Pattern Recognition:
• Listeriosis (Circling Disease): Listeria monocytogenes ascends CN V sensory branches → brainstem microabscesses; Triad: CN V (dropped jaw), CN VII (facial droop), CN VIII (head tilt/circling)
• Horner's Syndrome: Sympathetic trunk damage (runs with vagus in neck) → Miosis (constricted pupil), Ptosis, Enophthalmos, Dry nose (bovine specific—loss of sweating on muzzle)
• Laryngeal Hemiplegia (Roaring): Left Recurrent Laryngeal Neuropathy → paralysis of Cricoarytenoideus Dorsalis (only abductor) → arytenoid collapse into airway during inspiration
• Trigeminal Neuritis: Dropped jaw, inability to close mouth, jaw deviation toward lesion side
• Facial Paralysis: Drooping ear/lip, absent palpebral reflex (CN VII), widened palpebral fissure, food in cheek

Cranial Nerve Pathology

Understanding the anatomical course and function of cranial nerves enables precise localization of neurological lesions.

1. Listeriosis ("Circling Disease")

Etiology: Listeria monocytogenes bacteria ascend the sensory branches of CN V from mucosal abrasions (often from feeding coarse silage or hay). They cause microabscesses in the brainstem trigeminal nuclei and adjacent cranial nerve nuclei.

Clinical Presentation: Asymmetric cranial nerve deficits typical of brainstem lesions:

• CN V: Dropped jaw, facial analgesia (unilateral).
• CN VII: Facial paralysis—drooping ear and lip, absent palpebral reflex (cannot blink), widened palpebral fissure.
• CN VIII: Head tilt, circling toward affected side, nystagmus.
• IX, X, XII: Dysphagia, tongue paralysis.

Prognosis: Guarded to poor; requires aggressive antibiotic therapy (penicillin, oxytetracycline) and supportive care. Permanent deficits common if treatment delayed.

2. Horner's Syndrome (Angiology-Neurology Interface)

Etiology: Damage to the Sympathetic Trunk (which runs with the Vagus nerve in the carotid sheath in the neck). Causes loss of sympathetic tone to the head.

Classic Triad:

• Miosis: Constricted pupil (loss of sympathetic dilation).
• Ptosis: Drooping upper eyelid (Müller muscle atony).
• Enophthalmos: Sunken eye (retraction of globe due to loss of orbital smooth muscle tone).

Bovine Specific Sign: Loss of sweating on the nose on the affected side (dry nose/hyperthermia of the muzzle) due to loss of sympathetic innervation to cutaneous sweat glands. This is a key differentiator in cattle compared to small animals.

Common Causes: Traumatic reticuloperitonitis (hardware disease) with vagus involvement, neck trauma, guttural pouch infections (horses), brachial plexus avulsion.

3. Laryngeal Hemiplegia ("Roaring")

Pathophysiology: Neuropathy of the left Recurrent Laryngeal Nerve (longer course around aortic arch makes it vulnerable) causes paralysis of the Cricoarytenoideus Dorsalis (CAD) muscle—the ONLY abductor of the glottis.

Clinical Signs: The arytenoid cartilage collapses into the airway during inspiration, creating an audible roaring sound (stridor) and exercise intolerance. Common in large horses (Draft breeds, Thoroughbreds), rare but possible in cattle.

Diagnosis: Endoscopic examination of larynx shows failure of left arytenoid to abduct during inspiration.

4. Facial Nerve Paralysis

Signs: Drooping ear, drooping lip (commissure), absent palpebral reflex (cannot blink), widened palpebral fissure, food impaction in cheek (buccinator paralysis), and dry cornea (lacrimal gland paralysis leading to exposure keratitis).

Causes: Listeriosis (brainstem), otitis media/interna (nerve inflammation in facial canal), trauma to stylomastoid foramen region, guttural pouch disease (horses).

5. Trigeminal Neuritis

Unilateral: Jaw deviates toward affected side when opened; unilateral muscle atrophy.

Bilateral: "Dropped jaw"—inability to close mouth; tongue protrusion; inability to chew; profuse salivation; starvation if chronic.