( ( In ( ( the ( past ( , ( primary headache ) ) ) ) ( thought ( to ( be ( due ( to ( ( painful swelling ) ( of ( the blood ) ) ) ) ) ) ) ) ) ) ( ( vessels ( of ( the head ) ) ) ( ( has ( been ( called ( migraine ( or ( vascular headache ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (JJ past) (, ,) (JJ primary) (NN headache)) (VP (VBN thought) (S (VP (TO to) (VP (VB be) (ADJP (JJ due) (PP (TO to) (NP (NP (JJ painful) (VBG swelling)) (PP (IN of) (NP (DT the) (NN blood)))))))))))) (NP (NP (NNS vessels)) (PP (IN of) (NP (DT the) (NN head)))) (VP (VBZ has) (VP (VBN been) (VP (VBN called) (NP (NN migraine) (CC or) (NN vascular) (NN headache))))) (. .)))
In the past, primary headache thought to be due to painful swelling of the blood vessels of the head has been called migraine or vascular headache.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN blood) (NNS vessels)) (PP (IN in) (NP (DT the) (NN head)))) (VP (VBP dilate)))) (, ,) (NP (NP (DT a) (NN migraine)) (, ,) (NP (DT a) (JJ severe) (NN headache)) (, ,)) (VP (MD can) (VP (VB occur))) (. .)))