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Microtia and atresia

Photo: Microtia or atresia happens when the outer part of the ear doesn’t develop fully during pregnancy

What are microtia and atresia?

Microtia is a term used to describe under-development of the outer ear (pinna).

It can vary from quite minor changes (such as the ear being smaller than expected) to ‘classic microtia’ where the pinna is missing.

Classic microtia is often associated with absence of the ear canal – known as atresia. This is because the baby’s outer ear and ear canal develop together during pregnancy. In some cases the ear canal can look present from outside but ends at a ‘blind alley’ inside.

Types of microtia

  • Lobular type microtia: the outer ear is present but small and under-developed (peanut shaped). This is the most common type of microtia.
  • Conchal type microtia: the child has an ear canal although it may be very narrow (canal stenosis) or a blind ending with no eardrum. The outer ear is present and has a conchal bowl (middle part of the ear cartilage) but it is much smaller than normal. The upper part is often underdeveloped.
  • Small conchal type: the ear is smaller than usual but the key features of the outer ear are present, although they may have small differences in shape or form, such as a small conchal bowl. The ear canal is either missing (atresia) or has a narrow and blind ending.

Microtia happens more often in boys than in girls. It usually affects one side, which is known as unilateral microtia. It more often affects the right ear than the left. About one in 10 children are affected on both sides – this is known as bilateral microtia.

What is the cause of microtia and atresia?

Microtia or atresia happens when the outer part of the ear doesn’t develop fully during the early stages of pregnancy. The exact reason for isolated or non-syndromic (not associated with any other signs or symptoms) microtia or atresia remain unclear although it’s usually a random, one-off event.

It isn’t caused by anything the mother did or didn’t do before or during the pregnancy. Medical research has suggested that sometimes certain prescribed medications taken during pregnancy, or genetic and/or environmental factors may lead to a baby being born with microtia or atresia.

The possible causes will be explored at the first meeting with your specialist multidisciplinary team (professionals with specialised skills and expertise) who will work with you to support your child.

Microtia and deafness

There are different types of deafness that can be associated with microtia and atresia, depending on which part of the ear is not formed or working as it should.

Find out more in our factsheet Children with Microtia and Atresia