**Question:** Investigation of choice for Zenker's diverticulum is –

A. Barium swallow
B. Endoscopy
C. CT scan
D. X-ray chest

**Core Concept:**
Zenker's diverticulum is a bulging sac-like structure in the hypopharynx, typically found in the posterior pharyngeal wall. It is commonly associated with bulbar paresis and is often diagnosed using appropriate imaging techniques to visualize the anomaly and its relationship with surrounding structures.

**Why the Correct Answer is Right:**
The correct answer is A, Barium swallow. A barium swallow is a radiographic examination that involves consuming a contrast medium (barium) and taking X-rays to visualize the oesophagus and its abnormalities, including Zenker's diverticulum. This method is suitable for assessing the oesophageal motility, detecting obstruction or stricture, and assessing the relationship between the diverticulum and surrounding structures.

**Why Each Wrong Option is Incorrect:**
Option B, endoscopy, is a diagnostic procedure that involves inserting an endoscope into the gastrointestinal tract to visually examine the mucosa and underlying structures. While endoscopy can diagnose oesophageal pathologies, it is not the most accurate method for assessing the relationship between the diverticulum and surrounding structures or evaluating oesophageal motility.

Option C, CT scan, is a cross-sectional imaging technique that uses X-rays to create detailed images of internal structures. A CT scan can provide information about the diverticulum size, location, and relation to surrounding structures. However, it lacks the ability to assess oesophageal motility or identify the presence of strictures or obstructions.

Option D, X-ray chest, is a radiographic examination typically performed to evaluate the lungs and mediastinum. It is not a suitable method for investigating Zenker's diverticulum, as it only provides limited information about the oesophagus and its surrounding structures.

**Correct Answer Explanation:**
The correct answer (Barium swallow) is chosen due to its ability to accurately visualize the oesophagus and its relationship to surrounding structures, as well as assessing oesophageal motility. It is essential in diagnosing Zenker's diverticulum and determining its impact on the patient's overall health status.