Given the ubiquitous (but mistaken) belief that headaches are usually caused by eye problems, ophthalmologists will see many patients with headache as the chief complaint. Therefore, the ophthalmologist needs to be familiar with common primary headache syndromes. The neurologist, on the other hand, has broad experience in the area of primary headaches, but needs to be well-versed in ocular, orbital, and other secondary causes of headache and face pain.
Pain and sensation from the eye and face, as well as intracranial structures, are mediated by the trigeminal nerve, which is directly or indirectly involved in all pain syndromes of neuro-ophthalmic interest. After exploring trigeminal neuroanatomy and its clinical implications, clinical conditions causing facial numbness, headache, and other head and ocular pain are discussed.
The trigeminal nerve (cranial nerve [CN] V) is a mixed cranial nerve: In addition to its major sensory function, CN V provides motor innervation to the muscles of mastication. At its origin CN V does not contain autonomic fibers; however, parasympathetic innervation to the lacrimal gland and sympathetic fibers to the pupillary dilator travel briefly with peripheral segments of the nerve.
The trigeminal system also innervates cranial blood vessels (the trigeminovascular system), and in this role has the unusual ability to act as an effector as well as a sensor. Trigeminally innervated cranial blood vessels dilate after a nociceptive stimulus by way of chemical mediators released from the same sensory terminals that were activated by the stimulus; in this circumstance trigeminal nerves are serving as both the afferent and efferent limbs of a reflex. It is referred to as the trigeminovascular reflex and is believed to play an important role in the pathogenesis of primary headache syndromes such as migraine.
The sensory portion of the trigeminal nucleus is markedly elongated and stretches from the midbrain to the upper cervical segments in the spinal cord where it blends with the root entry zone of the spinal cord (Figure 13–1). The trigeminal nucleus is a major sensory integration area and receives input from more than CN V; it has afferent connections with the somatosensory cortex above, with spinal cord afferents below, from the reticular formation and red nucleus, in addition to sensory input from other cranial nerves (CNs VII, IX, and X).
Central and peripheral trigeminal representation of facial sensation.
(A) The central organization of the trigeminal nucleus corresponds to dermatomes that are ...