Mediastinal Hibernoma, A Rare Tumor Chaewoo Ahn, MD, and James C. Harvey, MD Department of Surgery, Kaiser Permanente Medical Center, Los Angeles, California
Hibernoma is an uncommon soft tissue tumor that is derived from the remnants of fetal brown fat. Review of the world medical literature revealed 90 cases, 6 of which were intrathoracic. We present the seventh case of intrathoracic hibernoma; in this case, the hibernoma was within the mediastinum without direct invasion of other structures. (Ann Thoruc Surg 1990;50:828-30)
H
ibernoma is a rare, benign soft tissue tumor composed of multiloculated fat cells derived from brown fat. The tumor was first described by Merkl [l]in 1906 as being composed of brown adipose tissue. The term hibernomu was proposed in 1914 by Gery (21 because of its morphologic similarity to the cells of the so-called hibernating gland of animals. By 1985, 80 cases of hibernoma were reported in the world medical literature [3]. The total grew to 89 in 1988 [4], and with an additional case reported in 1989 [5], the current total stands at 90. Of six reported intrathoracic hibernomas, five were confined within the subpleural chest [&lo], and one was intramyocardial [ll]. A 16-year-old Filipino boy was referred to the Thoracic Surgery service at Kaiser Permanente Medical Center, Los Angeles, CA, on January 20, 1989, because of a large anterior mediastinal mass that was discovered on a routine preemployment physical examination. The patient was in excellent health and completely asymptomatic. The past medical history and physical examination were noncontributory . A chest roentgenogram demonstrated a large mass in the left anterior mediastinum, inseparable from the cardiac silhouette (Fig 1).Computed tomography showed a 8 x 8 x 12-cm mixed-density mass, which was mainly fatty, in the left mediastinum, abutting the aortic and pulmonary arches and the left side of the heart without obvious invasion (Fig 2). On February 1, 1989, a median sternotomy was performed. A large, tan, lobulated and encapsulated, bilobed mass was found in the anterior-superior mediastinum. It was completely within the mediastinal pleura and extra: pleurally compressed the upper segment of the left lung. The left phrenic nerve was easily dissected free of the mass. The pericardium and major vascular structures
were not involved. The tumor was highly vascular but was removed without complication. The postoperative course was uneventful. The patient was discharged on the third postoperative day and has not shown any evidence of recurrence after 1 year. The fresh specimen was tan-brown, homogeneous, and encapsulated, with a buttery consistency. Attached to the specimen was a portion of a normal-appearing thymus that weighed 42 g and measured 8 x 3 x 3 cm. Light microscopic examination showed tumor cells arranged in lobules separated by fine reticulin fibers. Most of the cells were round or polygonal with monovacuolated or multivacuolated lipid-containing cytoplasm (Fig 3). These were mixed with cells having a less vacuolated, eosinophilic, granular cytoplasm. The nuclei were ovoid and spherical and central. A delicate fibrocollagenous and vascular capsule was present with inconspicuous mesothelial cells on the surface. The sections of thymus were normal. Comment Hibernomas are rare, benign tumors derived from brown adipose tissue, a specialized form of fat found in hibernating and nonhibernating animals. Brown fat was first
Accepted for publication May 7, 1990. Address reprint requests to Dr Ahn, Department of Surgery, Kaiser Permanente Medical Center, 1526 North Edgemont St, Los Angeles, CA 90027.
0 1990 by The
Society of Thoracic Surgeons
Fig 2 . Chest roentgenogram showing large opacity in left anterior mediastinum. 0003-4975/90/$3.50
Ann Thorac Surg 1990;50:828-30
Fig 2. Computed tomographic scan shows that the mass has a mixed density but is mainly fatty.
