Developmental disorders

I./3.3.: Renal ectopias

I./3.3.1.: Classification of ectopias

Renal ectopia might be longitudinal (anywhere along the vertebra, but most frequently in the pelvis), crossed, renal fusion and renal malrotation. Other type of classifications of renal ectopia: Primary ectopias (dystopia) and secondary ectopias. Secondary ectopias include ptosis, ptosis with malrotation, and motion due to tumors. Primary ectopias include ipsi- and contralateral types. Cranial and caudal locations (lumbal, ileolumbal, ileopelvic, pelvic), bilateral dystopia, dystopic fusionated kidneys (incl. horseshoe kidney) and dystopic solitary kidneys belong to the ipsilateral type.

I./3.3.2.: Longitudinal ectopia

In longitudinal ectopia the kidney is stuck in pelvic, sacral or lower lumbal level; the kidney might be located even in the thorax (mostly on the left side), but this is not the same as like the kidney ascended through the diaphragm herniation! Hypermobile kidneys might not be accounted among the lower located types. The task of the radiologist is to „search” for the kidneys in this case, to visualize the vascular structures, arteries and veins (aberrant ones as well). Pelvic ectopia (ectopic pelvis) is explicable from the development of the kidney (the ascensus is missing). In ectopia, other morphologic and functional disorders often cooccur (vesicoureteral reflux, hydronephrosis) due to the high junction of the ureter to the renal pelvis. Hypospadiasis and agenesis of the controlateral kidney occurs often as well.

The task of the radiologist is to control the origin of the renal arteries (does it originate from the iliac artery or from the aorta?), as well as to detect the non-rotation of the kidney with radiological methods (primarily by US): upfront turned pyelon can be observed. These can be visualized using MRI on unenhanced, T1 weighted images, fat-sat technique, directly after contrast media injection. Then we can perform late phase images as well, on which the kidney becomes generally hyperintense.

I./3.3.3.: Crossed dystopia of the kidney

The kidney is located on the contralateral side in crossed dystopia (the left kidney crosses more often than the right one). It is very often accompanied with other urogenital defects: urolithiasis (obstruction type), megaureter, hypospadiasis, ureteral reflux and subsequent uroinfection, urethral valves, multicystic kidney dysplasia and cryptorchismus as well.

The task of the radiologist is to visualize the location of kidneys, their relations to each other, to detect their fusion, to see the urine collecting system’s morphology and its sorroundings, to detect the possible reflux, to visualize the renal vascular structures (arteries and veins) and their relations to each other as well. The ectopic kidney can be recognised easily based on the ureter and the localisation of its vascular structures. The crossed kidney is usually located more lower as its normal place. Fusion of the kidneys often occurs in case of crossed ectopia, but it might be separated as well. The above mentioned anatomical clarification is often not possible by only one radiological method (US), we need to choose – because usually it’s about babies, small children – an other, radiation-free method (MRI).

I./3.3.4.: Renal fusion (for ex. pancake kidney, horseshoe kidney)

It might be various: horseshoe kidney, pancake or discoid kidney (complete fusion). In case of pancake kidney occurance of the other disorders (with urogenital and non-urogenital malformations, together with complex congenital disorders) is often. In females, these malformations included vaginal agenesis; in males, absence of descent of testis, sacral agenesis, caudal regression and anal disorders.

Horseshoe kidney develops if a parenchymal bridge evolves between the poles of the two kidneys (in the lower pole its occurence is more often than in the lower one, only appr. 10% in the upper pole). It is two-three times more often in boys/males than in females. It very often occurs with caudal ectopia  (please see the anatomical preparation of our case!). The occurance with other congenital disorders is common, including genitourinary congenital disorders (hypospadiasis, absence of descended testicles in boys; uterus bicornis in girls, ureter duplications, skeletal anomalies, anorectal, cardiovascular congenital disorders, anomalies of central nervous system. Genetically demonstrable disorder is relatively common: trisomy 18, Turner syndrome. Kidney fusions (usually lower pole) are radiologically detectable using US. Similarly, US can detect the disorder if the axis of the kidneys turns medially.

The isthmus is usually located in the level of 4th-5th lumbal vertebras, between the aorta and the inferior mesenteric artery. The renal pelvices turn foreward and the ureters originate from here (please see the anatomical preparation of our case!). Stone develops in horseshoe kidney and in its urine collecting system more often. Vesicoureteral reflux might be present in horseshoe kidney, hydronephrosis is the consequence of the frequent ureteropelvic stenosis. The task of the radiologist is to visualize the shape of the kidney, to assess the grade of fusion (if only one fibrous bridge or parenchymal connection exists or not) and to visualize the localisation, to assess the relation of the crossing subjects (arteries, aberrant arteries), to detect additional occurying anomalies/consequences (stone, reflux, hydronephrosis). Arteries (Doppler, duplex US) might for ex. stangulate the ureter, causing obstructions in the urine collecting system.

Both kidneys, parenchymal/fibrous bridge anterior to the aorta and both urine collecting/deflecting system can be visualized by US. If the pyelon is not dilated, it cannot be visible normally, because it does not contain urine. Only in case of urine stasis become the pyelon and the calyces visible (echolucent). Using CT (unenhanced, but it’s worth to administer contrast material), the localization of the (partially, with fibrous bridge, or with parenchyma) fusioned kidneys (the isthmus is usually located in the level of 4th and 5th lumbal vertebras), the enhancement of the cortex, medulla and the usually upfront turned pyelons is visible. In the excretory phase of contrast enhanced CT the contrast material appears in the ureters. It is worth to make coronal plane reconstructions as well, because the visualization of the locations of kidney fusion (usually in the lower pole) are well demonstrable.

I./3.3.5.: Renal malrotation

In renal malrotation it is radiologically important to visualize the location of the urine collecting system, to register how the pyelon usually turns upfront and the ureters originate anteriorly from it. Sometimes the pyelon might be placed laterally, or even – very rarely – dorsally or transversally along the anteroposterior axis.