Anterior Mediastinal Myelolipoma: A Case Report and Review of the Literature

Abstract

BACKGROUND Myelolipoma is a benign tumor, commonly found in the supra-renal gland, which is composed of mature fatty tissue admixed with hematopoietic elements. However, there are several extra-adrenal sites reported in the literature and thoracic myelolipoma is an unusual location for extra-adrenal myelolipoma. CASE REPORT We present the case of a 71-year-old man previously diagnosed with hypertension who was admitted due to a motor vehicle injury with a lumbar spine fracture. The patient developed non-ST segment elevation myocardial infarction during admission. A coronary angiogram revealed three-vessel disease. Triple coronary artery bypass grafting (CABG) surgery was planned. Upon opening the chest through median sternotomy, a retrosternal adherent mass was incidentally discovered. The mass was excised and histopathological evaluation showed it was myelolipoma in the anterior part of the mediastinum. CONCLUSIONS It is well known that myelolipoma occurs in extra-adrenal sites, and is rarely found at unexpected site, as in our case, which was found incidentally at the anterior mediastinum. With an extensive literature review, we found only 1 case located in the anterior mediastinum. It is crucial to know that myelolipoma can occur in the anterior mediastinum to avoid pitfalls with other differential diagnoses, especially when it is found incidentally and requires a frozen section examination, as it is difficult to diagnose through radiologic imaging only because it can overlap with tumors that are rich in either adipose tissue or hematopoietic elements. However, it affects patient management, and patients usually need only follow-up instead of going through invasive procedures for resection of non-functional tumors, especially in older patients or patients with comorbid diseases.

Figure 1.

Typical myelolipoma: Admixture of mature adipose tissue and bone marrow elements (hematoxylin and eosin [HE] stain at 4× power field).

Figure 2.

Trilineage hematopoiesis: Consists of erythroid cells, granulocytes, and megakaryocytes (hematoxylin and eosin [HE] stain at 20× power field).

Figure 3.

Osseous metaplasia: Heterotopic normal bone tissue (hematoxylin and eosin [HE] stain at 10× power field).

Figure 4.

Degenerative changes: Fibromyxoid area within the lesion (hematoxylin and eosin [HE] stain at 10× power field).

Figure 5.

Hemorrhagic area: Degenerative changes characterized by extravasated red blood cells (hematoxylin and eosin [HE] stain at 10× power field).

Figure 6.

Chondroid metaplasia: Cartilage tissue found at periphery of the lesion (hematoxylin and eosin [HE] stain at 20 x power field).