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Headache occurs in all age groups and accounts for 1% to 2% of emergency department evaluations and up to 4% of medical office visits; the causes are myriad (Table 6-1). Although most often a benign condition (especially when chronic and recurrent), headache of new onset may be the earliest or the principal manifestation of serious systemic or intracranial disease and therefore requires thorough and systematic evaluation.
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An etiologic diagnosis of headache is based on understanding the pathophysiology of head pain; obtaining a history, with characterization of the pain as acute, subacute, or chronic; performing a careful physical examination; and formulating a differential diagnosis.
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PATHOPHYSIOLOGY OF HEADACHE & FACIAL PAIN
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PAIN-SENSITIVE STRUCTURES
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Headache is caused by traction, displacement, inflammation, or distention of the pain-sensitive structures in the head or neck. Isolated involvement of the bony skull, most of the dura, or most regions of brain parenchyma does not produce pain.
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A. Pain-Sensitive Structures Within the Cranial Vault
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These include the venous sinuses (eg, sagittal sinus); anterior and middle meningeal arteries; dura at the base of the skull; trigeminal (V), glossopharyngeal (IX), and vagus (X) nerves; proximal portions of the internal carotid artery and its branches near the circle of Willis; brainstem periaqueductal gray matter; and sensory nuclei of the thalamus.
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B. Extracranial Pain-Sensitive Structures
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These include periosteum of the skull; skin; subcutaneous tissues, muscles, and arteries; neck muscles; second (C2) and third (C3) cervical nerves; eyes, ears, teeth, sinuses, and oropharynx; and mucous membranes of the nasal cavity.
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RADIATION OR PROJECTION OF PAIN
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The trigeminal (V) nerve carries sensation from intracranial structures in the anterior and middle fossae of the skull (above the cerebellar tentorium). Discrete intracranial lesions in these locations can produce pain that radiates in the trigeminal nerve distribution (Figure 6-1).
The glossopharyngeal (IX) and vagus (X) nerves convey sensation from part of the posterior fossa; pain originating in this area may also be referred to the ear or throat, as in glossopharyngeal neuralgia.
The upper cervical (C2-C3) nerves transmit stimuli from infratentorial and cervical structures; therefore, ...