From conception to birth a vast array of complex and fragile biological processes have to be completed before a miniature ball of pluripotent cells can become a human child, so it’s not so surprising that sometimes these processes can go a little awry. A recent case study published in BMJ Case Reports describes how one baby girl was born with a bizarre but seemingly harmless second mouth. The unusual duplicate feature was later removed and at six months the girl was found to be free from any significant side effects from the surgery.
The duplication of facial structures or sometimes even the entire head is called diprosopus and is a very rare condition. There have only been around 35 cases on human record since 1900, though there was a recent case involving a kitten born with two faces. In humans it appears to occur more often in females, though exactly why is unclear, and also often centers around the mouth.
In this instance, doctors first became aware that something wasn’t quite right with the development of the baby’s face during a scan in its third trimesters. They detected a mass to the right of the baby’s mouth but were unable to identify exactly what it was using ultrasound. More common explanations would’ve been a cyst, fibrous dysplasia, or teratoma, which is when one twin absorbs another during development. Once the baby was born all became clear.
"Duplication of craniofacial structures typically occurs as part of a syndrome and is often associated with cleft lip and cleft palate, Klippel-Feil syndrome and Pierre Robin sequence," the authors of the case study report. "Our patient's craniofacial duplication is a rare case that presented as an isolated anomaly, with no associated syndromes or abnormalities."
The second mouth, which showed up as a mass on the ultrasound, was found to have its own lip, cavity, teeth, and even a small tongue that moved synchronously with the tongue in her main mouth as she fed (images can be seen here for the curious). It was separated from the main mouth and fortunately didn’t impact the baby’s ability to eat or breathe. In fact, apart from the skin surrounding the second mouth occasionally getting a little raw, it didn’t appear to cause any significant problems.
The team of doctors was able to safely and successfully remove the second mouth when the baby was six months old, removing muscle, bone, mucous membrane, and esophageal tissue. They even found salivary glands and six unerupted teeth showing the extra growth, while small, really did contain all the features we find in our mouths. Apart from swelling and a minor nerve defect in the bottom lip the child’s face was largely unaffected by the ordeal, and the baby didn’t require any further treatment.
One possible error in development that can lead to diprosopus is a duplication of a structure called the pharyngeal arch during the fourth week of an embryo’s development. This arch has the capacity to diversify into teeth, the tongue, and other oral features. However, the doctors in this case report don’t believe this explanation applies to the baby in question as the features of the child’s “main” mouth were all found to be normal. As such, the baby girl with two mouths remains a medical mystery, but the story is an amazing demonstration of how complex the process of growing a human is and how far medicine has come in being able to successfully correct certain developmental slip-ups.