From neuroimaging to patients' bench: what we have learnt from trigemino-autonomic pain syndromes.
Trigeminal autonomic cephalalgias (TACs) are primary headaches including cluster headache, paroxysmal hemicrania, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT). A number of neuroimaging studies have been conducted in last decade showing involvement of brain areas included in the pain matrix. Apart from pain matrix involvement, other neuroimaging findings data deserve special attention. The hypothalamic activation reported in the course of TAC attacks coupled with the efficacy of hypothalamic neurostimulation to treat drug-resistant TAC forms clearly indicate the posterior hypothalamus as a crucial area in TAC pathophysiology. In animal models this brain area has been shown to modulate craniofacial pain; moreover, hypothalamic activation occurs in other pain conditions, suggesting that posterior hypothalamus has a more complex role in TAC pathophysiology rather than simply being considered as a trigger. In contrast, hypothalamic activation may serve as a crucial area in terminating rather than triggering attacks. It also could lead to a central condition facilitating initiation of TAC attacks.