Mediastinal and Extrapleural Fat Hypertrophy in Idiopathic Pulmonary Fibrosis on High-resolution CT: Comparison with Normal Individuals

Son, Kyu Ri; Lee, Hyun Ju; Lim, Kun Young; Lee, Chang Hyun; Goo, Jin Mo; Im, Jung Gi

Abstract

PURPOSE
We wished to compare the amount of mediastinal and extrapleural fat on high resolution CT for patients with idiopathic pulmonary fibrosis (IPF) with that of normal individuals, and we wished to evaluate the correlation between the amount of fat and the degree of pulmonary fibrosis.
MATERIALS AND METHODS
We selected a group of 25 patients with radiologically and clinically diagnosed IPF and we also selected another group of 25 age and gender-matched patients having no abnormalities on pulmonary function testing as well as HRCT as controls from our radiologic database search (mean age: 59 years, M:F=11:14). We measured the area of mediastinal and extrapleural fat at the levels of the aortic arch and at the origin of the right pulmonary artery and right inferior pulmonary vein on three sections of HRCT by using software (Rapidia; 3DMED, Seoul, Korea). The total amount of fat was calculated by summing up the areas of the mediastinal and extrapleural fat, which is corrected by the body mass index; we also evaluated statistical differences between the two groups. At same sections of CT, the ratio (%) of the honeycombing area to the total areas of the lung was calculated. We evaluated the relationship between the amount of extrapleural or mediastinal fat with the ratio (%) of the honeycombing area.
RESULTS
The total amount of fat in patients with IPF and normal individuals were 67.24+/-19.03 cm2 and 32.55+/-11.91 cm2, respectively. The fat amount corrected by body mass index was 280.48+/-74.43 mm2/kg/m2 in the IPF patients and 137.06+/-41.76 mm2/kg/m2 in normal individuals. The differences between two groups for the total amount of fat and fat amount, as corrected for by the body mass index, were statistically significant (p<0.0001). The ratio (%) of the honeycombing area and the total amount of fat showed a moderate correlation (rho= 0.43, p= 0.032).
CONCLUSION
Patients with IPF have a larger amount of mediastinal and extrapleural fat than normal individuals. The hypertrophy of mediastinal and extrapleural fat in IPF may be affected by the severity of the interstitial fibrosis of the lung.