<prompt> Keyhole sign is seen inPolycystic kidney diseaseRenal agenesisUreteropelvic junction obstructionBladder outlet obstruction  <response>: Distal obstruction of the urinary tract is more frequent in male fetuses, and the most common etiology is posterior urethral valves. Characteristically, there is dilatation of the bladder and proximal urethra, termed thekeyhole sign, and the bladder wall is thick Ref: Williams Obstetrics; 25th edition 