Rectovestibular fistula is the most common defect of the rectum and anal canal in females.

Imperforate anus has an estimated incidence of 1 in 5000 births. It affects boys and girls with similar frequency. However, imperforate anus will present as the low version 90% of the time in females and 50% of the time in males.

Imperforate anus is an occasional complication of sacrococcygeal teratoma.

Anorectal anomalies are medical problems affecting the structure of the anus and rectum. A person with an anorectal problem would have some sort of deformative feature of the anus or rectum, collectively known as an anorectal malformation.

Examples of anorectal anomalies include:

- Anal stenosis

- Imperforate anus

- Proctitis

- Anal bleeding

- Anal fistula

- Anal cancer

- Anal itching

- Hemorrhoid (piles)

With a high lesion, many children have problems controlling bowel function and most also become constipated. With a low lesion, children generally have good bowel control, but they may still become constipated.

For children who have a poor outcome for continence and constipation from the initial surgery, further surgery to better establish the angle between the anus and the rectum may improve continence and, for those with a large rectum, surgery to remove that dilated segment may significantly improve the bowel control for the patient. An antegrade enema mechanism can be established by joining the appendix to the skin (Malone stoma); however, establishing more normal anatomy is the priority.

A rectovestibular fistula, also referred to simply as a vestibular fistula, is an anorectal congenital disorder where an abnormal connection (fistula) exists between the rectum and the vulval vestibule of the female genitalia.

If the fistula occurs within the hymen, it is known as a rectovaginal fistula, a much rarer condition.

The prognostic outcomes for this type of cloaca are good for bowel control and urinary function. The surgical repair for this type of cloaca can usually be done by performing posterior sagittal approach without opening of the abdomen. A common channel longer than 3 cm in length usually has poor sphincter muscles and a poor sacrum, suggesting a prognostic outcome for bowel control and urinary function to be less likely. Common channels longer than 3 cm are generally considered more complex and more technically challenging in surgical repair.

Cloacas appear in a wide spectrum of variation in females born with the malformation. The single orifice, called a common channel, may occur varying in length from 1 to 10 cm. The length of the common channel can be used to judge prognostic outcomes and technical challenges during surgical repair. A common channel less than 3 cm in length usually has good sphincter muscles and a well-developed sacrum.

Anal stricture or anal stenosis is a narrowing of the anal canal. It can be caused by a number of surgical procedures including: hemorrhoid removal and following anorectal wart treatment.

The most common cause of non-duodenal intestinal atresia is a vascular accident in utero that leads to decreased intestinal perfusion and ischemia of the respective segment of bowel. This leads to narrowing, or in the most severe cases, complete obliteration of the intestinal lumen.

In the case that the superior mesenteric artery, or another major intestinal artery, is occluded, large segments of bowel can be entirely underdeveloped. Classically, the affected area of bowel assumes a spiral configuration and is described to have an "apple peel" like appearance; this is accompanied by lack of a dorsal mesentery.

Ileal atresia can also result as a complication of meconium ileus.

Fetal and neonatal intestinal atresia are treated using laparotomy after birth. If the area affected is small, the surgeon may be able to remove the damaged portion and join the intestine back together. In instances where the narrowing is longer, or the area is damaged and cannot be used for period of time, a temporary stoma may be placed.

Atresia is a condition in which an orifice or passage in the body is (usually abnormally) closed or absent.

Examples of atresia include:

- Biliary atresia, a condition in newborns in which the common bile duct between the liver and the small intestine is blocked or absent.

- Choanal atresia, blockage of the back of the nasal passage, usually by abnormal bony or soft tissue.

- Esophageal atresia, which affects the alimentary tract and causes the esophagus to end before connecting normally to the stomach.

- Imperforate anus, malformation of the opening between the rectum and anus.

- Intestinal atresia, malformation of the intestine, usually resulting from a vascular accident in utero.

- Microtia, absence of the ear canal or failure of the canal to be tubular or fully formed (can be related to Microtia, a congenital deformity of the pinna, or outer ear).

- Ovarian follicle atresia, the degeneration and subsequent resorption of one or more immature ovarian follicles.

- Potter sequence, congenital decreased size of the kidney leading to absolutely no functionality of the kidney, usually related to a single kidney.

- Pulmonary atresia, malformation of the pulmonary valve in which the valve orifice fails to develop.

- Renal agenesis, only having one kidney.

- Tricuspid atresia, a form of congenital heart disease whereby there is a complete absence of the tricuspid valve, and consequently an absence of the right atrioventricular connection.

- Vaginal atresia, a congenital occlusion of the vagina or subsequent adhesion of the walls of the vagina, resulting in its occlusion.

This may occur when there is a large mass of feces in the rectum (fecal loading), which may become hardened (fecal impaction). Liquid stool elements are able to pass around the obstruction, leading to incontinence. Megarectum (enlarged rectal volume) and rectal hyposensitivity are associated with overflow incontinence. Hospitalized patients and care home residents may develop FI via this mechanism, possibly a result of lack of mobility, reduced alertness, constipating effect of medication and/or dehydration.

