There are several forms of imperforate anus and anorectal malformations. The new classification is in relation of the type of associated fistula.

The classical Wingspread classification was in low and high anomalies:

- A low lesion, in which the colon remains close to the skin. In this case, there may be a stenosis (narrowing) of the anus, or the anus may be missing altogether, with the rectum ending in a blind pouch.

- A high lesion, in which the colon is higher up in the pelvis and there is a fistula connecting the rectum and the bladder, urethra or the vagina.

- A persistent cloaca (from the term cloaca, an analogous orifice in reptiles and amphibians), in which the rectum, vagina and urinary tract are joined into a single channel.

Imperforate anus is usually present along with other birth defects—spinal problems, heart problems, tracheoesophageal fistula, esophageal atresia, renal anomalies, and limb anomalies are among the possibilities.

Imperforate anus is associated with an increased incidence of some other specific anomalies as well, together being called the VACTERL association:

- V – Vertebral anomalies

- A – "Anal atresia"

- C – Cardiovascular anomalies

- T – Tracheoesophageal fistula

- E – Esophageal atresia

- R – Renal (kidney) and/or radial anomalies

- L – Limb defects

Other entities associated with an imperforate anus are trisomies 18 and 21, the cat-eye syndrome (partial trisomy or tetrasomy of a maternally derived number 22 chromosome), Baller-Gerold syndrome, Currarino syndrome, caudal regression syndrome, FG syndrome, Johanson-Blizzard syndrome, McKusick-Kaufman syndrome, Pallister-Hall syndrome, short rib-polydactyly syndrome type 1, Townes-Brocks syndrome, 13q deletion syndrome, urorectal septum malformation sequence, and the OEIS complex (omphalocele, exstrophy of the cloaca, imperforate anus, spinal defects).

If a colostomy is not performed immediately after birth, patients with rectovestibular fistulae may present later in life with complications including severe constipation and megacolon (abnormal dilation of the colon), requiring colostomy or further surgery.

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)

The diagnosis of a rectovestibular fistula can be made in female newborns if the vulva is stained with meconium (the earliest form of stool in an infant). The opening of the anus may be difficult to see due to its small size and position, but it may be visible as a thickening of the median perineal raphe with an obvious anal dimple. Patients with rectovestibular fistulae are commonly misdiagnosed with rectovaginal fistulae.

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.

Intestinal atresias are often discovered before birth: either during a routine sonogram which shows a dilated intestinal segment due to the blockage, or by the development of polyhydramnios (the buildup of too much amniotic fluid in the uterus). These abnormalities are indications that the fetus may have a bowel obstruction which a more detailed ultrasound study can confirm.

Some fetuses with bowel obstruction have abnormal chromosomes. An amniocentesis is recommended because it can determine not only the sex of the baby, but whether or not there is a problem with the chromosomes.

Other birth defects may co-exist, particularly in the heart, but sometimes also in the anus, spinal column, or kidneys. This is known as VACTERL association because of the involvement of Vertebral column, Anorectal, Cardiac, Tracheal, Esophageal, Renal, and Limbs. It is associated with polyhydramnios in the third trimester.

The diagnosis of duodenal atresia is usually confirmed by radiography. An X-ray of the abdomen shows two large air filled spaces, the so-called "double bubble" sign. The air is trapped in the stomach and proximal duodenum, which are separated by the pyloric sphincter, creating the appearance of two bubbles visible on x-ray. Since the closure of the duodenum is complete in duodenal atresia, no air is seen in the distal duodenum.

Atresias occurring distal to the duodenum are usually caused by vascular accidents or ischemic insult, such as jejunoileal atresia.

Surgical repair can sometimes result in complications, including:

- Stricture, due to gastric acid erosion of the shortened esophagus

- Leak of contents at the point of anastomosis

- Recurrence of fistula

- Gastro-esophageal reflux disease

- Dysphagia

- Asthma-like symptoms, such as persistent coughing/wheezing

- Recurrent chest infections

- Tracheomalacia

Anal fistulae can present with the following symptoms:

- skin maceration

- pus, serous fluid and/or (rarely) feces discharge — can be bloody or purulent

- pruritus ani — itching

- depending on presence and severity of infection:

Prognosis is usually very good, although complications are more likely to occur when there are serious congenital anomalies. Late complications may occur in about 12 percent of patients with duodenal atresia, and the mortality rate for these complications is 6 percent.

Any attempt at feeding could cause aspiration pneumonia as the milk collects in the blind pouch and overflows into the trachea and lungs. Furthermore, a fistula between the lower esophagus and trachea may allow stomach acid to flow into the lungs and cause damage. Because of these dangers, the condition must be treated as soon as possible after birth.

