Aural atresia is the underdevelopment of the middle ear and canal and usually occurs in conjunction with microtia. Atresia occurs because patients with microtia may not have an external opening to the ear canal, though. However, the cochlea and other inner ear structures are usually present. The grade of microtia usually correlates to the degree of development of the middle ear.

Microtia is usually isolated, but may occur in conjunction with hemifacial microsomia, Goldenhar Syndrome or Treacher-Collins Syndrome. It is also occasionally associated with kidney abnormalities (rarely life-threatening), and jaw problems, and more rarely, heart defects and vertebral deformities.

Microtia is a congenital deformity where the pinna (external ear) is underdeveloped. A completely undeveloped pinna is referred to as anotia. Because microtia and anotia have the same origin, it can be referred to as microtia-anotia. Microtia can be unilateral (one side only) or bilateral (affecting both sides). Microtia occurs in 1 out of about 8,000–10,000 births. In unilateral microtia, the right ear is most commonly affected. It may occur as a complication of taking Accutane (isotretinoin) during pregnancy.

Individuals with Nager syndrome typically have the malformations of the auricle, external auditory canal, and middle ear, including the ossicles. These malformations were found in 80% of individuals with Nager syndrome. Inner ear malformations, however, are not typically seen in this population. Middle ear disease is common among individuals with Nager syndrome. Chronic otitis media and Eustachian tube deformity can result in conductive hearing loss. For this reason, early detection and treatment for middle ear disease is crucial in this population. Sensorineural hearing loss is not a typical characteristic of Nager syndrome; however, a subset of individuals present with a mixed hearing loss, due to a progressive sensorineural component combined with the typical conductive hearing loss (Herrman "et al.", 2005).

"20% to 40% of children with microtia/anotia will have additional defects that could suggest a syndrome."

Treacher-Collins Syndrome: (TCS) A congenital disorder caused by a defective protein known as treacle, and is characterized by craniofacial deformities; malformed or absent ears are also seen in this syndrome. The effects may be mild, undiagnosed to severe, leading to death. Because the ear defects are much different in this disorder and not only affect the outer ear, but the middle ear as well, reconstructive surgery may not help with the child's hearing and in this case a Bone Anchored Hearing Aid would be best. BAHA will only work, however if the inner ear and nerve are intact.

Goldenhar Syndrome: A rare congenital birth defect that causes abnormalities of facial development. also known as Oculoauricular Dysplasia. The facial anomalies include underdeveloped, asymmetric half of the face. The defect is capable of affecting tissue, muscle, and the underlying bone structure of the side of the face with the abnormality.

Ablepharon-macrostomia Syndrome: (AMS) A rare genetic disorder characterized by various physical anomalies which affect the craniofacial area, the skin, the fingers, and the genitals.

Anotia ("no ear") describes a rare congenital deformity that involves the complete absence of the pinna, the outer projected portion of the ear, and narrowing or absence of the ear canal. This contrasts with microtia, in which a small part of the pinna is present. Anotia and microtia may occur unilaterally (only one ear affected) or bilaterally (both ears affected). This deformity results in conductive hearing loss, deafness.

Hearing loss with craniofacial syndromes is a common occurrence. Many of these multianomaly disorders involve structural malformations of the outer or middle ear, making a significant hearing loss highly likely.

Third window effect caused by:

- Superior canal dehiscence – which may require surgical correction.

- Widened vestibular aqueducts

Fluid accumulation is the most common cause of conductive hearing loss in the middle ear, especially in children. Major causes are ear infections or conditions that block the eustachian tube, such as allergies or tumors. Blocking of the eustachian tube leads to decreased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles and the tympanic membrane.

- acute or serous otitis media

- otitis media with effusion or 'glue ear'

- Perforated eardrum

- Chronic suppurative otitis media (CSOM)

- Cholesteatoma

- Otosclerosis, abnormal growth of bone in or near the middle ear

- middle ear tumour

- ossicular discontinuity as a consequence of infection or temporal bone trauma

- Congenital malformation of the ossicles. This can be an isolated phenomenon or can occur as part of a syndrome where development of the 1st and 2nd branchial arches is seen such as in Goldenhar syndrome, Treacher Collins syndrome, branchio-oto-renal syndrome etc.

- Barotrauma unequal air pressures in the external and middle ear. This can temporarily occur, for example, by the environmental pressure changes as when shifting altitude, or inside a train going into a tunnel. It is managed by any of various methods of ear clearing manoeuvres to equalize the pressures, like swallowing, yawning, or the Valsalva manoeuvre. More severe barotrauma can lead to middle ear fluid or even permanent sensorineural hearing loss.

Presence of inner ear abnormalities lead to Delayed gross development of child because of balance impairment and profound deafness which increases the risk of trauma and accidents.

