In this patient, a known case of thalassemia major, the lobulated presacral mass 3 arising from sacral bone appears to be due to extramedullary hematopoiesis. It typically occurs in paraspinal location 1 (as in this case). Lesion shows attenuation in CT greater than that of a skeletal muscle, and markedly low signal on MRI on both T1-weighted and T2-weighted images, owing to massive iron deposition 1, a sequela of repeated blood transfusions.
In the differential diagnosis of soft-tissue retroperitoneal masses, the low signal intensity on T2- weighted images is in favor of extramedullary hematopoiesis 2.
Very low signal on both T1-weighted and T2-weighted images of visualized skeleton is also a consequence of massive bone marrow iron deposition.