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Treacher Collins Syndrome Is More Asymmetric Than Traditionally Appreciated: A Three-Dimensional Cohort Study
Kirin Naidu
*, Sarah Barnett, David Perrault, Maura Guyler, Santiago Lopez, Scott Bartlett, Jordan W. Swanson, Sameer Shakir, Joseph A. Napoli, Jesse Taylor
Children's Hopsital of Philadelphia, Philadelphia, PA
Background: Treacher Collins syndrome (TCS) is classically described as bilateral and symmetric, yet clinically meaningful left-right differences are increasingly recognized. Previously published grading systems classify morphologic type rather than size, and it is unknown whether mandibular and zygomatic asymmetry occur on the same side within individual patients.
Methods: A retrospective review was performed of 36 patients with TCS who had preoperative CT imaging. Mandibular and zygomatic severity were graded bilaterally using previously published grading systems. Bilateral linear measurements including ramus height, body length, total mandibular length, ramus width, condyle height, and the ramus-to-corpus ratio were extracted from three-dimensional reconstructions. Inter-side asymmetry was quantified as the absolute difference divided by the mean of both sides, with 10% and 20% thresholds drawn from previously published systems.
Results: Categorical grading identified mandibular asymmetry in 23% of patients and zygomatic asymmetry in 25%. Continuous measurements revealed substantially greater asymmetry: 97% demonstrated ≥10% asymmetry in at least one measure and 83% exceeded 20%. Condyle height was the most asymmetric measurement (mean 34%, 94% ≥10%) and was not captured by grade-based asymmetry (p=0.23). In neonates ≤3 months, ramus heights varied by up to 7.4 mm between sides (15.9 vs 9.0 mm). Critically, the mandible and zygoma were asymmetric on the same side: when both structures were asymmetric, the more hypoplastic mandibular side matched the worse zygomatic side in 100% of assessable cases for ramus height (6/6), condyle height (7/7), and ramus-to-corpus ratio (6/6).
Conclusions: Mandibular and zygomatic hypoplasia in TCS are concordantly asymmetric, which may be consistent with a shared left-right gradient in neural crest contribution that categorical grading underestimates. Operative planning should be individualized at the hemiface and subunit level, with side-specific strategies for distraction, grafting, and implant design.
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