mediastinal extraadrenal myelolipoma is a very rare tumor composed of fat cells and mature bone marrow cells including normoblastic , granulocytic and megakaryocytic series . a 68-year - old man was referred to the itabashi central medical center for a surgical resection of posterior mediastinal tumor in november 2011 . chest radiography showed a mass on the right lower mediastinum ( fig .  1 ) . it was 2.5  cm in diameter beside the t8 and t9 thoracic vertebrae ( fig .  2 ) . according to t1 enhanced dual image at ( tr165 , te4.8 ) of magnetic resonance imaging ( mri ) , the tumor is revealed as high intensity ( fig . 3a ) ; however , at ( tr165 , te2.3 ) it is revealed as partially low intensity ( fig . it is 2.5  cm in diameter beside the t8 and t9 thoracic vertebraefig . 3magnetic resonance imaging ( mri ) . according to t1 enhanced dual image at ( tr165 , te4.8 ) 3a ) , however , at ( tr165 , te2.3 ) it is revealed as partially low intensity ( fig . it suggests that the tumor contains fat component chest radiography shows a mass on the right lower mediastinum chest ct shows a tumor located in the right posterior mediastinum . it is 2.5  cm in diameter beside the t8 and t9 thoracic vertebrae magnetic resonance imaging ( mri ) . according to t1 enhanced dual image at ( tr165 , te4.8 ) , the tumor is revealed as high intensity ( fig . 3a ) , however , at ( tr165 , te2.3 ) it is revealed as partially low intensity ( fig . it suggests that the tumor contains fat component we performed a tumor resection under video - assisted thoracoscopic surgery . the patient was discharged with no complications on the 7th operative day , and thereafter followed up as outpatient . in the macroscopic findings , size of the specimen was 3.0    2.7    2.5  cm , and was well circumscribed and encapsulated . a microscopic examination revealed a predominant mature adipose tissue with hematopoietic tissue ( fig . 4a microscopic examination reveals predominant mature adipose tissue with hematopoietic tissue a microscopic examination reveals predominant mature adipose tissue with hematopoietic tissue myelolipoma was first described by gierke in 1905 and the term  myelolipoma  was also used by oberling in 1929 [ 1 , 2 ] . myelolipoma is a benign nonfunctional tumor composed of extensive hematopoietic tissue and sparse fatty tissue , and is most often found in the adrenal grand . it mostly occurs to a unilateral adrenal cortex , but it is sometimes found in the anterior surface of sacrum and retroperitoneum around the kidney out of the adrenal gland . although there are reported cases of the tumor located in stomach , liver , lungs , and mediastinum , they are all very rare . the report of mediastinum such as this case is approximately 3  % of the whole myelolipoma , mostly in the lower posterior mediastinum vertebra [ 5 , 6 ] . theories on the origin of myelolipoma include the followings : ectopic hematopoietic stem cells originate and differentiate into myelolipoma.mesenchyma system cells of the ectopic adrenal tissue differentiate into myelolipoma [ 7 , 8 ] . mesenchyma system cells of the ectopic adrenal tissue differentiate into myelolipoma [ 7 , 8 ] . histologically , in case of myelolipoma , some blood - forming tissues are found in abundant adipose tissue where erythroblast pro - hyperplasia is not present , and the accumulation of lymphocyte is often present . ct shows the mass shadow that demonstrates a smooth and clear border and a localized low density area , whereas mri shows high intensity regions on both t1 , and t2-weighted image . in addition , by comparing original mri image and fat suppression image , it is able to find fat - consisting tumor . these findings are helpful in diagnosis . in this case , t1 enhanced dual image is useful for diagnose . most of the patients having this tumor are asymptomatic and often detected incidentally by chest x - ray examination . if pressure symptom or intratumoral bleeding is not seen , the patient is put to follow - up . however , it is very difficult to definitively diagnose a tumor occurring in the thoracic area . in case of the report , other differential diagnoses include a bronchogenic tumor , a malignant lymphoma , a lipoma , and a blood - forming organ tumor out of marrow . since it is difficult to distinguish among them before operation , eventually we are to depend on histological diagnosis . considering that other available methods such as aspiration cytology or ct - guided biopsy can be as invasive , video - assisted thoracoscopic surgery may be better as means of both diagnosis and treatment . although primary myelolipoma is very rare , knowledge of this tumor is important for the differential diagnosis of mediastinal tumor .
myelolipoma is an uncommon tumor composed of adipose tissue and normal hematopoietic elements , and is most often found in the adrenal glands . 
 we report a patient with a posterior mediastinal myelolipoma . 
 the 68-year - old male patient showed a right lower mediastinal shadow in a chest x - ray . 
 a computed tomographic scan demonstrated a right posterior mediastinal mass . 
 magnetic resonance imaging provided additional useful information . 
 the patient underwent a successful resection under video - assisted thoracoscopic surgery .