described by Velch in 1670. He noted a glandlike structure in the mediastinum of a woodchuck, a hibernating animal, and thought it to be associated with the thymus [12]. This was later recognized by Barkow in 1846 to be separate from the thymus, and he called it the "hibernating gland" [12]. Rasmussen [12] reviewed the morphology of this structure and discovered its presence in more than 50 species including nonhibernating animals such as rats, rabbits, cats, monkeys, and humans. In 1902, Shaw [13] demonstrated the axillary and subpleural fat of the human fetus and newborn to be largely brown fat, in contrast to the yellow fat of subcutaneous tissues. Finally, Bonnot [14] reported that brown fat in humans persisted through the embryonic, neonatal, and adult stages in those locations described in the embryo and the fetus. In the adult, brown fat is usually found in scattered foci along the esophagus, trachea, large vessels of the medi-
CASE REPORT AHN AND HARVEY MEDIASTINAL HIBERNOMA
829
astinum, posterior neck, and interscapular regions. Therefore, it is not surprising that the distribution of these tumors closely follows the sites of persistence of brown fat in the human adult as shown by the previously mentioned anatomical studies. The most common site of reported hibernomas is the subcutaneous tissues of the back, especially the interscapular area. Other frequent locations include the neck, axilla, thigh, and intrathoracic area [15]. A review of the world literature brings the total number of reported cases of hibernoma to 90. There have been 5 previously reported cases of intrathoracic hibernoma, all of which were confined to the subpleural chest and did not invade the mediastinum. All of these patients underwent successful thoracotomy and resection of tumor. None had evidence of recurrence after 1 year (Table 1). There has been 1 reported case of intramyocardial hibernoma, as revealed by an autopsy study of an 84-year-old woman [ll].The case presented here is the only other known reported case of mediastinal hibernoma. Although these tumors are considered benign and malignant transformation has not been reported, they tend to grow to large proportions ranging in size from 3 to 19 cm (151. Because hibernomas are well encapsulated and do not show infiltrative growth, they can be totally removed without sacrificing vital structures. Therefore, in the treatment of these tumors, especially if intrathoracic in location, surgical excision is curative. With the increasing incidence of routine chest roentgenograms, most of these tumors will be detected as asymptomatic opacities, as in the case presented here. These tumors tend to grow to large proportions and will eventually produce signs and symptoms accordingly, as noted in previous reports. For this reason and on the basis of their clinically indeterminate nature, complete surgical excision should be performed.
Fig 3. Cells with multivacuolated cytoplasm mixed with cells having a less vacuolated, eosinophilic granular cytoplasm. (Hematoxylin and eosin, x400 before 38% reduction.)
830
CASE REPORT AHN AND HARVEY MEDIASTINAL HIBERNOMA
Ann Thorac Surg 1990;50:828-30
Table 1. Clinical Features of Reported Intrathoracic Hibernomas Age Author
(Y)
Race
Sex
Kittle et a1 (61
42
w
F
Cough, wheeze
Gross and Wood [7]
39
W
M
Peabody et a1 [8] Beetstra and Quast [9]
31 22
w
B
M M
Left pleuritic pain, left arm paresthesias Left pleuritic pain Asymptomatic
May et a1 [lo]
26
w
M
Asymptomatic
Kindblom [ l l ]
84
W
F
Sinus arrhythmia, LBBB
B
=
black;
LBBB
=
left bundle-branch block;
Signs/Symptoms
Tumor Location Posterior base, left chest Apex, left chest Apex, left chest Apex, right chest Middle posterior, left chest Right atrium
Tumor Size (cm) 14
X
12 X 8
9X8X4 3X3X2 5X4X3 4X4X4 4X4X3
W = white.
References 1. Merkl H. Uber ein Pseudolipoma der Mamma (elgenartiger Fettzellentumor). Beitr Pathol Anat Allg Pathol1906;39:152-7. 2. Gery L. Discussion of Bonnel MF. Tumor du creaux de I'aissele. Bull Mem SOCAnat Paris 1914;89:110-2. 3. Kristensen S. Cervical hibernoma. Review of the literature and a new case. J Laryngol Otol 1985;99:105W. 4. Nigrisoli M, Ruggieri P, Picci P, Pignatti G. Case report 489: hibernoma of left thigh. Skeletal Radio1 1988;17432-5. 5. Paul MA, Koomen AR, Blok P. Hibernoma, a brown fat tumor. Neth J Surg 1989;41:85-7. 6. Kittle CF, Boley JO, Schafer PW. Resection of an intrathoracic "hibernoma." J Thorac Surg 1950;19:830-5. 7. Gross S, Wood C. Hibernoma. Cancer 1953;6:159-63. 8. Peabody JW Jr, Ziskind J, Buechner HA, Anderson AE.
lntrathoracic hibernoma, third reported case. N Engl J Med 1953;249:329-32. 9. Beetstra A, Quast WH. Intrathoracic hibernoma. Arch Chir Neerl 1958;10:203-13. 10. May CJ, Desopo ND, Yesner R. Intrathoracic hibernoma. Am Rev Respir Dis 1960;82:555-60. 11. Kindblom LG. Multiple hibernomas of the heart. Acta Pathol Microbiol Scand Sect A Pathol 1977;85A:122-6. 12. Rasmussen AT. The so-called hibernating gland. J Morphol 1923;38:147-205. 13. Shaw HB. Contribution to the study of the morphology of adipose tissue. J Anat Physiol 1902;36:1-13. 14. Bonnot E. The interscapular gland. J Anat Physiol 1909;43: 43-58. 15. Lawson W, Biller HF. Cervical hibernoma. Laryngoscope 1976;86:1258-67.
