue is found in hibernating animals, is rich in glycogen, cholesterol and phos- pholipids, and is thought to play a role in thermo- regulation and endocrine functions. Brown fat is also found in humans. It has the function of fat storage and is hypervascularized in contrast to white adipose tissue. 1,2 The amount of brown fat decreases during childhood, and in adults it accounts for only 1% of adipose tissue. We report the sonographic findings in 2 cases of this rare tumor of brown adipose tissue with its clinical, correlative imaging, and histopathological features. CASE 1 A 25-year-old woman was admitted to our hospital because her general practitioner was unable to remove under local anesthesia. a subcutaneous left-sided gluteal tumor measuring approximately 20 cm in diameter. The patient first became aware of this painless tumor 3 months earlier. Since that time, she had noticed no change in tumor size. Medical history revealed no other pathological findings. On physical examination, the tumor was soft and not mobile above the gluteal fascia. The overlying skin showed a discrete livid dis- coloration and was warm. No thrill was felt. The lower extremity had free range of motion and no sensory deficit was present. Sonography was performed using a Quantum 2000 scanner and a 7,5-MHz linear-array transdu- cer (Siemens Medical Solutions, Erlangen, Ger- many). Sonographically, the tumor appeared well defined, heterogeneous, and moderately echogenic compared with the underlying gluteal muscles and revealed hypervascularization on color Doppler flow imaging with a median color pixel density within the tumor ROIs of 2.1%, as measured in various areas of the lesion (Figure 1). The tumor measured 10.5 8.0 6.5 cm and was attached to the superficial gluteal fascia. CT revealed a tumor with heterogeneous density values. Peripherally, the tumor showed a density equivalent to muscle of 15 Hounsfield units (HU), whereas a hypodense area (–3 HU) could be observed centrally (Figure 2). Generally, the tumor was hyperdense compared with the surrounding subcutaneous fat tissue. After administration of Correspondence to: J. Hardes Ó 2005 Wiley Periodicals, Inc. 298 JOURNAL OF CLINICAL ULTRASOUND

Sonographic findings of hibernoma. A report of two cases

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Page 1: Sonographic findings of hibernoma. A report of two cases

Case Report

Sonographic Findings of Hibernoma. A Reportof Two Cases

Jendrik Hardes, MD,1 Stefanie Scheil-Bertram, MD,2 Erich Hartwig, MD,3 Carsten Gebert, MD,1

Georg Gosheger, MD,1 Michael Schulte, MD4

1Department of Orthopedics, Westfalische Wilhelms-Universitat, Albert-Schweitzer-Str. 33,48149 Munster, Germany2Institute of Pathology, University of Ulm, Germany3Department of Trauma, Hand- and Recontructive Surgery, University of Ulm, Germany4Department of Trauma and Reconstructive Surgery, Diakoniekrankenhaus Rotenburg (Wumme), Germany

Received 8 January 2004; accepted 2 February 2005.

ABSTRACT: We present 2 cases of hibernoma, a rarelipomatous tumor arising from brown fat tissue. Ineach case, a hyperechoic mass in comparison to sur-rounding musculature combined with elevated vascu-larization was highly suggestive of a liposarcoma. Asa rule, malignancy cannot be excluded safely by imag-ing modalities, and a preoperative biopsy should beperformed. Although rare, hibernomas should beconsidered in the differential diagnosis of lipomatoussoft-tissue tumors. ª 2005 Wiley Periodicals, Inc. Jclin Ultrasound 33:298–301, 2005; Published onlinein Wiley InterScience (www.interscience.wiley.com).DOI: 10.1002/jcu.20126

Keywords: hibernoma; lipoma; liposarcoma; color Dop-pler sonography; brown fat tumor; soft-tissue tumor

Hibernomas are rare tumors originating frombrown fat, a special form of fetal adipose tis-

sue. Brown adipose tissue is found in hibernatinganimals, is rich in glycogen, cholesterol and phos-pholipids, and is thought to play a role in thermo-regulation and endocrine functions. Brown fat isalso found in humans. It has the function of fatstorage and is hypervascularized in contrast towhite adipose tissue.1,2 The amount of brown fatdecreases during childhood, and in adults itaccounts for only 1% of adipose tissue. We reportthe sonographic findings in 2 cases of this raretumor of brown adipose tissue with its clinical,correlative imaging, and histopathological features.

CASE 1

A 25-year-old woman was admitted to our hospitalbecause her general practitioner was unable toremove under local anesthesia. a subcutaneousleft-sided gluteal tumor measuring approximately20 cm in diameter. The patient first became awareof this painless tumor 3 months earlier. Since thattime, she had noticed no change in tumor size.Medical history revealed no other pathologicalfindings. On physical examination, the tumorwas soft and not mobile above the gluteal fascia.The overlying skin showed a discrete livid dis-coloration and was warm. No thrill was felt. Thelower extremity had free range of motion and nosensory deficit was present.

