Causes:

Cluster headaches, like migraines, are likely due to an interaction of abnormalities in the blood vessels and nerves that affect regions in the face.

Abnormalities in the Hypothalamus

Evidence strongly suggests that abnormalities in the hypothalamus, a complex structure located deep in the brain, may play a major role in cluster headaches. Advanced imaging techniques have shown that a specific area in the hypothalamus is asymmetrical in these patients and is activated during a cluster headache attack.

The hypothalamus is involved in the regulation of many important chemicals and nerve pathways, including:

• Nerve clusters that regulate the body's biologic rhythms (its circadian rhythms)
• Serotonin and norepinephrine. These are neurotransmitters (chemical messengers in the brain) that are involved with well-and appetite.
• Cortisol (stress hormones)
• Melatonin (a hormone related to the body's response to light and dark)
• Beta-endorphins (substances that modulate pain)

By some not completely understood mechanism, the trigeminal nerve is also involved.

Circadian Abnormalities. Cluster attacks often occur during specific sleep stages. They also often follow the seasonal increase in warmth and light, beginning in summer and ending in the fall. Researchers have therefore focused attention on circadian rhythms, and in particular small clusters of nerves in the hypothalamus that act like biologic clocks.

The most important nervous cluster is the suprachiasmatic nuclei (SCN), which appears to help coordinate the body's activities (sleep/wake) with the environment (dark/light). Some studies support the idea that some failure in this biologic pacemaker may impair the pain control system and cause these terrible attacks.

The hormone melatonin is also involved in the body's biologic rhythms.

Dilation of Blood Vessels

Cluster headaches are associated with dilation (widening) of blood vessels and inflammation of nerves behind the eye.

Cluster headaches may be caused by blood vessel dilation in the eye area. Inflammation of nearby nerves may give rise to the distinctive stabbing, throbbing pain usually felt in one eye. The trigeminal nerves branch off the brainstem behind the eyes and send impulses throughout the cranium and face.

What causes these events and how they relate to cluster headaches are still unclear. Because blood vessel dilation appears to follow, not precede, the pain, some action originating in the brain is likely to be part of the primary process.

Abnormalities in the Sympathetic Nervous System

Some evidence suggests that abnormalities in the sympathetic (also called autonomic) nervous system may contribute to cluster headaches. This system regulates non-voluntary muscle actions in the body, such as in the heart and blood vessels.