Sunday, March 14, 2021

Middle Ear Effusion Case File

Posted By: Medical Group - 3/14/2021 Post Author : Medical Group Post Date : Sunday, March 14, 2021 Post Time : 3/14/2021
Middle Ear Effusion Case File
Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 47
A 12-year-old boy complains of a 2-week history of impaired hearing with his left ear. He states that music and voices seem “far away.” His medical problems include allergic rhinitis and asthma. On examination, he is afebrile, but his left eardrum displays a yellowish discoloration. The left drum moves very little with a puff of air. The right tympanic membrane appears normal.

 What is the most likely diagnosis?
 What is the clinical anatomy for this condition?

ANSWER TO CASE 47:

Middle Ear Effusion
Summary: A 12-year-old boy with allergic rhinitis and asthma has a 2-week history of difficulty hearing with his left ear. He is afebrile but has yellowish discoloration of his left tympanic membrane, which does not move well with insufflation.

• Most likely diagnosis: Middle ear effusion

• Clinical anatomy of the condition: Middle ear fluid impeding sound transmission by the middle ear ossicles


CLINICAL CORRELATION
Sound waves collected by the auricle and external acoustic meatus (canal) produce vibration of the tympanic membrane. These vibrations are transferred, in turn, to the ear ossicles, the malleus, the incus, and the stapes. Vibrations of the stapes produce movements of the endolymph within the cochlea, which are converted to the nervous impulse responsible for the sensation of hearing. Fluid within the middle ear cavity (effusion) diminishes the vibrations of the tympanic membrane and the ear ossicles. Effusions develop in the middle ear secondary to obstruction of the pharyngotympanic (auditory) tube, as with upper respiratory infections or allergic reactions. The insufflation of air through the otoscope in this patient does not induce the normal fluttering of the eardrum, further suggesting an effusion. An infectious process is unlikely in this case because of the absence of a fever or a red eardrum. Treatment of effusions includes antihistamines, decongestants, and, in severe cases, surgical incision of the tympanic membrane for drainage (myringotomy) and insertion of drainage tubes.


APPROACH TO:
The Ear

OBJECTIVES
1. Be able to describe the anatomy of the external acoustic meatus (canal)
2. Be able to describe the anatomy of the tympanic membrane and the three ear ossicles
3. Be able to identify the structures of the middle ear cavity and those that communicate with it


DEFINITIONS
INSUFFLATION: Act of blowing a powder or gas into a body cavity, in this case through the otoscope, to assess whether there is fluid in the middle ear.

PERILYMPH/ENDOLYMPH: The bony labyrinth of the inner ear contains the membranous labyrinth. Within the lumen of the membranous ducts is endolymph, a fluid similar in composition to intracellular fluid (low sodium, high potassium). The space between the ducts and the bony walls is filled with perilymph, a fluid similar in composition to normal extracellular fluid (high sodium, low potassium). The compartments that are filled with perilymph and endolymph do not communicate.

EFFUSION: Spread of a liquid into a space. In this case, the fluid is from the inflammatory response to the allergy.

MYRINGOTOMY: Procedure in which the tympanic membrane is pierced and tubes are inserted into the opening to drain the exudate.


DISCUSSION
The external ear is composed of the auricle, an elastic cartilage structure covered with skin and having several named parts, one of which is the concha, which funnels sound waves down the external acoustic meatus or canal (Figure 47-1). The meatus is lined with skin, and the wall of the lateral third is cartilaginous, whereas the medial two-thirds are bony. It has an anteromedial S-shaped course, which can be straightened by posterosuperior traction on the auricle.

