Urgent decisions and a tight spot: embolic infarction of a herniated cerebellar tonsil

A previously well 30-year-old woman presented at 17:30 with a sudden onset of dizziness, ataxia and headache. She was initially investigated with a CT scan of the brain and lumbar puncture, which yielded no diagnosis. Subsequent MR scan revealed multiple posterior circulation infarcts, along with a previously undiagnosed Arnold-Chiari 2 malformation with an associated syrinx of her cervical and thoracic spine. The infarct involved one of the herniated cerebellar tonsils. Oedema of an infarct in the herniated tonsils caused compression of the medulla at the foramen magnum, with associated neurological symptoms including Lhermitte's phenomenon and headache on valsalva manoeuvre. Owing to these symptoms a surgical decompression was performed. The most likely aetiology of her stroke was determined to be a paradoxical embolus via patent foramen ovale.