Flask-like ulcers extending to submucosa are characteristic of

E histolytica invades the intestinal epithelium and form discrete ulcers with a pinhead-sized center and raised edges, from which mucus, necrotic cells, and amebae pass. The trophozoites multiply and accumulate above the muscularis mucosae, often spreading laterally. A rapid lateral spread of the multiplying amebae follows, undermining the mucosa and producing the characteristic "flask-shaped" ulcer of primary amebiasis: a small point of entry, leading a narrow neck through the mucosa into an expanded necrotic area in the submucosa.Bacterial invasion usually does not occur at this time, the cellular reaction is limited, and damage is by lytic necrosis.Ref: Jawetz; 27th edition; Page no: 711