Paediatric ED calls: acute scrotal pain

The referral

Paediatric ED registrar, 05:40: 'Fifteen-year-old boy, woke an hour ago with sudden severe left testicular pain and vomited. The testis looks high and he will not let me touch it. I have asked for an ultrasound; can you see him?'

15-year-old boy, previously well, no medications; his mother is with him.