What remains of non-syndromic bicoronal synostosis?

More and more genetic syndromes are associated with bicoronal synostosis (BCS), making non-syndromic BCS (NSBCS) a shrinking entity. However, the numerical importance and clinical impact of syndromic BCS (SBCS) versus NSBCS have not been much studied. We retrospectively reviewed our experience with BCS over the last four decades in order to compare prevalence trends in SBCS and NSBCS. 195 patients were treated for BCS during the period 1978-2017: 104 (53.3%) were syndromic, 24 (12.3%) showed clinical and/or familial features suggesting a syndrome, although without final diagnostic confirmation, and 7 (3.5%) had associated extra-cranial malformations suggesting a syndromic context without identified genetic mutation; the remaining 61 (31.3%) were purely NSBCS. Surgery was required earlier in SBCS (21.7months, 95%CI 18.4-25.1) than in NSBCS (29.5months 95%CI 26.4-32.7). Prevalence of hydrocephalus and tonsillar herniation was significantly lower in NSBCS, and mortality concerned only SBCS. Prevalence of NSBC decreased significantly over the study period, likely because of more accurate testing, and decreased slightly over the last decade, possibly because of prenatal testing and abortion. NSBCS is now much less common than SBCS, and has a less aggressive clinical course, with lower rates of hydrocephalus, tonsillar herniation and mortality. This subgroup also deserves attention because it is likely that new discoveries are still to be made.