Pierre Robin syndrome
|Pierre Robin Sequence|
Pierre Robin syndrome (abbreviated to PRS, and also known as Pierre Robin sequence, Pierre Robin malformation, Pierre Robin anomaly or Pierre Robin anomalad) is a congenital condition of facial abnormalities in humans. PRS is a sequence, i.e. a chain of certain developmental malformations, one entailing the next. The three main features are micrognathia (abnormally small jaw or mandible) and glossoptosis resulting in airway obstruction caused by backwards displacement of the tongue base). A genetic cause to PRS was recently identified. Pierre Robin sequence may be caused by genetic anomalies at chromosomes 2,4, 11, or 17.
Signs and symptoms
PRS is characterized by an unusually small mandible (micrognathia), posterior displacement or retraction of the tongue (glossoptosis), and upper airway obstruction. Incomplete closure of the roof of the mouth (cleft palate) is present in the majority of patients, and is commonly U-shaped.
Causes and associated conditions
It is not known how this abnormality occurs in infants, but one theory is that, at some time during the stage of the formation of the bones of the fetus, the tip of the jaw (mandible) becomes 'stuck' in the point where each of the collar bones (clavicle) meet the sternum, effectively preventing the jaw bones from growing. It is thought that, at about 12 to 14 weeks gestation, when the fetus begins to move, the movement of the head causes the jaw to "pop out' of the collar bones. From this time on, the jaw of the fetus grows as it would normally, with the result that, when born, the jaw of the baby is much smaller (micrognathia) than it would have been with normal development, although it does continue to grow at a normal rate until the child reaches maturity.
Genetics and inheritance
It usually occurs as sporadic cases due to de-novo mutations. If inherited, it usually follows autosomal dominant pattern. Association with gene loci 2q24.1-33.3, 4q32-qter, 11q21-23.1, and 17q21-24.3 has been found. Recent studies have indicated that genetic dysregulation of SOX9 gene prevents the SOX9 protein from properly controlling the development of facial structures, which leads to isolated PRS. Similarly, KCNJ2 gene also has a role to play. Overlap with certain other genetic syndromes like Patau syndrome has also been found.
PRS may occur in isolation, but it is often part of an underlying disorder or syndrome. The most common is Stickler Syndrome. Other disorders causing PRS are Velocardiofacial syndrome, Fetal Alcohol Syndrome and Treacher Collins Syndrome.
The syndrome is generally diagnosed clinically shortly after birth. The infant usually has respiratory difficulty, especially when supine. The cleft palate is often U-shaped and wider than in cleft palate that is not associated with this syndrome.
The goals of treatment in infants with Robin sequence focus upon breathing and feeding, and optimizing growth and nutrition despite the predisposition for breathing difficulties. If there is evidence of airway obstruction (snorty breathing, apnea, difficulty taking a breath, or drops in oxygen), then the infant should be placed in the sidelying or prone position, which helps bring the tongue base forward in many children. One study of 60 infants with PRS found that 63% of infants responded to prone positioning (Smith and Senders, 2006, Int J Pediatr Oto). 53% of the infants in this study required some form of feeding assistance, either nasogastric tube or gastrostomy tube feedings (feeding directly into the stomach). In a separate study of 115 children with the clinical diagnosis of PRS managed at 2 different hospitals in Boston (Evans et al., 2006, In J Pediatr Oto), respiratory distress was managed successfully in 56% without an operation (either by prone positioning, short term intubation, or placement of a nasopharyngeal airway). In this study, gastrostomy tube feeding were placed in 42% of these infants due to feeding difficulties.
Gastroesophageal reflux (GERD) seems to be more prevalent in children with Robin sequence (Dudkiewicz, March 2000, CPCJ). Because reflux of acidic contents in the posterior pharynx and upper airway can intensify the symptoms of Robin sequence, specifically by worsening airway obstruction, it is important to maximize treatment for GER in children with PRS and reflux symptoms. Treatment may include upright positioning on a wedge (a tucker sling may be needed if the baby is in the prone position), small and frequent feedings (to minimize vomiting), and/or pharmacotherapy (such as proton pump inhibitors).
