A 36 year old Asian male complains of difficulty swallowing. Esophagoscopy reveals a polypoid mass that is subsequently biopsied. In addition to tumor cells, the esophageal biopsy show normal smooth muscle and striated muscle in the same section. Which poion of the esophagus was the source of this biopsy?

The middle third of the esophagus contains both striated and smooth muscle.The lower third of the esophagus, including the lower esophageal sphincter contain only smooth muscle.Some authors identify the cricopharyngeus muscle as an upper esophageal sphincter despite the fact that unlike a true sphincter, this muscle does not completely encircle the esophagus. The cricopharyngeus is composed exclusively of skeletal muscle, therefore, the biopsy could not have been from this area of the esophagus. Ref: Color Atlas of Cytology, Histology, and Microscopic Anatomy by Wolfgang Kuhnel