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Ann Thorac Surg 2008;85:1805-1806. doi:10.1016/j.athoracsur.2007.11.023
© 2008 The Society of Thoracic Surgeons
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Case Reports

Primary Mediastinal Myelolipoma

Mohammad Vaziri, MD*, Alireza Sadeghipour, MD, Abdolreza Pazooki, MD, Leila Zahedi Shoolami, MD

Iran University of Medical Sciences, Tehran, Iran

Accepted for publication November 7, 2007.

* Address correspondence to Dr Vaziri, Surgery Ward, Hazrat Rasool Hospital, Niayesh Ave, Shahrara, Tehran, 1445713, Iran (Email: dr_m_vaziri{at}yahoo.com).


   Abstract
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 Abstract
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Myelolipoma is a rare mesenchymal tumor composed of an admixture of fat and bone marrow–derived hematopoietic cells. It is typically an adrenal lesion, and mediastinal location is extremely unusual. We describe a 56-year-old man with nonspecific symptoms of cough and dyspnea and no underlying disease whose chest computed tomography showed a huge (25 x 15 cm) mediastinal tumor containing calcification. Surgical removal and subsequent pathologic examination of the tumor revealed myelolipoma. Primary myelolipoma should be considered in the differential diagnosis of large posterior mediastinal tumors containing calcification.


   Introduction
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Myelolipoma is a rare tumor that displays bone marrow elements admixed in an adipose tissue neoplasm [1]. It is usually discovered by pathologists incidentally at autopsy and, with rare exceptions, occurs in the adrenal gland [2]. We report a case of a surgically resected huge mediastinal extraadrenal myelolipoma, which is a very unusual site for this rare and exceptionally reported neoplasm.

A 56-year-old man, who was a farmer and a nonsmoker, was admitted to the Hazrat Rasool Hospital at Iran University of Medical Sciences due to dyspnea and cough that had been increasing during a 2-year period. No other complaints or previous disease were noted except a well-controlled hypertension. A decreased breath sound in the right lung was the only notable finding in the physical examination, and laboratory test results were also normal.

A chest roentgenogram showed a huge mass on the right side, with obliteration of the diaphragmatic contour (Fig 1). A chest computed tomography (CT) scan revealed a well-defined, giant, right-sided posterior mediastinal mass measuring about 25 x 15 cm. The mass contained patchy areas of necrosis and calcification that occupied most of the right thoracic cavity and led nearly to "tumor thorax" and with considerable compression of right main bronchus (Fig 2). Upper abdominal contents as seen in abdominal CT images were normal. No other diagnostic evaluation, including needle biopsy, was attempted, and surgical resection of the mass was planned.


Figure 1
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  		Fig 1. Chest roentgenogram shows a huge, right-sided mass with obliteration of the diaphragmatic contour.

 

Figure 2
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  		Fig 2. Chest computed tomography scan reveals a well-defined, giant, right-sided posterior mediastinal mass containing patchy areas of necrosis and calcification.

 
Intraoperative findings through a right posterolateral thoracotomy included a very large well-defined mass, and although no fixation or invasion to any surrounding structures was noted, the complete resection of such a huge mass was difficult and led to the division and ligation of the torn azygous vein and an intraoperative blood loss of approximately 1000 mL.

Macroscopic examination of the mass revealed an encapsulated, smooth, brown rubbery mass measuring 20 x 15x 10 cm. The cut section showed it was nonhomogeneous and associated with necrosis and calcification. Microscopic findings included lobules of fatty tissue separated by fibrous septa containing sheets of marrow cells, including myeloid and erythroid series and also megakaryocytes. Foci of fibroblastic proliferation were also noted, but no evidence of malignancy was identified. The final pathologic diagnosis was myelolipoma (Fig 3).


Figure 3
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  		Fig 3. Histologic examination of the mass shows polymorphic population of hematopoietic cells, including megakaryocytes associated with stromal fat cells (hematoxylin and eosin stain, x400 original magnification).

 
Unfortunately, the patient sustained a myocardial infarction on the third postoperative day and died. Although no postoperative bleeding was noted in draining chest tubes, intraoperative blood loss might have contributed to the occurrence of myocardial infarction. The patient's family did not permit an autopsy.


   Comment
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Myelolipoma is a microscopically similar process to extramedullary hematopoiesis, but it usually lacks evidence of a background hematologic disorder [3].

