To further delineate the nature of these lesions, MRI was performed. T1-weighted MRI of the abdomen revealed low-signal lesions in the perirenal and pararenal locations, and heterogeneously hyperintense lesions in the pelvicalyceal regions (Figure 3). The pelvicalyceal lesions extended inferiorly along the proximal ureters in a symmetric fashion. T2-weighted MRI showed these masses to be homogeneously low-signal in all locations (Figure 4). Mild heterogeneous gadolinium enhancement was seen only in the pelvicalyceal components (Figure 5). Signal abnormalities were also noted in the liver and spleen on other images (not shown). Based on the imaging findings, extramedullary hematopoiesis (EMH), leukemia, lymphoma, and disseminated malignancy were the leading differential diagnostic considerations.
CT- guided core biopsy and fine-needle aspiration of the right perirenal mass were performed. Hematoxylin and eosin stain showed numerous megakaryocytes, myeloid and erythroid precursors, and extracellular blood products (hemosiderin). No neoplastic cells were present. The final diagnosis was EMH (Figure 6).
Extramedullary hematopoiesis in the abdomen most commonly involves the liver and spleen. Several different theories for the phenomenon have been proposed.5,6 Recently, it has been postulated that hematogenous spread of multipotential stem cells occurs with eventual infiltration of various tissues and organs.5
Involvement of the kidneys with EMH is rare. It is more common in the parapelvic/pelvicalyceal areas (which are active during in utero erythrogenesis) than in the perirenal and pararenal locations. Perirenal and pararenal EMH can surround the kidneys without distorting their shape.7 In distinct contrast, our ultrasound showed significant hydronephrosis in large, echogenic kidneys. Other sonographic findings may be confused with renal cell carcinoma, renal lymphoma, or other diffuse pathologies such as polycystic kidney disease.8 Previous reports indicate that an enhancement pattern may be present in renal EMH .7,9
The signal characteristics of these lesions on MRI suggested the presence of blood/iron products. As paramagnetic substances, iron in ferrous and ferric states (deoxyhemoglobin, methemoglobin, and hemosiderin) can shorten T1 and T2. Higher concentrations of hemosiderin, however, can cause a disproportionately greater effect on T2. As a result, appearance of blood products can vary from slightly increased signal to strikingly low signal on T1-weighted imaging.10 Decreasing T2 relaxation rates will result in low signal on T2-weighted imaging.
An important consequence of renal involvement of extramedullary hematopoiesis is renal failure from either obstruction or parenchymal infiltration. Recognition of the various manifestations of EMH is important for a prompt diagnosis and proper treatment. No imaging characteristic is pathognomonic, and a biopsy is often necessary to establish the definitive diagnosis. The patient received bilateral ureteral stents and is currently receiving low-dose radiation.
Extramedullary hematopoiesis. Appl Radiol.