The terms used to describe different types of percussion notes are shown in Table 4.17.
Hyperresonance. Hyperrcsonance may be found over the lung which is markedly emphysematous, over a large thin-walled pulmonary cavity and also over a pneumothorax, particularly if the pleural pressure is above atmospheric level. An apparent finding of generalised hyperresonance should be accepted only with reservation, since a change in the absolute pitch of a percussion note is difficult to recognise and may depend mainly upon the thickness of the chest wall. It is not usually advisable to attempt to distinguish between normal resonance and hyperresonance when the percussion note is equally resonant on the two sides.
Dullness. The percussion note loses its normal resonance whenever aerated lung tissue is separated from the chest wall by pleural fluid or thickening, or when lung tissue is rendered airless by consolidation, collapse or librosis. Over such lesions the percussion note is impaired or dull. The most marked degree of dullness on percussion is associated with a large pleural effusion.
Fig. 4.20 Radiographic appearances of a right pleural effusion.
A horizontal section of hemithora* close to the upper margin of the effusion (represented by the horizontal arrow) shows that there is at this site a similar amount of liquid anteriorly, posteriorly and laterally. However, because of the shape of the hemithorax, the X-ray beams traverse more fluid laterally than they do centrally. This produces the characteristic radiographic shape ol a pleural effusion shadow with a curved upper margin ascending towards the axilla.
When an abnormality of the percussion note is due to pulmonary consolidation or collapse it is usually possible to identity the lobe or lobes involved by reference to the surface marking of the fissures but, unless a lobe is totally consolidated, the area over which the percussion note is impaired is often much smaller than would be expected from its surface marking. This is even more striking when a lobe is collapsed. With a pleural effusion the area of dullness on percussion is unrelated to the surface anatomy of the lobes. Except with loculated effusions, it is situated over the lower part of the hemithorax with the patient in the upright position. Pleural effusions of considerable size may not be detected during examination of the anterior chest when the patient is in a semirecumbent position because gravity causes the pleural liquid to accumulate posteriorly. When there are no pleural adhesions the radiograph shows an effusion to have a curved upper border, which misleadingly suggests more fluid being present laterally (Fig. 4,20).
Ill localising the position of a pulmonary or pleural lesion, use should be made of the breath sounds and voice sounds in addition to the percussion note. However, small lesions, such as areas of segmental consolidation or collapsc, may not produce any abnormal physical signs. Even with larger lesions the signs may be partly or completely obscured if the lungs are emphysematous.
The percussion note is impaired or dull whenever aerated lung is separated from chest wall by pleural fluid or thickening, or when lung tissue is rendered airiess by consolidation, collapse or fibrosis General hyperresonance on both sides is rarely of diagnostic significance.
Areas of impaired percussion are often smaller than anticipated from the surface markings.
Map out areas of impaired resonance by percussing from resonant to
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