The medial end of the meatus is closed by the tympanic membrane, a somewhat cone-shaped, 1-cm membrane composed of collagen and elastic fibers that is

Middle Ear anatomy

Figure 47-1. The middle ear. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:76.)

covered externally by thin skin and lined internally by the mucous membrane of the middle ear. The apex of the membrane’s cone is called the umbo. The reflected light of an otoscope, the cone of light, originates at the umbo and is directed anteroinferiorly. A process of the malleus (also called the “handle”) is applied to the medial surface of the membrane, and its tip is also attached at the umbo. The malleus has a lateral process that bulges the superior portion of the membrane laterally. The portion superior to the lateral process is the pars flaccida, and the remainder of the membrane is called the pars tensa. The three ear ossicles are the malleus, incus, and stapes, lateral to medial, across the tympanic or middle ear cavity. Each bone has distinctive features. With a normal tympanic membrane, the handle of the malleus is clearly visible, and the long process of the incus is often visible posterior to the malleus. The stapes is shaped much like a stirrup, and its footplate fits into the oval window on the medial wall of the tympanic cavity. Its in-and-out movement transmits pressure waves through the endolymph within the cochlea, where the nerve impulses for hearing are generated. Excessive movements of the ear ossicles with loud noise are dampened by the tensor tympani muscle, which is attached to the malleus, and the stapedius muscle, which is attached to the stapes. These muscles are innervated by CN V and CN VII, respectively.

The tympanic cavity is contained within the petrous portion of the temporal bone. Its features are usually described as being contained within a box with a roof, four walls, and a floor. Table 47-1 lists the bony features, related structures, and openings for each of the walls. The tympanic cavity is lined with a mucous membrane and contains the chorda tympani branch of CN VII and the tympanic plexus (CN IX) in addition to the ear ossicles and their associated muscles. Air pressure within the cavity is equalized with the nasopharynx through the pharyngotympanic or auditory tube.

Table 47-1 • WALLS OF THE TYMPANIC CAVITY

 

Roof

Floor

Lateral Wall

Medial Wall

Anterior

Wall

Posterior

Wall

Bony

feature

Tegmen

tympani of

temporal

bone

 

Tympanic

membrane,

malleus,

epitympanic

recess

Promontory,

prominence

of facial canal,

prominence

of lateral

semicircular

canal

 

Mastoid process,

pyramid

Related

structure

Middle

cranial

fossa

Internal

jugular

vein

External

acoustic

meatus,

chorda

tympani

Vestibular

apparatus,

CN VII

Carotid

artery, tensor

tympani

muscle

Mastoid air

cells, CN VII,

stapedius

muscle

Opening

 

 

 

 

Auditory

tube

Mastoid

aditus


COMPREHENSION QUESTIONS

47.1 A 4-year-old boy was noted to have recurrent ear infections. He underwent placement of tubes in the tympanic membranes 3 days previously and currently complains of some difficulty in tasting candy. Which of the following is the most likely explanation?
    A. Disruption of CN VIII
    B. Disruption of the chorda tympani
    C. Effects of the anesthesia
    D. Effects of the endotracheal tube

47.2 A 5-year-old girl complains of severe pain from her right ear due to an acute otitis media. Which of the following nerves is most likely responsible for carrying the sensation of pain from the tympanic membrane?
    A. CN VII
    B. CN VIII
    C. CN IX
    D. CN X

47.3 A 3-year-old boy had three episodes of otitis media over the past year. His mother asks the pediatrician why children tend to develop more ear infections than adults. Which of the following is the most likely anatomical explanation?
    A. Changes in the eustachian tube
    B. Changes in the external pinna
    C. Changes in the external ear canal
    D. Changes in the stapedius ossicle


ANSWERS
47.1 B. The chorda tympani, which is a branch of CN VII, courses behind the tympanic membrane and occasionally can be injured during surgery for ear tubes. The chorda tympani innervates the anterior two-thirds of the tongue.

47.2 C. The glossopharyngeal nerve (CN IX) is the afferent nerve for the sensory input from the internal surface of the tympanic membrane and the tympanic cavity.

47.3 A. The eustachian tube connects the middle ear to the oral cavity. The eustachian tube is shorter and more horizontal in a child than in an adult.


ANATOMY PEARL
 The outer one-third of the external acoustic meatus is cartilaginous, thereby facilitating the straightening of its S-shaped curvature.
 The cone of light is seen in the anteroinferior quadrant of the tympanic membrane.
 The tensor tympani and stapedius muscles of the middle ear are innervated by CN V and CN VII, respectively.
 The tympanic cavity communicates with the nasopharynx through the pharyngotympanic (auditory) tube.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:560−565. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:967−973, 978−979. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 94−96, 98, 100.

0 comments:

Post a Comment