Extramedullary hematopoiesis presenting as an asymptomatic posterior mediastinal mass: An unusual presentation.

Sir,

Extramedullary hematopoiesis (EMH) is the body's compensatory response to deficient erythropoiesis by the bone marrow or accelerated destruction of erythrocytes and refers to deposits of erythroid precursors in sites other than the bone marrow and peripheral blood.[1] Mostly, there are microscopic depositions of EMH tissues in various organs, but sometimes it manifests as hepatosplenomegaly or lymphadenopathy. Usually it is diagnosed incidentally and very rarely it presents as a posterior mediastinal mass clinically mimicking with many other benign or malignant mediastinal tumors. Intrathoracic EMH is a rare condition and only very few case reports have been described in patients with chronic myeloproliferative disorders specially myelofibrosis with myeloid metaplasia and spherocytic anemias.[2] The para-vertebral area is an uncommon site for EMH, with the possible exception of sporadically reported intrathoracic manifestations.[3]

A 45-year-old non-smoker, non-alcoholic asymptomatic patient with no respiratory complaints e.g. chest pain, breathlessness, cough, expectoration or hemoptysis and an insignificant past medical history presented to us for a routine health checkup for change of employment. The patient also denied for any past history of chest trauma or road traffic accident, blood transfusion, or significant medical and surgical illness. His general and systemic examinations were unremarkable except decreased intensity of breath sound in the bilateral inter-scapular area. Lab studies, including liver function tests, random blood sugar, renal function tests, alkaline phosphatase, and serum calcium were within normal limits and hemogram showed Hb 9.5 gm/dl with the total leukocyte count of 10800/μL and platelet count of 2,44000/μL. HIV serology was negative. Pulmonary function test and ECG had no abnormality. Chest X-ray PA view showed lobulated rounded/oval opacity in the bilateral paracardiac region [Figure 1]. Ultra sonography of the abdomen revealed mild spleenomegaly. A contrast-enhanced computerized tomography (CECT) scan of the chest [Figure 2a and b] showed heterogeneously enhancing with soft tissue attenuation bilateral posterior mediastinal masses in the para-vertebral area with internal tiny fat attenuation foci (arrows). The microscopic examination of Wright and modified Papanicolaou-stained smears prepared from fine needle aspiration (FNA) under the guidance of ultra-sonography, showed hyper-cellular smears composed of hematopoietic clusters of all precursors of erythroid, granulocyte and megakaryocytic series along with fibrillary and adipose elements [Figure 3a and b], favoring a diagnosis of EMH.

Figure 1

Chest X-ray PA view showing lobulated rounded/oval opacity in bilateral paracardiac region

Figure 2

Axial (a) and coronal reformatted. (b) Images of CECT chest in mediastinal window showing heterogeneously enhancing soft tissue attenuation bilateral posterior mediastinal masses with internal tiny fat attenuation foci (arrows)

Figure 3

(a) 10× and (b) 20× showing hypercellular smears composed of hematopoietic clusters of all precursors of erythroid, granulocyte and megakaryocytic series along with fibrillary and adipose elements

Further confirmation done by the peripheral blood film, which showed mild anisopoikilocytosis, mild microcytic hypochromic red blood cells, few elliptocytes, macrocytes, tear drop cells, target cells and fragmented red blood cells with neutrophillic predominant leukocytosis. Bone marrow aspiration and biopsy showed normocellular marrow without evidence of myelofibrosis, any leukemic process or thalassemia as the underlying cause for ongoing EMH. Later on patient transferred to department of oncology where he was treated with blood transfusion along with an iron chelating agent and radiotherapy.

The most common site for hematopoiesis is bone marrow, but a disturbance of blood formation in bone marrow leads to foci of hematopoiesis in unusual sites to supplement the deficient hematopoiesis known as EMH. There are wide varieties of pathologic conditions in which disturbance of the normal blood forming marrow may be associated with the formation of extramedullary hematopoietic tissue. Common causes of EMH include spherocytic anemia, erythroblastosis of newborn, thalassemia, pernicious anemia in period of relapse, macrocytic anemia of hepatic origin, carcinoma with bone marrow invasion, Hodgkin's disease, lymphoma, leukemia, osteosclerosis and myeloproliferative syndrome.

The mechanism of origin of these extramedullary foci is unknown, but there are several theories like embolization, direct extension, myelostimulation or redirected differentiation, which explain the events of EMH but none of them is widely acceptable.[4]

For EMH, the most common sites are the liver, spleen and lymph nodes. Other rare sites are the adrenal glands, hila of the kidneys, cartilage, broad ligaments, central nervous system, organizing thrombi, and adipose tissue. Clinical presentation of EMH varies depending on site involved and they mostly present with abdominal pain, lethargy, multiple joint pain and symptoms of anemia. Intra-thoracic EMH may lead to chest pain, breathlessness and some time dry cough. Radiologically the EMH masses may present as well demarcated, round and lobulated, non-pulsating masses located posteriorly in the para-vertebral region. Most common diagnostic modality is FNAC of the lesion along-with bone marrow aspiration/biopsy. Treatment of EMH is mostly symptomatic. Surgical treatment is not required in EMH, but it may be useful only for immediate symptomatic relief. Combined treatment with a blood transfusion and iron chelation is an ideal treatment for asymptomatic individuals because it relieves anemia and suppresses EMH and has been shown to be very effective when used in conjunction with surgery or radiotherapy.[5]

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