Detection of Extramedullary Hematopoietic Tissue in a Patient with Beta-Thalassemia Major on Tc99m-Sestamibi Parathyroid Scintigraphy

A 50-year-old male patient with a history of beta-thalassemia major was referred for dual-phase Tc-99m sestamibi scintigraphy due to elevated parathyroid hormone (108 pg/mL) and calcium serum (11.8 mg/dL) levels (normal ranges 14.5–87.1 pg/mL and 8.1–10.6 mg/dL, respectively). The patient was administered intravenously 740 MBq of Tc-99m sestamibi and underwent early (10 min postinjection) and delayed (2.5 h postinjection) static imaging of the neck and thorax on a dual-head gamma camera (Infinia, GE Healthcare) equipped with low-energy, high-resolution, parallel-hole collimators. Single-photon emission computed tomography (SPECT) imaging of the above regions was also performed using step-and-shoot mode (120 projections, 25 s/projection) on a 128 × 128 matrix. Both static and SPECT images revealed parathyroid adenoma inferior to the lower pole of the right thyroid lobe. Moreover, SPECT showed increased tracer uptake in a paraspinal region of the right hemithorax, as indicated in transverse and coronal images [Figure 1a, arrows], corresponding to known (from previous chest X-ray and CT) extramedullary hematopoietic tissue [Figure 1b, arrow].

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Figure 1 Transverse and coronal Tc-99m sestamibi SPECT images of the thorax (a) showing increased tracer uptake in extramedullary hematopoietic tissue of the right hemithorax shown on CT (b)

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Beta-thalassemia is a hereditary blood disorder characterized by abnormalities in the synthesis of beta-chains of hemoglobin. There are three forms of thalassemia: minor, intermedia, and major. The last one causes severe anemia which requires regular transfusions.[1]

Extramedullary hematopoiesis (EMH) occurs when there is poor production or quality of blood elements as a result of various diseases such as myelofibrosis, diffuse osseous metastases, leukemia, and hemoglobinopathies such as sickle cell disease and thalassemia.[2] These conditions lead to compensatory mechanisms of hematopoiesis, which result in expansion of hematopoietic tissue outside the bone marrow. EMH occurs in up to 20% of patients with blood transfusion independence, such as those with thalassemia intermedia, while in patients with thalassemia major who are poly-transfused, the incidence is low, i.e. <1%.[3] The most commons sites of EMH are the paravertebral regions, the liver, and the spleen, while sites in other organs such as the thymus, kidneys, adrenal glands, lymph nodes, cranial and peripheral nerves, spinal canal, paranasal sinuses, nasopharynx, and breast have also been described.[4] The typical appearance of a paraspinal lesion on the chest X-ray/CT is a smoothly, well-demarcated paraspinal mass.[5]

Although the uptake of bone marrow radiotracers in extramedullary hematopoietic sites has been described,[6] the uptake of other agents, such as sestamibi, has rarely been reported.[78] The uptake of a nonspecific, perfusion agent like sestamibi could be attributed to increased metabolic activity and perfusion as a result of robust hematopoiesis in cases of impaired production of blood elements.

In this case, EMH was found in beta-thalassemia major, where the incidence of EMH is remarkably lower compared with the intermedia form of the disease. Moreover, it was detected during sestamibi SPECT parathyroid scintigraphy, which highlights the importance of additional imaging and careful examination of other sites besides the organ or region of interest, as well as the information provided with the use of various radiotracers.