Liquid stool is more difficult to control than formed, solid stool. Hence, FI can be exacerbated by diarrhea. Some consider diarrhea to be the most common aggravating factor. Orlistat is an anti-obesity (weight loss) drug that blocks the absorption of fats. This may give side effects of FI, diarrhea and steatorrhea.

Anal warts are irregular, verrucous lesions caused by human papilloma virus. Anal warts are usually transmitted by unprotected, anoreceptive intercourse. Anal warts may be asymptomatic, or may cause rectal discharge, anal wetness, rectal bleeding, and pruritus ani. Lesions can also occur within the anal canal, where they are more likely to create symptoms.

Several definitions have been offered:

- "Absence of normal relaxation of pelvic floor muscles during defecation, resulting in rectal outlet obstruction".

- "Malfunction (a focal dystonia) of the external anal sphincter and puborectalis muscle during defecation".

- "[...] failure of [the external anal sphincter and puborectalis] muscle[s] to relax, resulting in maintenance of the anorectal angle and the difficulty with initiating and completing bowel movements".

- "[...] failure of relaxation (or paradoxic contraction) of the puborectalis muscle sling during defaecation, attempted defaecation or straining."

Proctitis is inflammation of the anal canal and the distal of the rectum.

Proctitis has many causes, such as infections or intercourse.

Tuberculosis proctitis can create a mucous discharge.

Anismus is classified as a functional defecation disorder. It is also a type of rectal outlet obstruction (a functional outlet obstruction). Where anismus causes constipation, it is an example of functional constipation. Some authors describe an "obstructed defecation syndrome", of which anismus is a cause.

The Rome classification subdivides functional defecation disorders into 3 types, however the symptoms the patient experiences are identical.

- Type I: paradoxical contraction of the pelvic floor muscles during attempted defecation

- Type II: inadequate propulsive forces during attempted defecation (inadequate defecatory propulsion)

- Type III: impaired relaxation with adequate propulsion

It can be seen from the above classification that many of the terms that have been used interchangeably with anismus are inappropriately specific and neglect the concept of impaired propulsion. Similarly, some of the definitions that have been offered are also too restrictive.

Toxic megacolon is mainly seen in ulcerative colitis and pseudomembranous colitis, two chronic inflammations of the colon (and occasionally, in the other type of inflammatory bowel disease, Crohn's disease). Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide, at least in ulcerative colitis. The prevalence is about the same for both sexes.

In patients with HIV/AIDS, cytomegalovirus (CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy. CMV may also increase the risk of toxic megacolon in non-HIV/AIDS patients with IBD.

A fistula is an abnormal connection between two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other hollow organs. Fistulas are usually caused by injury or surgery, but they can also result from an infection or inflammation. Fistulas are generally a disease condition, but they may be surgically created for therapeutic reasons.

In botany, the term is most common in its adjectival forms, where it is used in binomial names to refer to species that are distinguished by hollow or tubular structures. Monarda fistulosa, for example, has tubular flowers; Eutrochium fistulosum has a tubular stem; and Allium fistulosum has hollow or tubular leaves.

Various types of fistulas include:

Although most fistulas are in forms of a tube, some can also have multiple branches.

Risperidone, an anti-psychotic medication, can result in megacolon.

Proctitis has many possible causes. It may occur idiopathically (idiopathic proctitis). Other causes include damage by irradiation (for example in radiation therapy for cervical cancer and prostate cancer) or as a sexually transmitted infection, as in lymphogranuloma venereum and herpes proctitis. Studies suggest a celiac disease-associated "proctitis" can result from an intolerance to gluten.

A common cause is engaging in anal sex with partner(s) infected with sexual transmitted diseases in men who have sex with men. Shared enema usage has been shown to facilitate the spread of Lymphogranuloma venereum proctitis.

Megarectum is a large rectum as a result of underlying nerve supply abnormalities or muscle dysfunction, which remains after disimpaction of the rectum. The Principles of Surgery textbook describes any rectum that can hold more than 1500cc of fluid as a megarectum. The term megarectum is also used for a large rectal mass on rectal examination, a wide rectum on an abdominal x-ray, the presence of impaired rectal sensation or the finding of large maximal rectal volumes on anorectal manometry. In addition, can be the bloating of the colon due to infection, also called megacolon. On defecography, megarectum is suggested by a rectal width of >9 cm at the level of the distal sacrum.

Fraser syndrome is a disorder that affects the development of the child prior to birth. Infants born with Fraser syndrome often have eyes that are malformed and completely covered by skin. Also the child is born with fingers and toes that are fused together along with abnormalities within the urine tract. As this disorder relates to vaginal atresia, infants born with Fraser syndrome are also born with malformations in their genitals.

Unlike oesophageal varices, rectal varices are less prone to bleeding, are less serious when a bleed does occur, and are easier to treat because of the more accessible location.

Typically, treatment consists of addressing the underlying portal hypertension. Some treatments include portosystemic shunting, ligation, and under-running suturing. Insertion of a transjugular intrahepatic portosystemic shunt (TIPS) has been shown to alleviate varices caused by portal hypertension. Successful treatment of portal hypertension that subsequently reduces anorectal varices provides a confirmation of the initial diagnosis, allowing for a distinction between varices and hemorrhoids, which would not have been alleviated by reduction of portal hypertension.