Acute massive posterior stroke with tonsillar herniation in a scuba diver.

A transient female passenger in her 40s presented to the emergency department (ED) exhibiting drowsiness post-scuba diving. Despite normal initial vitals, she reported dizziness, sleepiness, and occipital headache. A computed tomography (CT) scan showed a severe posterior circulation acute infarction affecting various brain regions, resulting in significant mass effects and complications like 4th ventricle compression, cerebellar tonsillar herniation, and hydrocephalus. Extensive diagnostic tests, blood workup, and stroke evaluations revealed normal findings, except for an incidental patent foramen ovale (PFO). Collaboration with neurosurgery led to her transfer for life-saving extraventricular drain (EVD) insertion and posterior fossa decompression. Treatment included right-side EVD insertion, suboccipital craniectomy, and foramen magnum decompression. Postoperatively, she was extubated the next day, alert, without focal neurological deficits. Upon EVD removal, a repeat CT head scan showed regression of mass effect. She was discharged home safely after 16 days, fully ambulating.