Correlation between indocyanine green (ICG) patterns and real-time elastography images in lower extremity lymphedema patients

Abstract

Indocyanine green (ICG) lymphography is becoming a popular modality, but unfortunately it is not available in all institutions. Elastography is a relatively new ultrasonographic technique to evaluate tissue elasticity, which visualizes fluid retention as a red region in lymphedema patients. The aim of this study was to evaluate the correlation between elastography and ICG lymphology. Thirty-six legs in 18 patients with secondary lower extremity lymphedema (LEL) and 20 legs in 10 healthy volunteers were examined using elastography. Thirty-six legs in 18 secondary LEL patients were examined using ICG lymphography. Elastography was performed on both legs at the following three sites: medial thigh (MT), medial leg (ML), and anterior ankle (AA). The area of the red region in the subcutaneous tissue demonstrated by elastography was calculated using Image software. ICG lymphography findings were classified into the following four patterns: linear (ICG1), splash (ICG2), stardust (ICG3), and diffuse (ICG4) patterns. As ICG pattern progressed, the red region area was likely to increase. There was a correlation between ICG patterns and red region area according to the severity at bilateral MT (rs = 0.665), ML (rs = 0.623), and AA (rs = 0.668). Significant difference was demonstrated among group means of the red region area by analysis of variance (healthy vs. ICG1 vs. ICG2 vs. ICG3 vs. ICG 4: 14.4 ± 5.7 vs. 15.1 ± 10.3 vs. 25.2 ± 6.2 vs. 30.8 ± 9.4 vs. 35.0 ± 2.8; P < 0.001). The area of the red region in the subcutaneous tissue shown using elastography, which represents fluid, increases with the aggravation of lymphedema demonstrated by ICG patterns. As elastography is performed by ultrasonography, which is available in most institutions, elastography could be a useful alternative evaluation for lymphedema severity when ICG lymphography is not available.