Case Study 1

Thursday, February 4, 2010

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Case Study 1

A young man was taken to the emergency room with a knife wound in the right side of the
neck. The blade pierced the skin and the sternocleidomastoid muscle in a horizontal
plane at a point approximately 4 cm directly posterior to the angle of the mandible. Bleed-
ing from the wound was not substantial. Compresses were applied to the area, the bleed-
ing came under control, the skin was stitched and the patient was allowed to go home.

When he returned to have the stitches removed one week later, the following symptoms
were observed: his tongue deviated markedly to the right upon protrusion; the floor of the
mouth on the right side was relaxed and lengthened; the hyoid bone was tilted slightly from
the horizontal plane, the right side being higher than the left; a generalized weakness of
the infrahyoid muscles was present on the right side of the neck.

There was no sensory loss from the tongue or from the skin of the neck. Taste sensation
from the tongue was normal. The function of the sternocleidomastoid and platysma
muscles was unimpaired. After one year, function was restored to the tongue and associ-
ated structures.


1. Did the knife enter the posterior triangle of the neck?

No. It pierced the SCM directly and did not enter one of the major named triangles of the
neck. The SCM divides the anterior from the posterior triangle, etc., etc., but is not "in"
either triangle.

2. Damage to what structure would account for the symptoms described above?

Damage to the right hypoglossal nerve can account for all of the symptoms. As described
below, this nerve not only is motor to most tongue muscles, but it also carries fibers from
C 1 (and sometimes C 2) that supply the geniohyoid, superior belly of the omohyoid and
the thyrohyoid muscles. Recall, however, that the C 1 fibers are only traveling with the
hypoglossal nerve and strictu sensu are not part of it. Nevertheless, they probably would
have been cut or injured along with the hypoglossal fibers.

3. Why did the tongue deviate to the injured side?

On the right side, the denervated muscles do not have the same strength as the muscles
on the left (unaffected) side; hence, the muscles on the left overpower/override the right
muscles and the tip of the protruded tongue deviates to the weakened right side. The
tongue can be protruded in the midline only when the muscles on both sides work
together. The tongue is protruded solely by the muscles on the intact side; therefore,
when one hypoglossal nerve is severed or damaged, the protruded tongue deviates to the
paralyzed or weakened side.

4. What caused the problems with the hyoid bone and the infrahyoid muscles? Why were
the latter not totally denervated?

The problems relating to the position of the hyoid bone resulted from the fact that
C 1 fibers were running with the hypoglossal nerve. These fibers supply the geniohyoid
(a suprahyoid muscle) and two infrahyoid muscles, the superior belly of the omohyoid
and the thyrohyoid. The geniohyoid pulls the hyoid bone forward, shortens the floor of
the mouth, elevates the hyoid bone and helps to open the jaw. The floor of the mouth on
the right side was relaxed and lengthened because of the injury sustained by the nerve
to the geniohyoid. The thyrohyoid and omohyoid depress the hyoid bonee and the thyroid
cartilage during swallowing and speaking. Since the nerve supply to 2/4 infrahyoids were
damaged and the nerve supply to only 1/4 suprahyoids was injured, the right suprahyoids
were stronger than the righ infrahyoids and tended to elevate the right side of the hyoid

5. Account for the fact that only minimal bleeding occured from the site of the wound.

The knife did not penetrate sufficiently deep to sever either the internal or external carotid
arteries which lie medial (deep) to the hypoglossal nerve.

6. Describe the relationships of cranial nerves IX, X, XI and XII to the arteries and other
landmark structures in the neck.

The relationships of cranial nerves IX-XII, the carotid arteries and other structures in the
neck are of considerable importance. The glossopharyngeal nerve (IX) and the pharyngeal
branches of the vagus (X) lie lateral to the internal carotid and medial to the external carotid
arteries. The superior laryngeal nerve (from vagus) lies medial to both arteries. The main trunk of the vagus descends posterior to the internal and common carotid arteries. The
accessory nerve (XI) crosses the posterior triangle of the neck diagonally from the jugular
foramen to the anterior border of the trapezius muscle. The hypoglossal nerve (XII) is the
most superficial of the cranial nerves in this area. It descends from the hypoglossal canal,
hooks around the occipital artery and lies superficial to the internal and external carotid


7. Why do you think that the patient recovered use of the affected structures in this
particular case?

The nerve was not completely severed. The supra- and infrahyoids displayed weakness but
not paralysis, hence not all of the C 1 fibers were severed.

For additional information, refer to:
Netter plates: 24, 27, 29, 63, 65, 122, 123.
Snell, pages: 645-652, 656, 673, 681, 684, 709, 786, 801-802.

