Trigeminal Autonomic Cephalalgia
The trigeminal autonomic cephalalgia (TAC) headaches are similar to cluster headache but differ with respect to the duration and frequency of symptoms. They likely share a similar pathophysiology. Each painful episode tends to be of shorter duration although the frequency of episodes is higher. The sensation of restlessness or agitation can occur in both TACs and cluster headaches. The primary differences between TACs and cluster headache are the increased frequency of painful episodes with TAC and the fact that TAC can often be treated with indomethacin. Additionally the ability to prevent an episode with indomethacin is one of the diagnostic criteria for TAC headaches . Trigeminal autonomic cephalalgia can be further divided into paroxysmal hemicrania and hemicrania continua, the difference related to the duration of painful episodes and periods or remission.
Giant Cell Arteritis
Failure to recognize and treat giant cell arteritis (GCA) can lead to serious and permanent consequences. New onset headache without a prior headache history should alert the surgeon to the potential for GCA. Giant cell arteritis, an inflammatory condition of the cranial arteries, should be considered in any patient over the age of 50 with a new type of headache . If untreated, giant cell arteritis can lead to permanent vision loss. Serum erythrocyte sedimentation rate and C-reactive protein should be ordered and are typically abnormally high. If laboratory workup is equivocal or unclear and the suspicion remains high for giant cell arteritis, then a temporal artery biopsy should be pursued. The initiation of treatment for giant cell arteritis should not be delayed, and high-dose corticosteroids should be started immediately if there is suspicion for this disease  (Box 1.6).
Box 1.6: Giant Cell Arteritis 
A. Any new headache fulfilling criterion C
B. Giant cell arteritis (GCA) has been diagnosed
C. Evidence of causation demonstrated by at least two of the following:
- 1. Headache has developed in close temporal relation to other symptoms and/or clinical or biological signs of onset of GCA or has led to the diagnosis of GCA
- 2. Either or both of the following:
- (a) Headache has significantly worsened in parallel with worsening of GCA
- (b) Headache has significantly improved or resolved within 3 days of high-dose steroid treatment
- 3. Headache is associated with scalp tenderness and/or jaw claudication
D. Not better accounted for by another ICHD-3 diagnosis