May Be Caused by

 Common

Abscess

Adenocarcinoma

Anal carcinoma

Cloacogenic carcinoma

Crohn disease

Endometriosis

Hirschsprung disease

Imperforate anus

Invasion from adjacent neoplasm

Polyp

Prolapse

Radiation proctitis

Rectal trauma

Scirrhous carcinoma

Ulcerative colitis

Villous adenoma

 Uncommon

Actinomycosis

Amebiasis

Amyloidosis

Angioma

Bacillary dysentery

Carcinoid

Chagas disease

Colitis cystica profunda

Diverticulitis

Gastrointestinal stromal tumor

Hemangioma

Hemorrhoids

Herpes

Ischemic colitis

Lipoma

Lymphogranuloma venereum

Opportunistic infection

Pelvic lipomatosis

Pneumatosis cystoides intestinalis

Proctitis

Retroperitoneal fibrosis

Schistosomiasis

Solitary rectal ulcer syndrome

Trichuriasis

Tuberculosis

Varices