[The distribution and the characteristics in computed tomography (CT) of the lungs in primary Mycobacterium avium complex (MAC) infection].

We investigated the distribution and the characteristics of the lung lesions of patients with primary Mycobacterium avium complex (MAC) infections mainly by computed tomography (CT). They admitted to our hospital during the period from 1984 to 1995 and none of them had a medical history of tuberculosis or other lung diseases. The subjects consisted of fifty patients: fourteen male (average age +/- SD was 66.4 +/- 14.0 year old) and thirty six female (69.0 +/- 11.9 year old). Of 50 patients 24 were M. intracellulare infection, 10 were M. avium infection and others were not identified. First, by using the ratio of slices with lesions on CT to all CT slices from the apex to the base of the lungs, all the patients were divided into two groups; a slight group with less than 15.0% (n = 19) and a severe group with 15.0% or more (n = 31). Next, the density of abnormal shadows in each segment as divided into 5 grades; none (-), minimal (+/-), slight (+), moderate (+2) and severe (+3). The grading was done by taking into account the grade of distribution, density of lesions and destruction of lung parenchym found mainly on CT, and in addition by a standard roentogenographic and tomographic features supplemental. The characteristics frequently observed findings on CT in primary MAC infection patients were nodular (94%), cavitary (74%), bronchiectatic (62%), infiltrative (74%), atelectatic (56%), and pleural-thickened (36%) shadows. Comparing the incidence of segmental lesions in MAC infection patients by segment, it was higher in right and in left lung, but the difference was statistically not significant. As to the number of segments with lesions graded from (+/-) to (+3), many segments were infected unexpectedly: the mean value was 7.7 +/- 1.5 even in the slight group. The proportion of segments with relatively severe lesions graded from (+2) to (+3) in each segment was observed, and the rate in the slight group was 52.6% in S5, 28.9% in S4, 16.7% in S1 (S1 + 2a, b), and 16.7% in S2 (S1 + 2c). In severe group, it was 54.8% in S5, 45.2% in S4, 46.8% in S1 (S1 + 2a, b) 54% in S2 (S1 + 2c), 27.4% in S3 and 26.2% in S6, respectively. The rate of segments with lesions in the lower lobes were less frequent especially in the slight group while it was slightly higher in the severe group. Speculating the initial lesions in the slight group, it was assumed that there might be two types of foci; the one is relatively localized in the beginning and the other is a diffuse type with lesions in many segments even from its early stage. As to the location of initial lesions, the middle lobe and lingula were the most important sites, and the right upper lobe and the left upper division were the next.