On the diagram above, label structures 1 - 4, and then complete the chart below concerning
vagal innervation of the larynx.

Name Component Fibers Function(s) Symptoms Produced by a Lesion of this Structure
1 Superior
somatic motor; somatic
sensory; special sensory;
preganglionic parasympa-
thetic; (postganglionic
Forms an external and an
internal branch; this is the
parent nerve of 2 and 3
(see below)
All of those listed for 2 and
3 below since this is the
PARENT nerve.
2 Internal
somatic sensory; special
sensory; preganglionic
parasympathetic; (post-
ganglionic sympathetic)
Supplies region from
epiglottis down to vocal
No cough reflex; lack of
sensation above vocal
cords; no glandular
secretions released by
mucosal glands from
epiglottis to vocal cords, i.e.
region above vocal cords
3 External
somatic motor; somatic
sensory; (postganglionic
Regulates the cricothyroid
Hoarseness or a very low-
pitched voice; vocal cords
cannot be lengthened/
4 Recurrent
somatic motor; somatic
sensory; preganglionic
Motor to ALL instrinsic
muscles of larynx (NOT cricothyroid, however);
sensory to mucous mem-
brane below vocal folds;
glandular secretion from
mucosal glands below
vocal folds
Vocal Fold cannot be
AB-ducted on side of lesion;
folds come to rest halfway
between ab- and ad-ducted;
speech and breathing may
be impaired, especially if
the nerve is only partially


There are eleven rather typical complaints given below. Using what you have learned about
the cranial nerves, indicate which nerve (or nerves) you think has been compromised. Be
specific and be prepared to pinpoint the site of the lesion if possible.

1. "The reason why I did not leave the house sooner once the fire broke out was because
I could not smell the smoke."

Cr. I, olfactory

2. "I can't feel anything over my right cheek, lower lip or most of my tongue and my mouth
is almost totally dry."

Lesion might have been at or very near foramen ovale. The designation "almost or extremely
dry" usually accompanies complaints about the malfunctioning of the parotid; the description
"slightly dry or partially dry" usually goes along with impairment of the submandibular and/or
sublingual glands, with the parotid intact and functioning. Of course, if the lesion had been
bilateral even more spectacular symptoms would have been reported.

3. "I can no longer close my eye tightly or whistle a tune."

Cr. VII, motor supply to orbicularis oculi (temporal and zygomatic branches), orbicularis oris
(buccal branches) and buccinator (buccal branches)

4. "I seem to have a lot of difficulty turning my head now and I think that there is a big
difference in the contour of my neck."

Cr. XI, spinal accessory; motor supply to sternocleidomastoid and trapezius muscles.

5. "I keep having dizzy spells and feeling sick to my stomach (Cr. VIII, vestibulocochlear
. Yesterday I lost my balance as I was walking down the street. The muscles on the right
side of my face don't seem to be working right
(Cr. VII, facial nerve). I can barely taste my food
(Cr. VII, chorda tympani, special sensory), my mouth is rather dry (Cr. VII, chorda tympani,
parasympathetic, submandibular ganglion)
and my right eye is very dry. I seem to be making
almost no tears in that eye
(Cr. VII, parasympathetic, greater petrosal nerve, ptergopalatine
ganglion, zygomaticotemporal nerve to lacrimal nerve).

Lesion might have been at level of internal acoustic meatus.

6. "I know that you said my ear was infected, but why am I so sick to my stomach? I
seem to be coughing a lot but I don't think that I have a cold."

Cr. X, Vagus nerve, auricular branch.

7. "Last night I didn't dry my hair after I took a shower and went to bed with wet hair. I
woke up in the middle of the night because I felt so cold. Then, I decided to go to the
bathroom, and when I looked in the mirror I noticed that the corner of my mouth was
drooping and that I was drooling."

Sounds like Bell's palsy; Cr. VII, especially the motor, buccal and marginal/mandibular
branches to the orbicularis oris.

8. "After I had that lump removed from the right side of my chin, the right corner of my
mouth began to droop and the right side of my neck developed all these baggy folds."

Cr. VII, marginal and cervical branches to orbicularis oris and platysma muscles.

9. "Ever since that accident, I find that the dentist can drill my lower teeth and I don't
feel a thing!"

Cr. V 3, inferior alveolar nerve, sensory to lower teeth and gums.

10. "My right pupil isn't the same size as my left. In fact, it doesn't change its size; it is
always dilated."

Cr. III, parasympathetic, ciliary ganglion, nerve to sphincter pupillae.

11. "Ever since I suffered that blow on the side of my head, I have double vision. It causes
no end of trouble for me as I am going down the stairs."

Cr. IV, superior oblique.

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