Secondary
Vascular: ICH, SAH, CVST, malignant HTN
Infection: meningitis, encephalitis
Trauma: head/neck
Autoimmune: GCA
Metabolic: hypoxia, hypercapnia, CO poisoning
Idiopathic: trigeminal neuralgia, IIH, AACG
Iatrogenic: post-LP
Neoplastic: CNS tumour
Drugs: medication overuse headache, cocaine, alcohol
Functional: somatisation disorder