A rectangular bulge near the anal opening may be associated with anal fistula, surgical scarring, anal fissure, hemorrhoids, etc. 1. Fistula: If the patient is accompanied by obvious pressure and pain, moisture around the anus, viscous secretion, perianal itching and other symptoms, this rectangular bump may be caused by fistula. 2. Surgical scar: If the patient has undergone surgery in the anal area, plus the patient belongs to the keloid body, in the process of surgery due to leave wounds, the wound part of the tissue will gradually proliferate, the formation of purple-red bumps. 3. Anal fissure: If the patient has a bulge on both sides, and accompanied by obvious stinging sensation and bleeding in the stool and other phenomena, you need to consider that the stool is too hard caused by anal fissure. 4. hemorrhoids: there may be thrombosed external hemorrhoids, there is a bulge at the anal opening, oval or rectangular, hard to the touch, with obvious pain and itching, may also be accompanied by bleeding in the stool and other phenomena. Patients with rectangular bulge at the anal opening, in addition to the causes of the above diseases, palpation may also be the cervix in women, men may be the prostate gland; complex etiology, it is recommended to do further anoscopy and other related examinations to confirm the diagnosis, differential diagnosis, clear causes, and then carry out the appropriate treatment.