Sonography was performed using a Quantum2000 scanner and a 7,5-MHz linear-array transdu-cer (Siemens Medical Solutions, Erlangen, Ger-many). Sonographically, the tumor appeared welldefined, heterogeneous, and moderately echogeniccompared with the underlying gluteal muscles andrevealed hypervascularization on colorDoppler flowimagingwith amedian color pixel densitywithin thetumor ROIs of 2.1%, asmeasured in various areas ofthe lesion (Figure 1). The tumor measured 10.5 �8.0 � 6.5 cm and was attached to the superficialgluteal fascia.

CT revealed a tumor with heterogeneous densityvalues. Peripherally, the tumor showed a densityequivalent to muscle of 15 Hounsfield units (HU),whereas a hypodense area (–3 HU) could beobserved centrally (Figure 2). Generally, the tumorwas hyperdense compared with the surroundingsubcutaneous fat tissue. After administration of

Correspondence to: J. Hardes

� 2005 Wiley Periodicals, Inc.

298 JOURNAL OF CLINICAL ULTRASOUND

Page 2: Sonographic findings of hibernoma. A report of two cases

contrast medium, the tumor showed a heteroge-neous enhancement. MRI showed a reduced signalintensity on T1- and an elevated signal intensity onT2-weighted images in contrast to subcutaneoustissue. Following injection of gadolinium-DTPA,the tumor showed a central enhancement. Themar-gins showed no contrast enhancement (Figure 3).Because of the hypervascularization of the lesion, amalignant tumor could not be excluded, and there-fore a core needle biopsy was performed. No bleed-ing complications occurred. Histopathologically, thebiopsy specimen consisted of predominantly multi-

vacuolated adipocytes with interspersed univacuo-lar fat cells (Figure 4). A large number of capillarieswere observed. Nomitosis or nuclear pleomorphismwas noted. Therefore a diagnosis of liposarcomacould be excluded and the histopathological diagno-sis of a hibernoma was established. A wide excisionof the tumor was performed. Intraoperatively, thetumor was found to have infiltrated the gluteal fas-cia. The tumor showed a homogenous yellow-graycolor (Figure 5). No postoperative complicationswere observed, and the patient has been withoutevidence of recurrence for 8 years.

CASE 2

A 25-year-old man underwent MRI scan because ofleft shoulder pain due to a posttraumatic defect of

FIGURE 1. Color Doppler sonography shows vessels within the

tumor.

FIGURE 2. CT scan of the left gluteal region shows a central

hypodense area (�3 Hounsfield units) with a peripheral rim with

muscle-equivalent density values (15 Hounsfield units)

FIGURE 3. Fat-saturated, T1-weighted coronal MR scan shows

inhomogeneous contrast enhancement after gadolinium injection.

FIGURE 4. Photomicrograph shows multivacuolated fat cells with

interspersed univacuolated fat cells (HE 10X).

HIBERNOMA

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Page 3: Sonographic findings of hibernoma. A report of two cases

the rotator cuff. As an incidental finding on T1 andfat-saturated images, a homogeneous, hyperinten-sive tumor measuring 7 � 3 � 2 cm, between thelevator scapulae muscle and the trapezius musclewas detected and diagnosed as lipoma. Annual sono-graphic evaluation was recommended. The patientwas admitted to our department 18 months afterdetection of the lesion because sonographic evalua-tion revealed an increase in tumor sizewith localizedpain. The tumor was palpable on the medial marginof the scapula. It was freely movable, and no changeof temperature of the overlying skin was noted. Therange of motion of the left shoulder was limited andpainful, probably as a result of the defect in thesupraspinatus tendon.

Sonography revealed a homogeneous, mildly echo-genic, and hypervascularized tumor (Figure 6).On MRI, the tumor displayed a heterogeneouscontrast enhancement. The dorsal margin of thelesion showed no contrast enhancement. A wideresection of the tumor was performed. Intraopera-tively, the tumor was surrounded by a thin capsuleand showed no infiltration of the adjacent muscles.The tumor displayed a homogeneous yellow-graycolor. Histologically, mature adipose fat cells weremixed in with multivacuolated fat cells. Vascularchannels were found in connective tissue septae.No nuclear atypia was noted. The diagnosis of ahibernoma was made. The patient is without evi-dence of recurrence after 6 years.

DISCUSSION

Hibernoma was first reported in 1906 by Merkel,3

who found this tumor in the breast and named it apseudolipoma. Predilection sites are the inter-scapular area, axilla, neck, mediastinum, retro-peritoneum, and thigh.1,2 The peak incidence ofhibernoma is in the third and fourth decades of

life,4 with women slightly more often affectedthan men.2 Patients have usually been aware ofthis tumor for many years. Whilst normally slowgrowing, hibernomas have been reported torapidly increase in size up to 20 cm in diameter.2,5

Clinically, the tumor usually appears as a soft,freely mobile, nontender, palpable mass whenlocated in the subcutaneous tissue. It may alsodisplace other organs or connective tissue andmuscles.4 The results of physical examinationare often suggestive of a lipoma. In contrast tolipomas, however the overlying skin can be warm-er due to the rich vascularization of the tumor.1

As a first diagnostic step for a palpable soft-tissue tumor, sonography is recommended. Gray-scale images usually cannot distinguish reliablya lipoma, hibernoma, or low-grade liposarcoma.6

Fornage and Tassin7 reported that subcutaneouslipomas are well defined in 60% of cases and showvariable echogenicity. Isoechoic and hyperechoicpatterns are most commonly found in lipomas,

FIGURE 6. Case 2: Color Doppler sonogram shows a mildly echegenic

mass containing some color Doppler signals.

