DENTAL GROSS ANATOMY CASE 2.1

History A 36yo woman slept near an open window on a cold drafty night. Upon awakening she noticed that her face was distorted. She was not able to close her right eye and she had difficulty speaking, eating (but not swallowing) and drinking. Additionally, her sense of taste was impaired. She consulted her physician.

Examination Examination reveals that the patient’s face is immobile and without expression on the right side. Right forehead is without wrinkles and right eyebrow droops. Right lower eyelid sags and tears flow down her face. Right corner of her mouth sags, and she cannot purse her lips. Nose and mouth are deviated toward the unaffected side. When attempting to laugh, the facial distortion becomes more noticeable.

Diagnosis, Therapy and Further Course A diagnosis was made. Therapy included electrical stimulation, massage and active exercises of the facial muscles. After five weeks the patient was almost completely recovered and only traces of the paralysis could be seen.

1a. What is the diagnosis? b. What major structure was affected?   Bell’s palsy (facial paralysis) 1b. What major structure was affected? Facial nerve (VII)

PEOPLE AFFLICTED WITH BELL’S PALSY (DAMAGE TO FACIAL NERVE)

What is (are) the underlying cause(s) of this condition?   One cause is inflammation of VII in the facial canal. The cause of the inflammation may be a viral infection or exposure to cold (as in this case). As VII runs through the facial canal in the petrous part of the temporal bone even slight swelling of the nerve would subject it to destructive pressure. Some authors believe that exposure to cold causes constriction of the stylomastoid branch of the posterior auricular artery which supplies VII. This could also lead to Bell’s palsy. It should be noted that some cases of Bell’s palsy occur without any known cause.

VII. FACIAL N. VII entering internal auditory meatus VII in facial canal of temporal bone

Posterior auricular a. ( supplies VII) VII

3a. What is the name of the foramen by which this major structure leaves the base of the skull? b. Name the five terminal branches of this structure. 3a. What is the name of the foramen by which this major structure leaves the base of the skull?   Stylomastoid foramen 3b. Name the five terminal branches of this structure. Temporal, Zygomatic, Buccal, (marginal) Mandibular and Cervical branches (“To Zanzibar By Motor Car”)

Stylomastoid foramen (exit of VII)

Temporal branches Zygomatic branches Posterior auricular n. (to occipitalis m.) Main trunk of VII TO ZANZIBAR BY MOTOR CAR Buccal branches Marginal mandibular branch Cervical branch

4a. Why were wrinkles absent from the patient’s forehead and why did the right eyebrow droop? b. Why was the patient unable to purse her lips and why did liquids run out of the corner of her mouth when she tried to drink? 4a. Why were wrinkles absent from the patient’s forehead and why did the right eyebrow droop?   Paralysis of frontalis muscle   4b. Why was the patient unable to purse her lips and why did liquids run out of the corner of her mouth when she tried to drink? Paralysis of orbicularis oris muscle

Frontalis m. Orbicularis oris m.

4c. Paralysis of which muscle resulted in food collecting in the vestibule of the patient’s mouth? What is the anatomical origin of this muscle? What is its embryological origin? Is it a true muscle of mastication? 4c. Paralysis of which muscle resulted in food collecting in the vestibule of the patient’s mouth? What is the anatomical origin of this muscle? What is its embryological origin? Is it a true muscle of mastication?   Paralysis of buccinator muscle. Anatomically it originates from the pterygomandibular raphe and from the alveolar processes of the maxilla and mandible. It is NOT a true muscle of mastication (derived from pharyngeal arch 1). Rather, it is a muscle of facial expression (e.g., used in smiling) which, like all muscles of facial expression, is derived from pharyngeal arch 2.

Buccinator m.

