Extramedullary hematopoiesis

Clinical History

A 27-year-old female patient presented with coughing and a persistent back pain. She denied fever, dyspnoea, wheeze, night sweats and haemoptysis.

Imaging Findings

A 27-year-old female patient presented with coughing and a persistent back pain. She denied fever, dyspnoea, wheeze, night sweats and haemoptysis. Haematological examination showed a haemoglobin level of 1.2 mmol·L^–1, haematocrit value of 0.16, mean corpuscular volume of 90.0 fL, mean corpuscular haemoglobin concentration of 412 g·L^–1, red blood cell count of 2.7x10¹² cells·L^–1, reticulocyte count of 0.11, white blood cell count of 23x10⁹ cells·L^–1, and platelet count of 1072x10⁹ platelets·L^–1. Posteroanterior chest radiograph showed well-marginated bilateral, paraspinal masses, and diffuse expansion of ribs with increased trabecular pattern. The computed tomography of the chest revealed widening of the ribs and well-circumscribed bilateral paravertebral soft tissue mass adjoining the thoracic vertebra, without bone erosion. The peripheral blood smear showed marked anisopoikilocytosis, microcytosis, hypochromia, normoblasts and target cells. The haemoglobin electrophoresis findings revealed the diagnosis of beta-thalassemia intermedia. Her anaemia was controlled by transfusion of packed red blood cells. Since complications due to extramedullary haematopoiesis (EMH), such as spinal cord compression, haemothorax or pleural effusion were not determined, no additional radiotherapy or hydroxyure therapy was applied, due to their myelotoxic, cytostatic or hepatotoxic side-effects. Because her serum ferritin was very high, the patient was given chelation therapy. She was recommended for periodic controls.

Discussion

The terms myeloid metaplasia and extramedullary hematopoiesis (EMH) are used to describe a pathologic process of ectopic haematopoietic activity that may occur in any organ system but that primarily affects the liver and spleen. It occurs with a variety of chronic anemias and myeloproliferative disorders, such as sickle cell anemia, polycythemia vera, chronic myelogenous leukemia, and thalassemia. The liver, spleen, and lymph nodes are frequently involved as extraosseous locations because these are hematopoietic organs during embryonic life. It is rarely seen in Gaucher's disease, Paget's disease, alcohol-related macrocytosis, and congenital dyserythyropoietic anaemia. EMH usually occurs as a compensatory phenomenon with chronic anemia. This erythroid response is most often microscopic but can result in organomegaly or the development of tumour-like masses usually involving the liver, spleen and lymph nodes. Less frequently involved sites include the kidney, adrenal glands, breasts, spinal cord, intrathoracic cavity, pleura, pericardium and intracranial cavity. When the bone marrow dysfunction is obvious and intrathoracic EMH is suspected, the presence of the characteristic findings on a chest roentgenogram and chest CT scan should suffice to make the diagnosis. These characteristic findings are: widening of the ribs, unilateral or bilateral well-circumscribed lobulated paravertebral mass lesions usually located caudal to the sixth thoracic vertebrae, subpleural paracostal masses without bony erosion, absence of calcification, and the presence of adipose tissue within the mass. Bone abnormalities are evident on plain radiographs. Expansion of the bone marrow is seen as osteoporosis with coarsened trabeculation. With severe involvement, there is expansion of the bony cortex. Spinal cord involvement may be suggested by the presence of paraosseous masses seen on chest radiographs. Along with the bone abnormalities, CT demonstrates extramedullary hematopoiesis as a soft-tissue mass that is often adjacent to involved bone. Extramedullary hematopoiesis can be distinguished from the epidural fat because the former has attenuation similar to that of muscle and shows enhancement with intravenous administration of contrast material. MR imaging is the most effective method of demonstrating extramedullary hematopoiesis in the epidural space and is indicated on an urgent basis when symptoms of spinal cord compression are present. On T1-weighted images, extramedullary hematopoiesis is seen as an extramedullary mass with signal intensity slightly higher than that of the adjacent red marrow of the vertebrae. Similar findings are seen on T2-weighted images, with the signal intensity of extramedullary hematopoiesis being only slightly higher than that of bone marrow. Use of contrast material is unnecessary. T2-weighted sequences may be useful, however, to demonstrate the high signal intensity of an injured spinal cord. This high signal intensity is due to oedema, myelomalacia, or gliosis of the spinal cord due to chronic compression. Intrathoracic EMH is most often asymptomatic and treatment is usually unnecessary, except in the presence of complications. Massive haemothorax, symptomatic pleural effusion, and spinal cord compression are complications of intrathoracic EMH. Since the haematopoietic tissue is highly radiosensitive, low-dose radiation has been suggested as an effective method for controlling symptomatic pleural effusion or masses.

Differential Diagnosis List

Final Diagnosis

beta-thalassemia intermedia

URL:	https://eurorad.org/case/3927
DOI:	10.1594/EURORAD/CASE.3927
ISSN:	1563-4086