Many groups developed the methods to quantitatively analyze low attenuation area (LAA) on chest CT in patients with cystic
lung diseases. Especially in
COPD, it was reported that the cumulative size distribution of LAA clusters follows a power law characterized by the exponent D, which reflect the fractal dimension of terminal airspace geometry. We hypoyhesized that the quantitative charateristics of LAA clusters including fractal property might indicate the different features of the progression of
cysts in cystic
lung diseases. The aim of this study was to apply the CT image-based method of characterizing the size distribution of LAA clusters for
lymphangioleiomyomatosis (
LAM) and
Birt-Hogg-Dubé syndrome (BHDS) to disclose their features of the progression of pulmonary
cysts. 40 patients with
COPD, 52 patients with
LAM, and 18 patients with BHDS who had undergone CT scans at our institute between January 2002 and August 2009 were included. Differences among these diseases in the quantitative characteristics of LAA clusters {i.e., extent, number, size, fractal property, and the relationship between these quantitatives} were assessed. The Chi-sqsuare test, unpaired t-test, and one-way analyses of variance with Tukey post-hoc tests were used to compare groups, spline model with an interaction terms were used to assess the relationship between extent and number, and exponential regression model was used to assess the relationship between extent and size. Statistically significant differences separated the three diseases in extent and number (P < 0.001). Number was significantly correlated with extent in
COPD (P < 0.001), but was not so in
LAM and BHDS when extent exceeded 11.5% and 20.8%, respectively. Size was significantly correlated with extent in
COPD and
LAM (P < 0.001), but was not so in BHDS. The percentage of CT images with fractal property was higher in
COPD than that in
LAM and BHDS (95.8%, 92.9% and 63.0%, respectively). In conclusion, our study has demonstrated for the first time the different characteristics of the size distribution of LAA clusters among
COPD,
LAM and BHDS, and indicated that this method is useful for exploration of the pathophysiology in cystic
lung diseases.