Ureteral obstruction is a frequent urologic complication after kidney transplant and usually occurs in the early postoperative period. Inguinal herniation of the transplanted ureter is a rare but potentially correctable cause of late obstructive uropathy. We report a 57-year-old male kidney transplant recipient who presented with hydronephrosis and acute kidney injury. Ultrasonography showed moderate to severe hydronephrosis of the renal allograft. Renal scintigraphy with 99mTc-diethylenetriamine pentaacetic acid revealed delayed tracer transit and abnormal radiotracer accumulation inferior to the urinary bladder, suggestive of distal ureteral obstruction. Abdominopelvic computed tomography confirmed herniation of the distal transplanted ureter into a right inguinal hernia. This case highlights the diagnostic value of 99mTc-diethylenetriamine pentaacetic acid renal scintigraphy for identification of uncommon causes of late ureteral obstruction in kidney transplant recipients. Inguinal herniation of the transplanted ureter should be considered in patients with posttransplant hydronephrosis and compatible clinical findings.

Key words : Inguinal hernia, Kidney transplantation, Nuclear medicine, Ureteral obstruction

Introduction
Posttransplant monitoring is essential for preservation of renal allograft function and includes regular laboratory evaluation, imaging studies, and surveillance for donor-specific antibodies and infections.¹ Ureteral obstruction is a relatively common urologic complication after kidney transplant, occurring in approximately 5% to 10% of recipients, and is most frequently observed in the early postoperative period due to ischemic strictures or technical anastomotic problems.^2,3 Other causes of obstruction include external compression by lymphocele or hematoma, ureteral kinking, fibrosis, urolithiasis, viral infections such as polyomavirus, and malignancy.^4,5 In contrast, late obstructive uropathy caused by herniation of the transplanted ureter is exceedingly rare.^6-9 We report a case in which renal scintigraphy played a pivotal role for identification of this unusual etiology of posttransplant ureteral obstruction.

Case Report
A 57-year-old man with end-stage kidney disease of unknown etiology underwent living-donor kidney transplant 7 years prior to presentation. Four years after transplant, he developed urinary tract obstruction and was treated with ureteral reimplant. He presented with fever, urinary retention, gross hematuria, and a rising serum creatinine level of 3.2 mg/dL compared with a baseline value of 2.0 mg/dL. Physical examination revealed enlargement of the right hemiscrotum. Ultrasonography demonstrated moderate to severe hydronephrosis of the transplanted kidney. We subsequently performed renal scintigraphy with 99mTc-diethylenetriamine pentaacetic acid (Figure 1). The flow phase showed mildly reduced perfusion of the renal allograft, while the functional phase demonstrated moderately decreased renal function. Delayed visualization of the urinary bladder and retention of radiotracer within the renal pelvis and proximal ureter were observed, with partial response following furosemide administration, which are findings consistent with partial urinary tract obstruction. An abnormal focus of tracer accumulation was detected inferior to the bladder, raising suspicion of distal ureteral herniation. Abdominopelvic computed tomography confirmed a right inguinal hernia containing the distal segment of the transplanted ureter, associated with proximal hydroureteronephrosis. The patient initially underwent decompression by nephrostomy, followed by delayed surgical repair of the inguinal hernia. During 1 year of follow-up, renal function remained stable, and no further episodes of urinary tract infection were observed.

Discussion
Obstructive uropathy after kidney transplant may present with acute kidney injury, urosepsis, and graft dysfunction.¹⁰ Ultrasonography commonly reveals hydroureteronephrosis but often fails to identify the underlying cause.^7-10 Typical etiologies include ureterovesical junction obstruction, ureteral kinking or injury, ischemia, fibrosis, stone formation, lymphocele, and strictures. Herniation of the transplanted ureter represents an exceptionally rare cause of obstruction and may occur through the inguinal canal, femoral ring, or obturator canal.¹¹ Reported risk factors include older recipient age, male sex, obesity, excessive ureteral length, placement of the ureter over the spermatic cord, prior hernia repair, and a prolonged interval since transplant exceeding 5 years.^3,10 Bosmans and colleagues reported that all published cases occurred in male patients, most on the ipsilateral side of the transplanted kidney, with a mean interval of 12 years between transplant and hernia development.³ To our knowledge, this case represents the first report in which renal scintigraphy demonstrated abnormal tracer accumulation inferior to the bladder, suggesting an extravesicular abnormality. This functional finding prompted further anatomic assessment with computed tomography, which confirmed the diagnosis. This case illustrates the complementary role of functional imaging with renography and cross-sectional imaging with computed tomography or magnetic resonance imaging in the evaluation of unusual causes of posttransplant urinary obstruction.

Conclusions
Although inguinal herniation of the transplanted ureter is a rare cause of obstructive uropathy, it should be considered in kidney transplant recipients who develop late-onset hydronephrosis, particularly in the presence of predisposing risk factors. Careful physical examination combined with appropriate imaging modalities, including renal scintigraphy and abdominopelvic computed tomography, can facilitate timely diagnosis and help prevent irreversible graft damage.