Head and Cranial Nerves
One should note the shape of the head and face, the range of motion of the cervical spine, and the intrinsic reflexes of the facial muscles. The skull and the neck vessels are auscultated, and the functions of the cranial nerves are tested.
3.3.1 Head and Cervical Spine
The examiner should first note the general appearance of the head and cervical spine (e.g., sunken temples in Steinert myotonic dystrophy) and the patient’s facial expressions (e.g., paucity of facial expression in Parkinson disease). Next, the range of motion of the cervical spine is tested: young, healthy persons should be able to turn the neck and head almost 90 degrees in either direction, so that the eye that is farther from the examiner disappears behind the root of the patient’s nose. Further, the patient should be able to incline the head laterally 45 degrees in either direction and to rotate it 60 degrees to the right or left when the neck is maximally flexed (this rotation occurs only at the atlantoaxial and atlanto-occipital joints).
Testing for meningismus is performed with the patient supine. This finding, if present, usually indicates meningeal irritation due to meningitis or subarachnoid hemorrhage, but is sometimes a reflex response to a mass lesion in the posterior fossa. Meningismus consists of isolated opposition to neck flexion, while the head can still be rotated. To test for meningismus, the examiner flexes the neck of the supine patient by passively bending the head forward. In genuine meningismus, the Lasègue sign (see section ▶ 13.1.2, Radicular Syndromes due to Intervertebral Disk Herniation) is usually positive, often with a positive Bragard sign as well. If attempted passive flexion of the neck also induces flexion of the lower limbs at the knee or hip joint, this is called a positive cervical Brudzinski sign. This sign is often accompanied by a positive Kernig sign: when the patient is in the sitting position, the knee cannot be passively extended, and when the patient is supine, passive straight leg raising induces reflex knee flexion.
Auscultation of the skull may reveal a pulse-synchronous bruit over an arteriovenous fistula or malformation. A carotid bruit may be due to stenosis.
The intrinsic reflexes of the facial musculature should always be examined. Tapping a finger placed over the lateral canthus of the patient’s eye normally induces contraction of the ipsilateral orbicularis oculi muscle. This reflex normally weakens (habituates) on repeated tapping; if it does not, or if there is excessively intense, bilateral contraction of the orbicularis oculi when the examiner taps on the patient’s glabella (the glabellar or nasopalpebral reflex), then Parkinson disease or another type of bilateral lesion of the corticobulbar pathways is probably present. Tapping on a tongue depressor held loosely on the patient’s lips may induce lip protrusion (positive snout reflex). The masseter reflex (jaw jerk reflex) is elicited by gently tapping the patient’s jaw from above when the patient’s mouth is half open. Another way to elicit this reflex is to tap on a tongue depressor laid on the patient’s mandibular teeth. Very intense contraction of the perioral musculature indicates bilateral involvement of the corticobulbar pathways; the most common cause is a microangiopathic lacunar state. The corneomandibular reflex (“winking jaw phenomenon”) consists of deviation of the slightly opened jaw when the cornea is touched. Its presence on only one side, or any marked asymmetry, implies an interruption of the ascending and descending brainstem pathways terminating in the pontomesencephalic reticular formation.
3.3.2 Cranial Nerves
Next, the cranial nerves are examined individually. ▶ Fig. 3.3 and ▶ Table 3.3 provide an overview of the anatomy and function of the 12 cranial nerves. The clinical syndromes associated with lesions of individual cranial nerves are presented systematically in Chapter ▶ 12. In the current chapter, we will describe the main examining techniques and a selection of the important abnormal findings that can be elicited with each technique.
Anatomic substrates (peripheral and central); innervated structures
Vestibulocochlear nerve (statoacoustic nerve, auditory nerve)
Abbreviation: CNS, central nervous system.
