Kidney dystopia

Renal dystopia is a congenital abnormal position of the kidney (accounts for 2.8% of all renal anomalies).

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Causes renal dystopia

The causes of renal dystopia are the disruption of embryonic migration and rotation of the organ from the pelvis to the lumbar region. The process of 90% rotation begins after the kidney has risen above the aortic bifurcation, so the cessation of migration at early stages is always combined with incomplete rotation. The lower the organ is located, the more its rotation is disrupted. In this case, the renal sinus and pelvis are directed forward or laterally. The process of kidney rotation may be incomplete, even when the organ is in its place. Depending on the level at which the upward migration of the kidney has stopped, pelvic, iliac and lumbar renal dystopia are distinguished.

Thoracic renal dystopia is a special case that occurs with excessive migration of the organ into the chest cavity due to a congenital diaphragmatic hernia; it occurs on the left twice as often as on the right. Renal dystopia can be unilateral or bilateral. Renal dystopia without displacement to the opposite side is called homolateral. Much less often, during migration to the lumbar region, the kidney is displaced to the opposite side, and then crossed (heterolateral) dystopia develops.

The structure of the renal vessels in renal dystopia is atypical and has two features - multiple main arteries and their atypical origin (abdominal aorta, aortic bifurcation, common iliac and hypogastric arteries). In 1966, A. Ya. Pytel and Yu. A. Pytel proposed to consider the level of origin of the renal arteries from the aorta as an absolute anatomical sign of renal dystopia. The norm is considered to be the origin of the renal arteries at the level of the body of the first lumbar vertebra, which occurs in 87% of people. Other levels of origin of the renal arteries from the aorta are characteristic of renal dystopia. Based on this, it is necessary to distinguish the following types of renal dystopia.

• Subdiaphragmatic renal dystopia. The renal arteries originate at the level of the 12th thoracic vertebra, as a result of which the kidney is located very high and can even be located in the chest (thoracic kidney).
• Lumbar dystopia of the kidney. The renal arteries branch off from the aorta at the level from the second lumbar vertebra to the bifurcation of the aorta, as a result of which the kidney is located somewhat lower than usual.
• Iliac dystopia of the kidney. The renal arteries typically branch off from the common iliac arteries, resulting in the kidney being located in the iliac fossa.
• Pelvic dystopia of the kidney. The renal arteries originate from the internal iliac artery, as a result of which the kidney may occupy a medial position in the sacral fossa or between the rectum and the urinary bladder in men and in the Douglas pouch in women. The ureter in such a kidney is always short.

In foreign literature, these variants of dystopia are not strictly distinguished.

Crossed (heterolateral) renal dystopia is characterized by the displacement of one or both kidneys to the opposite side, so it can be unilateral or bilateral. Crossed (heterolateral) renal dystopia occurs after the kidney has shifted upward above the aortic bifurcation. With this anomaly, the kidney is an independent, anatomically and functionally fully developed organ, since each metanephros duct is embedded in its metanephrogenic blastema. Very often, crossed (heterolateral) and asymmetric dystopia (L-shaped, S-shaped) are mistakenly combined into one group.

They differ in that during the development process, with asymmetric dystopia, both metanephros ducts are introduced into one metanephrogenic blastema, often leading to a common cortical layer and fibrous capsule. Dystopia of the kidney with fused kidneys is always secondary, since during the development process these kidneys are not able to move upward.

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Symptoms renal dystopia

Symptoms of renal dystopia depend on its type. The greatest clinical significance is pelvic renal dystopia. This circumstance is caused by the pressure of the kidney on neighboring organs (iliac vessels, pelvic sympathetic plexus, rectum, bladder, uterus), and therefore clinical manifestations can occur even in the absence of a pathological process in the abnormal kidney. In addition, a dystopic kidney is often mistaken for a volumetric formation, and surgical intervention has its own characteristics and difficulties. There are known observations of pelvic dystopia of a single kidney and even tragic cases of removal of such a kidney, mistaken for a tumor.

Analyzing the place of origin of the renal artery in pelvic dystopia, in half of the observations it originates from the common iliac artery, and not from the internal iliac, as noted by A. Ya. Pytel and Yu. A. Pytel, and the reference point was to a greater extent the medial location in the sacral fossa. Most dystopic kidneys (75%) have abnormal blood supply. Symptoms of lumbar renal dystopia are not so significant. Much more significant is thoracic renal dystopia, since an abnormal kidney is often mistaken for such diseases as an abscess, tumor, encapsulated pleurisy.

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Diagnostics renal dystopia

Traditional radiological diagnostic methods (ultrasound, isotope renography, excretory and retrograde urography) allow with a high probability to suspect one or another type of renal dystopia. Traditional angiography provides information on the angioarchitectonics and, accordingly, on the variant of location.

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Treatment renal dystopia

Modern diagnostic methods (MSCT, MRI) accurately determine the type of renal dystopia, urodynamics, relationships with neighboring organs and help to choose the optimal treatment method with which renal dystopia will be cured.