What are Microtia and Atresia?

Microtia is the absence of an ear or an underdeveloped outer ear.

Atresia is hearing loss due to the absence of an ear canal.

Microtia and Atresia are congenital birth defects of the ear. Microtia is when the outer ear does not fully develop during the first trimester of pregnancy or when the outer ear is absent, (known as anotia). Atresia is the absence of the ear canal, resulting in hearing loss. Microtia and Atresia occurs in every 1 out of 6,000 to 12,000 births.

There are four grades of Microtia and Atresia:
Grade 1:  Smaller than normal, but the ear has mostly normal anatomy.
Grade 2 – Part of the ear looks normal, usually the lower half.  The canal may be normal, small or completely closed.
Grade 3 – Just a small remnant of “peanut-shaped” skin and cartilage. There is no canal, which is called aural atresia.
Grade 4 – Complete absence of both the external ear and the ear canal, also called “anotia.”

How Does Microtia Happen?

We know that microtia occasionally can occur for different reasons – yet more often usually has no known cause. Importantly, parents could not have inadvertently caused the microtia nor have been able to prevent the condition. Therefore, parents should not feel ‘guilty’ and should focus on a beautiful baby rather than an ear.

Exposure:  One very infrequent known reason for microtia comes from environmental exposure. Extremely rarely, an unusual medicine taken during pregnancy can cause changes in the formation of structures in an embryo. A mother would usually know about such rare medicines. For example, Accutane™ which is a very high dose of vitamin A for very severe acne, can cause microtia – yet that medicine is prescribed rarely and the recipient (mother) would have needed to sign special consent forms before such a prescription would even have been given.  Another medication example that is known from historical effect is Thalidomide.

NOTE: Regular prescription medicines such as antibiotics and routine vitamins are not felt to cause ear malformations. Other environmental exposures such as diet, household agents or lifestyle do not seem to play an obvious role either. Maternal health conditions are typically not associated with microtia although diabetes might have a relationship that as yet is unclear.

Why Does Atresia Happen?

Aural Atresia is the result of an underdeveloped ear canal with hearing loss or when the ear canal is absent, following birth.  Aural Atresia usually will be present in most cases when Microtia is present. In other cases, a narrowed ear canal may be present, where the eardrum can still be viewed, but the canal itself is narrow. This condition is called stenosis or referred to as being a stenoic ear canal. Canal stenosis can affect one ear or both ears and is associated with a high incidence of cholesteatoma. A Cholesteatoma is an abnormal bundle of skin growths in the middle ear located behind the eardrum. Cholesteatomas often develop as cysts or pouches that shed layers of old skin, which build up inside the middle ear. The build up of this bundle of skin inside the ear can increase in size and eventually break through and destroy bones in the middle ear that are used for hearing, causing hearing loss.  Permanent hearing loss, dizziness, and facial muscle paralysis are rare, but can result from continued cholesteatoma growth.  Patients with complete atresia and who have stenosis can have hearing loss.

Genetics and Microtia/Aural Atresia:

Another reason for microtia to occur is genetic. Sometimes the genetics are clear cut such as with Treacher Collins Syndrome, a dominantly inherited condition, which involves both ears as well as facial structures. At other times, a gene is inferred as a possible cause. For example, a child might have an obvious microtia and the family will later learn that a distant relative had a minor ear issue such as a preauricular skin tag (a tag in front of the ear). Rarely, and more obviously demonstrating an inherited pattern, several family members will have microtia. Additionally, some ethnic groups have a higher or lower incidence of microtia which does not prove, yet suggests, a genetic population predisposition. Since microtia does not obviously follow Mendel’s classic laws of genetics from the pea experiments that we all learned in high school biology (recessive and dominant), any genetic impact on ear formation seems a bit more complex and will take time to clarify. As an example of still unclear genetic influence, twins can exhibit combinations of microtia – opposite side microtia, same side microtia, both side microtia, or only one twin displaying microtia.  The twin studies indicate that microtia is influenced by genetic as well as environmental factors.

Quick Facts:

  • Microtia and Atresia occurs in 1 out of every 5,000 births, but can be affected regionally.
  • Approximately 500 babies are born with Microtia and Atresia in the United States each year.
  • Ears are 85% fully grown by six years of age.
  • The right ear is more commonly affected by Microtia.
  • Microtia and Atresia typically occurs more often in males.
  • Microtia and Atresia is more common in the Asian, Native American, Ecuadorian, and Latino/Hispanic ethnicities, but is least commonly found in African Americans.
  • Microtia and Atresia can occur independently on its own or it can be associated with other syndromes such as Treacher Collins, Nager Syndrome, Branchio Oto Renal Syndrome, and Goldenhar Syndrome.
  • Microtia and Atresia can an affect either the left or right ear (unilaterally) or both ears (bilaterally).
  • For most patients, Microtia seems to be “idiopathic.” Therefore, we do not know at this time what causes the condition.

To make an appointment, e-mail us at:   MicrotiaAtresiaClinic@VUMC.org or call ph:  615-343-6166.