Interact CardioVasc Thorac Surg 2009;9:717-719. doi:10.1510/icvts.2009.209247
© 2009 European Association of Cardio-Thoracic Surgery
Case report - Thoracic oncologic |
Resection of intrapericardial hibernoma associated with constrictive pericarditis
Alper Ucak,
Kaan Inan,
Burak Onan* and
Ahmet Turan Yilmaz
Department of Cardiovascular Surgery, GATA Haydarpasa Education Hospital, Istanbul, Turkey
Received 11 April 2009;
received in revised form 18 June 2009;
accepted 22 June 2009
*Corresponding author. GATA Haydarpasa Egitim Hastanesi, Kalp ve Damar Cerrahisi Klinigi, Tibbiye Caddesi, Uskudar, Istanbul, 34668 Turkey. Tel.: +90-553-6223878; fax: +90-216-3487880.
E-mail address: burakonan{at}hotmail.com (B. Onan).
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Abstract
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Hibernoma is a benign soft-tissue tumor, which arises from the remnants of fetal brown adipose tissue. Out of less than 300 cases of hibernoma described to date, pericardial sac is an unusual localization to develop. When the tumor increases in size, this benign pathology can lead to compression of cardiac chambers and cause life-threatening complications in an asymptomatic patient. Here, the authors present the case of a 20-year-old male who underwent an operation for the treatment of constrictive pericarditis, in which an intrapericardial sessile lesion over diaphragmatic surface of pericardial sac was incidentally discovered. The tumor was excised and diagnosed as hibernoma. No recurrence was evident two years after the procedure.
Key Words: Intrapericardial hibernoma; Constrictive pericarditis; Cardiac tamponade
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1. Introduction
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Hibernoma is a benign soft-tissue tumor, which arises from the remnants of fetal brown adipose tissue. The tumor usually develops along the esophagus and the trachea, posterior neck, interscapular area and around the great vessels of the mediastinum including vena cava [1]. According to our literature review, less than 300 cases of hibernoma have been reported to date. Of these cases, less than 30 with various clinicopathological features have been diagnosed within the chest [2, 3]. However, we are not aware of any previous report of an intrapericardial hibernoma that was associated constrictive pericarditis as potential stimuli for the pathogenesis.
We report herein a case of intrapericardial hibernoma, which was incidentally diagnosed in a patient operated for constrictive pericarditis, and demonstrate the pathological features of this rare intrathoracic tumor that should be remembered in differential diagnosis of intrathoracic tumors.
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2. Case report
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A 20-year-old male presented with exertional dyspnea and palpitation that had increased within the last three months. The patients had no weight loss or loss of appetite during this period. The medical history was unremarkable except for a history of atypical pneumonia one year ago. Cardiac auscultation revealed decrease in intensity of S1 and S2. Physical examination also showed jugular venous distension, pitting edema in lower extremities. Besides, abdominal palpation showed hepatomegaly. Laboratory data, respiratory function tests and arterial blood gas analysis were within the normal limits. A chest roentgenogram showed enlargement of cardiac silhouette with an increased cardiothoracic index. A transthoracic echocardiography diagnosed an increase in the thickness of pericardium suggesting constrictive pericarditis. No fluid collection was observed in pericardial space but a space-occupying lesion of 1 cm in thickness was suspected over the diaphragmatic surface. Nevertheless, the tumor was not clearly visualized because of thickened pericardium. There was minimal compression of the right ventricle on diastole by the lesion. The right cardiac chambers were also dilated, and left ventricular ejection fraction was 42%. A subsequent computed tomography scan showed diffuse thickening (5 mm) of the pericardium and diffuse calcification, confirming constrictive pericarditis. Thus, an operation was planned to relieve the clinical symptoms and to diagnose the cause of pericardial thickening as well as intrapericardial mass lesion causing right ventricular compression.
On median sternotomy, the mediastinum was explored and constrictive pericarditis was diagnosed macroscopically but pericardial specimens were sent for pathological examination. After pericardiactomy, a sessile lesion was incidentally discovered over diaphragmatic surface of the pericardium (Fig. 1). There was no pericardial effusion or evident major compression of the right ventricle or vena cava detected perioperatively. The mass was removed easily from pericardial space with blunt dissection. There was no invasion of surrounding structures including the right ventricle, diaphragm and inferior vena cava. The lesion was soft, lobulated, and sessile lesion of 1 cm in thickness suggesting a lipoma or lipomatous hypertrophy involving the mediastinum. However, pathologic sections diagnosed hibernoma, which revealed clear multivacuolated cells filled with lipid droplets and granular intense eosinophilic cytoplasm (Fig. 2). Additionally, the sections excluded an infection, tuberculosis or other bacterial causes, and malignancy but documented severe calcification of pericardial tissue due to constrictive pericarditis. The patient was discharged home uneventfully on postoperative day 10. The patient is currently well, and no recurrence was evident two years after the procedure.
