CHAPTER 21 Brainstem and Multiple Cranial Nerve Syndromes he brainstem is a compact structure, with cra- the lower motor neurons of the CN nuclei. With a nial nerve (CN) nuclei, nerve fascicles, and few exceptions, CNs innervate structures of the head T long ascending and descending tracts all and neck ipsilaterally. A process affecting the brain- closely juxtaposed. Structures and centers in the reticu- stem long tracts on one side causes clinical abnormal- lar formation control many vital functions. Brainstem ities on the opposite side of the body. For this reason, diseases are serious and often life threatening. focal brainstem lesions are characterized by “crossed” Involvement of the intricate network of neural struc- syndromes of ipsilateral CN dysfunction and contra- tures often causes a plethora of clinical findings. lateral long motor or sensory tract dysfunction. For Brainstem syndromes typically involve dysfunction of instance, in the right side of the pons, the nuclei for one or more CNs. Deficits due to dysfunction of indi- CNs VI and VII lie in proximity to the right corti- vidual nerves are covered in the preceding chapters. cospinal tract, which is destined to decussate in the This chapter discusses conditions that cause dysfunc- medulla to innervate the left side of the body. The tion beyond the distribution of a single CN, involving patient with a lesion in the right pons will have CN more than one CN, or conditions that involve brain- findings on the right, such as a sixth or seventh nerve stem structures in addition to the CN nucleus or fasci- palsy, and a hemiparesis on the left. cles. The first part covers intramedullary disorders of This crossed deficit will often be associated with the brainstem, and the second part covers disorders that symptoms reflecting dysfunction of other brainstem involve multiple CNs in their extramedullary course. structures or their connections. Because of the rich Some may argue it is sufficient to recognize that a vestibular and cerebellar connections, patients with brainstem disorder exists and to define the process more brainstem disease often have dizziness or vertigo, precisely with an imaging study. However, some impor- unsteadiness, imbalance, incoordination, difficulty tant clinical conditions may cause major brainstem dys- walking, nausea, and vomiting. Pharyngeal and laryn- function without dramatically changing the appearance geal muscles are innervated by neurons in the brain- of the imaging study. Examples of processes easily missed stem, and patients often have dysarthria or dysphagia. radiographically include Wernicke’s disease, progres- Dysfunction of CNs III, IV, and VI or their connec- sive bulbar palsy (PBP), progressive supranuclear palsy, tions may cause ocular motility abnormalities. Unless basilar artery migraine, Whipple’s disease, syringobulbia, the process has impaired the reticular activating sys- olivopontocerebellar atrophy, and Gerstmann-Sträussler- tem, these patients are normal mentally—awake, Scheinker syndrome. With disorders causing multiple alert, able to converse (though perhaps dysarthric), CN deficits, the imaging studies are often not helpful. not demented, not confused, and not aphasic. The fourth ventricle and cerebral aqueduct lie nearby; if these are involved, patients may develop obstructive BRAINSTEM SYNDROMES hydrocephalus. Although most pathologic processes that involve the brainstem occur in other parts of the In the brainstem, descending motor tracts prior to brain, some disorders are characterized by primarily decussation, as well as ascending sensory pathways brainstem involvement (e.g., central pontine myelin- that have already crossed, lie in intimate relation to olysis, medulloblastoma, and olivopontocerebellar 345 Chapter 21.indd 345 10/30/2019 4:14:27 PM 346 SECTION D | THE CRANIAL NERVES atrophy). With vascular lesions, the clinical deficit horizontal gaze palsy, internuclear ophthalmoplegia depends on whether the occlusive process has involved (INO), or impaired taste, with contralateral corti- the paramedian perforating, short circumferential, or cospinal weakness and impaired lemniscal sensation. long circumferential branches of the basilar artery. Thrombosis of the lateral pontine branches of the From an anatomical standpoint, brainstem syn- basilar artery produces ischemia that may involve the dromes may be localized by considering the rostral middle and superior cerebellar peduncles, the ves- to caudal level and the medial to lateral level. The tibular and cochlear nuclei, the facial and trigeminal rostral to caudal localization is determined by the motor nuclei, the trigeminal sensory nucleus, and the CN involvement. Abnormality of CN III or IV, or a spinothalamic tract. Findings may include