Hibernoma is an uncommon soft tissue tumor that is derived from the remnants of fetal brown fat. Review of the world medical literature revealed 90 cases, 6 of which were intrathoracic. We present the seventh case of intrathoracic hibernoma; in this case, the hibernoma was within the mediastinum without direct invasion of other structures. (Ann Thoruc Surg 1990;50:828-30)
H
ibernoma is a rare, benign soft tissue tumor composed of multiloculated fat cells derived from brown fat. The tumor was first described by Merkl [l]in 1906 as being composed of brown adipose tissue. The term hibernomu was proposed in 1914 by Gery (21 because of its morphologic similarity to the cells of the so-called hibernating gland of animals. By 1985, 80 cases of hibernoma were reported in the world medical literature [3]. The total grew to 89 in 1988 [4], and with an additional case reported in 1989 [5], the current total stands at 90. Of six reported intrathoracic hibernomas, five were confined within the subpleural chest [&lo], and one was intramyocardial [ll]. A 16-year-old Filipino boy was referred to the Thoracic Surgery service at Kaiser Permanente Medical Center, Los Angeles, CA, on January 20, 1989, because of a large anterior mediastinal mass that was discovered on a routine preemployment physical examination. The patient was in excellent health and completely asymptomatic. The past medical history and physical examination were noncontributory . A chest roentgenogram demonstrated a large mass in the left anterior mediastinum, inseparable from the cardiac silhouette (Fig 1).Computed tomography showed a 8 x 8 x 12-cm mixed-density mass, which was mainly fatty, in the left mediastinum, abutting the aortic and pulmonary arches and the left side of the heart without obvious invasion (Fig 2). On February 1, 1989, a median sternotomy was performed. A large, tan, lobulated and encapsulated, bilobed mass was found in the anterior-superior mediastinum. It was completely within the mediastinal pleura and extra: pleurally compressed the upper segment of the left lung. The left phrenic nerve was easily dissected free of the mass. The pericardium and major vascular structures
were not involved. The tumor was highly vascular but was removed without complication. The postoperative course was uneventful. The patient was discharged on the third postoperative day and has not shown any evidence of recurrence after 1 year. The fresh specimen was tan-brown, homogeneous, and encapsulated, with a buttery consistency. Attached to the specimen was a portion of a normal-appearing thymus that weighed 42 g and measured 8 x 3 x 3 cm. Light microscopic examination showed tumor cells arranged in lobules separated by fine reticulin fibers. Most of the cells were round or polygonal with monovacuolated or multivacuolated lipid-containing cytoplasm (Fig 3). These were mixed with cells having a less vacuolated, eosinophilic, granular cytoplasm. The nuclei were ovoid and spherical and central. A delicate fibrocollagenous and vascular capsule was present with inconspicuous mesothelial cells on the surface. The sections of thymus were normal. Comment Hibernomas are rare, benign tumors derived from brown adipose tissue, a specialized form of fat found in hibernating and nonhibernating animals. Brown fat was first
Accepted for publication May 7, 1990. Address reprint requests to Dr Ahn, Department of Surgery, Kaiser Permanente Medical Center, 1526 North Edgemont St, Los Angeles, CA 90027.
0 1990 by The
Society of Thoracic Surgeons
Fig 2 . Chest roentgenogram showing large opacity in left anterior mediastinum. 0003-4975/90/$3.50
Ann Thorac Surg 1990;50:828-30
Fig 2. Computed tomographic scan shows that the mass has a mixed density but is mainly fatty.