FIGURE 5. Photograph of the cut section of the hibernoma shows

hemorrhagic areas peripherally.

HARDES ET AL

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Page 4: Sonographic findings of hibernoma. A report of two cases

whereas a hypoechoic mass is associated with abroader differential diagnosis, including malig-nant tumors.7 In our 2 cases, the hibernomaswere hypoechoic in comparison with the sur-rounding subcutaneous fat.

However, even a hyperechoic soft-tissue tumorwith increased vascularization is suspicious of amalignant tumor. Belli et al8 reported that asmany as 70% of lipomas showed no flow signalon color Doppler sonography. Futani et al6

reported that the detection of more than 2 colorDoppler signals on color Doppler sonographywithin an area of 3 cm2 was suggestive of a well-differentiated liposarcoma. The present 2 casesdemonstrate that, in addition to malignant soft-tissue tumors, hibernoma is to be considered inthe differential diagnosis in the case of increasedvascularization. The presence of vascular chan-nels on color Doppler sonography in a case ofhibernoma has also been reported by Cook et al.1

Cross-sectional imaging studies (CT or MRI)are needed for preoperative planning.2 The hyper-vascularization of the tumor explains the hetero-geneous contrast enhancement seen on CT andMRI in most cases.2,5,9

Tissue characterization of hibernomas and otherlipomatous tumors with MRI, CT, and angiographyis not possible because of the high variability in sig-nal intensities seen in such tumors.9 The hypervas-cular and heterogeneous features of a hibernoma,seen on CT and MRI, distinguish it from a lipoma,which is hypovascular or avascular. However, it isdifficult to distinguish hibernomas from hypervas-cular maligant or benign soft-tissue tumors such aslow-grade liposarcomas, fibrosarcomas, malignantfibrous histiocytomas, and rhabdomyosarcomas orfrombenign angiolipomas, lipoblastomas, or heman-giomas.2,4

Most authors recommend a preoperative openbiopsy in lesions with a diameter of more than 3cm or a wide resection of tumors less than 3 cm indiameter.1,9 Accurate diagnosis can be facilitatedby selective sampling of the area of increased vas-cularization, which most likely represents a siteof viable malignancy.6 However, because of theincreased potential for hemorrhage, some authorshave chosen not to perform a biopsy when a hiber-noma is suspected.2,4

Histopathological diagnosis of hibernoma isstraightforward.10 Hibernoma contains 3 differentcell types in varying distribution: large, polygonal,multivacuolated cells with a granular cytoplasmand a central nucleus; univacuolated fat cells witha peripheral nucleus as in white fat tissue; andsmaller round cells with an eosinophil, granularcytoplasm.11 Intermediate forms between lipomaand hibernoma are not rare.11

There has been no report of malignant hiber-noma.2 Therefore, marginal resection is the therapyof choice, which is usually easily performed whenthe lesion is encapsulated. No local recurrenceshave been reported after complete resection.2,10

REFERENCES

1. Cook MA, Stern M, de Silva RD. MRI of a hiber-noma. J Comput Assist Tomogr 1996;20:333.

2. Rigor VU, Goldstone SE, Jones J, et al. Hibernoma.A case report and discussion of a rare tumor. Can-cer 1986;57:2207.

3. Merkel H. On a pseudolipoma of the breast [in Ger-man]. Beitr Path Anat 1906;39:152.

4. Kindblom LG, Angervall L, Stener B, et al. Inter-muscular and intramuscular lipomas and hiber-nomas. A clinical, roentgenologic, histologic, andprognostic study of 46 cases. Cancer 1974;33:754.

5. Dale PA, Frassica FJ, Reiman HM, et al. Hiber-noma. A case report. Orthopedics 1987;10:1587.

6. Futani H, Yamagiwa T, Yasojimat H, et al. Distinc-tion between well-differentiated liposarcoma andintramuscular lipoma by power Doppler ultrasonog-raphy. Anticancer Res 2003;23:1713.

7. Fornage BD, Tassin GB. Sonographic appearancesof superficial soft tissue lipomas. J Clin Ultrasound1991;19:215.

8. Belli P, Costantini M, Mirk P, et al. Role of colorDoppler sonography in the assessment of musculo-skeletal soft tissue masses. J Ultrasound Med 2000;19:823.

9. Deseran MW, Seeger LL, Doberneck SA, et al. Casereport 840: hibernoma of the right gracilis muscles.Skeletal Radiol 1994;23:301.

10. Nigrisoli M, Ruggieri P, Picci P, et al. Case report489: hibernoma of left thigh. Skeletal Radiol 1988;17:432.

11. Angervall L, Nilsson L, Stener B. Microangio-graphic and histological studies in 2 cases of hiber-noma. Cancer 1964;17:685.

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