Abnormal renal rotation
Citation, DOI & article data
Abnormal renal rotation, also known as renal malrotation, refers to an anatomical variation in the position of the kidneys, in particular to anomalous orientation of the renal hilum. It may occur unilaterally or bilaterally. It is almost always an asymptomatic incidental finding.
Malrotation is rare, perhaps under-reported, and in one autopsy series, a prevalence of ~1 in 2000 was reported 1. It is more common in males.
The renal hilum is normally directed anteromedially. The renal hilum is initially oriented anteriorly, but during its ascent from the pelvis, the kidney rotates 90° along its longitudinal axis to its more typical orientation.
Anomalies in this process can result in 1,2:
- incomplete rotation or non-rotation (most common): hilum faces anteriorly, ureters are located laterally
- excessive rotation (hyper-rotation): hilum faces posteriorly; renal vessels are located posteriorly
- reversed rotation: hilum faces laterally, renal vessels are located anteriorly, ureter is located laterally
Sagittal rotation, i.e. kidney rotation around its hilum in the sagittal plane, is another type of rotation, which as yet does not have an embryological explanation. It is asymptomatic and is virtually always discovered incidentally on imaging 5.
- on CT urography, the renal pelvis of a non-rotated kidney will project anteriorly 3
- malrotation can be demonstrated when the calyces project medially to the renal pelvis
The exact cause of malrotation of the kidneys is unclear, though it has been hypothesized that malrotation may occur if the ureteric bud inserts into an abnormal region of metanephric mesenchyme. Its association with renal ectopia suggests that the process of ascent and rotation are related.
- abnormal renal rotation may cause partial ureteropelvic junction (UPJ) obstruction, which can result in increased incidence of urolithiasis and infection
- the malrotated kidney is prone to stasis, increasing the risk of urolithiasis
- 1. Pediatric Uroradiology. Springer. (2008) ISBN:3540330046. Read it at Google Books - Find it at Amazon
- 2. Radiology Illustrated: Uroradiology. Springer (2012). ISBN:3642053211. Read it at Google Books - Find it at Amazon
- 3. Dunnick R, Sandler C, Newhouse J. Textbook of Uroradiology. Lippincott Williams & Wilkins. (2012) ISBN:1451109164. Read it at Google Books - Find it at Amazon
- 4. Kelly CR, Landman J. The Netter Collection of Medical Illustrations - Urinary System. Saunders. (2012) ISBN:1437722385. Read it at Google Books - Find it at Amazon
- 5. Tsai H-Y, Lee M-H, Chen H-C, Chen H-C , Guh J-Y. Sagittally malrotated kidney: a case series of two patients. Surgical and Radiologic Anatomy (2015) 37:551–553 doi:10.1007/s00276-014-1376-5