For example, if a patient develops headache for the first time (or a new headache type appears), and at the same time a brain tumor is diagnosed, it could be logically concluded that headache is secondary to the tumor. In this case, one headache diagnosis shall be given: 7.4 Headache attributed to intracranial neoplasia. In other words, “a de novo headache occurring with another disorder recognized to be capable of causing a headache is always diagnosed as secondary”.

Important to mention that this remains true even when the headache has the characteristics of a primary headache (migraine, TTH, etc.). It could happen in clinical practice that a pre-existing primary headache worsens or becomes chronic in close temporal relation to an acute causative disorder. In this case, both the diagnoses of primary and secondary headache should be given, provided that there is good evidence that the disorder can cause headache. For example, 2.3.2 Chronic TTH not associated with pericranial tenderness and 10.3.4 Headache attributed to pre-eclampsia or eclampsia.

Secondary headaches are listed in Part II of the ICHD-3 beta (Chaps. 5, 6, 7, 8, 9, 10, 11, and 12) and include: