Sudden onset of subarachnoid block after subdural catheterization: a case of arachnoid rupture?

We describe a patient who received an apparently uneventful extradural block in labour but developed rapid extension of neural block within minutes of receiving her first incremental dose 2 h later. Computed contrast tomography revealed radio-opaque dye within both the subdural and subarachnoid spaces, but none within the extradural space. This case report demonstrates that subdural spread of low-dose local anaesthetics is not always clinically distinguishable from extradural analgesia and that the arachnoid membrane may subsequently perforate with potentially serious consequences.