EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
96. Malformations of The Urinary System
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- Introduction: many anomalies rise as a result of disturbances of renal development. Abnormalities of the kidneys and ureters are seen in 3-4% of the population. Morphologically, anomalies involving the excretory part, the collecting part, or both, can be distinguished. Modifications of shape, position, and blood supply are also seen
- HYPOPLASIA: underdevelopment of tissue or an organ usually caused by a decrease in cell numbers or atrophy due to a destruction of some elements
- APLASIA: defective development or congenital absence of the organ
- AGENESIS: unilateral absence of a kidney is relatively common; bilateral agenesis is rare and incompatible with postnatal life
- The result of failure of the ureteric bud to develop, failure of the bud to grow into the metanephric mass of mesoderm and induce nephron formation, or failure of the mesonephric ducts to descend to the area of the ureteric bud
- In the female, the m?llerian ducts are also affected and may result in an absence of the uterus and part of the vagina
- HORSESHOE KIDNEY: seen in 1/600 births; U-shaped kidney that lies at the level of the lower lumbar vertebrae. Its ascent is prevented by the inferior mesenteric artery
- During migration from the sacral region, the 2 metanephric blastemas can come in contact with each other, most often at the lower poles and fuse on the median line, forming the classic form of the horseshoe kidney
- The ureters, which pass in front of the zone of kidney fusion, are usually normal
- Often no symptoms exist, but it may be associated with abnormalities of the renal pelvis and kidney and favor obstruction and infection
- POLYCYSTIC KIDNEYS: common, death occurs at or shortly after birth if bilateral, with severe renal insufficiency
- This form of kidney is caused by defective junction between the metanephric origin of the kidney and the derivatives of the ureteric bu As a result of the absence of a connection between the collecting and excretory parts of the tubules, urine cannot be evacuated, pressure increases in the glomerulotubular system, and distention develops. Cystic degeneration follows, and the kidney rapidly loses its ability to function
- Other causes may be cysts from remnants of the first rudimentary nephrons, which normally degenerate, or abnormal development of the collecting tubules
- RENAL DUPLICATIONS are rather frequent, but may remain completely latent without any effect on urinary function. Different types, as a result of precocious division of the ureteric bud into 2 branches, result in the formation of
- Complete double ureters (unilateral or bilateral)
- Partial double ureters
- Double kidney: where the division also involves the metanephric blastema
- SUPERNUMERARY KIDNEYS: rare; the result of complete division of the ureteric bud; often seen with a bifid ureter or separate ureters
- When 1 of the 2 ureters remains very short and the second kidney remains low, we refer to the abnormally placed kidney as supernumerary rather than a double kidney
- ECTOPIC URETERAL ORIFICES: the ureter opens anywhere, except into the trigone of the urinary bladder, and the complaint is usually incontinence
- In the male, it usually opens into the prostatic urethra, prostatic utricle, or seminal gland
- In the female, it usually opens into the urethra, the vagina, or vestibule
- Caused by ureteric bud developing more cranially than usual from the mesonephric duct
