#2614 Extramedullary hematopoiesis resembling an asymptomatic renal mass: an unusual presentation

Abstract Background and Aims Extramedullary hematopoiesis (EMH) is the body's compensatory response to deficient erythropoiesis by the bone marrow or accelerated destruction of erythrocytes. The term refers to deposits of erythroid precursors in organs outside the bone marrow, most frequently occurring in the liver, spleen and lymph nodes. We report a case of perirenal EMH revealed by ultrasound (US) integrated with magnetic resonance imaging (MRI) in a patient with primary myelofibrosis. This case reveals the importance of point-of-care US (POCUS) to complete the nephrological examination and better direct the diagnostic process. Method A 68 yo man with a myeloproliferative disease was referred to nephrologists due to the discovery of altered creatinine and urea values in the blood tests (1.6 and 65 mg/dl, respectively, eGFR 43 ml/min EPI-CKD), reduction of hemoglobin value (6,4 g/dl) despite erythropoietin (EPO) and iron supplements, and for renal cysts follow-up. The standard urinalysis showed no abnormalities and negative fecal occult blood tests. Physical examination and US were performed during outpatient visit. Results On US abdominal evaluation, an already known severe splenic enlargement was found (LD 18 cm, Fig. 2), with the presence of two peri centimetric accessory spleens at the hilum. In the prone position, a bilobed, isoechoic structure was noticed emerging from the posterior profile of the upper pole of the left kidney: it measured 3.7 cm and didn't show a clear solution of continuity with the renal parenchyma. The color evaluation did not reveal hypervascularization. The uncertain nature of the lesion led us to perform an MRI, which showed bilaterally, along the posterior capsular margin, an isointense tissue thickening on T1 and slightly hyperintense and inhomogeneous on T2 with signs of diffusivity restriction, compatible in the first hypothesis with perirenal EMH (Fig. 1).These findings were absent in the annual US performed in hematology; they entered into the differential diagnosis with cysts or renal lesions. US first and then MRI made it possible to diagnose EMH and clinically justify the anemia and the low recent response to EPO. Conclusion Primary myelofibrosis is characterized by bone marrow fibrosis and the proliferation of megakaryocytes and granulocytes in the bone marrow and may result in progressive pancytopenia and EMH. Foci of EMH may develop or enlarge significantly after splenectomy, perhaps due to the loss of filtering function of the spleen. The kidney is an unusual site for EMH and it can be asymptomatic clinically. There have been few previous reports of EMH renal involvement, that can be parenchymal, intrapelvic or perirenal. In our patient, EMH diagnosis was coincidental but allowed us to place differential diagnosis with other diseases such as tumors, lymphomas, lipomatosis, renal inflammatory or infectious tissue, which generally present as a perirenal or parapelvic mass of uncertain etiology. In this case, POCUS allowed us to locate the mass and characterize it, excluding obstructive renal failure, and to establish a differential diagnosis with complex cysts or lymph node packages or others. Despite the reduced eGFR, renal function was stable in the previous and following months. According to the literature, we decided to perform only radiological exams because of the kidney biopsy risk of significant bleeding. In patients with hematologic disorders, it is important to investigate the presence of renal structural changes that require radiological follow-up and that could affect long-term prognosis.