Introduction

• Cranial nerve deficits may be indicative of peripheral involvement of individual nerves or of central lesions.
• As peripheral nerve neuritides they resemble the peripheral neuropathies in pathology and etiology Nerve trauma neuropathy.
• Cause: may be caused by trauma or be idiopathic, immunological, neoplastic or inflammatory.

Cavernous sinus syndrome

• With lesions of the cavernous sinus (venous structure that lies on the floor of the skull and encircles the pituitary) abnormalities of CNs III, IV, VI and the ophthalmic branch of V as well as sympathetic input to the eye may be seen.
• Causes in older dogs include neoplasia, both primary and metastatic and granulomatous disease.

Trigeminal nerve disease

• Trigeminal nerve abnormalities can occur with infiltrating neoplasia (lymphosarcoma, leukemias) that involve a branch or the entire nerve.
• Other cranial nerves (VII) and the sympathetic system may be involved concurrently.
• Animals with systemic hematological neoplasia that develop cranial nerve abnormalities should be evaluated for extension of the tumor to these sites.
• The lesion is found with CT or MRI.
• Nerve sheath tumors may arise within the trigmenial nerve.
• Clinical signs of unilateral temporalis and masseter muscle ipsilateral to the lesion are most common.
• The lesion is found with CT and, more often, MR imaging.
• Surgical treatment can result in long-term resolution of the disease.

Facial nerve

• Facial paresis or paralysis is the most common abnormality seen with facial nerve disease. This can occur as an idiopathic condition (especially in Cocker Spaniels) as a result of otitis media/interna, with trauma, and with tumor of the middle ear canal.
• Hypothyroidism is an associated cause in some dogs.
• Hyperinsulinism (islet cell tumor) and other metabolic abnormalities may also present with facial paralysis.
• Rarely, primary tumor of VII (nerve sheath tumor, lymphosarcoma  , or meningiomas  involving the facial nerve are found.
• The opposite of a facial paresis, hemifacial spasm is suspected to be due to hypersensitivity of the facial nerve.
• Contrary to the situation with a facial paresis, the philtrum is deviated toward the affected side of the face. The ear on this side is often directed caudally and the palpebral fissure is smaller due to contraction of the muscles innervated by the facial nerve.
• Neoplastic, inflammatory and traumatic causes are possible.
• Hemifacial may also occur without obvious cause in dogs.

Vestibulocochlear nerve

• Older dogs (Canine Geriatric vestibular disease  ) are most commonly affected. No cause is defined.
• Clinical signs are of an acute, severe, peripheral vestibular disorder with nystagmus (horizontal or rotary), head tilt (toward the side of the lesion), rolling and falling.
• Often these animals are initially so incapacitated that they are misdiagnosed with cerebrovascular accidents.
• Clinical signs, while initially severe, are restricted to the vestibular system.
• If Horner's syndrome or facial nerve paresis are found concurrently, other differentials should be considered.
• Differential diagnosis of peripheral vestibular disease include otitis interna  and neoplasia (squamous cell carcinoma  of the middle ear).
• Otoscopic examination, bulla radiographs, and possibly, other advanced imaging studies (CT, MRI) are normal.
• Clinical signs usually improve dramatically in 1-2 weeks.
• The nystagmus usually resolves quickly whereas a mild head tilt may persist.
• No treatment has proved beneficial. Recurrence is possible.
• A similar, poorly defined idiopathic neuropathy involving the vestibular nerve has been described.
• Clinical features are similar to those described above and ancillary diagnostic testing is normal.
• Improvement in clinical signs is noted over the ensuing several weeks, regardless of treatment.
• Other conditions include otitis media, tumors of the middle ear, toxicity, eg metronidazole .
• Tumor of the caudal fossa such as choroid plexus tumors and meningiomas  may cause vestibular signs.
• Other signs indicative of central vestibular localization such as conscious proprioceptive deficits are not always seen.
• Older animals with persistent (>2 weeks) vestibular signs, even if these signs are consistent with peripheral disease, should have advanced imaging performed to assess both the central and peripheral vestibular areas.

Cranial nerve IX and X disease

• Disease of cranial nerves IX and X result primarily in dysphagia and laryngeal/pharyngeal problems.
• Dysphagia may be seen with myopathy, peripheral neuropathy, and neuromuscular junction disease.
• Central causes are rarer, but disease involving these cranial nerve nuclei may result in dysphagia or pain when swallowing.
• Hydrocephalus, tumor, and inflammatory diseases (primary encephalitis) are possible.
• Laryngeal paralysis may occur without obvious cause particularly in older, large breed, dogs.

• Laryngeal paralysis may also be a component of a more diffuse peripheral neuropathy necessitating a complete evaluation of the limbs and head.
• Diagnosis : history, clinical signs, laboratory tests, brain stem auditory evoked potentials (vestibulocochlear), CT or MRI.