Учебники / LECTURE NOTES ON Diseases of the Ear, Nose and Throat Bull 2002

Pars flaccida

Fig. 1.1 The normal tympanic membrane (left). The shape of the incus is visible through the drum at 2o’clock. (Courtesy of MPJ Yardley.)

RELATIONS OF EXTERNAL, MIDDLE AND INNER EAR

Fig. 1.2 Diagram to show the relationship between the external, middle and inner ears.

The Ear 3

ANATOMY OF MIDDLE EAR AND MASTOID

AIR CELLS

Attic

Incus

Malleus

Lateral sinus

Lateral semicircular canal

Mastoid air cells

Stapes

Round-window niche

Fig. 1.3 Diagram to show the anatomy of the middle ear and mastoid air cells.

horizontal in the infant than in the adult and secretions or vomit may enter the tympanic cavity more easily in the supine position. The tube is normally closed and is opened by the palatal muscles on swallowing.This is impaired by the presence of a palatal cleft.

THE FACIAL NERVE

The facial nerve is embedded in bone in its petrous part but exits at the stylomastoid foramen (Fig. 1.3). In infants, the mastoid process is undeveloped and the nerve very superficial.

THE LEFT TEMPORAL BONE

Supra-meatal triangle

Zygoma

Tympanic ring

Fig. 1.5 A preparation showing the bony inner ear of semicircular canals and cochlea (Preparation by Mr S Ell.)

THE MASTOID CELLS

The mastoid cells form a honeycomb within the temporal bone, acting as a reservoir of air to limit pressure changes within the middle ear.The extent of pneumatization is very variable and is usually reduced in chronic middleear disease.

6Chapter 2: Clinical Examination of the Ear

large extent on colour, it is essential that the battery should be in good condition to give a white light.

A common error in examination of the tympanic membrane is to use too small a speculum; the largest that can be inserted easily should be used. Good auriscopes are expensive but are a worthwhile investment. Important points in the examination of the ear are listed in Box 2.1.

EXAMINATION OF THE EAR

1Look for any previous scars.

2Examine the pinna and outer meatus by head-mirror or room lighting.

3Remove any wax or debris by syringing, or by instruments if you are practised in this.

4Pull the pinna gently backwards and upwards (downwards and backwards in infants) to straighten out the meatus.

5Insert the auriscope gently into the meatus and see where you are going by looking through the instrument. If you cannot get a good view, either the speculum is the wrong size or the angulation is wrong.

6Inspect the external canal.

7Inspect all parts of the tympanic membrane by varying the angle of the speculum.

8Do not be satisfied until you have seen the membrane completely.

9The normal appearance of the membrane varies and can only be learnt by practice. Such practice will lead to the recognition of subtle abnormalities as well as the more obvious ones.

Box 2.1 Examination of the ear.

middle ear (shaded).

the cochlear fluids. It may be remediable by surgery and so it is important it is recognized.The hearing by bone conduction will be normal in pure conductive deafness.

Sensorineural deafness (Fig. 3.2)

Sensorineural deafness results from defective function of the cochlea or of the auditory nerve, and prevents neural impulses from being transmitted to the auditory cortex of the brain.

Mixed deafness

Mixed deafness is the term used to describe a combination of conductive and sensorineural deafness in the same ear.

RINNE’S TEST

This test compares the relative effectiveness of sound transmission through the middle ear by air conduction (AC), and bypassing the middle ear by bone conduction (BC). It is usually performed as follows: a tuning fork of 512 Hz (cycles per second) is struck and held close to the patient’s ear; it is then

Testing the Hearing 9

SENSORINEURAL DEAFNESS

Fig. 3.2 Sensorineural deafness is caused by an abnormality of the cochlea or the auditory nerve (shaded).

placed firmly on the mastoid process and the patient is asked to state whether it is heard better by BC or AC.

Interpretation of Rinne’s test

If AC>BC–called Rinne positive–the middle and outer ears are functioning normally.

If BC>AC – called Rinne negative – there is defective function of the outer or middle ear.

Rinne’s test tells you little or nothing about cochlear function. It is a test of middle-ear function.

WEBER’S TEST

This test is useful in determining the type of deafness a patient may have and in deciding which ear has the better-functioning cochlea. The base of a vibrating tuning fork is held on the vertex of the head and the patient is asked whether the sound is heard centrally or is referred to one or other ear.

In conductive deafness the sound is heard in the deafer ear.

In sensorineural deafness the sound is heard in the better-hearing ear (Figs 3.3–3.5)

SYMMETRICAL HEARING IN BOTH

EARS

AUDIOMETRY

PURE TONE AUDIOMETRY

Pure tone audiometry provides a measurement of hearing levels by AC and BC and depends on the cooperation of the subject.The test should be carried out in a sound-proofed room. The audiometer is an instrument that generates pure tone signals ranging from 125 to 12 000 Hz (12 kHz) at variable intensities.The signal is fed to the patient through ear phones (for AC) or a small vibrator applied to the mastoid process (for BC). Signals of increasing intensity at each frequency are fed to the patient, who indicates when the test tone can be heard.The threshold of hearing at each frequency is charted in the form of an audiogram (Figs 3.6–3.8), with hearing loss expressed in decibels (dB). Decibels are logarithmic units of relative intensity of sound energy.When testing hearing by BC, it is essential to mask the opposite ear with narrow-band noise to avoid cross-transmission of the signal to the other ear.