**Question:** Chain of lakes appearance is seen in-

A. Acute pancreatitis
B. Acute appendicitis
C. Acute cholecystitis
D. Acute pyelonephritis

**Core Concept:**
Chain of Lakes appearance refers to the characteristic ultrasound appearance of acute pyelonephritis (AP), which is a severe acute inflammation of the renal parenchyma. The term "Chain of Lakes" describes the sonographic appearance of multiple, small, hypoechoic (low echoic) regions in the renal cortex and medulla, resembling a chain of lakes. These regions are separated by thin hyperechoic (high echoic) zones representing the renal collecting system.

**Why the Correct Answer is Right:**
The correct answer, D, refers to Acute Pyelonephritis (AP), a condition characterized by severe inflammation of the renal parenchyma caused by bacterial infection, usually ascending from the urinary tract. The ultrasound appearance of AP demonstrates the Chain of Lakes appearance, as mentioned above.

**Why Each Wrong Option is Incorrect:**
A: Acute pancreatitis (AP) exhibits a different ultrasound appearance, characterized by hypoechoic (low echoic) pancreatic necrosis and fluid collections.
B: Acute appendicitis (AA) typically presents with hypoechoic (low echoic) appendiceal wall thickening and fluid collection, not the Chain of Lakes appearance.
C: Acute cholecystitis (AC) shows gallbladder wall thickening and pericholecystic fluid, not the Chain of Lakes appearance.

**Clinical Pearl:**
The ultrasound appearance of Chain of Lakes represents a valuable clinical clue pointing towards a renal infection, allowing for a prompt diagnosis and initiation of appropriate antibiotic therapy. Infection in the kidney can lead to acute renal parenchyma inflammation, resulting in the described ultrasound pattern. A high index of suspicion, along with clinical correlation and appropriate imaging modalities, is essential for accurate diagnosis of AP, AA, AC, or other potential differential diagnoses.