Abnormal renal rotation

Abnormal renal rotation (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.

Epidemiology
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.

Gross anatomy
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 nonrotation (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.

Radiographic features
Urography
malrotation can be demonstrated when the calyces project medially to the renal pelvis
on CT urography, the renal pelvis of a nonrotated kidney will project anteriorly 3
Development
The exact cause of malrotation of the kidneys is unclear, though it has been hypothesised 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.

Related pathology
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
References
Related Radiopaedia articles
Anatomy: Abdominopelvic
skeleton of the abdomen and pelvis[+]
muscles of the abdomen and pelvis[+]
spaces of the abdomen and pelvis[+]
abdominal and pelvic viscera
gastrointestinal tract[+]
spleen[+]
hepatobiliary system[+]
endocrine system[+]
urinary system
kidney
renal pelvis[+]
renal sinus
avascular plane of Brodel
variants
number[+]
fusion[+]
location
ectopic kidney[+]
abnormal renal rotation
nephroptosis
shape[+]
ureter[+]
urinary bladder[+]
urethra[+]
embryology[+]
male reproductive system[+]
female reproductive system[+]
blood supply of the abdomen and pelvis[+]
lymphatics[+]
innervation of the abdomen and pelvis[+]