Introduction

• Trigeminal nerve branches: ophthalmic, maxillary, mandibular.
• Most common trigeminal neuropathy is idiopathic mandibular paralysis.
• Cause: inflammation, neoplasia, trauma.
• Signs:
  • Ophthalmic branch: corneal anesthesia, loss of sensation to nasal septal mucosa, skin on dorsum of nose, upper eyelid, eye medial canthus.
  • Maxillary branch: loss of sensation to eye lateral canthus, lower eyelid, skin of the cheek, side of the nose, muzzle, palates, mucous membrane of nasopharynx, teeth and gingiva of upper jaw.
  • Mandibular branch: unilateral or bilateral paralysis of masticatory muscles → inability to close mouth, difficulty eating and drinking. Loss of sensation to mandibular portion of the face and oral cavity.
• Diagnosis: signs, histopathology, MRI.
• Treatment: supportive care.

Pathogenesis

Etiology

• Idiopathic.
• Space-occupying lesions, eg neoplasia.
• Trauma to head, especially jaw.
• Trigeminal nerve abnormalities can occur with infiltrating neoplasia (lymphosarcoma, leukemias Leukemia ), that involve a branch or the entire nerve.
• Other cranial nerves (VII), and the sympathetic supply to the eye may be involved concurrently.
• Animals that have systemic hematological neoplasia that develop cranial nerve abnormalities should be evaluated for extension of the tumor to these sites.
• Nerve sheath tumors Nerve sheath: neoplasia may arise within the trigeminal 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.
• Trigeminal neuritis is an idiopathic inflammatory disease of the mandibular branches of V bilaterally:
• • The dog presents with a dropped jaw.
  • The etiology is unknown.
  • A non-suppurative inflammatory neuritis in the motor branches of the trigeminal nerve and its ganglion has been confirmed in some cases.
  • Most dogs should improve with time (within 2-10 weeks).
  • No treatment has shown benefit.

Pathophysiology

• Inflammation or degeneration trigeminal nerve → loss of trigeminal nerve function → loss of sensation to face and mouth, loss of motor function to masticatory muscles → unable to close jaw → masticatory muscle atrophy.
• A unilateral dysfunction of all three branches of V is almost always associated with a peripheral V lesion (outside the brain stem), because the nuclear areas of V are so extensive that central destruction of all of these nuclei would be incompatible with life.
  Remember, just because a lesion is peripheral it does not mean that it is not intracranial, eg a tumor involving CN V in the trigeminal canal.

Diagnosis

Treatment

Outcomes