What classic deformity is associated with achalasia on barium swallow?

The classic deformity associated with achalasia observed on a barium swallow study is referred to as the "bird's beak" appearance. This term describes the characteristic narrowing of the distal esophagus at the level of the lower esophageal sphincter, which becomes unable to relax properly due to the loss of peristalsis and increased muscle tone in achalasia. As a result, when barium is swallowed, it can fill the esophagus normally up to the point where the sphincter fails to open, leading to a tapered, pointed appearance reminiscent of a bird's beak.

In achalasia, this sign is critical as it helps differentiate the condition from other esophageal disorders and assists in the diagnosis. The narrowing at the lower esophagus causes a functional obstruction, leading to symptoms such as dysphagia and regurgitation, which patients often present with. Recognizing this classic radiologic finding is essential for medical practitioners when evaluating esophageal conditions.