D81. Isolated Nonsyndromic Lambdoid Synostosis: A Single Center’s 30-year Experience with 31 Patients

PURPOSE: Isolated lambdoid synostosis is the rarest form of craniosynostosis. This study examines long-term outcomes of lambdoid synostosis. METHODS: We performed a retrospective cohort study of patients with isolated nonsyndromic lambdoid craniosynostosis from 1993-2023. Primary outcomes were surgical burden and perioperative complications. Among patients with a postoperative scan at age 3.5 or older, we conducted volumetric, linear, and angular analyses on earliest and most recent CT scans, as well as age- and sex-matched normal control scans. Frontofacial features were assessed by craniofacial surgeons using long-term clinical photos. RESULTS: Mean age at first surgery was 1.3±1.2 years. 27 (84%) underwent 1 cranial vault surgery, 3 (10%) underwent 2, and 1 (3%) underwent 3. Mean age of patients included in the morphometric analysis (n=12) was 9.7±5.9 years at postoperative scan. Preoperatively, the lambdoid cohort had a lower posterior vault volume than normal controls (0.76 versus 0.95, p=0.03). Postoperatively, the lambdoid cohort continued to have a lower posterior vault volume ratio (0.90 versus 1.05, p=0.02) while demonstrating a greater cranial base angle than the control cohort (3.8 versus 1.5 degrees, p=0.02). Middle vault (0.89 versus 0.98, p=0.01) and posterior vault volume ratios (0.85 and 1.02, p=0.002) were lower, while posterior fossa defection (167.6 versus 162.1 degrees, p=0.03) and cranial base angles (4.1 versus 1.8 degrees, p=0.01) were greater in the lambdoid cohort at all time points. Frontofacial feature analysis results are forthcoming. CONCLUSION: Improved understanding of the long-term outcomes of isolated unilateral lambdoid synostosis may assist in guiding clinical and surgical management.