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Ann Thorac Surg 2002;74:573-575
© 2002 The Society of Thoracic Surgeons

Case report

Pulmonary myelolipoma

Carlos J. Sabate, MDa, David M. Shahian, MD*a

a Department of Thoracic and Cardiovascular Surgery, Lahey Clinic, Burlington, Massachusetts USA

Accepted for publication April 1, 2002.

* Address reprint requests to Dr Shahian, Department of Thoracic and Cardiovascular Surgery, Lahey Clinic, 41 Mall Rd, Burlington, MA 01805 USA
e-mail: david.m.shahian{at}lahey.org


   Abstract
Top
 Abstract
Introduction
 Comment
 References
 
Myelolipoma is an extremely rare, benign pulmonary lesion, usually presenting as an asymptomatic pulmonary nodule. We describe myelolipoma of the lung in a 54-year-old man, present on roentgenogram for 20 years, and we review the natural history, pathology, diagnosis, and management of such lesions.


   Introduction
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 Abstract
 Introduction
Comment
 References
 
Myelolipoma is a rare, benign, typically asymptomatic lesion consisting of fat, myeloid, and erythroid marrow elements [1–15]. The most common location is the adrenal gland, but extra-adrenal lesions have also been described [16], particularly in the presacral or perirenal space. Intrathoracic myelolipomas have rarely been reported [5–7, 17]. We describe a pulmonary myelolipoma in a 54-year-old man and comment on the pathology, natural history, diagnosis, management, and prognosis of this lesion.

A 54-year-old Caucasian man presented with a 20-year history of a lung lesion in the left upper lobe. Initial roentgenography of the chest at our institution in 1987 revealed a smooth, well-demarcated 1.8-cm left upper lesion, present on x-ray films at another institution for at least 7 years previously. By January 2000, the lesion had increased in diameter to 2.5 cm (Fig 1A), and the patient was referred to the Department of Thoracic Surgery. A Computed tomographic (CT) scan (Fig 1B) revealed a smooth and well-defined lesion of fat density in the upper lobe with no significant adenopathy. The patient was asymptomatic, and the only pertinent medical history was hypercholesterolemia.



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  		Fig 1. (A) Chest roentgenogram and (B) computed tomographic scan reveal a well-circumscribed solitary pulmonary nodule in the left upper lobe.

 
Because of growth in size of the lesion, surgical removal was recommended. Through a limited muscle sparing approach in the fifth intercostal space, we performed a wide enucleation of a 2.5-cm nodule from the left upper lobe. Frozen section revealed myelolipoma, and no further resection was performed. The patient had an uneventful postoperative course.

The resected lesion was well circumscribed, and sectioning revealed brown, focally congested tissue. Although no bone was visible macroscopically, the tissue was gritty and difficult to cut. After decalcification, both the frozen and permanent histological sections (Fig 2) revealed an admixture of mature adipose and hematopoietic tissue. The adipose component predominated, ranging from 60% to 100% in the sections represented. The hematopoietic tissue was composed of myeloid, erythroid, and megakaryocytic cell lines in normal proportion and displaying normal maturation. Benign lymphoid aggregates were present as well as several bony spicules.



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  		Fig 2. High-power (x400) magnification shows an admixture of adipose and cellular elements, including two lymphoid aggregates in the center of the field.

 

   Comment
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 Abstract
 Introduction
 Comment
References
 
Myelolipomas were first described in the early part of the 20th century. They are uncommon, benign, and asymptomatic lesions typically found in middle and in older age, and there is a slight female predominance [4, 11]. Myelolipomas most commonly present as solitary, well-circumscribed adrenal nodules. They have occasionally been described in association with endocrine or hormonal disorders, including Conn’s syndrome, Cushing’s disease, congenital adrenal hyperplasia, exogenous steroid use [4, 5, 10, 11], and in other conditions associated with increased cortisol production, such as diabetes, hypertension, and obesity [5].

Extraadrenal myelolipomas occur less frequently and have been reported in the liver, stomach, mesentery, spleen, retroperitoneum, presacral area, leptomeninges, and thorax [4, 5, 10, 11, 15]. Most such extraadrenal lesions are asymptomatic and discovered at autopsy, where their incidence is reported to be 0.08% to 0.2% [11]. Because of the growing use of magnetic resonance imaging (MRI) and CT scanning, such lesions are an increasingly common incidental finding [11].

In a review of 22 extraadrenal myelolipomas conducted by Hunter and associates [5] in 1991, more than 50% occurred in the presacral retroperitoneum. Kenney and associates [11] reported 86 myelolipomas at the Armed Forces Institute of Pathology between 1981 and 1997 for which CT scans were part of the diagnostic evaluation. Ten of these were extraadrenal, most in the retroperitoneum or pelvis, but one thoracic lesion was identified. The lesions were not associated with endocrine disorders in this group. Among other cases of intrathoracic myelolipomas reported in the literature, the posterior mediastinum is the most common site [1, 8, 9, 12, 16], representing four of the five mediastinal lesions in a 1993 review by Strimlan and Khasnabis [13]. Pulmonary lesions are quite rare and typically pleural-based [5–7, 17].

Histologically, myelolipoma is a benign tumor composed of mature adipose tissue and hematopoietic cells, including myeloid, erythroid, and megakaryocytic elements, and occasionally lymphocytes [4, 5]. They may contain areas of internal hemorrhage and subsequent calcification. As opposed to true bone marrow, reticular sinusoids or bone spicules are typically not present [11], although there were small spicules in our case.

