Histopathologic correlation of the three-layered intravascular ultrasound appearance of normal adult human muscular arteries

The purpose of this study was to correlate intravascular ultrasound images from normal peripheral muscular arteries with the microscopic arterial components by using surgical microdissection techniques. There has been uncertainty about the precise anatomic constituents that are represented by the intravascular ultrasound three-layer image in human peripheral arteries. Forty of 66 grossly normal human femoropopliteal arterial segments obtained at autopsy were found to have a three-layered appearance and were subjected to selective surgical microdissection of intima, media, or adventitia. After microdissection, arteries were imaged with a 30 MHz intravascular ultrasound system; two observers blindly reviewed video tapes to assess for the presence or absence of a one-, two-, or three-layered arterial appearance. Removal of internal elastic lamina and/or intima results in a weak but evident inner ultrasound acoustic interface as a result of the media, which is normally echolucent. Removal of the adventitia and/or external elastic lamina results in a weak outer ultrasound acoustic interface. Isolated removal of the media does not alter the three-layered ultrasound image. In normal adult human femoropopliteal arteries the inner bright acoustic reflection (layer) is derived from the interface of blood with the intima and internal elastic lamina and the second bright interface (third layer) is from the external elastic lamina and adventitia. The midecholucent zone is the result of the media. However, any portion of the arterial wall, including muscular media, can act as an acoustic interface.