History
    A 38-year-old woman presented with mild fever, chill, and yellowish productive cough for 45 days.

Findings
    Chest radiograph showed bilateral areas of ground-glass opacity and numerous micronodules predominantly in middle and lower lung zones. High-resolution CT scans showed randomly distributed micronodules in both lungs. Some of the nodules contained microcavitation predominantly in nondependent areas of both lungs. Poorly-defined centrilobular nodules, branching linear structure, and areas of lobular consolidation with peribronchial wall thickening were also seen in the right upper lobe, anterior and lateral basal segment of the right lower lobe, and lingular segment of the left upper lobe.

Discussion
    Miliary tuberculosis results from the lymphohematogenous dissemination of massive numbers of viable organisms in 2-6% of primary tuberculosis [1, 2]. The disease can occur in postprimary tuberculosis when the host's defense mechanism is overwhelmed. In early stage of miliary tuberculosis, chest radiographs may appear normal. Follow-up radiographs obtained a week or more later usually show a poorly defined haze through both lungs. Typical nodules of 1-2 mm become recognizable even later. High-resolution CT scans show poorly- or well-defined 1-2 mm nodules widely disseminated through the lungs in association with diffuse reticulation, nodular interlobular septa, nodular irregularity of vessels, subpleural dots, and studded fissures [1. 2].
    Ko et al. [3] reported reversible cystic disease in patients with pulmonary tuberculosis. In their study, the cystic lesions were associated with surrounding areas of centrilobular nodules or consolidation. Cystic lesions were presumed to result from one of the following three mechanisms. First, drainage of necrotic lung parenchyma in the areas of consolidation, coupled with check valve bronchiolar obstruction caused by edematous luminal narrowing with mural inflammation of the involved bronchiole, may have caused cyst formation. Second, cystic lesions might represent areas of dilated bronchiole. Chronic granulomatous inflammation in pulmonary tuberculosis is usually present in the bronchiolar walls and is associated with intraluminal caseous material. This granulomatous lesion in the bronchiolar walls may induce peribronchiolar fibrosis, which results in cyst formation. Third, the mechanism of cyst formation (subpleural emphysema) in some studies of pulmonary tuberculosis is presumed to be interstitial air leakage with tubercle rupture and caseation necrosis. The cavitary micronodules in our case may have resulted from drainage of caseation materials from the enlarged miliary nodules with bronchial communication.

References
1. Lee KS, Im J-G. CT in adults with tuberculosis of the chest: characteristic findings and role in management. AJR 1995;14:1361-1357
2. McGuinness G, Naidich DP, Jagirdar J, Leitman B, McCauley DI. High resolution CT findings in miliary lung disease. J Comput Assist Tomogr 1992;16:384-390
3. Ko KS, Lee KS, Kim YK, Kim SJ, Kwon OJ, Kim JS. Reversible cystic disease associated with pulmonary tuberculosis: radiologic findings. Radiology 1997;204:165-169