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Suspected incomplete cauda equina syndrome — MRCEM SBA MCQ

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HardProcedures, imaging and diagnosticsSuspected incomplete cauda equina syndromeMRCEM SBA

A 38-year-old woman presents at 22:00 with three days of low back pain radiating down both legs. Since this afternoon, she has had reduced sensation when wiping after using the toilet and has needed to strain to pass urine. Examination confirms reduced perineal pinprick sensation; leg power is preserved. She passes 280 mL of urine, and an immediate bladder scan shows a post-void residual of 70 mL. Emergency MRI is available at the hospital, and she has no MRI contraindication. What is the most appropriate diagnostic plan?

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Correct answer: A — Arrange emergency lumbar MRI during this attendance.

The new perineal sensory loss and change in urinary sensation and emptying, together with bilateral radicular pain, raise concern for **incomplete cauda equina syndrome**. Preserved leg power and the ability to void do not remove that concern. Crucially, a post-void residual of 70 mL is an adjunctive finding, not a test that excludes cauda equina compression. The UK GIRFT pathway calls for emergency MRI as soon as possible when recent cauda equina symptoms are suspected; it advises against using bladder-scan results alone to decide whether to request MRI. The patient should remain under emergency assessment, be kept nil by mouth in case surgery is needed, and be referred immediately to the spinal surgical service if MRI confirms compression. ([gloshospitals.nhs.uk](https://www.gloshospitals.nhs.uk/media/documents/GIRFT_CES_Guidelines_2023_EJRRVj5.pdf)) **B** and **C** delay the definitive investigation despite new sacral symptoms; the low residual does not justify either delay. **D** substitutes CT despite MRI being available and suitable; the national pathway considers CT or CT myelography when MRI is absolutely contraindicated. **E** gives a repeat bladder scan decision-making authority it does not have in this presentation. ([gloshospitals.nhs.uk](https://www.gloshospitals.nhs.uk/media/documents/GIRFT_CES_Guidelines_2023_EJRRVj5.pdf))

Reference: GIRFT National Suspected Cauda Equina Syndrome Pathway (2023) — https://www.gloshospitals.nhs.uk/media/documents/GIRFT_CES_Guidelines_2023_EJRRVj5.pdf Post-void bladder ultrasound in suspected cauda equina syndrome—data from medicolegal cases and relevance to magnetic resonance imaging scanning (2022) — https://pubmed.ncbi.nlm.nih.gov/35182176/