Kidney fusion

Fusion of the kidneys is an anomaly with the fusion of two opposite kidneys into one organ. It occurs in 3.5% of cases of kidney malformations.

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Causes renal fusions

The cause of fusion is the fusion of two metanephrogenic blastemas at the earliest stage of embryonic development - before the migration of the kidneys from the caudal parts of the embryo. As a result, the processes of migration of the renal structures to the lumbar region of its rotation are disrupted. Therefore, fused kidneys are always dystopic. Ingrowth of the metanephros ducts occurs without anomalies, therefore the histological structure of the kidneys is not disrupted, and the ureters always flow into the bladder in a typical place. The vast majority of patients with renal fusion (88.6%) have abnormal blood circulation.

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Symptoms renal fusions

Fusion of the kidneys can be unilateral (I-shaped kidney) and bilateral (horseshoe-shaped, gallet-shaped or lump-shaped, L-shaped kidney). S-shaped kidney also refers to unilateral fusion of the kidneys.

Bilateral fusion of the kidneys can be symmetrical (each kidney is located homolaterally) or asymmetrical (one kidney is located heterolaterally).

In symmetrical fusion, the kidneys can be connected by their lower poles, rarely by their upper poles, forming a so-called horseshoe-shaped kidney, or by their entire surface, creating a galette-shaped or lump-shaped kidney.

Horseshoe kidney is the most common anomaly of the form (0.25% of the population). Among all defects, it is quite common - 2.8%. Fusion of the lower segments is usually noted, and in 1.5-3.8% - the upper ones. Horseshoe kidney in 70% of cases has an abnormal blood supply (according to our data - 84.62%). The structure of the renal calyces is unusual: the upper group is more developed, the lower one is underdeveloped.

Diseases in the horseshoe kidney occur much more often than in the normal one - from 75 to 80% of observations. According to A.V. Ayvazyan and A.M. Voyno-Yasenetsky. pathological process in the horseshoe kidney is detected in 68.6% of observations, and the most common are hydronephrosis - 41.7%, urolithiasis - 23.6%. pyelonephritis - 19.4%, hypertension - 15.2%. In case of hydronephrosis, plastic surgery is combined with isthmus resection. When kidney stones are detected, all modern treatment methods are used, including DLT and KLT. as well as open surgeries. However, the share of the latter in the structure of surgical treatment decreases from year to year due to the advent of minimally invasive techniques. Treatment of pyelonephritis is aimed at restoring urodynamics and prescribing pathogenetic treatment.

An extremely rare anomaly, not described in the classification of N.A. Lopatkin and A.V. Lyulko, is the so-called disc-shaped kidney, in which fusion occurs not only by all poles, but also by the medial lateral surfaces.

A gallet-shaped or lump-shaped kidney has a common cortex and a fibrous capsule. This extremely rare developmental defect is diagnosed with a frequency of one case per 26,000 autopsies. In this case, the organ is usually located in the small pelvis homolaterally or heterolaterally. The renal pelvis is always located anteriorly. In clinical practice, a lump-shaped kidney can be mistaken for a tumor of the retroperitoneal space and removed.

Asymmetric fusion is characterized by the location of one of the kidneys heterolaterally. This occurs for two reasons: fusion of metanephrogenic blastemas with displacement of one of them to the opposite side or ingrowth of metanephros ducts into one metanephrogenic blastema and reduction of the homolateral blastema.

An L-shaped kidney occurs when the lower pole of one kidney and the upper pole of the other kidney fuse, and when one of them is transversely positioned. An S-shaped kidney is formed when the lower pole of one kidney fuses with the upper pole of the other kidney and when they are vertically positioned. In an S-shaped kidney, the calyxes of one half of the kidney are directed laterally, and the calyxes of the other are directed medially. If embryonic rotation is complete and the calyxes of both kidneys are directed in the same direction, then such a kidney is called I-shaped. Thus, I-shaped and S-shaped kidneys can be classified as unilateral fusions.

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Diagnostics renal fusions

Diagnosis of shape anomalies is not difficult. Already at the ultrasound stage it is possible to obtain information about the type of this or that kidney fusion, as well as about pathological processes in it.

The advantages of MRI and MSCT over angiography include less invasiveness of the study, as well as obtaining more complete information about the state of the renal parenchyma, urinary tract and relationships with adjacent organs.

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