<prompt> Adder head appearance is seen in:UreterocoeleDuplication of ureterUrethral diverticulum.Mega ureter  <response>: Ans: a Ureterocoele Ref: Bailey, 24th ed, p. 1310Ureterocoele: Cystic enlargement of intramural portion of ureter. Adder heaed appearance in excretory urography is typical.Other important radiographic appearance Spring onion appearance- Ureterocoele Spider leg appearance- Polycystic kidney Flower vase appearance- Horse shoe kidney Rim sign or crescent sign- Hydronephrosis Sandy patches, foetal head in pelvis- Schistosomiasis bladder Golf hole ureter, thimble bladder- TB kidney Soap bubble appearance- Hydronephrosis Clubbing of calyces- Hydronephrosis Meniscus sign- CBD stone Reverse J sign with hydronephrosis- Retrocaval ureter Drooping flower appearance- Ectopic ureter Irregular filling defects, spider leg appearance- Renal cell carcinomaUrographically early filling of the bulbous terminal ureter is noted, a finding that has been referred as a spring onion appearanceSome notes on radiological investigations in urology Rapid sequence urography is carried out in patients with suspected reno vascular hypertension. Urethroscopy is confirmatory for stricture of urethra. Infusion urography-in compromised renal function Diuretic urography-PUJ obstruction Micturating cysto urethrography-investigation of choice for VUR and posterior urethral valve. Retrograde urethrogram is the best to visualize penile urethra. 