Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:secondary hydrocephalus, presumably by dysfunction of the nigrostriatal dopaminergic system (and consequent decrease in dopamine) induced by hydrocephalus [27] or by direct compression of the rostral midbrain by the expanding third or fourth ventricles [3, 13, 40].
Category: