The Pierre Robin Sequence (PRS) is not well known by the public. But for many of the children who have this disorder, characterized by micrognathia (abnormally small jaw), glossoptosis (downward displacement of the tongue toward the pharynx), respiratory distress, the upper airway obstruction can lead to considerable swallowing and feeding difficulties. Additionally, 60 to 90 percent of children with this disorder have a cleft palate. A new study being presented before pediatric otolaryngologists confirms through computer tomography that a enhanced surgical procedure to produce new bone growth of the jaw is an effective treatment for this disorder.

The cause of Pierre Robin sequence occurs in pre-birth and is associated with a small mandible (jaw) which prevents the relatively large tongue (pseudomacroglossia) from descending thereby preventing the palatal shelves from fusing in the midline. This explains the high incidence of cleft palate deformity

Management of Pierre Robin sequence varies in accordance to the degree of its severity. Conservative management options include prone positioning and placement nasopharyngeal airway stents. Significant airway obstruction mandates more aggressive therapy including tongue lip adhesion, hyomandibulopexy, and subperiosteal release of the floor of mouth musculature. Tracheostomy can commonly be used for management of upper airway obstruction in PRS; however, it is associated with high costs and significant associated morbidity and mortality. The average age of removal of the tracheostomy tube for children with PRS is 3.1 years.

Mandibular distraction osteogenesis is a surgical treatment where new bone is made across a bony cut (osteotomy). This procedure, essentially lengthening the jaw through bone growth, offers an alternative to traditional methods of airway management in PRS infants. As the jaw is lengthened, the tongue base moves forward by its anterior muscular attachments to the mandible.

The traditional method of mandibular distraction utilized multidirectional external distractors. These distractors allow for multiplanar manipulation of the mandibular segments, allowing fine adjustment to the maxillomandibular relationship. Now, new, unidirectional internal microdistractor have allow placement of inconspicuous internal devices with minimal morbidity. Infants tolerate these internal distractors more readily. They offer minimal risk of dislodgement while avoiding scars associated with tracking external distractor pins through soft tissue and skin. A drawback is that they do not allow fine adjustment of mandibular segments to correct any occlusal disharmony that may occur during the distraction process.

A new study set out to analyze changes in the craniofacial anatomy based on pre and post distraction CT scans. This entailed the evaluation of three infants with PRS who underwent unidirectional distraction using internal microdistractors for relief of tongue base/ hypopharyngeal airway obstruction. The author of ?Quantitative Ct Analysis of the Mandible After Distraction Osteogenesis in Infants with Pierre Robin Sequence (PRS),? is Saswata Roy MD MS at the Children's Memorial Hospital in Chicago, IL. His findings will be presented at The Twentieth Annual Meeting of the American Society of Pediatric Otolaryngology (ASPO) http://www.aspo.us

being held May 27-30, 2005, at the J.W. Marriott Las Vegas Resort in Las Vegas, NV.

Methodology: The research involved a consecutive series of infants with PRS and severe upper airway obstruction who underwent mandibular distraction with the same internal unidirectional device. Standardized serial CT scans were obtained. The CT data was extracted and analyzed with Medical Image Analysis Software AVW v.5.0 for mandibulo-maxillary arch harmony, hypopharyngeal airway volume, geniohyoid distance and mandibular length.

Results: The purpose of this study is to analyze pre and post operative CT scans to evaluate the skeletal changes that occur with mandibular distraction osteogenesis. The purpose of this study is also to determine if unidirectional vector forces are sufficient to achieve maxillomandibular harmony. Key findings were:

-- There is a significant increase in mandibular bone volume after distraction osteogenesis. This holds true even after accounting for the overall growth of the maxilla and the craniofacial skeleton.

-- The study also demonstrates that vertical and horizontal mandibular lengthening is possible with unidirectional internal distractor devices. Gaining multidirectional bone growth is achieved by the design of the osteotomy and oblique nature of the distraction vectors. The results show good maxillomandibular harmony with no open bite or crossbite deformities.

-- The geniohyoid relationship remained relatively constant after mandibular distraction with only a 14 percent increase. This support the notion that the hyoid moves forward as the distal mandibular segment is anteriorly distracted. A significant feature of PRS is glossoptosis or the collapse of the base of tongue against the posterior pharyngeal wall. The study data revealed a 199 percent increase in the distance between the hyoid and the posterior pharyngeal wall. This is supported by a 150 percent increase in the mid-sagittal cross-sectional airway and a 192 percent increase in the three-dimensional airway volume with distraction osteogenesis.

Conclusion: This data supports the basic principle of mandibular distraction osteogenesis in airway management of the microganthic infant. The goal of the mandibular distraction osteogenesis is to advance the mandible and concurrently bring the tongue base forward by its muscular attachments along the floor of the mouth. External hardware has long been used in performing this procedure. However, the study showed internal microdistractor devices more easily tolerated by infants and accepted by parents. It is likely that the plasticity and malleability of the infant mandible allows sufficient bony remodeling to achieve good maxillomandibular arch alignment with unidirectional advancement. Mandibular distraction with internal devices provide good maxillomandibular harmony, advance the hyoid anteriorly to increase the hypopharyngeal space and airway volume, and increase bone length and substance. Internal mandibular distraction represent a significant advance in management of upper airway obstruction in the micrognathic infant.

Editor's note: Pictures of these children before and after surgery are available as well as the CT's of their jaws before and after surgery.

American Society of Pediatric Otolaryngology (ASPO)
http://www.aspo.us