described by Velch in 1670. He noted a glandlike structure in the mediastinum of a woodchuck, a hibernating animal, and thought it to be associated with the thymus [12]. This was later recognized by Barkow in 1846 to be separate from the thymus, and he called it the "hibernating gland" [12]. Rasmussen [12] reviewed the morphology of this structure and discovered its presence in more than 50 species including nonhibernating animals such as rats, rabbits, cats, monkeys, and humans. In 1902, Shaw [13] demonstrated the axillary and subpleural fat of the human fetus and newborn to be largely brown fat, in contrast to the yellow fat of subcutaneous tissues. Finally, Bonnot [14] reported that brown fat in humans persisted through the embryonic, neonatal, and adult stages in those locations described in the embryo and the fetus. In the adult, brown fat is usually found in scattered foci along the esophagus, trachea, large vessels of the medi-
CASE REPORT AHN AND HARVEY MEDIASTINAL HIBERNOMA
829
astinum, posterior neck, and interscapular regions. Therefore, it is not surprising that the distribution of these tumors closely follows the sites of persistence of brown fat in the human adult as shown by the previously mentioned anatomical studies. The most common site of reported hibernomas is the subcutaneous tissues of the back, especially the interscapular area. Other frequent locations include the neck, axilla, thigh, and intrathoracic area [15]. A review of the world literature brings the total number of reported cases of hibernoma to 90. There have been 5 previously reported cases of intrathoracic hibernoma, all of which were confined to the subpleural chest and did not invade the mediastinum. All of these patients underwent successful thoracotomy and resection of tumor. None had evidence of recurrence after 1 year (Table 1). There has been 1 reported case of intramyocardial hibernoma, as revealed by an autopsy study of an 84-year-old woman [ll].The case presented here is the only other known reported case of mediastinal hibernoma. Although these tumors are considered benign and malignant transformation has not been reported, they tend to grow to large proportions ranging in size from 3 to 19 cm (151. Because hibernomas are well encapsulated and do not show infiltrative growth, they can be totally removed without sacrificing vital structures. Therefore, in the treatment of these tumors, especially if intrathoracic in location, surgical excision is curative. With the increasing incidence of routine chest roentgenograms, most of these tumors will be detected as asymptomatic opacities, as in the case presented here. These tumors tend to grow to large proportions and will eventually produce signs and symptoms accordingly, as noted in previous reports. For this reason and on the basis of their clinically indeterminate nature, complete surgical excision should be performed.
Fig 3. Cells with multivacuolated cytoplasm mixed with cells having a less vacuolated, eosinophilic granular cytoplasm. (Hematoxylin and eosin, x400 before 38% reduction.)
830
CASE REPORT AHN AND HARVEY MEDIASTINAL HIBERNOMA
Ann Thorac Surg 1990;50:828-30
Table 1. Clinical Features of Reported Intrathoracic Hibernomas Age Author
(Y)
Race
Sex
Kittle et a1 (61
42
w
F
Cough, wheeze
Gross and Wood [7]
39
W
M
Peabody et a1 [8] Beetstra and Quast [9]
31 22
w
B
M M
Left pleuritic pain, left arm paresthesias Left pleuritic pain Asymptomatic
May et a1 [lo]
26
w
M
Asymptomatic
Kindblom [ l l ]
84
W
F
Sinus arrhythmia, LBBB
B
=
black;
LBBB
=
left bundle-branch block;
Signs/Symptoms
Tumor Location Posterior base, left chest Apex, left chest Apex, left chest Apex, right chest Middle posterior, left chest Right atrium
Tumor Size (cm) 14
X
12 X 8
9X8X4 3X3X2 5X4X3 4X4X4 4X4X3
W = white.
References 1. Merkl H. Uber ein Pseudolipoma der Mamma (elgenartiger Fettzellentumor). Beitr Pathol Anat Allg Pathol1906;39:152-7. 2. Gery L. Discussion of Bonnel MF. Tumor du creaux de I'aissele. Bull Mem SOCAnat Paris 1914;89:110-2. 3. Kristensen S. Cervical hibernoma. Review of the literature and a new case. J Laryngol Otol 1985;99:105W. 4. Nigrisoli M, Ruggieri P, Picci P, Pignatti G. Case report 489: hibernoma of left thigh. Skeletal Radio1 1988;17432-5. 5. Paul MA, Koomen AR, Blok P. Hibernoma, a brown fat tumor. Neth J Surg 1989;41:85-7. 6. Kittle CF, Boley JO, Schafer PW. Resection of an intrathoracic "hibernoma." J Thorac Surg 1950;19:830-5. 7. Gross S, Wood C. Hibernoma. Cancer 1953;6:159-63. 8. Peabody JW Jr, Ziskind J, Buechner HA, Anderson AE.
lntrathoracic hibernoma, third reported case. N Engl J Med 1953;249:329-32. 9. Beetstra A, Quast WH. Intrathoracic hibernoma. Arch Chir Neerl 1958;10:203-13. 10. May CJ, Desopo ND, Yesner R. Intrathoracic hibernoma. Am Rev Respir Dis 1960;82:555-60. 11. Kindblom LG. Multiple hibernomas of the heart. Acta Pathol Microbiol Scand Sect A Pathol 1977;85A:122-6. 12. Rasmussen AT. The so-called hibernating gland. J Morphol 1923;38:147-205. 13. Shaw HB. Contribution to the study of the morphology of adipose tissue. J Anat Physiol 1902;36:1-13. 14. Bonnot E. The interscapular gland. J Anat Physiol 1909;43: 43-58. 15. Lawson W, Biller HF. Cervical hibernoma. Laryngoscope 1976;86:1258-67.
