Crocodile Tears Syndrome

Excerpt

The term “crocodile tears” is derived from the ancient belief that crocodiles weep after killing their victims. “crocodile tears syndrome,” also known as Bogorad syndrome, is the shedding of tears while eating or drinking in patients recovering from Bell palsy. It is also referred to as gustatory lacrimation.

Anatomy

The anatomy of the facial nerve is a mixed nerve that has motor, sensory, and parasympathetic components.

The facial nerve has the following functional components:

1. The special visceral efferent component (branchial motor) innervates the muscles of facial expression, stylohyoid, posterior belly of digastric, and the stapedius muscle, which are derived from the second branchial arch.

2. General visceral efferent (visceral motor) gives autonomic (parasympathetic) innervation to the lacrimal, salivary, and mucosal glands.

3. Special visceral afferent (special sensory) carries taste sensation from the anterior two-thirds of the tongue.

4. General somatic afferent (general sensory) carries sensation from the skin of the concha of the external ear.

Facial Nerve Nuclei

The facial motor nucleus is a collection of lower motor neurons in the lower part of the pons innervating the muscles of facial expression and stapedius. The part of the nucleus supplying the muscles of the lower half of the face receives cortico-nuclear innervation from the opposite hemisphere, whereas the part of the nucleus supplying the muscles of the upper part of the face receives bilateral corticonuclear innervation.

Behind the motor nucleus are the superior salivatory and lacrimatory nuclei, which are parasympathetic. The superior salivatory nucleus receives information from the hypothalamus and taste sensation from the oral cavity. It innervates the submaxillary and sublingual salivary glands via preganglionic fibers.

The lacrimatory nucleus receives information related to emotional responses from the hypothalamus. Information from the sensory nuclei of the trigeminal nerve is also received by the lacrimatory nucleus, which brings about reflex lacrimation upon irritation of the cornea or conjunctiva.

Facial Nerve Course and its Branches

The facial nerve consists of a motor and sensory root. The motor root loops around the abducens nucleus in the floor of the fourth ventricle and emerges at the junction of the pons and medulla along with the sensory root. The 2 roots travel along with the eighth cranial nerve to reach the internal acoustic meatus, and the 2 roots fuse at the lower part of the meatus to form a single trunk. Within the meatus, the nerve gets divided into three parts by 2 bends, following which it exits the skull via the stylomastoid foramen. The facial nerve then crosses the stylomastoid process and enters the parotid gland at its posteromedial surface. It divides into its terminal branches at the angle of the mandible:

1. Temporal branches

2. Zygomatic branches

3. Buccal branches

4. Mandibular branch

5. Cervical branch

Branches Within the Facial Canal

1. Greater (superficial) petrosal nerve arises from the geniculate ganglion. It carries parasympathetic preganglionic fibers and continues as the nerve of the pterygoid canal finally synapses with the pterygopalatine ganglion. Postganglionic fibers from the pterygopalatine ganglion synapse with mucosal glands of the nose, palate, pharynx, and also lacrimal gland.

2. The nerve to the stapedius supplies the stapedius muscle, which dampens excess vibrations of the stapes muscle.

3. Chorda tympani carries taste from the anterior two-thirds of the tongue to the brain via the middle ear.

Anatomically, the facial nerve (nervus intermedius) contains fibers for both the submandibular salivary gland and the lacrimal gland. After the facial nerve passes through the geniculate ganglion, the secretomotor fibers for the submandibular salivary gland travel with the main nerve trunk, whereas the secretory fibers to the lacrimal gland disaffiliate from the facial nerve to join the greater petrosal nerve. These secretory fibers then relay in the sphenopalatine ganglion before innervating the lacrimal gland.