An Enigmatic Route to the Contralateral Pelvicalyceal System on Antegrade Pyelogram

Abstract

Introduction:

The authors present the rare yet enigmatic phenomenon of ‘pyelo-renal’ backflow.

Case Presentation:

An eight-month-old boy with multiple congenital anomalies underwent left Anderson-Hynes Pyeloplasty for pelvi-ureteric junction obstruction. Antegrade dye-study done through the nephrostomy revealed obstruction at the level of the pelvi-ureteric junction, yet the contrast was visualized in the pelvis of contralateral kidney and urinary bladder (pyelo-venous backflow) masquerading as vesicoureteric reflux. The phenomenon of ‘pyelo-renal’ backflow along with pyelo-tubular, pyelo-interstitial, pyelo-sinusal and pyelo-lymphatic backflow have been described and the respective mechanisms discussed.

Conclusion:

The phenomenon is known to happen in the presence of obstruction to outflow from renal pelvis thereby creating a closed compartment. Injection of contrast at a pressure above the critical limit may result in forniceal tears and back-flow of contrast into the renal tubules and beyond.

CLINICAL HISTORY

The case is an 8-month-old boy born with a spectrum of congenital anomalies including syndromic facies, high anorectal malformation, congenital hydrocephalus, and left-sided pelviureteric junction obstruction. He underwent posterior sagittal anorectoplasty for high anorectal malformation, insertion of ventriculo-peritoneal medium pressure shunt (Chhabra shunt) for congenital hydrocephalus, and left-sided Anderson–Hynes dismembered pyeloplasty, each at a different pediatric surgical center.

Ultrasound of the kidney, ureter, and bladder revealed the presence of left hydronephrosis without ureteric dilatation. The right kidney and ureter were unremarkable. Indications for pyeloplasty included left renal function of 18% and obstructive pattern on renal dynamic scan. Pyeloplasty was started by lumboscopic approach but had to be converted to lumbotomy. Left ureter distal to the site of obstruction was of very poor quality: papery thin wall and a lumen too small to accommodate even a 0.025” guide wire. Consequently, a stentless pyeloplasty was performed, but a 6 Fr infant feeding tube was inserted through the lower-pole parenchyma into the renal pelvis.

Accompanying images show the antegrade pyelography done on this patient on postoperative day 10.

Question of Relevance: How does one justify the presence of contrast in various locations in the image provided?

Figure 1A: Tubing of ventriculo-peritoneal shunt is visualized with tip positioned in the supra-hepatic region. Left renal pelvis is dilated with nephrostomy catheter in-situ. Trickle of contrast is seen into the ureter but not reaching the urinary bladder.

Figure 1.

Radiological images of antegrade pyelography done on post-operative day 10 after left-sided Anderson-Hynes dismembered pyeloplasty. (a) 1-Pyelotubular or pyelocanalicular backflow. 2-Pyelointerstitial backflow. 3-Pyelosinusal backflow. 4-Pyelolymphatic backflow. (b) 5-Contrast visualized in the pelvis of the contralateral kidney due to pyelovenous backflow. 6-Excretion of contrast into the urinary bladder

An inquisitive eye will appreciate the presence of pyelotubular [Figure 1a, label 1], pyelointerstitial [Figure 1a, label 2], pyelosinusal [Figure 1a, label 3], and pyelolymphatic backflow [Figure 1a, label 4].

Pyelovenous backflow [Figure 1a, label 5] is not visible, but there is indirect evidence for its presence (see section on Discussion).

Figure 1b: Presence of contrast in the contralateral pelvis (5) and in the urinary bladder (6) reflecting excretion of contrast from the systemic circulation.

The contrast from the pyelorenal backflow entered the systemic circulation and was excreted by the right kidney. This can be mistaken for vesico-ureteric reflux on the right side.

DISCUSSION

The entity “pyelorenal backflow,” also called as “spontaneous pyelorenal backflow,” refers to the backflow of contrast material out of the renal collecting system.[1,2] Also described as spontaneous, it is usually seen in cases with acute ureteral obstruction. The sudden buildup of positive pressure inside the renal pelvis due to reasons such as stone and tumor may result in backflow of contrast via any one of the following pathways:

1. Pyelotubular or pyelocanalicular backflow

2. Pyelovenous backflow

3. Pyelolymphatic backflow

4. Pyelointerstitial backflow

5. Pyelosinusal or pyelosinus backflow.

Mechanism of pyelorenal backflow

Of all the pathways of reflux described, only pyelocanalicular or pyelotubular backflow may happen without any anatomical damage to the integrity of the kidney. All the other types of backflow may happen only after forniceal rupture.

