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Lower Cranial Nerve Dysfunction
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Lower Cranial Nerve Dysfunction
CN IX Glossopharyngeal Nerve Function, Assessment & Dysfunction
Assessment: Gag Reflex
CN IX: Glossopharyngeal Nerve
Visceral Sensory: Innervates the oropharynx, carotid body and sinus, posterior 1/3 of the tongue, middle ear cavity and Eustachian tube.
Somatic Sensory: Provides taste sensation to the posterior 1/3 of the tongue.
Parasympathetic: Provides parasympathetic innervation to the parotid gland.
Motor: Innervates the stylopharyngeus muscle of the pharynx.
Dysfunction: Absent gag reflex
Fun Fact; Glossopharyngeal neuralgia may be associated with syncope in 10% of the cases due to reflex bradycardia (efferent limb of reflex via vagal nerve) or occasionally induced by swallowing.
CN X Vagus Nerve Function, Assesment & Dysfunction
The vagus nerve is the longest cranial nerve. It contains motor and sensory fibers and, because it passes through the neck and thorax to the abdomen, has the widest distribution in the body. It contains somatic and visceral afferent fibers, as well as general and special visceral efferent fibers.
CN X: Vagus Nerve
-Motor: Innervation of pharynx, larynx and soft palate.
-Sensory: Innervates the skin of the external acoustic meatus and the internal surfaces of the laryngopharynx and larynx. Provides visceral sensation to the heart and abdominal viscera.
-Special Sensory: Provides taste sensation to the epiglottis and root of the tongue.
-Parasympathetic: Innervates the smooth muscle of the trachea, bronchi and gastro-intestinal tract and regulates heart rhythm.
Assessment: CN IX and X are evaluated together.
-Have patient say "ah" and the palate should elevate symmetrically with no sign of uvula deviations and patient will likely gag.
Dysfunction Assessment Findings:
-One side is paretic and the uvula is lifted away from the paretic side.
- Of note: Bilateral absence of the gag reflex is common among healthy people and may not be significant.
The spinal accessory nerve innervates two muscles – the sternocleidomastoid and trapezius.
Purely Motor Nerve:
-Sternocleidomastoid: Lateral flexion and rotation of the neck when acting unilaterally, and extension of the neck.
-Trapezius; It is made up of upper, middle, and lower fibers. The upper fibers of the trapezius elevate the scapula and rotate it during abduction of the arm. The middle fibers retract the scapula and the lower fibers pull the scapula inferiorly.
CN XI Accessory Nerve Function, Assessment & Dysfunction
CN XI: Spinal Accessory Nerve
Assessment:
-Look for wasting of muscle and have patient rotate their head and shrug their shoulders, both normally and against resistance.
Dysfunction:
-Muscle wasting and partial paralysis of the sternocleidomastoid, resulting in the inability to rotate the head or weakness in shrugging the shoulders. Damage to the muscles may also result in an asymmetrical neckline.
The spinal accessory nerve is notable for being the only cranial nerve to both enter and exit the skull.
Purely Motor Nerve; The hypoglossal nerve is responsible for motor innervation of the vast majority of the muscles of the tongue (except for palatoglossus).
CN XII Hypoglossal Nerve Function, Assessment & Dysfunction
Assessment: Protrude Tongue, push tongue against cheek.
CN XII; Hypoglossal Nerve
Dysfunction: Deviation of the tongue towards the damaged side on protrusion, as well as possible muscle wasting and fasciculations (twitching of isolated groups of muscle fibers) on the affected side.
It's rare to see damage to the twelfth cranial nerve on its own
Cause of LCN Dysfunction
Causes of LCN Dysfunction
-Hemmorhage of blood with Vascular Compression
-Trauma; TBI, Skull base fracture
-Ischemic Lesions of Medulla; Occlusion of the distal portion of Vertebral artery and PICA
-Tumor/Neoplasm that infiltrate the brainstem or cause compression
-Infectious; Sarcoidosis
-Metabolic; Diabetes
-Genetic; ALS
-Nutritional; Vitamin B12 Deficiency
-Degenerative; Eagle-syndrome (elongated styloid process)
-Iatrogenic; s/p Carotid or Thyroid surgery
-Immunological; MS or GBM
Symptoms of LCN Dysfunction
Symptoms of Lower Cranial Nerve Dysfunction:
-Dysphagia and need for acute and often a long-term Feeding Tube.
-Coughing and Inability to control secretions with need for frequent suctioning and often trach placement to protect airway.
-Dysarthria, Hoarse Voice, Hypophonia
-Autonomic Dysfunction with Gastrointestinal Compromise, Heart Rate, Breathing and Blood Pressure variabiliity that can lead to Dizziness and Syncope
-Weakness of Trapezius, Sternocleimastoid and Tongue Muscles.
-Neuralgic Pain rare but sometimes seen with glossopharyngeal involvement with paroxysmal painful attacks of electric shock-like sensation to the ear, pharynx, neck, tonsil or base of tongue.
Symptomatic Management
Treatment Modalities
Prevention is key with early neurosurgical intervention by one of our many talented neurosurgeons!!!
BUT: Long-term symptom management is critical.
-Patient/Family/Caregiver Support and Education
-Feeding Tube Placement (Acute vs. Long-term)
-Trach placement for airway protection
-Frequent Tracheal and Oral suctioning
-Proper identification/diagnosis of autonomic instability and management; May need to avoid BB etc.
-Meds for drooling; SL Atropine, Glycopyrrolate, Scopolamine Patch, or even Botox into the salivary gland. *Weigh risks and benfits of using anti-cholinergics*
-Speech and Dietary Therapy to assist with speech and swallowing and prevent malnutrition/anemia.
-Bowel Regimen
-Sleep Support
Imaging Modalities
MRI; GOLD STANDARD
-MRI's with contrast are preferred to view the soft tissues of the posterior fossa and cranial nerves.
-The Axial view is better to see CN VII-XII. (Coronal View is best for CN I-VI).
-Have to be very knowledgeable about the expected location and trajectory from the nuclear to the nerve root entry zone.
-CT allows, usually, an indirect view of the nerve and is useful to demonstrate the intraosseous segments of cranial nerves, the foramina through which they exit skull base and their pathologic changes.
-The best way to detect cranial nerve pathology is to compare the size and signal intensity of the paired nerves.
-SSFP MRI; steady-state free procession (SSFP) sequences are good for the visualization of the cisternal spaces of cranial nerves. These sequences typically show dark cranial nerves against a background of bright CSF.
-Tractography is a 3D modeling technique used to visually represent nerve tracts to assist with posterior fossa brain tumor resections.
Examples of Imaging
Axial T2-weighted MRI