Fig. 3.3 The cranial nerves: overview of their sites of exit from the brainstem, components, and areas of innervation. I = olfactory nerve, II = optic nerve, III = oculomotor nerve, IV = trochlear nerve, V = trigeminal nerve, VI = abducens nerve, VII = facial nerve, VIII = vestibulocochlear nerve, IX = glossopharyngeal nerve, X = vagus nerve, XI = accessory nerve, XII = hypoglossal nerve. (Reproduced from Bähr M., Frotscher M. Neurologisch-topische Diagnostik. 9th ed. Stuttgart: Thieme; 2009.)
The first two cranial nerves (the olfactory and optic nerves) are actually not peripheral nerves at all, but rather are portions of the brain that happen to be situated in the periphery. The remaining 10 structurally and functionally resemble the other peripheral nerves of the body. They have motor, somatosensory, special sensory, and autonomic functions.
Cranial Nerve I: Olfactory Nerve
The sense of smell is tested individually in each nostril. The patient is asked to close his or her eyes and then to identify (or at least perceive) aromatic substances such as coffee, peppermint, cinnamon, or vanilla that are held under the open nostril. Three-quarters of normal individuals can correctly identify coffee grounds. If there is doubt about the patient’s ability to smell, asafetida (onion extract), a substance with an unpleasant odor, is used. Only a complete loss of the sense of smell (anosmia; see section ▶ 12.1), not a mere diminution of it, is neurologically relevant. Anosmia is most commonly a sequel of severe traumatic brain injury but may also be due to frontal tumors, particularly olfactory groove meningioma, or postinfectious abnormalities of the nasal mucosa, for example, after an upper respiratory “cold,” or in ozena.
If it is unclear whether anosmia is of neurologic origin, the patient is given a dilute ammonia solution to smell. The unpleasant irritation that this produces is mediated, not by the olfactory nerve, but by the trigeminal nerve. If the patient fails to react, then he or she is probably suffering either from an acute process affecting the nasal mucosa (e.g., acute rhinitis) or from a psychogenic disturbance. The anosmia is not neurogenic in either case.
Cranial Nerve II: Optic Nerve
Inspection of the optic nerve papillae (optic discs) with the ophthalmoscope is an important technique for assessment of the optic nerve. Abnormal pallor indicates an optic nerve lesion ( ▶ Fig. 3.4b). In addition, inspection of the fundus can provide evidence of subacutely or chronically elevated intracranial pressure: in papilledema, the papillae are raised and hyperemic, and their margins are blurred. Enlarged retinal veins indicate impaired venous drainage due to intracranial hypertension (cf. ▶ Fig. 12.3). A raised papilla with blurred margins can also be a sign of an inflammatory process affecting the optic nerve (see section ▶ 12.2.2, ▶ 18.104.22.168).
Fig. 3.4 Optic disc (papilla) of the right eye. a Normal disc. b Pale, atrophic disc. (These images are provided courtesy of the Department of Ophthalmology, University of Bern.)
Intracranial hypertension causes papilledema, which can be seen by ophthalmoscopy. Papilledema may, however, be absent if the intracranial hypertension is acute.
For neurologic purposes, visual acuity is usually tested with a wallchart seen from a distance. Patients who wear eyeglasses should wear them for this test.
Visual field testing is of special importance in neurology. The visual fields can be roughly assessed in the neurologist’s office or at the bedside with so-called finger perimetry (or digital confrontation; ▶ Fig. 3.5). The examiner sits directly in front of the patient and the patient fixes one eye on the examiner’s nose. The examiner then moves a finger in each of the four quadrants of the visual field, testing first the right eye, then the left. The patient is asked whether he or she can see the finger. This method can reveal a major visual field defect, for example, bitemporal hemianopsia or quadrantanopsia (see section ▶ 12.2.1). If the visual acuity is impaired, the visual fields of the two eyes should be tested separately; if the visual acuity is normal, the visual fields can be tested with both eyes open, because the lesion, if any, lies behind the optic chiasm and any visual field defect will therefore be homonymous.
Fig. 3.5 Testing the visual fields by digital confrontation. a Double simultaneous testing for the detection of visual hemineglect. b Individual testing of all four quadrants of the visual field of each eye.