Chest ImagingPneumocystis carinii pneumonia
(PCP), the most common opportunistic
pulmonary infection seen in patients with
AIDS. Chest film abnormalities are frequently present, yet in 10-39% of cases, the chest radiograph is normal. The diagnosis in such situations is suggested by clinical and laboratory findings such as shortness of breath, lowered concentration of P
aO
2, decreased diffusing capacity, and, occasionally, an abnormal gallium lung
scan. Of interest is a recent article showing that LDH levels did not distinguish between PCP and non-PCP pneumonias. In another study the use of HRCT scanning reduced the need to
perform bronchoalveolar lavage or suggested another diagnosis (chiefly airways disease) rather than PCP. The diagnosis is confirmed by observing
P. carinii in sputum, bronchoalveolar lavage, or lung
biopsy samples.
In most patients with PCP, chest films are abnormal and reveal diffuse bilateral and usually fairly symmetrical, fine reticular opacities. Variations in this pattern occur frequently and include unilateral or focal lung opacities of the same quality or, rarely, focal alveolar consolidation. Occasionally, the interstitial pattern is medium to coarse (Fig.1), and on rare occasions a miliary pattern is observed. Focal nodules, measuring 1-2 cm in diameter, with or without cavitation, have also been attributed to P. carinii infection. The cavity walls are generally thicker than those observed with pneumatocoeles (Fig.2). The outer margins may be irregular or smooth. Cavitary nodules of PCP are usually solitary and fairly pathognomonic. Occasionally, cavitary nodules of Cryptococcus, Aspergillus, Staphylococcus, or bronchogenic carcinoma origin may have a similar appearance.
With appropriate therapy, improvement in the radiographic findings is expected within 7-10 days. Without therapy, rapid progression to a worsened, diffuse heterogeneous and, in later stages, severe bilateral homogeneous consolidation may occur. Therapy with intravenous trimethoprim-sulfamethoxazole (TMP/SMX) may lead to worsening of the chest film abnormalities within 4 days of beginning treatment. This is most likely to be caused by pulmonary oedema due to the large amount of fluid required for intravenous therapy with this antibiotic and does not necessarily indicate worsening of pneumonia. If warranted, diuretic therapy will often result in rapid improvement in the patient's radiographic and clinical state. Eventually, complete resolution of radiographic abnormalities is expected, although in some instances residual interstitial opacities are observed. Adjunctive therapy with corticosteroids has been recommended for patients with moderate to severe PCP. Rapid improvement in the chest film findings may be observed after this regimen. A complication of steroid use may be an increase in secondary fungal infections.
A few interesting complications of PCP have been recognized with some frequency in the last several years. Spontaneous pneumothorax has been observed in approximately 5 - 10% of patients with PCP (Fig.3). The size of pneumothorax has varied from small to extremely large and may require tube thoracostomy, chemical pleurodesis, talc poudrage or surgery. Occasionally, in patients too ill to undergo surgery or for outpatient care a Heimlich valve has been successful. The aetiology of the pneumothorax is somewhat controversial; the timing of the pneumothoraces is probably not related to treatment but is apparently due to infection with P. carinii itself. Pneumothorax in AIDS patients is virtually pathognomonic of PCP. In some instances, pneumatocoeles precede the appearance of pneumothorax. In one series, 10% of patients with PCP were fou probably poor coverage of the upper lobes by aerosolized pentamidine. These unprotected areas are thus more likely to harbour P. carinii and to be selectively involved in pneumonia. Other unusual features of this therapy, including pneumothorax, pneumocystomas, pleural fluid, and hilar lymphadenopathy, have also been reported. Nevertheless, the presence of pleural fluid or hilar or mediastinal lymphadenopathy should suggest a diagnosis other than PCP.
HC
PGO