Diagnostic imaging methods
To reliably confirm the absence of the organ, radionuclide imaging is used — renoscintigraphy (renogram). The study is performed using a special radiopharmaceutical — 99mTc-dimercaptosuccinic acid (99mTc-DMSA). On scan images evaluated in anterior and posterior projections, the classic picture of agenesis is characterized by a complete absence of radiopharmaceutical uptake in the region of the missing kidney.
Magnetic resonance imaging (MRI) allows for the detailed detection of associated malformations that often accompany agenesis. For example, in male patients, the absence of the right kidney may be combined with the absence of the right testicle. In such cases, MRI clearly visualizes the following abnormalities:
- An underdeveloped distal ureter representing the remnant of the ureteric bud.
- The ectopic insertion of this ureteral remnant directly into the prostatic urethra.
- The presence of only rudimentary testicular tissue in the inguinal canal.
Embryology and development of the arterial bed
During intrauterine development, the kidneys undergo a complex ascent, moving from the minor pelvis to the lumbar region. Throughout this pathway, the source of arterial blood supply changes: it is provided by aortic branches located progressively more cranially.
At the initial stage of migration, the organ is supplied by the lateral sacral artery. The final stage of establishing a permanent blood supply from the abdominal aorta is completed strictly at the level of the second lumbar vertebral body (L2). Normally, all temporary arteries that supplied the kidney at the early stages of its development and were located below the L2 level must undergo complete involution.
Vascular anomalies: arteries and veins
Any disruption in the mechanism of embryonic vessel involution leads to the formation of accessory renal arteries. This anomaly is extremely common in the human population:
- Unilateral (unilaterally) accessory arteries persist in approximately 30% of people.
- Bilateral (bilaterally) variants are less common — about 10% of cases.
The frequency of such additional vessels is significantly higher in any disruptions of normal abnormal renal ascent.
In addition to the arterial bed, anomalies can also affect venous drainage. Normally, the left renal vein passes anterior to the abdominal aorta and drains into the inferior vena cava. During the embryonic period, a circum-aortic venous ring functions around the aorta. Involution anomalies of this ring lead to the formation of atypical venous drainage:
- Retro-aortic left renal vein (retro-aortic left renal vein) — the vessel passes posterior to the aorta.
- Circum-aortic left renal vein (circum-aortic left renal vein) — the venous trunk encircles the aorta on both sides.
Briefly: answers to topical questions
What diagnostic imaging methods are used to detect renal agenesis and associated anomalies?
Ultrasound, radioisotope, and magnetic resonance imaging methods are used to detect renal agenesis and associated malformations.
- Ultrasound examination (ultrasound) — allows for antenatal diagnosis of agenesis, and color Doppler mapping confirms the absence of renal arteries.
- Renoscintigraphy (renogram) — performed with 99mTc-dimercaptosuccinic acid; scan images visualize the absence of radiopharmaceutical uptake in the projection of the kidney.
- Magnetic resonance imaging (MRI) — used to detect associated urogenital anomalies, such as ectopic insertion of the ureteral remnant or the presence of rudimentary testicular tissue.
What associated malformations of the female reproductive system occur with renal agenesis?
With renal agenesis in females, associated Müllerian duct anomalies occur in 70% of cases.
- Vaginal and uterine agenesis (Mayer–Rokitansky–Küster–Hauser syndrome) — absence of the uterus and upper vagina with intact ovaries and fallopian tubes.
- Unicornuate uterus (Unicornuate Uterus) — also refers to Müllerian duct anomalies associated with renal pathology.
Which sonographic signs indicate bilateral renal agenesis in a fetus on ultrasound?
During fetal ultrasound, bilateral renal agenesis is characterized by a set of specific sonographic signs.
- Absence of kidneys — fetal kidneys are not visualized.
- Absence of the urinary bladder — the urinary bladder is not detected during scanning.
- Severe oligohydramnios — a significant decrease in the amniotic fluid volume.
- Fetal growth restriction (FGR) — a symmetric form of growth restriction is frequently observed.
- Absence of renal arteries — detected using color Doppler mapping.
The L2 level is the final stop of the kidney during migration. Accessory arteries are the "forgotten tracks" along its path of ascent from the minor pelvis.
Class and exam questions
How often does congenital absence of the kidney occur?
Congenital renal agenesis is detected at a frequency of 1 case per 500–1000 live births.
Which agent is used for scintigraphic diagnostics?
99mTc-dimercaptosuccinic acid (99mTc-DMSA) is used. In agenesis, the agent does not accumulate in the projection of the missing kidney.
Where does the blood supply to the kidney originate at the earliest stage of embryogenesis?
At the initial stage of ascent from the pelvis, the organ is supplied by branches of the lateral sacral artery.
What causes the formation of a retro-aortic left renal vein?
The pathology arises due to impaired involution of the embryonic circum-aortic venous ring.
What else to study on this topic
- Mechanisms of normal renal ascent in embryogenesis
- The role of the ureteric bud in the formation of the urogenital system
- Variants of ureteral ectopia and their clinical significance
- Differential diagnostic imaging of accessory renal arteries
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