**Core Concept**
Achalasia cardia is a primary esophageal motility disorder characterized by the failure of the lower esophageal sphincter (LES) to relax, leading to difficulty in swallowing and regurgitation of food. This condition is often associated with a dilated esophagus.

**Why the Correct Answer is Right**
The radiologic feature suggestive of achalasia cardia is the "bird's beak" appearance on a barium swallow study. This occurs due to the failure of the LES to relax, causing a tapered narrowing of the distal esophagus. The esophagus above the LES becomes dilated, giving it a characteristic "bird's beak" shape.

**Why Each Wrong Option is Incorrect**
**Option A:** A sigmoid esophagus is more commonly associated with diffuse esophageal spasm, not achalasia.
**Option B:** An esophageal stricture would present as a focal narrowing of the esophagus, not a diffuse tapering as seen in achalasia.
**Option C:** A hiatal hernia may cause gastroesophageal reflux disease (GERD) symptoms, but it does not cause the characteristic "bird's beak" appearance of achalasia.

**Clinical Pearl / High-Yield Fact**
Achalasia cardia is often associated with other conditions such as esophageal webs, eosinophilic esophagitis, and Barrett's esophagus. A high index of suspicion is necessary for early diagnosis and treatment.

**Correct Answer:** C.