The term “microtia” is intuitive

In Latin, micro means “small”, and otia means “ear.” Microtia is a birth deformity of the ear that occurs in about one in every 10,000 live births.

Microtia can occur with other congenital abnormalities, but is most often seen as an isolated, independent deformity and is often associated with a small or absent ear canal.

Those who are most commonly affected include Asians, Hispanics and Caucasians. Males and females are affected at approximately the same rates.

Microtia is classified into four different types:

Grade I: A slightly small ear with a shape much like a normal ear, often accompanies by a small but narrow ear canal.
Grade II: A partial or hemi- ear with usually an absent ear canal.
Grade III: Absence of most of the external ear, with a small “peanut” shaped remnant ear lobule and an absent ear canal and ear drum (atresia). This is the most common grade of microtia.
Grade IV: Total absence of the ear or anotia.

Microtia occasionally can occur for different reasons

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. Thalidomide have the same results.

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.

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 and 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.

Atresia/Aural Atresia

Atresia is absence or underdevelopment of the ear canal and middle ear structures. Microtia is almost always accompanied by atresia because the outer ear and the middle ear develop around the same time during fetal development. Some microtia patients have what appears at first look to be a normal canal, but many of them end in a blind pouch, no connection into middle ear.

Some patients have small ear canals, but their middle ear may be normal, and as a result their hearing can be normal, or they may have an underdeveloped middle ear resulting in significant conductive hearing loss. Sensorineural function is usually normal, as the cochlea and neural elements of hearing are unaffected.

Important aspects

Microtia and Atresia occurs in 1 out of every 5,000 births, but can be affected regionally.
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.