Ans. c (Cricopharynx). (Ref. Diseases of ENT by PL Dhingra, 3rd /pg. 290)# Inferior constrictor muscle has two parts:- Thyropharyngeus (oblique fibers)- Cricopharyngeus (transverse fibers)# Between these two parts exists a potential gap, known as "Killan's dehiscence" (gateway of tears).# Clinical significance:- Perforation during esophagoscopy- Pharyngeal pouchPHARYNGOESOPHAGEAL DIVERTICULUM (ZENKER DIVERTICULUM)# General Considerations- Zenker diverticulum originates from the posterior wall of the esophagus, in a triangular area of weakness limited:SS inferiorly by the cricopharyngeus muscle andSS superiorly by the inferior constrictor muscles (ie, the Killian triangle).- As the diverticulum enlarges, it tends to deviate from the midline, mostly to the left.# Pathogenesis- Zenker diverticulum results from either a lack of coordination between the pharyngeal contraction and the opening of the UES or a hypertensive UES.- Because of the increased intraluminal pressure, there is progressive herniation of mucosa and submucosa through the Killian triangle.Clinical Findings - Essentials of Diagnosis- Dysphagia, (the most common symptom)- Regurgitation of undigested food (with risk of aspiration).- Gurgling sounds in the neck.- Halitosis.# Imaging Studies- A barium swallow is the investigation of choice. It can also show a hiatal hernia.# Treatment- The standard treatment consists of excision of -the diverticulum and myotomy of the cricopharyngeus muscle, including the upper 3 cm of the posterior esophageal wall.- For small diverticula (ie, < 2 cm), myotomy alone is sufficient. As an alternative to the conventional treatment, a transoral endoscopic approach, using an endoscopic stapling instrument, can be used for diverticula between 3 cm and 6 cm in size.# Prognosis- The prognosis is excellent in about 90% of cases.