Regional ventilation-perfusion mismatch in interstitial pneumonia. Correlation between scintigraphy and CT.

Interstitial pneumonia is one of the many causes of a scintigraphic ventilation-perfusion (V/Q) mismatch. To evaluate the morphologic features of V/Q mismatched areas in patients with interstitial pneumonia, we correlated the findings on lung scintigraphy using Kr-81m and Tc-99m MAA with CT scan findings. Of 41 patients, 20 (49%) had a high V/Q mismatched areas. All of these areas corresponded to cystic air spaces shown on CT, and most of the showed a honeycomb pattern. Ventilation-perfusion matched defects were seen in 23 patients (56%). The matched defects corresponded to cystic air spaces (honeycomb or bullous changes) or lung attenuation changes of varying degrees on CT. Cystic air spaces with high V/Q mismatch are considered to be normally ventilated. To distinguish mismatched areas of interstitial pneumonia from areas of pulmonary embolism, it may be necessary to compare scintigraphic findings with CT.