Asian Cardiovasc Thorac Ann 2002;10:189-190
© 2002 Asia Publishing EXchange Pte Ltd
Mediastinal Myelolipoma
Gao Bing, MD,
Hiroshi Sugimura, MD,
Shuichiro Sugimura, MD,
Yoshinobu Hattori, MD,
Tadashi Iriyama, MD,
Hideki Kano, MD
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Department of Thoracic Surgery Fujita Health University School of Medicine and Health University College Toyoake City, Aichi, Japan
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Gao Bing, MD Tel: 81 75 751 3784 Fax: 81 75 751 4960 email: gaobing_cn{at}yahoo.com Department of Cardiovascular Surgery, Faculty of Medicine, Kyoto University, 54 Kawara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
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ABSTRACT
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Myelolipoma is a rare tumor, and a mediastinal location is extremely unusual. The main pathologic feature is the coexistence of mature adipose tissue and bone marrow cells; the presence of megakaryocytes is essential for diagnosis. The successful removal of a mediastinal myelolipoma in a 59-year-old man is described.
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INTRODUCTION
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Myelolipoma is a very rare tumor that occurs mostly in the adrenal gland. It is composed of adipose tissue and normal hematopoietic elements. The tumor is detected only infrequently in extraadrenal sites including the mediastinum.
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CASE REPORT
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A 59-year-old man with a history of hypertension and bronchitis was found to have an abnormal mass in the right posterior mediastinum, on computed tomography (CT) of the chest. Surgery was recommended, but the patient refused. Four months later, CT revealed the mass had enlarged, and he was admitted for treatment. Physical examination was normal. Laboratory investigations showed normal red blood cell morphology and white blood cell counts, total protein and albumin levels were decreased, and total bilirubin was elevated. A chest radiograph indicated an abnormal mass with clear margins, 3 x 2 cm in size, in the right posterior mediastinum. Chest CT (Figure 1
) and magnetic resonance imaging showed a mediastinal mass adjacent to the 10th thoracic vertebra. Evidence of tumor invasion of the vertebrae or lungs was unclear. There were no abnormal CT findings at other sites. Surgery was performed through a standard right thoracotomy, revealing a red-colored soft elastic mass that appeared to be filled with blood. Tumor invasion of the vertebra was not seen, and complete excision of the tumor was achieved. The postoperative course was uneventful. Pathology showed predominant mature adipose tissue and bone marrow that was composed of normoblastic, granulocytic, and megakaryocytic series (Figure 2). The pathological findings were consistent with a diagnosis of myelolipoma, and no sign of ma-lignancy was observed. The diagnosis of myelolipoma was confirmed by the existence of ectopic megakaryocytes.
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Figure 1. Computed tomography of the chest showing a mediastinal mass adjacent to the 10th thoracic vertebra.
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Figure 2. Pathology of the excised tumor showed predominant mature adipose tissue and bone marrow tissue composed of normoblastic, granulocytic, and megakaryocytic series (Elastica van Gieson stain, original magnification x40).
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DISCUSSION
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Extraadrenal myelolipomas have been found on rare occasions in the perisacral region, liver, lung, perirenal region, and mediastinum. Since the first report by Suzuki and colleagues1 in 1988, there have been only 12 cases of mediastinal myelolipoma reported in Japan. There are several hypotheses regarding the pathogenesis of myelolipomas, for example, fetal bone marrow remnants, bone marrow cell embolism, and heterotopic reticulum cells of the adrenal gland.2 The tumor in this case was not thought to arise from reticulum cells because it was in the mediastinum. The finding of megakaryocytes outside of bone marrow is essential in the diagnosis of myelolipoma.3
Myelolipoma may be associated with endocrine disorders such as hermaphroditism, Cushing's disease, Addison's disease, obesity of unknown cause, Nelson's syndrome, and congenital adrenal hyperplasia.4,5 The incidental finding of myelolipoma in patients with such conditions has led to speculation that adrenocorticotropin over-secretion might play a role in the pathogenesis of adrenal myelolipomas. However, the results of endocrine evalua-tions are variable.5 If the tumor becomes large, it may compress neighboring organs. Tumor rupture and bleeding have also been reported.
Both CT and magnetic resonance imaging are useful in the diagnosis of myelolipomas. Kikuchi and colleagues6 described the characteristic findings: a mass with fatty tissue density, mixed with hematopoietic tissue, bleeding, and calcification, appearing as partial high-density areas on CT; and magnetic resonance findings on a thoracic vertebra-weighted scan of a tumor with an adipose component showing the same high-intensity signal as normal subcutaneous tissue, and a hematopoietic component with intensity similar to that of pleural effusion. CT-guided needle biopsy of the tumor can provide a definite diagnosis if ectopic megakaryocytes are confirmed.6 Recently, some cases of myelolipoma have been diagnosed and treated thoracoscopically; however, Gould and colleagues7 suggested that it might not be necessary to remove the tumor if myelolipoma is diagnosed by needle biopsy. Kenney and colleagues8 recommended that such tumors be resected if they grow to more than 10 cm in diameter, because of the risk of rupture and bleeding, but there is no consensus on when they should be removed.
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REFERENCES
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Suzuki T, Mushiaki T, Hori G, Tonozuka H, Suzuki H, Noguchi H, et al. A case of primary myelolipoma of the posterior mediastinum [Japanese]. Nihon Kyobu Shikkan Gakkai Zasshi
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Kashimura H, Nakahara A, Kawakita I, Taninaka A, Matsuzaki S. Case of adrenal myelolipoma with effective use of ultrasonic-guided needle biopsy [Japanese]. Nippon Shokakibyo Gakkai Zasshi
1982;79:1788–93.[Medline]
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Akasaka Y, Kuwabara J, Kudo T, Ishikawa Y, Masuda T. A case of myelolipoma of the adrenal gland [Japanese]. J Jpn Soc Clin Cytol
2000;39:111–2.
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Yildiz L, Akpolat I, Erzurumlu K, Aydin O, Kandemir B. Giant adrenal myelolipoma: case report and review of the literature. Pathol Int
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Boronat M, Moreno A, Ramón y Cajal S, Pineda E, Lucas T, Estrada J. Subclinical Cushing's syndrome due to adrenal myelolipoma. Arch Pathol Lab Med
1997;121:735–7.[Medline]
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Kikuchi E, Nonaka S, Tachibana M, Baba S, Murai M. Clinical study on 7 cases of surgically treated adrenal myelolipoma [Japanese]. Endocrine Surg
1997;14:303–7.
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Gould JD, Mitty HA, Pertsemlidis D, Szporn AH. Adrenal myelolipoma: diagnosis by fine-needle aspiration. AJR Am J Roentgenol
1987;148:921–2.[Free Full Text]
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Kenney PJ, Wagner BJ, Rao P, Heffess CS. Myelolipoma: CT and pathologic features. Radiology
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