Pterygoid hamulus Buccinator m. Pterygomandibular raphe Superior pharyngeal constrictor m. Mandible Buccinator also originates from alveolar processes of maxilla and mandible

PHARYNGEAL ARCH MUSCLES V3 VII IX X X Muscles of mastication: Arch 1 Muscles of facial expression: Arch 2 (INCLUDING BUCCINATOR)

4d. Why couldn’t the patient close her right eye? What serious complication might be the result? 4d. Why couldn’t the patient close her right eye? What serious complication might be the result? The orbicularis oculi muscle which closes the eye (orbital part—forceful closure; palpebral part—light closure) was paralyzed. As a result, lacrimal fluid is not spread over the cornea which can then become inflamed and dry, leading to corneal ulceration.

Orbicularis oculi m. (orbital part) Orbicularis oculi m. (palpebral part)

In this patient there was sagging of the lower eyelid and spilling of tears down the side of her face. What is the pathway by which tears normally drain from the conjunctival sac? 5. In this patient there was sagging of the lower eyelid and spilling of tears down the side of her face. What is the pathway by which tears normally drain from the conjunctival sac?   Tears are “sucked up” by capillary action into the lacrimal punctum and lacrimal canaliculus (one in each eyelid) and then pass into the lacrimal sac. The sac is drained by the nasolacrimal duct, which empties into the inferior meatus of the nasal cavity.

Superior lacrimal papilla and punctum Lacrimal gland (orbital part) Lacrimal canaliculi Lacrimal gland (palpebral part) Lacrimal sac Ducts of lacrimal gland (open into superolateral part of conjunctival sac) Nasolacrimal duct Opening of nasolacrimal duct (into inferior meatus of nasal cavity) Inferior lacrimal papilla and punctum

6a. Why did this patient experience impairment of taste? b. Where, precisely, was the loss of taste sensation? 6a. Why did this patient experience impairment of taste?  Taste was impaired because the chorda tympani nerve was affected. The chorda tympani is a branch of VII which arises in the facial canal just superior to the stylomastoid foramen.   6b. Where, precisely, was the loss of taste sensation?  The chorda tympani supplies taste buds on the anterior two-thirds of the tongue (ipsilateral side).

COURSE OF VII IN FACIAL CANAL Int. auditory meatus Geniculate ganglion (sensory) Greater petrosal n. (autonomic to lacrimal gland) VII in facial canal of temporal bone Nerve to stapedius m. (paralysis > hyperacusis) Pterygopalatine ganglion (autonomic) Stylomastoid for. Chorda tympani n. (autonomic to submandibular & sublingual glands, taste from ant. 2/3 of tongue) VII leaves the cranial cavity through the internal auditory meatus , travels through the facial canal in the temporal bone, and emerges at the base of the skull through the stylomastoid f. (note: VII has the longest intraosseous course of any cranial nerve (COA, 5th ed., p. 1143 ). In the facial canal, VII makes a sharp bend or genu, and this is where the geniculate ganglion is located. The skeletal motor branches to the muscles of facial expression arise after VII emerges from the stylomastoid foramen. These branches fan out onto the face to reach their respective muscles. The branch to the stapedius m. (a tiny muscle in the middle ear which damps the movement of the stapes and protects the inner ear from loud sounds) arises while VII is in the facial canal. The autonomic (parasympathetic) fibers in VII travel in two branches. Some leave VII via the greater petrosal n. and synapse in the pterygopalatine ganglion. From there postsynaptics go to the lacrimal gland. Other parasympathetic fibers leave VII via the chorda tympani n., which branches off just superior to the stylomastoid f. These fibers synapse in the submandibular ganglion, and from there distribute to the submandibular and sublingual glands. 4. The special sensory (taste) fibers coming from the anterior 2/3 of the tongue travel back to VII via the chorda tympani n. The cell bodies of these special sensory neurons (as well as the cell bodies of the general sensory neurons in VII which come from the skin of the external ear) lie in the geniculate ganglion. Submandibular ganglion (autonomic) Branches to muscles of facial expression

Additional note: According to Moore & Agur (Essential Clinical Anatomy), VII is the most frequently paralyzed cranial nerve.

END OF CASE 2.1

TIME 2011 (DS-1): ~30 MIN. (went well) 2012 (DS-1): ~25 min.