The Lower Cranial Nerves

Here we consider the clinical presentations of dysfunction of cranial nerves IX−XII. Lesions of the glossopharyngeal and vagus nn. produce dysphagia, hoarseness, and dysphonia. Lesions of the accessory n., depending on their level, produce weakness of the sternocleidomastoid m. and trapezius m. Lesions of the hypoglossal n. produce ipsilateral weakness of the tongue.

Lesions of the Glossopharyngeal and

Vagus Nerves

Anatomy. The anatomical course and distribution of these nerves is described above on p. 18.

Typical deficits. A unilateral lesion of the glossopharyngeal and vagus nn. causes ipsilateral weakness of the soft palate and posterior pharyngeal wall, which is evident as the curtain sign (Fig. 11.23, see also Fig. 3.13, p. 26). The associated sensory deficit causes dysphagia and unilateral paralysis of the vocal cord causes hoarseness. The patient usually does not notice the loss of sensation in the external auditory canal or the loss of taste on the posterior third of the tongue.

Causes. Palsy affecting the ninth and tenth cranial nerves can be caused by infarction of the corresponding brainstem nuclei (e. g., in Wallenberg syndrome, p. ).

Lesions of the peripheral nerve trunks can be caused by a mass in the posterior fossa or by a bony fracture impinging on the nerves at their site of exit from the jugular foramen. In the latter case, the injury involves not only these nerves, but also the accessory n. (Siebenmann syndrome). Finally, isolated neuritis of these nerves can occur, e. g., in the setting of herpes zoster, or as a cryptogenic event.

Accessory Nerve Palsy

The anatomy and method of examination of the accessory n. are described above.

Typical deficits. A lesion of the purely motor main trunk of the accessory n. causes paralysis of the sternocleidomastoid m. and of the upper portion of the trapezius m. (Fig. 11.24). Lesions of the accessory n. in the lateral triangle of the neck, however, are much more common. These spare the sternocleidomastoid m. and weaken only the upper portion of the trapezius m., causing a shoulder droop and an externally rotated position of the scapula (i. e., tilting of the caudal angle of the scapula

a

Fig. 11.23 Curtain sign revealing left-sided palatopharyngeal weakness in a 36-year-old patient with Wallenberg syndrome. a Normal appearance at rest. b Elicitation of the gag reflex is fol-

b

lowed by pulling of the palate and posterior pharyngeal wall to the unaffected right side. (From: Mumenthaler M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986.)

Hypoglossal Nerve Palsy

The anatomy and technique of examination of the hypoglossal n. are described above on p. 27.

Typical deficits. The ipsilateral half of the tongue is paretic and, in the course of time, becomes atrophic. When the tongue is protruded, it deviates to the paretic side. This condition is illustrated in Fig. 3.16, p. 27.

Causes. Unilateral hypoglossal nerve palsy is usually due to a bony fracture or a mass lesion—rarely, a congenital malformation—in the posterior cranial fossa. Carotid dissection is another possible cause. Rarely, isolated hypoglossal nerve palsy arises as a postinfectious or cryptogenic event.

Differential diagnosis. Unilateral tongue weakness can also be of central origin, i. e., due to a lesion of the corticobulbar pathway to the hypoglossal nerve nucleus (Fig. 11.18). Central weakness is unaccompanied by atrophy.

Bilateral tongue weakness and atrophy in the setting of true bulbar palsy (p. 80, p. 155) is due to progressive loss of motor neurons in the nucleus of the hypoglossal nerve on both sides of the medulla. The observable abnormalities are slowly progressive and accompanied by fasciculations of the tongue.

Tongue weakness in pseudobulbar palsy (p. 80) is due to bilateral, usually ischemic damage of the central corticobulbar pathways. Because the lesion is central, no atrophy or fasciculations are seen. Examination reveals dysarthria, dysphagia, and abnormal prominence of the perioral reflexes.

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c

Fig. 11.24 Proximal left accessory nerve palsy with weakness of both the sternocleidomastoid m. and the trapezius m. a Even in the resting position, the upper edge of the trapezius m. is visibly thinner than on the right side, and the left sternocleidomastoid m. is barely discernible. b When the patient turns her head to the left, the intact right sternocleidomastoid m. is clearly seen. c When the head is turned to the right, there is only faint contraction of the left sternocleidomastoid m. (From: Mumenthaler M.: Didaktischer Atlas der klinischen Neurologie. 2nd edn, Springer, Heidelberg 1986.)