Ectopic hematopoietic tissue almost always accompanies a severe form of hemolytic anemia such as hereditary spherocytic anemia, thalassemia, sickle cell anemia, or pernicious anemia, and the mass is frequently bilateral on CT examination. Thus, the diagnosis of an intrathoracic extramedullary hematopoiesis could not be considered in this patient.

Myelolipoma is typically an adrenal lesion, and most cases are hormonally inactive and found incidentally. The extraadrenal location of myelolipoma is extremely unusual and has been reported in retroperitoneum, stomach, liver, mediastinum, bilateral paravertebral sulci [4], lung [5], and presacral, perirenal, and thoracic spine [6].

There is no characteristic finding leading to a preoperative diagnosis of extraadrenal myelolipoma, but these tumors are usually single, well-circumscribed, and encapsulated, and are most commonly seen in middle-aged and elderly persons. A CT-guided biopsy and fine needle aspiration has been reported to be useful to avoid a surgery in asymptomatic patients and in the presence of appropriate clinical settings [7, 8].

The choice of one or more invasive diagnostic procedures depends primarily on the presence or absence of local symptoms and the location and extent of the lesion. If local symptoms of invasive disease are present, such as severe chest pain, pleural effusion, or superior vena cava obstruction, a biopsy is definitely indicated [9]. None of these signs were present in our patient, and more important, the size of the mass and duration of the symptoms made the diagnosis of an invasive disease unlikely. Thus, owing to the lack of definite indications for performing transthoracic needle biopsy, we omitted such a diagnostic procedure.

Surgical resection of an undiagnosed mass is the usual method of diagnosis in this rare tumor, and pathologic examination of the specimen reveals adult fat containing active marrow elements. The presence of megakaryocytes is essential for the diagnosis [10].

We note that the described mediastinal myelolipoma in this report had some considerable and distinctive features, including a gigantic size and the presence of calcification in CT imaging. Few mediastinal tumors contain calcification, and include teratoma (20% to 43% of cases), malignant nonseminomatous germ cell tumors, thymolipoma, epithelioid hemangioendothelioma, and solitary fibrous tumor. Although rare, extraadrenal myelolipoma should be considered in the differential diagnosis of a well-defined solid mediastinal mass containing calcification.


   References
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 Abstract
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 References
 

  1. Montgomery E. Soft tissue tumorsIn: Silverberg SG, editor. Silverberg principle and practice of surgical pathology and cytology. 4th ed.. London, UK: Churchill Livingstone; 2006. pp. 340.
  2. Kim K, Koo BC, Davis JT, Franco-Saenz R. Primary myelolipoma of mediastinum J Comput Tomogr 1984;8:119-123.[Medline]
  3. Rosai J. MediastinumIn: Rosai J, editor. Rosai and Ackerman's surgical pathology. 9th ed.. St. Louis, MO: Mosby; 2004. pp. 494.
  4. Franiel T, Fleischer B, Raab BW, Fuzesi L. Bilateral thoracic extra-adrenal myelolipoma Eur J Cardiothorac Surg 2004;26:1220-1222.[Abstract/Free Full Text]
  5. Sabate CJ, Shahian DM. Pulmonary myelolipoma Ann Thorac Surg 2002;74:573-575.[Abstract/Free Full Text]
  6. Omdal DG, Baird DE, Burton BS, Goodhue WW, Giddens EM. Myelolipoma of the thoracic spine AJNR Am J Neuroradiol 1997;18:977-979.[Abstract/Free Full Text]
  7. Kawanami S, Watanabe H, Aoki T, et al. Mediastinal myelolipoma: CT and MRI appearances Eur Radiol 2000;10:691-693.[Medline]
  8. Spanta R, Saleh HA, Khatib G. Fine needle aspiration diagnosis of extraadrenal myelolipoma presenting as a pleural mass Acta Cytol 1999;43:295-298.[Medline]
  9. Shields TW. Diagnostic investigation of mediastinal massesIn: Shields TW, Locicero J, Ponn RB, Rusch VW, editors. General thoracic surgery. 6th ed.. Philadelphia, PA: Lippincott Williams & Wilkins; 2005. pp. 2499.
  10. Gao B, Sugimura S, Hattori Y, Iriyama T, Kano H. Mediastinal myelolipoma Asian Cardiovasc Thorac Ann 2002;10:189-190.[Abstract/Free Full Text]



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This Article
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