LAUSR

INTRODUCTION Arachnoid cysts are benign cerebrospinal fluid collection within a duplication of arachnoid membrane and, when found in the retrocerebellar site, they may be associated with tonsils herniation. This rare situation of coexisting retrocerebellar arachnoid cyst (AC) and Chiari malformation type 1 (CM-1) have been previously reported in few cases (10 patients) with syringomyelia and hydrocephalus described to be the most relevant issues. The aim of this paper is to describe 3 pediatric cases of this condition with a systematic review of the literature, underlining the importance of surgical management tailored to the pathogenic mechanism. RESULTS A case of a 10 months-old baby with coexisting AC and CM-1 with tri-ventricular hydrocephalus treated with endoscopic third ventriculostomy, a case of 1 a year-old baby with a huge retrocerebellar AC and CM-1 treated with a cysto-peritoneal shunt and a case of a 15 years old with retrocerebellar AC causing symptomatic CM-1 treated with C0-C2 decompression, AC fenestration and duraplasty have been described. A long-term follow-up have been reported. CONCLUSION Surgical management of coexisting ACs and CM-1 should not aim at the complete resolution of the cyst or of tonsils herniation, especially when pediatric patients are treated. Rather, the purpose of neurosurgeon should be to understand the underlying pathogenic mechanism and, then, restoring both the CSF flow in the posterior fossa and the dynamic equilibrium between ventricles, cyst and subarachnoid space.