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Suspected cauda equina syndrome with possible early pregnancy during lactation — DFSRH MCQ

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HardMRI SafetySuspected cauda equina syndrome with possible early pregnancy during lactationDFSRH

A 34-year-old woman presents 4 months after a term birth with acute severe lower-back pain, bilateral sciatica, new saddle sensory loss and urinary retention. Emergency assessment raises strong suspicion of cauda equina syndrome, and immediate MRI of the lumbosacral spine is requested. The radiologist expects unenhanced sequences to answer the clinical question; gadolinium-based contrast would be considered only if an unexpected lesion required further characterisation. She is amenorrhoeic and breastfeeding her healthy term infant but is mixed feeding, so does not meet the criteria for lactational amenorrhoea as contraception. She has used no other contraception and had condomless intercourse 10 days ago. A high-sensitivity urine pregnancy test today is negative. Renal function is normal, and MRI screening identifies no implant, foreign body or other contraindication. She is concerned about both a possible early pregnancy and interruption of breastfeeding. Which is the most appropriate imaging plan?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Perform unenhanced MRI now in Normal operating mode, reserve gadobutrol for clinically essential information after joint risk–benefit assessment, and continue breastfeeding if it is administered

Explanation lettering: C = shown as B · E = shown as C · B = shown as E

The negative test 10 days after condomless intercourse does not exclude a very early pregnancy; testing is reliable for this purpose at least 21 days after the last intercourse. However, suspected cauda equina syndrome requires immediate imaging, so investigation must not be deferred. Current MHRA guidance supports clinically indicated MRI during pregnancy using Normal operating mode, minimised exposure and appropriate safety precautions. Gadolinium should generally be avoided in pregnancy and used only when clinically essential after collaborative assessment of maternal benefit and potential fetal risk. Here, unenhanced sequences are expected to answer the urgent question. A is unsafe because waiting another 11 days risks irreversible neurological injury. B is inappropriate because CT is less effective for assessing the cauda equina and introduces ionising radiation without solving the diagnostic problem. C correctly avoids delay and breastfeeding interruption but exposes a possibly pregnant patient to contrast that is not routinely required. D appropriately prioritises unenhanced MRI but gives unnecessary breastfeeding advice: commonly used macrocyclic gadolinium agents transfer poorly into milk and have low oral bioavailability, so breastfeeding need not be interrupted for a healthy term infant. E integrates urgency, possible early pregnancy, contrast restriction and lactation safety.

Reference: MHRA Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use (August 2026, fifth edition V5.0.2) — https://assets.publishing.service.gov.uk/media/601bd9dbe90e0711cb20c2d7/MRI_guidance_2021-4-03c.pdf Using contrast agents during breastfeeding (11 April 2025) — https://sps.nhs.uk/articles/using-contrast-agents-during-breastfeeding/ Doing a pregnancy test (Date not stated; checked 19 August 2026) — https://www.nhs.uk/pregnancy/trying-for-a-baby/doing-a-pregnancy-test/