The etiology of myelolipoma is unknown. Possibilities include development from embryonic mesenchymal rests in the adrenal gland, hematogenous bone marrow emboli, stress-induced reticuloendothelial cell metaplasia, and proliferation of embryonic rests of hematopoietic stem cells [4, 5, 10, 11, 13, 14].

Radiographic findings
On plain x-ray film, intrathoracic myelolipoma appears as a pulmonary or mediastinal mass, typically solitary and well circumscribed. CT scan [8, 9, 11, 14] demonstrates a completely or partially encapsulated mass whose density depends on the relative proportion of fat (low density) versus hematopoietic tissue (high density). Areas of higher density due to hemorrhage may be seen, and, rarely, small amounts of calcification may be seen. There may be enhancement after administration of intravenous contrast [8, 9, 14].

On MRI, the lesion demonstrates high signal intensity on T1 weighted images which is isointense to surrounding mediastinal and subcutaneous fat [8, 14]. Fat suppression images will demonstrate loss of signal in the fatty components of the lesion [14]. Myeloid elements have low signal intensity on T1 weighted images and intermediate intensity on T2 weighted images [8, 14]. Signal enhancement may occur after administration of gadolinium [14].

Diagnosis
CT scan or MRI demonstration of fat in a well-circumscribed pulmonary nodule is usually indicative of a benign diagnosis. In addition to the characteristic radiographic findings, fine-needle aspiration of myelolipomas has been the most commonly used diagnostic modality in modern reports [4, 8]. The aspirate may reveal adipose and hematopoietic cells, the latter including all three cell types normally seen in marrow [4].

Treatment
In our patient, the likelihood of a benign lesion was extremely high because of its chronicity and radiographic appearance. However, as in this case, myelolipomas may grow and they may subsequently hemorrhage or compress adjacent structures. For these reasons, and to confirm the histologic diagnosis, removal was indicated. Given the demonstrated growth of the lesion, we did not believe that percutaneous needle biopsy would have altered this recommendation. Conservative resection is appropriate because neither recurrence nor malignant degeneration has been reported.


   References
Top
 Abstract
 Introduction
 Comment
 References
 

  1. Rudnicka L., Papla B., Malinowski E. Mediastinal myelolipoma. A case report. Pol J Pathol 1996;47:143-145.[Medline]
  2. Oliva A., Duarte B., Hammadeh R., Ghosh L., Baker R.J. Myelolipoma and endocrine dysfunction. Surgery 1988;103:711-715.[Medline]
  3. Krag D., Reich S.B. Heterotopic bone marrow (myelolipoma) of the mediastinum. Chest 1972;61:514-515.[Abstract/Free Full Text]
  4. Spanta R., Saleh H.A., Khatib G. Fine needle aspiration diagnosis of extraadrenal myelolipoma presenting as a pleural mass. A case report. Acta Cytol 1999;43:295-298.[Medline]
  5. Hunter S.B., Schemankewitz E.H., Patterson C., Varma V.A. Extraadrenal myelolipoma. A report of two cases. Am J Clin Pathol 1992;97:402-404.[Medline]
  6. Zunarelli E., Criscuolo M., Malavolta L., Piccinini L., Barbolini G. A case of lung myelolipomatosis in a patient with bronchial carcinoid. Panminerva Med 1999;41:175-178.[Medline]
  7. Ziolkowski P., Muszczynska-Bernhard B., Dziegiel P. Myelolipoma: the report of two cases in pulmonary location. Pol J Pathol 1996;47:141-142.[Medline]
  8. Kawanami S., Watanabe H., Aoki T., et al. Mediastinal myelolipoma: CT and MRI appearances. Eur Radiol 2000;10:691-693.[Medline]
  9. Kim K., Koo B.C., Davis J.T., Franco-Saenz R. Primary myelolipoma of mediastinum. J Comput Tomogr 1984;8:119-123.[Medline]
  10. Fowler M.R., Williams R.B., Alba J.M., Byrd C.R. Extra-adrenal myelolipomas compared with extramedullary hematopoietic tumors: a case of presacral myelolipoma. Am J Surg Pathol 1982;6:363-374.[Medline]
  11. Kenney P.J., Wagner B.J., Rao P., Heffess C.S. Myelolipoma: CT and pathologic features. Radiology 1998;208:87-95.[Abstract/Free Full Text]
  12. Minamiya Y., Abo S., Kitamura M., Izumi K. Mediastinal extraadrenal myelolipoma: report of a case. Surg Today 1997;27:971-972.[Medline]
  13. Strimlan C.V., Khasnabis S. Primary mediastinal myelolipoma. Cleve Clin J Med 1993;60:69-71.[Medline]
  14. Kammen B.F., Elder D.E., Fraker D.L., Siegelman E.S. Extraadrenal myelolipoma: MR imaging findings. AJR Am J Roentgenol 1998;171:721-723.[Free Full Text]
  15. Brietta L.K., Watkins D. Giant extra-adrenal myelolipoma. Arch Pathol Lab Med 1994;118:188-190.[Medline]
  16. Foster J.B.T. Primary thoracic myelolipoma: a case report. Arch Pathol 1958;65:295-297.
  17. Saleeby E.R. Heterotopia of bone marrow without apparent cause. Am J Pathol 1925;1:69-76.



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