Clinical relevance of pyelorenal backflow

It seems that pyelorenal backflow is nature's own protective and possibly compensatory mechanism to absorb urine in acutely obstructed systems. Not only does this result in relief of symptoms arising out of acute obstruction and dilatation but also allows the continued excretion through the contralateral kidney.

Pyelotubular or pyelocanalicular backflow

Pyelotubular or pyelocanalicular backflow [Figure 1a, label 1] is the only genuine component of pyelorenal backflow which may happen without forniceal rupture. It is a result of opacification of terminal portions of collecting ducts; hence, it is not a “backflow” in real sense of the word. It can be appreciated in the image provided as a wedge-shaped area, with the appearance of “streaks” or “blush” signifying reflux of contrast from the renal calyx to the papillary ducts in the renal medulla.

Pyelointerstitial backflow

Pyelointerstitial backflow [Figure 1a, label 2] happens only after forniceal rupture and is attributed to backflow of contrast from the pyramids into the subcapsular tubules in the renal interstitium.

Pyelosinusal backflow

Pyelosinusal backflow [Figure 1a, label 3] is the most common form of pyelorenal backflow seen in cases with acute ureteral obstruction. This is responsible for the development of urinomas in cases with urinary obstruction. The contrast escapes into the renal sinus. It may further dissect through the renal sinus, thereby escaping into the renal hilum and diffuse along the renal infundibulae, proximal ureter, and other planes in the retroperitoneum.

This collection may get absorbed into systemic circulation through the capillaries and lymphatic system or persist as an urinoma. Rarely, in neonates, it may escape into the peritoneal cavity and result in urinary ascites.

Pyelolymphatic backflow

Pyelolymphatic backflow [Figure 1a, label 4] refers to retrograde flow of contrast material into the perirenal lymphatics draining medially. It is appreciated on computed tomography images as tiny serpiginous tubular channels which begin from an intrarenal location and are directed toward the hilum of the kidney and course along with the ureter in a caudal direction corresponding to the retroperitoneal para-aortic lymph node chain.

Pyelovenous backflow

Pyelovenous backflow (not visualized directly in images provided) is a retrograde flow of contrast material through the interlobar veins into the arcuate renal veins and eventually into the venous circulation.

Pyelovenous backflow may not be picked up on contrast studies because the high flow rate in the otherwise patent renal vein and the inferior vena cava dilutes the relatively small amount of contrast material. Indirect evidence for the same [Figure 1b, label 5] is provided by contralateral excretion of contrast absorbed systemically from the affected side.

The presence of a partially obstructing thrombus in the renal vein of inferior vena cava may slow down the flow sufficiently, resulting in the visualization of pyelovenous backflow. Similar flow dynamics may operate in cases with the “nutcracker phenomenon.”

Clinical features

Pyelorenal backflow is often diagnosed on contrast studies and is picked up by the radiologist or the clinician only if he/she is aware of this entity. Per se pyelorenal backflow is not associated with any symptoms specific to its identity, but it may serve to ameliorate the symptoms of acute ureteral obstruction.

Histopathological examination may reveal the anatomical breach in the fornix of the pelvic cavity extending up to the renal parenchyma.

The management of pyelorenal backflow includes treating the cause of acute ureteral obstruction.

What this case adds to our knowledge

In the index case, the contrast was visualized in the contralateral pelvis [Figure 1b, label 5] and also in the urinary bladder [Figure 1b, label 6] in delayed images.

Pyelorenal backflow resulted in contrast entry into the systemic circulation from the left kidney and its excretion by the contralateral normal kidney. This resulted in visualization of contrast in the contralateral system. Renal excretion of contrast is seen even if the small quantity of the contrast enters the systemic circulation. Just in case, one is unaware of this entity or is not alert to the possibility, it is easily confused with vesico-ureteric reflux on the contralateral side, thereby complicating the diagnosis further.

What this discussion adds to literature

The authors felt the need to publish these findings to sensitize the young generation of pediatric surgeons and pediatric radiologists, especially those “in the making” to the possibility of pyelorenal backflow.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.