Pathophysiology of Headache: Primary Headaches, Secondary Headaches
Primary headaches are migraine, cluster and tension headache. Primary headaches are benign, chronic and not life threatening. Headache is considered primary when a disease or other medical condition does not cause the headache. Most primary headaches fall into three main types: tension-type, migraine, and cluster headaches. Tension headache is the most common primary headache and accounts for 90% of all headaches. After tension headache, the second most frequently occurring primary headaches are Migraine. Migraine is referred to as a neurovascular headache because it is most likely caused by an interaction between blood vessel and nerve abnormalities. Cluster headache is a less common type of primary headache. Cluster headache sometimes referred to as a neurovascular headache, evidence now suggests that its cause may lie in the hypothalamus, a region deep in the brain that regulates, among other functions, the biologic rhythms of the body.
Secondary headaches are sometimes life threatening, may be secondary to metastasis or malignant cancer and cerebral bleeding. Early diagnosis of secondary headache is essential to avoid life-threatening complications. Secondary headache may be resulting from life threatening disease such as brain tumor, brain hemorrhage or head injury. Secondary headaches are classified based on etiology, not on symptom profile. Recent origin headache in a patient with history of disease known to cause intracerebral complications must be further investigated. Patients with pre-existing primary headaches sometimes experience exacerbations, which may follow further expensive investigations to rule out life threatening secondary headaches. In this circumstance, the known cause of headache may have worsened the pre-existing primary headache. Alternatively, it may have caused a new type of secondary headache. Secondary headaches are caused by other medical conditions, such as sinus infections, neck injuries, and strokes. About 2% of headaches are secondary to abnormalities or infections in the nasal or sinus passages, and they are commonly referred to as sinus headaches.
Traumatic injury to head and neck may cause headache which is classified as secondary headache. Head injury may cause subdural or epidural hematoma if ignored can lead to cerebral herniation and criticaloutcome of complications. Neck injury following work accident or auto accident causes occipital neuralgia and occipital headache. Intracranial arterial aneurysm or cerebral arterial swelling can cause severe throbbing headache. Infection such as meningitis or encephalitis can cause pain mostly in frontal and occipital area of head. In few cases of inflammatory disease of eye, ear, nose and sinuses pain simulating headache referred to temporal, frontal or occipital region. Shingles or post herpetic neuralgic pain of trigeminal nerve or facial nerve can also cause severe headache in frontal or temporal dermatome.