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Cauda Equina Syndrome is a true neurologic and surgical emergency. Unfortunately, no constellation of symptoms or exam findings is 100% sensitive. In fact, no single symptoms predicts the radiographic finding of cauda equina syndrome with an accuracy greater than 65%.
The most common symptoms are sciatica (96%), micturition dysfunction (89%), saddle anesthesia or hypoethesia (81%) and defecation dysfunction (47%).
Urinary postvoid residual (PVR) capacity is frequently used as a paraclinical exam of the urethral sphincter and detrusor muscle tone. A normal PVR is less than 50 mL, and is increased in cauda equina. It should be noted though that it can be increased in patients on narcotics as well.
MRI of the lumbosacral spine is the imaging study of choice, and contrast enhancement is not necessary in most cases, as it's frequently diskogenic in nature. In cases where an infiltrative cause is suspected, such as infection or metastasis, contrast may be useful.
References
Tarulli AW. Disorders of the Cauda Equina. Continuum Lifelong Learning Neurol 2015;21(1):146 158