Final answer:
The direct consequence of an upper urinary tract obstruction in a single ureter is hydronephrosis, which is the dilation of the kidney(s) due to the blockage of urine flow.
Step-by-step explanation:
The consequence of an upper urinary tract obstruction in a single ureter is hydronephrosis. Hydronephrosis is the enlargement of one or both of the kidneys caused by obstruction of the flow of urine. Kidney stone formation can indeed lead to a blockage of the ureter, but the direct consequence of such an obstruction is the dilation of the renal pelvis and calyces (hydronephrosis), not the stone itself. Dilation of the urethra is not typically associated with upper urinary tract obstruction, and anuria refers to a complete lack of urine excretion which can be a result of renal failure but is not a direct consequence of a single ureter obstruction.