Fig. 1

a Ultrasound image obtained by applying a linear probe parallel to the spine (right Th8) at slightly lateral (toward the ribs) the transverse process and b a color Doppler image at the same site. The three white arrows indicate the internal intercostal membrane leading to the superior costotransverse ligament. Two blood vessels were observed to have expanded to fill the intercostal/paravertebral space, where blood vessels are often not recognized. The diameters of these two vessels were 4.1 mm and 2.6 mm, respectively, which are larger than the respective diameters of normal intercostal arteries and veins (1.4 ± 0.3 mm) [3]