6. Headache attributed to cranial or cervical vascular disorder

Primary or secondary headache or both?
When a headache occurs for the first time in close temporal relation to a cranial or cervical vascular disorder, it is coded as a secondary headache attributed to that disorder. This remains true when the new headache has the characteristics of any of the primary headache disorders classified in Part One of ICHD-3 (beta). When a pre-existing headache with the characteristics of a primary headache disorder becomes chronic, or is made significantly worse (usually meaning a two-fold or greater increase in frequency and/or severity), in close temporal relation to a cranial or cervical vascular disorder, both the initial headache diagnosis and a diagnosis of 6. Headache attributed to cranial or cervical vascular disorder (or one of its subtypes) should be given, provided that there is good evidence that the disorder can cause headache.

Introduction
The diagnosis of headache and its causal link is easy in most of the vascular conditions listed below because the headache presents both acutely and with neurological signs and because it often remits rapidly. The close temporal relationship between the headache and these neurological signs is therefore crucial to establishing causation.
In many of these conditions, such as ischaemic or haemorrhagic stroke, headache is overshadowed by focal signs and/or disorders of consciousness. In others, such as subarachnoid haemorrhage, headache is usually the prominent symptom. In a number of other conditions that can induce both headache and stroke, such as dissections, cerebral venous thrombosis, giant cell arteritis and central nervous system angiitis, headache is often an initial warning symptom. It is therefore crucial to recognize the association of headache with these disorders in order to diagnose correctly the underlying vascular disease and start appropriate treatment as early as possible, thus preventing potentially devastating neurological consequences.
All of these conditions can occur in patients who have previously suffered a primary headache of any type. A clue that points to an underlying vascular condition is the onset, usually sudden, of a new headache, so far unknown to the patient. Whenever this occurs, vascular conditions should urgently be looked for.

For headache attributed to any of the vascular disorders listed here, the diagnostic criteria include whenever possible:

A. Headache fulfilling criterion C
B. A cranial or cervical vascular disorder known to be able to cause headache has been demonstrated
C. Evidence of causation demonstrated by at least two of the following:

    1. headache has developed in temporal relation to the onset of the cranial or cervical vascular disorder
    2. either or both of the following:

      a) headache has significantly worsened in parallel with worsening of the cranial or cervical vascular disorder
      b) headache has significantly improved in parallel with improvement of the cranial or cervical vascular disorder

    3. headache has characteristics typical for the cranial or cervical vascular disorder
    4. other evidence exists of causation

D. Not better accounted for by another ICHD-3 diagnosis.