This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Which of the following is not seen on ultrasound in acute pyelonephritis? 
Select and explain. 
A. Grossly enlarged kidney, B. Focal area of hypoechogenecity, C. Perinephric collection (pus in the perinephric space), D. Increased vascularity
D: Increased vascularity
Answer: D: Increased vascularity 
Explanation: Ans. d. Increased vascularity In acute pyelonephritis, Color and power Doppler evaluation typically shows decreased perfusion in the affected parenchyma, which has been attributed to aeriolar vasoconstriction and interstitial edema in response to bacterial infection. Features of Pyelonephritis on Ultrasound Paiculate matter in the collecting system Gas bubbles (emphysematous pyelonephritis) Abnormal echogenicity of the renal parenchyma FocaUsegmental hypoechoic regions Diffuse or focal enlargement of the kidney, sometimes with a mass-like lesion Color and power Doppler evaluation typically shows decreased perfusion in the affected parenchyma, which has been attributed to aeriolar vasoconstriction and interstitial edema in response to bacterial infection.