IUHS Student-2-Student USMLE Step 1 Recall
Kidney
Congenital Anomalies/Cystic Disease
Agenesis of the Kidney
total bilateral agenesis, which is incompatible with life, is usually encountered in stillborn infants...this is called Potter Syndrome...
Potter Facies: flattened nose, low-set ears, and recessed chin...with no amniotic fluid baby is crushed...Club Foot...
bilateral renal agenesis -> oligohydramnios -> limb deformities, facial deformities, pulmonary hypoplasia...
Babies with Potter's can't "Pee" in utero..
it is often associated with many other congenital disorders (limb defects, hypoplastic lungs) and leads to early death...
unilateral agenesis is an uncommon anomaly that is compatible with normal life, if no other abnormalities exist...
the opposite kidney is usually enlarged as a result of compensatory hypertrophy...
some patients eventually develop progressive glomerular sclerosis in the remaining kidney as a result of the adaptive changes in hypertrophied nephrons and in time chronic renal failure...
Hypoplasia of the Kidney
renal
hypoplasia refers to failure of the kidneys to develop to a normal size...
this anomaly may occur bilaterally, resulting in renal falure in early childhood, but it is more commonly encountered as a unilateral defect...
true renal hypoplasia is extremely rare, most cases reported probably represent acquired scarring due to vascular, infectious, or other parenchymal diseases rather than an underlying developmental failure...
differentiation between congenital and acquired atrophic kidneys may be impossible, but a truly hypoplastic kidney should show no scars and should posses a reduced number or renal lobes and pyramids, six or fewer...
in one form of hypoplastic kidney, oligomeganephronia, the kidney is small but the nephrons are markedly hypertrophied...
there are decreased numbers of calyces and lobes...
Ectopic Kidneys
the development of the definitve metanephros may occur in ectopic foci, usually at abnormally low levels...
these kidneys lie either just above the pelvic brim or sometimes within the pelvis...
they are usually normal or slightly smaller in size but otherwise are not remarkable...
b/c of their abnormal position, kinking or tortuosity of the ureters may cause some obstruction to urinary flow, which predisposes to bacterial infections...pyelonephritis...
Hosrseshoe Kidney
horsehshoe kidneys get trapped under inferior mesenteric artery and remain low in the abdomen...
fusion of the upper or lower poles of the kidneys produces a horseshoe -shaped structure continuous across the midline anterior to the great vessels...
this anomaly is common and is found in about 1 in 500 to 1000 autopsies...
ninety per cent of such kidneys are fused at the lower lobe, and 10% are fused at the upper pole...
often associated with Trisomy 18...
patients have normal renal function but may be predisposed to renal calculi...
inferior mesenteric artery restricts movement of horseshoe kidney...
Autosomal Dominant (Adult) Polycystic Kidney Disease
affects
1 of every 400 to 1000 live births and accounting for about 10% of cases of
chronic renal failure requiring transplantation or dialysis...
incomplete penetrant...also, locus heterogeneity is in affect between chromosome 16 and 4...
autosomal dominant...mutation of PKD1 gene on chromosome 16...the PKD1 gene produces a transmembrane protein called polycystin 1...
in gross apearance, the kidneys are usually bilaterally enlarged and may achieve enormous sizes...
can secrete renin...
the external surface of the kidney appears to be composed solely of a mass of cysts, up to 3 to 4 cm in diameter, with no intervening parenchyma...
associated with berry aneurysms and subsequent subarachnoid hemorrhage (worst headache of your life)...liver cysts,
mitral valve prolapse, and colonic diverticula...
microscopic examination reveals functioning nephrons dispersed between the cysts...the cysts may be filled with a clear serous fluid or, more usually, with turbid, red to brown, sometimes hemorrhagic fluid...
as these cysts enlarge, they may encroach on the calyces and pelvis to produce pressure defects...
the cysts arise from the tubules throughout the nephron and therefore have variable lining epithelia...
on occasion, papillary epithelial formations and polyps project into the lumen...
bowman capsules are occasionally involved in cyst formation, and glomerular tufts may be seen within the cystic space...
there is flank and back pain and hematuria...
Autosomal Recessive (Childhood) Polycystic Kidney Disease
kidneys are enlarged and have a smooth external appearance...on cut section, numerous small cysts in the cortex and medulla give the kidney a spongelike appearance...
dilated elongated channels are present at right angles to the cortical surface, completely replacing the medulla and cortex...
on microscopic examination, there is saccular or, more commonly, cylindrical dialtion of all collecting tubules...
the cysts have a uniform lining of cuboidal cells, reflecting their origin from the collecting tubules...
the disease is invariably bilateral...in almost all cases, there are multiple epithelium-lined cysts in the liver as well as proliferation of portal bile ducts...
the cysts are oriented in a radial fashion with their long axis at right angles to the capsule...may also have multiple hepatic cysts and congenital hepatic fibrosis....
oligohydramnios is present b/c of lack of renal function...