Ketamine abuse would cause interstitial cystitis [1], which on images are characterized by wall thickening of a very small-sized bladder. The patients with ketamine cystitis usually present with urgency, frequency, and dysuria, which is related with decreased bladder capacity [1]. Some patients with ketamine abuse may have unilateral or bilateral hydronephrosis or hydroureter in addition to cystitis [1]. Although a history of ketamine abuse is necessary to make a diagnosis, cystitis in a young adult or teenager is very unusual, and a high suspicion of ketamine-induced urological diseases should be raised especially in negative result of urine culture.

Flank herniation after nephrectomy is occasionally seen on images. It occurs as flank wall weakness after nephrectomy via retroperitoneal approach. Typically, retroperitoneal fat would herniate through the weakened flank wall area. By comparing the wall contour of the normal side, flank herniation on images could be easily identified. Sometimes, adjacent bowel loops also herniate though the weakened flank wall.

Colocutaneous fistula after nephrectomy is rare. Fistulography is useful to confirm communication of the skin and the colon. CT usually could detect the skin defect caused by a colocutaneous fistula; however, it is sometimes difficult to make sure of the colonic communication to the skin defect on CT.

Urothelial carcinomas of the ureteral stump occur in the residual ureteral stump after nephroureterectomy. The standard surgery for urothelial carcinomas of the upper renal tract is nephroureterectomy with bladder cuff excision. However, the most distal part of the ureter to ureterovesical junction (UVJ) might remain unremoved by technical limitations hindering bladder cuff excisions. The remaining part of the ureter is called ureteral stump. The ability of tracing the ureteral stump on images is fundamental for diagnosing ureteral stump cancer, which could be traced from the UVJ to the remaining distal ureteral segment. On computed tomography or magnetic resonance image, urothelial carcinomas of the ureteral stump could be diagnosed by identifying abnormal enlargement of the ureteral stump occupied by a soft tissue mass with contrast enhancement.

Renal subcapsular hematoma is a complication of ESWL [2]. It typically appears as a lenticular shape lesion with obvious mass effect on the adjacent renal parenchyma by a tight renal capsule. The ipsilateral kidney could be displaced by the hematoma; however, the compressed, deformed, and depressed renal parenchyma adjacent to the hematoma is conspicuous. Sometimes, subcapsular hematoma could cause hypertension by hemodynamic changes of ipsilateral kidney, which is called page kidney. Chronic subcapsular hematoma usually accompanies adjacent fibrosis and ipsilateral renal atrophy.

Iatrogenic renal vascular injury could occur following percutaneous procedures such as percutaneous nephrostomy and renal biopsy or surgery including nephrectomy, partial nephrectomy, renal bisection, etc. [3, 4]. The iatrogenic renal vascular injury could present as renal arterial pseudoaneurysms, arteriovenous fistula (AVF), contrast medium extravasation, or even arteriocalyceal fistula [3, 4]. On renal angiography and computed tomography angiography, a renal arterial pseudoaneurysm shows a contrast medium pooling supplied by a renal artery which has delayed washout. Renal AVF could occur alone or in the presence of renal pseudoaneurysm. The presence of renal AVF on renal angiography is evidence by the presence of early drainage vein connecting the supplying renal arterial branch, and the ipsilateral main renal vein is also earlier opacified accordingly. Contrast extravasation on renal arteriography shows contrast medium flowing out the supplying artery and usually shows an irregularly shaped contrast pooling. Transcatheter arterial embolization could stop renal bleeding with successful clinical outcomes for patients with iatrogenic vascular injury [4].

The diagnosis of urine leakage from renal collecting system after renal surgery is usually straightforward. On retrograde pyelography (RP), the renal collecting system is normally opacified by contrast medium injection via the inserted ureteral stenting. If there is contrast opacification beyond the renal collecting system, urine leakage is suggested. On computed tomography (CT), excretory phase is usually necessary for confirmation urine leakage from the collecting system after contrast medium opacification. On the other hand, CT on arterial or nephrographic phase could be unable to make a diagnosis of urine leakage by the inability of confirmation of perinephric fluid being urine origin. Ureteral stenting and percutaneous nephrostomy have been commonly used for treatment of urine leakage from renal collecting system after surgery [5].

Ureteral injury usually resulted from iatrogenic causes, most commonly by gynecological or colorectal surgery [6]. Occasionally, ureteral injury occurs during urological procedures [7]. Excretory urography (EU) and retrograde pyelography (RP) have been traditionally used to diagnose ureteral injury [7]. On RP and EU, contrast extravasation from the ureter has shown if there is ureteral wall defect in iatrogenic trauma. Computed tomography urography (CTU) could show imaging signs of ureteral rupture as well, which may include contrast extravasation from the ureter, hydronephrosis, urinoma formation, and hydroureter proximal to ureteral injury site. Transection or ligation of the ureter could be resulted from iatrogenic ureteral injury, too. In these cases, hydronephrosis with proximal hydroureter with complete nonvisualization of the ureter distal to the injury site is the main finding.

Stone of allograft ureter is uncommon. On excretory urography (EU) and retrograde pyelography (RP), ureteral stone could appear as a filling defect of round or oval shape if it is detectable by sufficient size and radiopaque density. Unenhanced computed tomography (CT) is the most accurate for detecting ureteral stone of their high density. If there is uncertainty of the high density foci in the ureter or transplant ureter, enhanced CT of excretory phase is useful for localization and confirmation.

Bladder rupture after TURBT is an uncommon complication [8]. Most of them are extraperitoneal rupture of the urinary bladder [8]. Bladder rupture is diagnosed on cystography, computed tomography (CT) of excretory phase, or computed tomography cystography (CT cystography) by contrast extravasation from the urinary bladder. Sometimes, the wall defect responsible for bladder rupture could be seen on computed tomography. Among cystography, CT of excretory phase and CT cystography, CT cystography has the best accuracy for diagnosing bladder rupture by combination of pros of cystography as direct contrast medium injection into the urinary bladder cavity and CT as a cross-sectional imaging modality with better sensitivity to detect small contrast medium extravasation from the urinary bladder.