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Fig. 1. Operative view demonstrates the localization of intrapericardial hibernoma over diaphragmatic surface of the pericardium. Relationship of the tumor with inferior vena cava and thickened pericardium is demonstrated.
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Fig. 2. Histologic micrograph shows ‘multivacuolated cells’ showing a centrally localized nucleus (inset), which confirms the diagnosis of Hibernoma (H&E x400).
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3. Discussion
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Hibernoma is a rare benign tumor of brown adipose tissue. Trauma to the fat cells by any stimuli, such as infection, or inflammation can be responsible for the occurrence of hibernoma. The tumor usually manifests as a slowly growing, encapsulated, painless soft-tissue mass without clinical significance. Echocardiography and magnetic resonance imaging are useful modalities on diagnosis. The mean tumor size reported was 9.3 cm in diameter (range, 1–24 cm) [3]. When the tumor develops, compression of the surrounding structures can be evident according to the size and localization of the tumor. Therefore, compression of the chambers of the heart can be observed, as done in our case.
Hibernoma is a tumor diagnosed mostly in adults and most commonly develop outside the mediastinum. The thigh is the most common site for the typical hibernoma and lipoma-like hibernoma variants [2, 3]. Out of more than 300 cases of hibernoma described to date, less than 30 were intrathoracic hibernoma that involved pleural cavity mostly, the mediastinum in four cases, the pericardium in one case that was presented with pericardial effusion rather than a space-occupying mass lesion in pericardial space and the right atrium in one case [3–6]. Therefore, pericardial space is an atypical localization for the occurrence of adipose tissue tumors as well as hibernoma. According to our literature review, none of these cases showed compression of cardiac chambers, or presented with an inflammatory process.
The mechanism for the growth of hibernoma with intrapericardial localization in the current case is not clear. Considering the etiology, it has been described that vestiges of brown fetal fat can persist around the great vessels of the mediastinum [1]. This can explain the occurrence of hibernoma around great vessels including the junction of inferior vena cava and the right atrium in pericardial space. On the other hand, there are various hypotheses put forward to explain the origin of hibernoma at unusual sites, where brown fat tissue is not present in adults. These hypotheses include aberrant differentiation of mesenchyma cells, ectopic growth or migration of adipose tissue [2]. Although it is difficult to draw a conclusion with a single case, we believe that an inflammatory or infectious process, such as constrictive pericarditis can lead to activation of fetal brown fat cell remnants localized around inferior vena cava and intrapericardial hibernoma.
Hibernoma is one of the tumors of adipose tissue that reveals specific cells, termed ‘multivacuolated adipocytes’ (Fig. 2, inner view). In pathologic sections, the presence and quantity of these cells help to diagnose hibernoma and to exclude the other types of adipose tumors including lipoma, lipomatous hypertrophy and liposarcoma [7]. The authors concluded that a diagnosis of hibernoma should always be taken into consideration in cases where macroscopic criteria for lipomatous hypertrophy or lipoma are not satisfied and the quantity of multivacuolated cells represents the overwhelming majority of the cells in the lesion [7, 8]. According to the key histological appearance, four variants were identified, each showing the prototypical cell type of hibernoma described previously; typical hibernoma mostly: a mixture of pale hibernoma cells and white fat cells, the lipoma-like variant with only scattered hibernoma cells among fat cells, the myxoid variant and a spindle cell variant. Additionally, it has been noted that no atypia was found within the fatty component in cases with hibernoma [3].
Because the tumor usually has a well-defined capsule and does not show infiltrative growth pattern, surgical excision is always recommended without sacrificing vital structures. Furlong and colleagues [3] stated in their large series of 170 cases that behavior of hibernoma was benign for all and tumor is not expected to recur with complete excision. Nevertheless, a residual tumor tissue after resection should not be considered neoplastic.
In conclusion, intrapericardial localization for hibernoma is uncommon. The diagnosis of typical ‘multivacuolated adipocytes’ establishes the diagnosis although there are four different histological variants of this pathology. Because the tumor displaces rather than invades adjacent structures, resection of hibernoma is safe and necessary when tumor causes compression of adjacent structures. Our experience confirmed that hibernoma is a benign tumor without showing recurrence after surgery.
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References
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Abstract
1. Introduction