Chiari malformation in syndromic and non-syndromic lambdoid craniosynostosis: a longitudinal cohort study

BACKGROUND: We investigated the association between Chiari-I-Malformation (CM1) and all types of lambdoid-involved craniosynostosis, aiming to distinguish the impact of suture fusion from underlying diagnosis. METHODS: We conducted a retrospective cohort study of lambdoid craniosynostosis patients born between 2000 and 2024. Patients were classified as clinically non-syndromic or syndromic, the later subdivided into 'known craniosynostosis syndromes' (e.g., Crouzon/Pfeiffer, Apert), 'syndromic other' (e.g., ZIC1, HUWE-1), and clinically syndromic (without known mutation). RESULTS: Of 2341 patients with craniosynostosis, 133 had lambdoid involvement: 22 had isolated unilambdoid synostosis (11 non-syndromic, 11 syndromic), 4 had isolated bilambdoid synostosis (all syndromic), and 107 had multisuture synostosis (13 non-syndromic, 94 syndromic). All but 17 underwent early vault expansion; foramen magnum decompression was not routinely performed.CM1 occurred in 2/22 (9%) with isolated unilambdoid synostosis, 9/23 (39%) with multisuture synostosis with unilambdoid involvement, and 38/88 (43%) with bilambdoid involvement.Among multisuture cases, CM1 developed in 6/10 clinically syndromic, 6/12 'syndromic other', 6/13 non-syndromic, and 29/69 (42%) known craniosynostosis syndromes (including 23/49 (47%) Crouzon/Pfeiffer).Ultimately, 12/49 (24%) CM1-patients received CM1-associated surgery (2 clinically syndromic, 8 Crouzon/Pfeiffer, 2 'syndromic other'). CONCLUSIONS: Baseline MRI for CM1 screening appears not indicated in unisutural unilambdoid synostosis, regardless of syndromic diagnosis. Baseline MRI seems indicated for all multisuture cases with lambdoid involvement. Follow-up imaging may be limited to symptomatic patients, provided routine consultation with counseling on warning signs is done. The need for CM1-associated surgery appears more related to the underlying diagnosis than to the lambdoid fusion's impact on skull growth alone.