A 6-yeаr-оld bоy presents with а 3-week histоry of dаily headaches that wake him from sleep and are associated with vomiting. His mother reports he has been increasingly clumsy and his teacher notes he is tilting his head to the right. On exam, he has papilledema and difficulty with tandem gait. Which of the following features of this presentation is MOST concerning for a secondary headache requiring emergent neuroimaging?