A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 62-year-old woman with type 2 diabetes mellitus is brought to the emergency room because of a 3-day history of fever and shaking chills. Her temperature is 39.4°C (103°F). Examination of the back shows right costovertebral angle tenderness. Analysis of the urine shows WBCs, WBC casts, and gram-negative rods. Ultrasound examination of the kidneys shows no signs of obstruction. Biopsy of the patient's kidney is most likely to show which of the following?
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A
Polygonal clear cells filled with lipids and carbohydratesIncorrect. Polygonal clear cells filled with lipids and glycogen describe renal cell carcinoma (clear-cell type), which presents as a mass with hematuria, not an acute febrile pyuria.
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B
Polymorphonuclear leukocytes in tubulesCorrect. Acute pyelonephritis is characterized histologically by polymorphonuclear leukocyte infiltration of the tubules and interstitium with neutrophil casts.
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C
Cystic dilation of the renal medullaIncorrect. Cystic dilation of the renal medulla describes medullary sponge kidney, an asymptomatic congenital finding that may predispose to stones — not consistent with acute febrile illness.
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D
Tubular eosinophilic castsIncorrect. Tubular eosinophilic casts ("thyroidization" with hyaline/colloid casts) is a feature of chronic pyelonephritis with scarring, not the acute neutrophilic process described here.
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E
Crescent formation in Bowman spaceIncorrect. Crescent formation in Bowman space is the histologic hallmark of rapidly progressive glomerulonephritis, which presents with hematuria, RBC casts, and rapidly rising creatinine — not the acute febrile pyelonephritis described here.
↑ Tap an answer to reveal the reasoning
Answer: B. Fever, flank pain (costovertebral angle tenderness), pyuria with WBC casts, and gram-negative rods on urinalysis define acute pyelonephritis. In a diabetic with ascending E. coli infection, the renal histopathology classically shows polymorphonuclear (neutrophil) infiltration of the renal tubules and interstitium, often with neutrophil casts within tubular lumens. Macroscopically the kidney shows wedge-shaped suppurative areas with sparing of the glomeruli early in disease.
WBC casts are pathognomonic for tubulointerstitial inflammation — almost always pyelonephritis (when bacteria are present) or acute interstitial nephritis (when eosinophils predominate). The absence of obstruction on ultrasound is reassuring; obstruction would have required emergent decompression.
Management is empiric IV antibiotics (e.g., ceftriaxone or fluoroquinolone) tailored to culture results. Diabetics are at higher risk for complications including emphysematous pyelonephritis and renal abscess.
**Why each option:**
**A.** Polygonal clear cells filled with lipids and glycogen describe renal cell carcinoma (clear-cell type), which presents as a mass with hematuria, not an acute febrile pyuria.
**B.** Correct. Acute pyelonephritis is characterized histologically by polymorphonuclear leukocyte infiltration of the tubules and interstitium with neutrophil casts.
**C.** Cystic dilation of the renal medulla describes medullary sponge kidney, an asymptomatic congenital finding that may predispose to stones — not consistent with acute febrile illness.
**D.** Tubular eosinophilic casts ("thyroidization" with hyaline/colloid casts) is a feature of chronic pyelonephritis with scarring, not the acute neutrophilic process described here.