Renal dysplasia is the result of complete obstruction at either renal pelvis or proximal ureter prior to the 10 th week of gestation and inhibition of ureteral bud branching. There is no continuity between the lower urinary tract and the dysplastic nephronic elements.
Most cases are sporadic, the minority is familiar (see the text bilateral renal agenesis).
The kidney looks grossly abnormal, renculisation is absent. Numerous cysts of several centimeters in diameter are seen in the most common type (multicystic dysplasia), small kidney with only a few or no cysts at all is reffered to as an solid or aplastic dysplasia.
Ureters are filiform, atretic partially or all of its lenght.
The dysplastic kidney does not produce any urine. In bilateral dysplasia the prognosis is as bad as in bilateral renal agenesis, death occurs due to respiratory failure.
Multicystic renal dysplasia, bilateral, 20-week fetus: Multicystic renal dysplasia, Macro, autopsy (72070)
Multicystic renal dysplasia, detail: Multicystic renal dysplasia, Macro, autopsy (72069)
Multicystic renal dysplasia, 23-week fetus: Multicystic dysplasia of the kidney, Macro, autopsy (72141) Multicystic dysplasia of the kidney, Macro, autopsy (72140)
The structure is disorganized. There is considerable increase in connective tissue and multiple large cysts. Cartilage, thich nervous trunks, hematopoetic islands which are not seen in normal kidney are frequently found in dysplastic kidney. The glomeruli and proglomeruli are sparse. The histological hallmark of renal dysplasia is presence of so called primitive tubules which are lined by cubical or cylindrical epithelium and surrounded by concentric fibromuscular connective tissue. Large cysts are derived from from uteteral bud branches that failed to induce nephron formation.