The most common pattern of injectate spread seen on MRI with both approaches to PCB was spread within the body of the psoas muscle around the lumbar branches (L2-4), with cephalad spread to the lumbar nerve roots. One catheter resulted in injectate between the psoas and quadratus lumborum muscles.

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Introduction Magnetic resonance imaging (MRI) provides excellent visualisation of distribution of injectate after peripheral nerve blocks. The aim of this study was to investigate the distribution of contrast media after psoas compartment block (PCB) performed via two approaches.Methods: Four volunteers were enrolled in a cross-over study.Volunteers underwent PCB with catheter placement performed via Capdevila's approach followed one week later by PCB performed as per Winnie's approach. MRI of contrast distribution was performed after each PCB. Images were subsequently reviewed by a radiologist unaware of PCB approach used.