The internal surface area of the lung in emphysema.

: Quantitative histological studies on the lung are time consuming and for the pathologist may not reveal much additional imformation in relation to the time spent. Sixty-eight cases of emphysema were studied. The percentages of the lung tissue destroyed by alveolar, bronchiolar and bullous emphysema were determined by macroscopic point counting. The internal surface area (I.S.A.) and internal surface area at a standard lung volume of 3,000 ml(I.S.A.3,000) were determined by the mean linear intercept (M.L.I.) method. There was a significant correlation between both the M.L.I. and I.S.A.3,000 and the percentage of lung tissue destroyed. The M.L.I. was the most accurate guide to the presence of emphysema. The I.S.A. was the least reliable indication of emphysema. Cases of alveolar duct emphysema were both over and underdiagnosed on macroscopic point counting. It is therefore suggested that in cases with alveolar duct emphysema, apparently normal lungs or where full pulmonary function tests are available, quantitative histological studies should be carried out. In other cases it is possible to derive the I.S.A. and I.S.A.3,000 from the percentage of emphysema as determined macroscopically, without recourse to histological methods.