ipsilateral vertical gaze abnormality, indicates a midbrain lesion; cerebellar ataxia and dysfunction of CNs V, VII, and CN VI or VII, or a horizontal gaze palsy—a pontine VIII, with contralateral loss of pain and temperature lesion; CN VIII—a pontomedullary junction lesion; sensation on the trunk and extremities. Occlusion of and CNs IX, X, XI, or XII—a medullary lesion. the internal auditory artery causes unilateral deafness Because of the vast longitudinal extent of the spinal and impaired vestibular function. tract of CN V, facial sensory abnormalities can occur with lesions anywhere from the pons to the cervical spinal cord. CLASSICAL BRAINSTEM SYNDROMES The long motor tracts tend to lie medial, and the long sensory tracts lateral, in the brainstem. Somatic Many of the early neurologic pioneer clinicians motor nuclei (extraocular and hypoglossal) are para- described the clinical findings due to a focal process median; branchiomotor nuclei are more lateral. affecting the brainstem. These physicians practiced in Involvement of descending motor tracts or somatic an era when disorders such as tuberculoma, syphilitic motor nuclei indicates medial lesions; involvement of gumma, and tumor were seen much more often than long sensory tracts, branchiomotor nuclei, and special today. Many of the classical brainstem syndromes sensory nuclei indicates lateral lesions. The cerebel- as originally described were not due to ischemia, lar peduncles also lie laterally. The alar plate–derived and the effects of tuberculoma, gumma, and similar sensory nuclei lie laterally and are separated from the lesions are not limited to vascular distributions. Some basal plate–derived motor nuclei by the sulcus limi- degree of mismatch has therefore resulted between tans (Figures 11.2 and 11.4). Paramedian perforators the classic descriptions and the current environment from the basilar artery perfuse the midline structures; when most brainstem syndromes are due to ischemia. circumferential arteries perfuse the lateral structures. There has also been significant drift of many of the There are therefore medial and lateral medullary eponymic syndromes through failure to honor pre- syndromes; medial and lateral inferior, middle, cisely the original descriptions. Liu et al. pointed out and superior pontine syndromes; and the midbrain the variability in textbook descriptions of Claude’s, syndromes. The posterior inferior cerebellar artery Benedikt’s, and Nothnagel’s syndromes and noted (PICA) supplies the lateral medulla; the anterior the difference in textbook descriptions compared inferior cerebellar artery (AICA) supplies the inferior to the original papers. Box 21.1 contains a discus- lateral pons; and the superior cerebellar artery (SCA) sion of the classical eponymic brainstem syndromes, supplies the superior lateral pons. Paramedian lesions largely from a historical perspective, and Table 21.1 are typically lacunar; lateral lesions are more often summarizes the clinical features. from disease of the larger circumferential vessels. The Wallenberg described the lateral medullary syn- lateral medullary and pontine syndromes are often drome (LMS), the most common form of brainstem referred to by their vascular territory designations: stroke. Wallenberg’s original patient had an occlusion PICA, AICA, and SCA. of the PICA, but LMS is most often due to isch- Occlusion of medial pontine branches of the emia in the PICA distribution because of vertebral basilar artery may cause involvement of the nuclei of artery occlusion (Figure 21.1). Typical manifestations CNs VI and VII or their emerging fibers, the medial include vertigo, nausea and vomiting, nystagmus, longitudinal fasciculus (MLF), the corticospinal hoarseness, dysphagia, dysphonia, singultus, ipsi- tract, the medial lemniscus, and the pontine parame- lateral hemiataxia, and numbness of the ipsilateral dian reticular formation. Clinical manifestations may face and contralateral body. Occipital headache or include ipsilateral facial nerve palsy, abducens palsy, pain in the back of the neck may occur at the onset; Chapter 21.indd 346 10/30/2019 4:14:27 PM CHAPTER 21 | BRAINSTEM AND MULTIPLE CRANIAL NERVE SYNDROMES 347 BOX 21.1 Classical Brainstem Syndromes Midbrain Syndromes the midbrain tectum and is often neoplastic. Weber described a patient with a hematoma of one Nothnagel’s original patient had a pineal sarcoma. cerebral peduncle, which damaged the corticospi- Pontine Syndromes nal and corticobulbar tracts and the exiting third Millard and Gubler separately described patients nerve. The patient had a contralateral hemipare- with an ipsilateral lower motor neuron facial nerve sis involving face, arm, and leg and an ipsilateral palsy and contralateral hemiparesis due to a lesion complete third