**Question:** Investigation of choice in acute cholecystitis

**Core Concept:** Acute cholecystitis is an inflammation of the gallbladder, typically caused by gallstones or bacterial infections. Effective diagnosis relies on identifying the cause, severity, and complications of the disease.

**Why the Correct Answer is Right:**

**Correct Answer: D.** Abdominal ultrasound (US) is the preferred investigation for acute cholecystitis due to the following reasons:

1. **High Sensitivity:** Ultrasound has a high sensitivity (85-90%) in detecting gallstones, which are the primary cause of acute cholecystitis. It can visualize gallstones, gallbladder wall thickening, and fluid collections around the gallbladder.
2. **Non-invasive:** Ultrasound is a non-invasive, radiation-free, and widely available procedure, making it a safe and convenient choice for diagnosis.
3. **Accuracy:** Ultrasound can differentiate between acute and chronic cholecystitis, assess the severity and complications of the disease, such as pericholecystic fluid, gallbladder wall edema, and gallbladder wall thickening.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Computed Tomography [CT] scan):** While CT is sensitive in identifying complications, it is less sensitive in detecting gallstones and has higher radiation exposure, making ultrasound the preferred choice.
B. **Option B (Liver function tests):** Liver function tests assess liver function and are not specifically tailored to diagnose acute cholecystitis.
C. **Option C (Blood tests):** Blood tests assess general wellbeing and do not directly diagnose acute cholecystitis.

**Why the Correct Answer is Right:**

Acute cholecystitis is often triggered by gallstones or bacterial infections. Identifying the cause and assessing the severity of the condition is crucial for appropriate management. Ultrasound is highly sensitive in detecting the primary causes (gallstones) and assessing complications. CT is sensitive in detecting complications but lacks sensitivity in detecting gallstones. Liver function tests and blood tests primarily evaluate general health and are not specific to diagnose acute cholecystitis.

**Why Each Wrong Option is Incorrect:**

A. CT scan: Although CT is sensitive in detecting complications, it is less sensitive in detecting gallstones and exposes patients to ionizing radiation, making ultrasound the preferable choice.
B. Liver function tests: Liver function tests evaluate liver function and are not specifically designed to diagnose acute cholecystitis.
C. Blood tests: Blood tests assess general health status and are not specifically designed for diagnosing acute cholecystitis.