## **Core Concept**
Zenker's diverticulum is a type of esophageal diverticulum that occurs in the upper posterior part of the esophagus, specifically in the cricopharyngeal area. It is a condition characterized by the herniation of the mucosa through a weakness in the muscular wall of the esophagus. Complications arise mainly due to the accumulation of food in the diverticulum.

## **Why the Correct Answer is Right**
The commonest complication of Zenker's diverticulum is **aspiration pneumonia**. This occurs because food can accumulate in the diverticulum and then be aspirated into the lungs, leading to pneumonia. The anatomical location of Zenker's diverticulum, just above the cricopharyngeus muscle, predisposes to this complication due to the proximity to the airway entrance.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While dysphagia is a symptom of Zenker's diverticulum due to the mechanical obstruction caused by the diverticulum itself, it is not considered a complication but rather a presenting symptom.
- **Option B:** Esophageal stricture could be a complication of various esophageal conditions, including severe inflammation or scarring, but it is not the most common complication of Zenker's diverticulum.
- **Option C:** (No option provided, assuming a mistake) Typically, other complications might include diverticulitis, but aspiration pneumonia remains the most critical and common complication.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with Zenker's diverticulum are at high risk of aspiration pneumonia, which can be life-threatening. Therefore, early diagnosis and treatment, such as diverticulectomy or myotomy of the cricopharyngeus muscle, are crucial to prevent this complication.

## **Correct Answer:** D. Aspiration pneumonia.