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What is Keyhole sign is seen in and explain in detail?
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 the"keyhole" sign, and the bladder wall is thick (Ref: William's Obstetrics; 25th edition)