This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal Radiology, Subject name: Radiology
[{'content': '"Bird beak" appearance on barium swallow study is seen in: \nSelect and explain. \nA. Achalasia cardia, B. Carcinoma esophagus, C. Hiatus hernia, D. Diffuse esophageal spasm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Barium study feature of few esophageal diseases Diffuse esophageal spasm: "Yo-Yo" motion of barium "Corkscrew" appearance (scalloped configuration of barium column) "Rosary-bead/Shish kebab" configuration (compamentalization of barium column) Feline esophagus: Gastroesophageal reflux disease Double-barrel esophagus: Mallory-Weiss tear Intramural abscess Intraluminal diveiculum Achalasia cardia: "Bird beak" deformity Absence of primary peristalsis below level of cricopharyngeus Candidal esophagitis: Cobble stone mucosa Cytomegalovirus esophagitis: Giant ovoid flat ulcers (vasculitis of submucosal vessels) Herpes esophagitis: Discrete superficial punctate/linear serpentine/stellate/diamond shaped ulcers Hiatus hernia: Epiphrenic bulge > 4 longitudinal coarse thick gastric folds above gastroesophageal junction or in the suprahiatal pouch Distance between B ring and hiatal margin > 2 cm Scleroderma: Esophageal shoening Sliding hiatus hernia Carcinoma oesophagus: Rat-tail esophagus Shouldering sign', 'role': 'assistant'}]