In nasopharyngeal cannulation (or placement of the nasopharyngeal airway or tube), the infant is fitted with a blunt-tipped length of surgical tubing (or an endotracheal tube fitted to the child), which is placed under direct visualization with a laryngoscope, being inserted into the nose and down the pharynx (or throat), ending just above the vocal cords. Surgical threads fitted through holes in the outside end of the tube are attached to the cheek with a special skin-like adhesive material called 'stomahesive', which is also wrapped around the outside end of the tube (but not over the opening at the end) to keep the tube in place. This tube or cannula, which itself acts as an airway, primarily acts as a sort of "splint" which maintains patency of the airway by keeping the tongue form falling back on the posterior pharyngeal wall and occluding the airway, therefore preventing airway obstruction, hypoxia and asphyxia. Nasopharyngeal airways are not available at every center, however, when available, nasopharyngeal cannulation should be favored over the other treatments mentioned in this article, as it is far less invasive; it allows the infant to feed without the further placement of a nasogastric tube. This treatment may be utilized for multiple months, until the jaw has grown enough so that the tongue assumes a more normal position in the mouth and airway (at birth, the jaws of some infants are so underdeveloped that only the tip of the tongue can be seen when viewed in the throat). Some institutions discharge the infant home with a nasopharyngeal tube in place (Citation: KD Anderson, May 2007, CPCJ).
Distraction osteogenesis (DO), also called a "Mandibular Distraction", can be used to correct abnormal smallness of one or both jaws seen in patients with Robin Sequence. Enlargement of the lower jaw brings the tongue forward, preventing it from obstructing the upper airway. The process of DO begins with preoperative assessment. Doctors use three-dimensional imaging to identify the parts of the patient's facial skeleton that need repositioning and determine the magnitude and direction of distraction. They may then select the most appropriate distraction device or sometimes have custom devises fabricated. When possible, intraoral devices are used.
DO surgery starts with an osteotomy (surgical division or sectioning of bone) followed by the distraction device being placed under the skin and across the osteotomy. A few days later, the two ends of the bone are very gradually pulled apart through continual adjustments that are made to the device by the parents at home. The adjustments are made by turning a small screw that protrudes through the skin, usually at a rate of 1 mm per day. This gradual distraction leads to formation of new bone between the two ends. After the process is complete, the osteotomy is allowed to heal over a period of six to eight weeks. A small second surgery is then performed to remove the device.
The cleft palate is generally repaired between the ages of 6½ months and 2 years by a plastic surgeon, an oromaxillofacial surgeon, or an otorhinolaryngologist (ENT surgeon). In many centres there is now a cleft lip and palate team comprising these specialties, as well as a coordinator, a speech and language therapist, an orthodontist, sometimes a psychologist or other mental health specialist, an audiologist, and nursing staff. The glossoptosis and micrognathism generally do not require surgery, as they improve to some extent unaided, though the mandibular arch remains significantly smaller than average. In some cases jaw distraction is needed to aid in breathing and feeding. Lip-tongue attachment is performed in some centres, though its efficacy has been recently questioned.
Children affected with PRS usually reach full development and size. However, it has been found internationally that children with PRS are often slightly below average size, raising concerns of incomplete development due to chronic hypoxia related to upper airway obstruction as well as lack of nutrition due to early feeding difficulties or the development of an oral aversion. However, the general prognosis is quite good once the initial breathing and feeding difficulties are overcome in infancy. Most PRS babies grow to lead a healthy and normal adult life.
The most important medical problems are difficulties in breathing and feeding. Affected infants very often need assistance with feeding, for example needing to stay in a lateral(on the side) or prone(on the tummy) position which helps bring the tongue forward and opens up the airway. Babies with a cleft palate will need a special cleft feeding device (such as the Haberman Feeder). Infants who are unable to take in enough calories by mouth to ensure growth may need supplementation with a nasogastric tube. This is related to the difficulty in forming a vacuum in the oral cavity related to the cleft palate, as well as to breathing difficulty related to the posterior position of the tongue. Given the breathing difficulties that some babies with PRS face, they may require more calories to grow (as working of breathing is somewhat like exercising for an infant). Infants, when moderately to severely affected, may occasionally need nasopharyngeal cannulation, or placement of a nasopharyngeal tube to bypass the airway obstruction at the base of the tongue. in some places, children are discharged home with a nasopharyngeal tube for a period of time, and parents are taught how to maintain the tube. Sometimes endotracheal intubation or tracheostomy may be indicated to overcome upper respiratory obstruction. In some centers, a tongue lip adhesion is performed to bring the tongue forward, effectively opening up the airway. Mandibular distraction can be effective by moving the jaw forward to overcome the upper airway obstruction caused by the posterior positioning of the tongue. Given that a proportion of children with Robin sequence will have Stickler syndrome, it is important that a child with PRS have an evaluation by an optometrist or ophthalmologist in the first year of life looking for myopia that can be seen in Stickler syndrome. Because retinal detachment that can occur in Stickler syndrome is a leading cause of blindness in children, it is very important to recognize and be thoughtful of this diagnosis.
The prevalence has been estimated at 1 in 10,000 births, but exact values are hard to know because some that have the symptoms rarely have Pierre-Robin sequence (without any other associated malformation).
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