Ans. a. Chronic pyelonephritis with hydronephrosis (Ref: Robbins 9/e p933-935, 8/e p943-961)In a 45-year old male with history of recurrent ureteric calculi, who presented with fever: Right-sided nephrectomy was performed. Grossly kidney shows hydronephrosis with evidence of scarring. Microscopically changes predominantly involve tubules and interstitium. Most probable diagnosis would be Chronic pyelonephritis with hydronephrosis.Chronic Pyelonephritis* Insidious in onset, may present with clinical manifestations of acute recurrent pyelonephritis with back pain, fever, frequent pyuria, and bacteriuria.* Gross examination: Irregularly scarred kidney; if bilateral, the involvement is asymmetric.* Hallmark of chronic pyelonephritis: Coarse, discrete, corticomedullary scar overlying a dilated, blunted, or deformed calyx.* Most of the scars are in the upper and lower poles, consistent with the frequency of reflux in these sites.* Microscopic changes: Predominantly involve tubules and interstitium.* Dilated tubules with flattened epithelium may be Ailed with colloid casts (thyroidization).* Glomeruli may appear normal except for periglomerular fibrosis, but a variety of glomerular changes may be present, including ischemic fibrous obliteration as well as secondary changes related to hypertension.Adult Polycystic Kidney Disease* Gross Appearance: Kidneys are usually bilaterally enlarged and may achieve enormous sizes.* The external surface appears to be composed solely of a mass of cysts, up to 3 to 4 cm in diameter, with no intervening parenchyma.* 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.Renal Cell Carcinoma* Usually presents as a yellowish, spherical mass in one pole of the kidney.* In clear cell carcinoma, the growth pattern varies from solid to trabecular (cordlike) or tubular (resembling tubules). The tumor cells have a rounded or polygonal shape and abundant clear or granular cytoplasm; the latter on special stains contains glycogen and lipids.* Papillary carcinoma is composed of cuboidal or low columnar cells arranged in papillary formations. Psammoma bodies may be present. The stroma is usually scanty but highly vascularized.* Chromophobe renal carcinoma is made up of pale eosinophilic ceils, often with a perinuclear halo, arranged in solid sheets with a concentration of the largest cells around blood vessels.* Collecting duct carcinoma is a rare variant showing irregular channels lined by highly atypical epithelium with a hobnail pattern.* Sarcomatoid changes arise infrequently in all types of renal cell carcinoma and are a decidedly ominous feature of these tumors.Cystic Dysplastic Kidney* Dysplasia can be unilateral or bilateral and is almost always cystic.* Gross appearance: Kidney is usually enlarged, extremely irregular, and multicystic.* The cysts vary in size from microscopic structures to some that are several centimeters in diameter.* The characteristic histologic feature is the presence of islands of undifferentiated mesenchyme, often with cartilage, and immature collecting ducts.