COMPARING CT WITH SPECT IN CHRONIC PULMONARY THROMBOEMBOLISM - ARE HYPERDENSITIES DUE TO HYPERPERFUSION

Purpose of this study was to assess the aetiology of inhomogenous lung parenchymal attenuation in patients with chronic pulmonary thromboembolism, presenting as sharply demarcated areas of increased and decreased density on computed tomography. Material and methods: In 52 patients with chronic pulmonary thromboembolism, computed tomography (CT) was compared with perfusion scintigraphy (including SPECT) and agreement was assessed: ''good'' (all hyperdense CT segments are perfused on scan), ''moderate'' or ''poor'' (one or two resp. three or more hyperdense CT segments are not perfused). Results: 44 of the 52 patients showed an inhomogeneous pulmonary attenuation on CT. Correlation of hyperdense areas with perfused lung parenchyma was graded as ''good'' in 26 cases, ''moderate'' in 14 and ''poor'' in 4 cases. In 40 of these 44 patients, scintigraphy revealed additional perfusion defects in homogeneously lucent areas on CT. In 6 of 8 patients with entirely homogeneous lung density on CT, SPECT revealed perfusion defects. Conclusion: In patients with chronic pulmonary thromboembolism, increased lung density on CT is caused by hyperperfused lung parenchyma distally to patent pulmonary arteries. SPECT proves to be more sensitive in diagnosing perfusion inhomogeneities.