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Background:Bilambdoid and sagittal synostosis (BLSS), also called “Mercedes Benz synostosis,” is a multisutural craniosynostosis that has been described as a specific entity. However, this synostotic pattern can also be found in syndromic craniostenosis. To better define this entity we reviewed our experience with bilambdoid and sagittal synostosis.Methods:We searched our prospective database for cases of bilambdoid and sagittal synostosis among all types of craniosynostosis. Two groups were distinguished – patients with isolated BLSS and the group of syndromic craniostenosis for whom BLSS was observed at initial presentation. We reviewed the clinical findings, associated diseases, and their management specifically for isolated BLSS patients.Results:Thirty-nine patients were diagnosed with bilambdoid and sagittal synostosis among 4250 cases of craniosynostosis treated in our department over a period of 42 years. Among them, 8 were finally diagnosed as Crouzon syndrome. Of the 31 patients identified with isolated bilambdoid and sagittal synostosis, 25 (81%) were males and 6 (19%) were females. The average age at diagnosis was 17 months. At diagnosis, 16% of the population presented with papillary edema and 58% posterior digitate impressions. Two types of craniofacial dysmorphy were observed – a pattern with narrow occiput (71% of cases) and a pattern with dolichocephaly (29% of cases). Cerebellar tonsillar herniation was the most frequently associated malformation (61% of the isolated BLSS). Surgical management evolved during the years, and several surgical techniques were used to treat patients with BLSS, including isolated biparietal vault remodeling, posterior vault remodelling, and posterior vault expansion with internal or external distraction. In some cases, a craniocervical junction decompression was also performed. The mean follow-up was 82 months (7 years). The overall mental development was within normal limits in most children, but a mental delay was found in 25%.Conclusion:Bilambdoid and sagittal synostosis constitute an isolated entity in almost 80% of the cases, whereas in the remaining 20% it is part of a faciocraniosynostosis syndrome. Two phenotypes may be found. Early surgical management is indicated, and several techniques can be used in this heterogeneous population. A cerebellar tonsillar prolapse is present in a majority of cases.