What Causes Macrostomia?

Medically Reviewed on 6/22/2022
What Causes Macrostomia?
Macrostomia is a rare cause of the facial deformity, where clefts forms on either or both sides of the face when a baby is born.

Macrostomia is the enlargement of the mouth at the oral commissure. It is often caused when maxillary and mandibular portions of the first branchial arch fail to unite normally in a fetus during embryonic development.

  • Macrostomia is a rare cause of the facial deformity, where clefts forms on either or both sides of the face when a baby is born.
  • They are mostly seen on the right cheek and have a higher incidence in males.
  • On average, it occurs 1 in every 150,000 to 300,000 live births. The clefts result from improper development and fusion of the facial bones and jaw.
  • Rarely, it could be a part of genetic disorders, such as the Ablepharon-macrostomia syndrome.

At seven weeks of gestation, the lips separate from the alveolar areas, leading to the formation of a vestibule and maxillary and mandibular swelling that then merges laterally to form the cheeks. An incomplete union results in macrostomia, which is seen either on single or both sides.

The defects of the first brachial arch arise from inadequate arterial blood supply occurring during a period of rapid and critical facial growth and development.

4 variations of macrostomia

  1. Complete lateral facial cleft: The facial cleft runs from the corner of the mouth toward the bottom of the ear. The outside of the ear on the affected side of the face appears normal, and a region of soft tissue connects the cleft to the right lateral posterior hard palate. Internally there is no soft palate.
  2. Simple macrostomia: It is less severe because it does not affect the facial muscles and is not associated with any soft tissue or bone deformities. A small cleft extends from the mouth and can be repaired surgically.
  3. Macrostomia with diastasis of the facial musculature: Clefts in this variant are slightly more severe than the ones seen in simple macrostomia. It does not have bone deformities but includes minor soft tissue deformities. The defining feature is muscle diastasis, which is the separation of the masseter muscle. This can be partially corrected with surgery.
  4. Isolated facial musculature diastasis: The facial cleft in this case results in a more severe muscle separation even though there is not a true open cleft. Bones in the region remain unaffected, and the phenotype appears as an indentation of the cheek rather than an open cleft. The external ear in this phenotype can be affected.


Conception: The Amazing Journey from Egg to Embryo See Slideshow

How is macrostomia treated?

Surgical reconstruction of the defect is the main therapeutic option. The surgical repair of macrostomia bears structural, functional, and cosmetic concerns.

5 goals that are achieved with surgery for macrostomia

  1. Formation of symmetric lips and oral commissure
  2. Reconstruction of the orbicularis oris muscle to restore labial function
  3. Reconstruction of the commissures of the mouth with a natural-looking contour
  4. Closure of the defect with a minimally visible scar
  5. Prevention of future scar contracture with lateral migration of commissures

There are several surgical options for the correction of macrostomia, including Z-plasty, W-plasty, triangular flaps, and straight-line closure.

Incisions are placed along the borders of the cleft, both inside and outside the mouth. The muscles are then brought into continuity, including the oral sphincter (orbicularis oris). The wound is then closed from the inside out.

What is the recovery from macrostomia surgery?

Recovery from surgical correction of macrostomia is relatively simple. Sutures are absorbable and do not require removal. The surgery takes less than two hours and can be done on an outpatient basis. Patients must avoid contact sports or rough play for a period of at least three to four weeks. A soft diet is required for up to six weeks.

What are the risks and complications of macrostomia surgery?

Fortunately, complications from macrostomia repair are limited. Typical surgical risks include bleeding, infection, anesthesia complications, and bad scarring. Additionally, there is a chance of asymmetry and a possibility for further surgical procedures. Anesthesia pre-evaluation could be required in syndromic patients with airway issues or other systemic problems, such as cardiac, pulmonary, or endocrinology defects.

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Medically Reviewed on 6/22/2022
Image Source: iStock image

l Moutran H. Macrostomia. Medscape. https://emedicine.medscape.com/article/878332-overview

OMIM. Macrostomia, Isolated. https://www.omim.org/entry/613545