Symptoms include:

- Straining during defecation

- Mucous rectal discharge

- Rectal bleeding

- Sensation of incomplete evacuation (tenesmus)

- constipation, or more rarely diarrhea

- fecal incontinence (rarely)

Fistulae between the trachea and esophagus in the newborn can be of diverse morphology and anatomical location; however, various pediatric surgical publications have attempted a classification system based on the below specified types.

Not all types include both esophageal agenesis and tracheoesophageal fistula, but the most common types do.

The letter codes are usually associated with the system used by Gross, while number codes are usually associated with Vogt.

An additional type, "blind upper segment only" has been described, but this type is not usually included in most classifications.

The condition is thought to be uncommon. It usually occurs in young adults, but children can be affected too.

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.

Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types:

- Extrasphincteric fistulae begin at the rectum or sigmoid colon and proceed downward, through the levator ani muscle and open into the skin surrounding the anus. Note that this type does not arise from the dentate line (where the anal glands are located). Causes of this type could be from a rectal, pelvic or supralevator origin, usually secondary to Crohn's disease or an inflammatory process such as appendiceal or diverticular abscesses.

- Suprasphincteric fistulae begin between the internal and external sphincter muscles, extend above and cross the puborectalis muscle, proceed downward between the puborectalis and levator ani muscles, and open an inch or more away from the anus.

- Transphincteric fistulae begin between the internal and external sphincter muscles or behind the anus, cross the external sphincter muscle and open an inch or more away from the anus. These may take a 'U' shape and form multiple external openings. This is sometimes termed a 'horseshoe fistula.'

- Intersphincteric fistulae begin between the internal and external sphincter muscles, pass through the internal sphincter muscle, and open very close to the anus.

- Submucosal fistulae pass superficially beneath the submucosa and do not cross either sphincter muscle.

Abnormal descent of the perineum may be asymptomatic, but otherwise the following may feature:

- perineodynia (perineal pain)

- Colo-proctological symptoms, e.g. obstructed defecation, dyschesia (constipation), or degrees of fecal incontinence

- gynaecological symptoms, e.g. cystocele (prolapse of the bladder into the vagina) and rectocele (prolapse of the rectum into the vagina)

- lower urinary tract symptoms, e.g. dysuria (painful urination), dyspareunia (pain during sexual intercourse), urinary incontinence & urgency

Other researchers concluded that abnormal perineal descent did not correlate with constipation or perineal pain, and there are also conflicting reports of the correlation of fecal incontinence with this condition.

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 condition mainly occurs in women, and it is thought by some to be one of the main defects encountered problem in perineology.

Symptoms and signs in the newborn can be sepsis, abdominal mass, and respiratory distress. Other abdominopelvic or perineal congenital anomalies frequently prompt radiographic evaluation in the newborn, resulting in a diagnosis of coincident vaginal atresia. Symptoms for vaginal atresia include cyclical abdominal pain, the inability to start having menstrual cycles, a small pouch or dimple where a vaginal opening should be, and pelvic mass when the upper vagina becomes filled with menstrual blood. Signs and symptoms of vaginal atresia or vaginal agenesis can often go unnoticed in females until they reach the age of menstruation. Women may also experience some form of abdominal pain or cramping.

An anal fissure, fissure in Ano or rectal fissure is a break or tear in the skin of the anal canal. Anal fissures may be noticed by bright red anal bleeding on toilet paper and undergarments, or sometimes in the toilet. If acute they may cause pain after defecation, but with chronic fissures, pain intensity is often less. Anal fissures usually extend from the anal opening and are usually located posteriorly in the midline, probably because of the relatively unsupported nature and poor perfusion of the anal wall in that location. Fissure depth may be superficial or sometimes down to the underlying sphincter muscle.

Vaginal atresia is a condition in which the vagina is abnormally closed or absent. The main causes can either be complete vaginal hypoplasia, or a vaginal obstruction, often caused by an imperforate hymen or, less commonly, a transverse vaginal septum. It results in uterovaginal outflow tract obstruction. This condition does not usually occur by itself within an individual, but coupled with other developmental disorders within the female. The disorders that are usually coupled with a female who has vagina atresia are Rokitansky-Mayer- Küster-Hauser syndrome, Bardet-Biedl syndrome, or Fraser syndrome.

Umbilical cord ulceration and intestinal atresia is a rare congenital disease that leads to intestinal atresia, umbilical cord ulceration and severe intrauterine haemorrhage. Only 15 cases have so far been reported, though newer studies are beginning to conclude that this disease has a higher incidence rate than has been previously reported. A particular study has given intestinal atresia and umbilical cord ulceration a clear link after 5 such cases were reported at the time of publication.