Hydronephrosis is distension and dilation of the renal pelvis calyces, usually caused by obstruction of the free flow of urine from the kidney, leading to progressive atrophy of the kidney. In cases of hydroureteronephrosis, there is distention of both the ureter and the renal pelvis and calices. (As in the case below)

A 34-year-old with a 3-year history of polycythemia that required monthly phlebotomy. His medical history was significant for congenital nephrogenic diabetes insipidus, with a urine output of approximately 12 to 15 liters per day. Physical examination revealed euvolemia and massive, palpable kidneys. The results of laboratory tests showed a hemoglobin level of 20.2 g per deciliter (reference range, 13.5 to 18.0) and a serum creatinine level of 1.6 mg per deciliter (141 μmol per liter) (reference range, 0.7 to 1.2 mg per deciliter [62 to 106 μmol per liter]). The patient showed no shortness of breath and was not hypoxic. Before the initiation of phlebotomy, his red-cell mass was elevated. An elevated serum erythropoietin level of 49.1 U per liter (reference range, 3.7 to 31.5) and the absence of a V617F mutation in the Janus kinase 2 (JAK2) gene suggested secondary polycythemia. Computed tomographic imaging of the abdomen without the use of contrast material revealed a markedly distended urinary bladder (dagger), severe bilateral megaureter (arrows), and extreme bilateral hydronephrosis with paper-thin renal cortices (arrowheads). Uncontrolled nephrogenic diabetes insipidus may result in marked nonobstructive hydronephrosis, which may subsequently cause local renal hypoxia, increased erythropoietin production, and polycythemia. For this patient, the prescription of captopril and hydrochlorothiazide decreased urinary output to 7 to 9 liters per day and permitted the frequency of his therapeutic phlebotomy to be reduced to once every 3 months. Chih-Chien Sung, M.D. et al. Published in N Engl J Med 2011; 365:e1 July 7, 2011

Source: Wikipedia, N Eng J Med 2011; 365:e1 July 7,2011

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