A 32 year old man presents with severe right flank pain after a drinking binge. He reports experiencing similar episodes for several years, with pain lasting from several hours to a few days.

Interestingly, in the past,  he abstained from alcohol for six weeks and remained completely symptom-free.

He has:

Normal renal function
No urinary tract infection
A family history of renal stones

A point of care renal ultrasound is performed

Longitudinal view : The right kidney demonstrates marked hydronephrosis with a massively dilated renal pelvis.

Transverse view of the right kidney

Transverse view: The renal pelvis measures over 7 cm in diameter, producing a characteristic ballooned appearance.

Transverse view with colour Doppler. There is no flow with Colour Doppler within the anaechoic structure

Transverse view in slow motion. This is a slowed down sweep through the right kidney in the transverse plane. Note that the pelvic cystic structure is not entirely concave and communicates with the dilated calyces excluding a renal cyst.

A CT with contrast was organised which showed a pelviureteric junction stenosis with cortical parenchymal thinning secondary to extrinsic compression by an ectopic inferior right renal artery.

 

 

Mid pole coronal view

lower pole coronal view

CT Findings

CT urography demonstrated:

  • Severe right hydronephrosis
  • Dilated renal pelvis
  • A lower-pole accessory (crossing) renal artery traversing the ureteropelvic junction
  • No ureteric calculus

The patient subsequently underwent laparoscopic pyeloplasty, with reconstruction of the ureter anterior to the crossing vessel.

His symptoms resolved following surgery. 

Understanding UPJ Obstruction

The ureteropelvic junction (UPJ) is where the renal pelvis narrows to become the ureter.

Obstruction at this point prevents normal urinary drainage, resulting in progressive hydronephrosis.

Although UPJ obstruction is usually diagnosed during infancy, some patients remain asymptomatic until adulthood.

Adult presentation commonly includes:

  • Intermittent flank pain
  • Nausea and vomiting
  • Episodes precipitated by increased urine production (alcohol, caffeine or large fluid intake)
  • Recurrent urinary tract infections
  • Haematuria

The classic intermittent pain after drinking large volumes of fluid is known as Dietl’s crisis, a characteristic presentation of intermittent UPJ obstruction.

 

What Causes UPJ Obstruction?

Most congenital UPJ obstruction results from an intrinsic narrowing of the junction due to abnormal smooth muscle development.

Less commonly, there is extrinsic compression from a crossing lower-pole renal vessel.

Accessory renal arteries are common anatomical variants, occurring in approximately 25–30% of the population. However, only a small proportion cause clinically significant obstruction. A crossing vessel may contribute to obstruction but is not always the primary cause.

Mimics of Hydronephrosis: 

  1. Extrarenal pelvis
  2. Parapelvic cysts
  3. Prominent renal vasculature and vascular malformations.

Extrarenal pelvis:

  • Easy to confuse with hydronephrosis.
  • Anatomical variant (10% of population)
  • The renal pelvis is outside the renal sinus and therefore not surrounded by fat
  • The pelvis is larger and more distensible
  • Usually asymptomatic but stone formation and infection have been reported
  • Unlike hydronephrosis it is not associated with dilated calyces, parenchymal thinning, hydroureter or enlarged kidney
  • Tip : An easy way to differentiate an extra renal pelvis from hydronephrosis is to place the patient prone . In the prone position , hydronephrosis will remain, an  extrarenal pelvis will collapse

Parapelvic cysts: 

  • Easy to confuse with hydronephrosis
  • Describes cysts around the renal pelvis or renal sinus
  • The cysts do not communicate with the collecting system
  • Probably lymphatic in origin
  • Mainly asymptomatic but may cause haematuria, hypertension, hydronephrosis or become infected
  • Unlike hydronephrosis, it is not associated with dilated calyces, parenchymal thinning, hydroureter or enlarged kidney
  • More spherical in shape than hydronephrosis
  • Tip: In the transverse view the cyst does not appear connected with the calyceal system
  • Differentiation with hydronephrosis is confirmed with a CT scan with contrast 

