Posterior cranial fossa dimension and descent of cerebellar tonsils after arachnoid cysto‐peritoneal shunting

Abstract

Background Descent of cerebellar tonsils (CT) has been reported following shunting of supratentorial (ST) arachnoid cyst. The phenomenon has been attributed exclusively to a difference in pressure gradient between ST space and the posterior fossa (PF). We aimed our study at determining the association between the posterior cranial fossa volume (PCFV) in this phenomenon.Materials and Methods We compare posterior fossa volume in two children with shunted left arachnoid cyst but Chiari like condition in one.Results The PCFV was 137.7c.c in the chiari 1 patient compared with 145.6cc in the control group peer. The PCFV area in the chiari 1 patient was 204.9cm2 while the control had 207.9cm2.The supratentorial volume (SV) measured 1055.1c.c in the chiari 1 patient compared with 898.2c.c in control group peer. The area of the supratentorial region was 742.9cm2 in the chiari 1 patient versus 687.7cm2 in the control. The prepontine and pre‐medullary cistern measured 4.4mm in the chiari 1 patient while control was 6.3mm and 7.7mm respectively.The percentage ratio of the posterior cranial fossa volume to the supratentorial volume (PCFV/SV X 100) in the chiari 1 patient was 13.0 versus 16.4 in the control.Conclusion Our findings emphasize the relevance of skull anatomy on the development of Chiari like condition.