- Incidence of accidents can be decreased by using visual or vibrotactile alarm systems in homes as well as in schools.

- Anticipatory education of parents, health providers and educational programs about hazards can help.

In addition to medications, hearing loss can also result from specific chemicals: metals, such as lead; solvents, such as toluene (found in crude oil, gasoline and automobile exhaust, for example); and asphyxiants. Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.

Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system. For some ototoxic chemical exposures, particularly styrene, the risk of hearing loss can be higher than being exposed to noise alone.

- Solvents

- toluene, styrene, xylene, "n"-hexane, ethyl benzene, white spirits/Stoddard, carbon disulfide, jet fuel, perchloroethylene, trichloroethylene, "p"-xylene

- Asphyxiants

- carbon monoxide, hydrogen cyanide

- Heavy metals

- lead, mercury, cadmium, arsenic, tin-hydrocarbon compounds (trimethyltin)

- Pesticides and herbicides - The evidence is weak regarding association between herbicides and hearing loss; hearing loss in such circumstances may be due to concommitant exposure to insecticides.

- paraquat, organophosphates

Some medications may reversibly affect hearing. These medications are considered ototoxic. This includes loop diuretics such as furosemide and bumetanide, non-steroidal anti-inflammatory drugs (NSAIDs) both over-the-counter (aspirin, ibuprofen, naproxen) as well as prescription (celecoxib, diclofenac, etc.), paracetamol, quinine, and macrolide antibiotics. The link between NSAIDs and hearing loss tends to be greater in women, especially those who take ibuprofen six or more times a week. Others may cause permanent hearing loss. The most important group is the aminoglycosides (main member gentamicin) and platinum based chemotherapeutics such as cisplatin and carboplatin.

On October 18, 2007, the U.S. Food and Drug Administration (FDA) announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors, which are used for erectile dysfunction.

Michel aplasia, also known as complete labyrinthine aplasia (CLA), is a congenital abnormality of the inner ear. It is characterized by the bilateral absence of differentiated inner ear structures and results in complete deafness (anacusis).

Michel aplasia should not be confused with michel dysplasia. It may affect one or both ears.

"Aplasia" is the medical term for body parts that are absent or do not develop properly. In Michel aplasia, the undeveloped (anaplastic) body part is the bony labyrinth of the inner ear. Other nearby structures may be underdeveloped as well.

There is still some discussion on whether FND is sporadic or genetic. The majority of FND cases are sporadic. Yet, some studies describe families with multiple members with FND. Gene mutations are likely to play an important role in the cause. Unfortunately, the genetic cause for most types of FND remains undetermined.

OAFNS is a combination of FND and oculo-auriculo-vertebral spectrum (OAVS).

The diagnosis of OAVS is based on the following facial characteristics: microtia (underdeveloped external ear), preauricular tags, facial asymmetry, mandibular hypoplasia and epibulbar lipodermoids (benign tumor of the eye which consists of adipose and fibrous tissue).

There still remains discussion about the classification and the minimal amount of characteristics. When someone presents with FND and the characteristics of OAVS, the diagnosis OAFNS may be made.

As the incidence of OAFNS is unknown, there are probably a lot of children with mild phenotypes that aren’t being diagnosed as being OAFNS.

The cause of OAFNS is unknown, but there are some theories about the genesis. Autosomal recessive inheritance is suggested because of a case with two affected siblings and a case with consanguineous parents. However, another study shows that it is more plausible that OAFNS is sporadic.

It is known that maternal diabetes plays a role in developing malformations of craniofacial structures and in OAVS. Therefore, it is suggested as a cause of OAFNS. Folate deficiency is also suggested as possible mechanism.

Low-dose CT protocols should be considered in diagnosing children with OAFNS.

Ear agenesis is a medical condition in which people are born without ears.

Because the middle and inner ears are necessary for hearing, people with complete agenesis of the ears are totally deaf. Minor agenesis that affects only the visible parts of the outer ear, which may be called microtia, typically produces cosmetic concerns and perhaps hearing impairment if the opening to the ear canal is blocked, but not deafness.

Eye agenesis is a medical condition in which people are born with no eyes.

Known causes include physical trauma, acoustic neuroma, measles, labyrinthitis, microtia, meningitis, Ménière's disease, Waardenburg syndrome, mumps (epidemic parotitis), and mastoiditis.

A 1998 study of schoolchildren found that per thousand, 6-12 had some form of unilateral hearing loss and 0-5 had moderate to profound unilateral hearing loss. It was estimated that in 1998 some 391,000 school-aged children in the United States had unilateral hearing loss.

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.

Johnson–McMillin syndrome is a neuroectodermal syndrome that consist of conductive hearing loss and microtia.