A retrocaval ureter is a rare congenital anomaly, in which the ureter passes behind the inferior vena cava (IVC) and is compressed between the IVC and vertebrae, which results in a progressive hydronephrosis and hydroureter (1, 2). The etiology is assumed to be abnormal embryologic development of the IVC, due to absence of the subcardinal vein in the lumbar portion. The anomaly is usually observed in the right ureter. A left retrocaval ureter is an extremely rare anomaly, which always is associated with duplicated IVC.

CT urography is not a routine examination for assessing the donor's kidneys, but a non-invasive imaging study to evaluate delayed opacification or dilated upper urinary tract of the unknown cause (3). However, CT urographic findings of a left retrocaval ureter are rarely reported in the English Literature. A kidney with a right retrocaval ureter is not contraindicated to allograft transplantation and showed a good post-transplant outcome in a few case reports (4, 5). However, there were no reports regarding allograft transplantation of a left retrocaval ureter from a living related donor.

The purpose of our case report was to provide CT urographic findings of a left retrocaval ureter and to show a short-term outcome of allograft transplantation.

A 24-year-old man was referred to get a work up for kidney transplantation as a donor. He looked healthy and had no history of past medical or surgical treatment, trauma, or hereditary disease. No signs or symptoms of urinary tract were found on physical examination. Complete laboratory evaluation, including urinalysis, complete blood count, blood urea nitrogen (BUN), creatinine and electrolytes were within normal limits. CT angiography of the renal artery revealed duplicated IVC below the left renal vein and left hydronephrosis. Thus, CT urography was conducted for further evaluation of left urinary obstruction. Excretory CT urography showed severely dilated left upper urinary tract, in which the left ureter was compressed between the left IVC and vertebrae because the ureter passed behind the IVC (Fig. 1A). Three dimensional reconstruction images showed characteristic hairpin turn ("J" shape deformity) of the left ureter, strongly suggesting a left retrocaval ureter (Fig. 1B, C).

The recipient is a 51-year-old female who had chronic renal failure from IgA nephropathy. Pre-transplantation laboratory tests revealed poor renal function, including elevated BUN (29.0 mg/dL), serum creatinine (5.26 mg/dL), and reduced estimated glomerular filtration rate (eGFR) (8.6 mL/min/1.73 m²). Despite the left retrocaval ureter, the left kidney from a living-related donor had a potential for kidney transplantation. On the operation field, the left ureter was dilated tortuously just before it passed behind the left IVC, and then, it turned laterally to the IVC. The main renal artery, main renal vein and ureter were dissected and ligated. After the surgery, the donor was uneventfully discharged. Five month follow-up revealed normal urinalysis, BUN level (16.9 mg/dL), and slightly elevated serum creatinine level (1.31 mg/dL).

The recipient's postoperative course was uneventful and discharged from the hospital three weeks after the surgery with good renal function: BUN of 15.5 mg/dL, and serum creatinine of 1.28 mg/dL. At the last visit, 5 months after receiving transplantation, she revealed a creatinine of 1.25 mg/dL and an eGFR of 37.2 mL/min/1.73 m². Ultrasonography of the transplanted kidney revealed mild hydronephrosis and hydroureter without sign of ureter obstruction.

A retrocaval ureter is a rare congenital anomaly with an incidence of 1 per 1000 live births and this anomaly is caused by an abnormal development of IVC (1, 2). Normally, IVC originates from the supracardinal and subcardinal veins, respectively. If the IVC inferior to the kidney is formed by subcardinal vein, it will be located anterior to the ureter and will form a retrocaval ureter. A retrocaval ureter is three times more common in males (6) and more common on the right side. A left retrocaval ureter may occur and is associated with duplicated IVC (1, 2). Most patients do not present with symptoms until the third or fourth decade of life, and symptoms depend on the degree of ureteral obstruction or the presence of complications. Intermittent flank pain is often noted as the first complaint. Occasionally, recurrent urinary tract infection, hematuria, pyelonephritis, or stone formation is noted (7).

A retrocaval ureter has been previously diagnosed by intravenous urography and retrograde pyelography, and venography (4, 5). Currently, CT scan is the best imaging modality for diagnosis of urinary anomaly. CT urography is a useful tool for diagnosis of a right retrocaval ureter, which demonstrates the anatomy of the ureter and IVC clearly (6, 8, 9). Three dimensional reconstruction CT images make it possible to reach a conclusive diagnosis of retrocaval ureter by means of depicting a ureter passing behind the IVC without invasive diagnostic procedures. CT urography also helps a surgeon accurately to estimate the length or degree of the dilated ureter segment prior to donor's nephrectomy. A left retrocaval ureter have been rarely reported in terms of CT urographic findings (10). Our case showed that the basic imaging features of a left retrocaval ureter were as same as those of a right retrocaval ureter, except the presence of a left IVC. CT urography is not an essential examination prior to renal transplantation, but it will be helpful for evaluating urinary anomaly in a donor like our case.

To date, there are two case reports about allograft transplantation of a right retrocaval ureter (4, 5). Both of these reports demonstrated that dilated ureter segment of the retrocaval ureter should be used for uretero-neocystostomy because non-dilated ureter segment caused functional obstruction due to no peristalisis. In our case of a left retrocaval ureter, uretero-neocystostomy was also made with dilated ureter segment, instead of non-dilated ureter segment; thus, the patient was discharged without sign of ureter obstruction.

In conclusion, CT urography can provide useful imaging features to a surgeon about making preoperative diagnosis and surgical planning of a left retrocaval ureter. A left kidney with a retrocaval ureter may achieve a good outcome of allograft transplantation.