Prominent renal vasculature and vascular malformations

  • Easy to differentiate from hydronephrosis with colour Doppler.  Vascular structures will demonstrate flow

Learning Points

Remember these key messages:

  • Intermittent flank pain after alcohol or large fluid intake should raise suspicion for UPJ obstruction.
  • POCUS readily identifies hydronephrosis but usually cannot determine the underlying cause.
  • Crossing renal vessels are a recognised cause of extrinsic UPJ obstruction but are not responsible for every case.
  • CT angiography or MR angiography helps define vascular anatomy before surgery.
  • Early diagnosis can prevent progressive renal damage while relieving years of recurrent symptoms.

References

  1. Korean J Intern Med. 2003 Mar; 18(1): 57–60. Hydronephrosis by an Aberrant Renal Artery: A Case Report
    Byoung Seok Park, M.D., Taek Kyun Jeong, M.D., Seong Kwon Ma, M.D., Soo Wan Kim, M.D., Nam Ho Kim, M.D., Ki Chul Choi, M.D., and Yong Yeon Jeong, M.D.*
  2. Unusual course of accessory renal artery and its clinical significance: a case report T. Ramesh Rao1, Prakashchandra Shetty1 and Suresh Rao2* 1Department of Anatomy and Cell Biology Histology, American University of Antigua , Manipal Campus, KMC International Center, Manipal University, Manipal, Karnataka, India
  3. Double Accessory Right Renal Arteries.Dr. Neelesh Kanaskar1 Dr. Vaishali Paranjape 2 Dr. Jyoti Kulkarni3Sapna Shevade41,2,3,4 (Department of Anatomy, Dr. D.Y.Patil Medical College/Dr. D.Y.Patil University, Pune, India)
  4. HYDRONEPHROSIS & UPJ OBSTRUCTION DUE TO AN ACCESSORY RENAL ARTERY By: Tanner Burton https://www.ornh.mb.ca/wcm-docs/docs/rw_2018/burton,_tanner.
  5. Sunday Abba, Amanuel Tesfay, Peter Ekanem. ACCESSORY RENAL ARTERY AND ITS CLINICAL SIGNIFICANCE. Int J Anat Res 2013;03:155-57.
  6. Baskin LS. Congenital ureteropelvic junction obstruction. In: Post T, ed. UptoDate. Waltham, MA: Wolters Kluwer; 2018.
  7. Rev Urol. 2001 Winter; 3(1): 42–51. PMCID: PMC1476031 PMID: 16985690 UPJ Obstruction in the Adult Population: Are Crossing Vessels Significant? Michael Grasso, III, MD, Robert P Caruso, MD, and Courtney K Phillips, MD
  8. The Ultrasound Mimics of Hydronephrosis May 10, 2019 https://www.renalfellow.org/2019/05/10/the-ultrasound-mimics-of-hydronephrosis/
  9. https://www.slideshare.net/Melkholy/renal-us-drdoaa-sharaf-md
  10. Clin Case Rep. 2017 Oct; 5(10): 1720–1721. Published online 2017 Aug 24. doi: 10.1002/ccr3.1143 Extrarenal pelvis mimicking hydronephrosis: a case for caution Abhilash Koratala corresponding author 1 and Deepti Bhattacharya 1
  11. Urol Clin North Am. 1998 May;25(2):289-93.Crossing vessels. Endourologic implications.Gupta M1, Smith AD.Author information Department of Urology, Columbia University, New York, New York, USA
  12. Int J Exp Pathol. 2011 Jun; 92(3): 168–192. Congenital ureteropelvic junction obstruction: human disease and animal models
    Julie Klein,*† Julien Gonzalez,*† Mathieu Miravete,*† Cécile Caubet,*† Rana Chaaya,*† Stéphane Decramer,*†‡ Flavio Bandin,‡ Jean-Loup Bascands,*† Bénédicte Buffin-Meyer,*† and Joost P Schanstra*