Optic nerve elongation during fronto-facial surgery for Crouzon syndrome: 3D quantification and clinical implications.

Objective: Fronto-facial monobloc advancement with internal distraction (FFMBA) is a key procedure in the management of syndromic craniosynostoses. FFMBA involves circumferential dissection and linear enlargement of the orbit, potentially leading to mechanical stress on the optic nerve (ON). Several reports of transient vision loss during the distraction process led us to investigate ON shape modifications during facial advancement, with the aim to potentially refine current clinical guidelines on postoperative management and the distraction schedule.

Methods: Twenty-six patients with Crouzon syndrome were included in this study. ONs were segmented on pre- and postoperative CT scans. Distraction amplitudes, linear and curved lengths, and cross-section diameters of the ON were assessed along the main axis of the nerve. A two-level hierarchical multivariate linear model was used to screen for factors associated with ON morphology.

Results: The mean age at FFMBA was 4.4 ± 3.8 years. Two patients presented with transient impaired vision during distraction. The final mean fronto-orbital and temporo-zygomatic distraction amplitudes were 18 ± 4 mm and 18 ± 6 mm, respectively. At the end of distraction, ONs were elongated (+1.8 mm for curved lengths, p = 0.013), and their mean cross-section was reduced (-1.9 mm2, p < 0.001) in the proximal intraorbital portion (first 15 mm). In the 2 patients with visual symptoms, functional impairment was associated with ON area reduction (OR 0.487, p < 0.001) and increased temporo-zygomatic distraction amplitude (OR 2.240, p < 0.001).

Conclusions: ON was elongated during FFMBA, with proximal diameter reduction. Transient visual impairment with normal fundus examination during distraction seemed to have a morphological basis, based on 2 cases. These results suggest the importance of vision monitoring associated with fundus examination during distraction, and advocate for early extubation after FFMBA to allow clinical follow-up.