Bladder ultrasonography in the assessment of cauda equina syndrome in the emergency department: a literature review.

For cauda equina syndrome (CES), current clinical assessment in the emergency department usually involves perianal sensation (PAS) and anal tone (AT). Neither reliably predict magnetic resonance imaging (MRI) demonstrating a large central disc prolapse (MRI+). Other clinical examination findings increase the probability of MRI+. Other tests of sacral nerve root function include anal squeeze (AS) and the bulbocavernosus reflex (BCR). If BCR, PAS and AT, and AS are combined and they are all normal, CES can be excluded in almost all cases. Portable bladder ultrasonography is now commonly used to assess bladder function, particularly in measuring the post-void residual urinary volume (PVR). PVR is deemed normal at <50ml. If the PVR is <200ml and there are no objective signs, MRI+ is rare. If the PVR is >200ml, MRI+ is found in 43% of cases. The combined assessment of PAS, AT and AS (and BCR in selected cases) and PVR increases the specificity and sensitivity of a clinical diagnosis of CES (i.e. maximising MRI+ and minimising MRI-). Recommendations for when to perform MRI are made.