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ICG Lymphography and Its Application
Key Points
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Indocyanine green (ICG) lymphography clearly visualizes superficial lymph flows in real time without ionized radiation exposure.
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Dynamic ICG lymphography, dual-phase fluorescent image observation, is important to maximize the efficacy of ICG lymphography for lymphatic mapping and appropriate severity staging.
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ICG lymphography findings change from “linear,” to “splash,” to “stardust,” and finally to “diffuse” pattern with the progression of lymphedema.
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ICG lymphography allows pathophysiologic severity staging for secondary lymphedema and classification of primary lymphedema.
Introduction
Although lymphoscintigraphy is considered a gold standard for lymph flow imaging, there are many drawbacks in lymphoscintigraphy necessitating another modality; obtained images are obscure and it has a risk of ionized radiation exposure. Near-infrared fluorescent lymphography using indocyanine green (ICG), or ICG lymphography, has been developed for lymphedema evaluation. ICG lymphography is becoming popular, since it allows much clearer visualization of superficial lymph circulation than other imaging modalities. As ICG lymphography allows real-time fluorescent imaging, pre/intraoperative navigation for lymphatic surgeries can be applied with the use of ICG lymphography into lymphaticovenular anastomosis (LVA), vascularized lymph node transfer (LNT), lymph-interpositional-flap transfer (LIFT), and liposuction in various parts of lymphedema, such as arm, leg, facial, and genital lymphedema. Dynamic ICG lymphography, dual-phase ICG lymphography, has been developed to allow pathophysiologic lymphedema evaluation and intraoperative mapping/navigation of lymphatics with only one ICG injection ( Fig. 7.1 ).
Characteristic ICG Lymphography Findings
ICG lymphography findings are classified into two patterns: the normal “linear” pattern and the abnormal “dermal backflow (DB)” pattern. The DB pattern can be subdivided into “reticular,” “splash,” “stardust,” and “diffuse” patterns. The reticular pattern is an atypical DB pattern seen at an early transient phase, whereas splash, stardust, and diffuse patterns are DB patterns seen at a late plateau phase; the reticular pattern seen at a transient phase may change to a stardust or diffuse pattern at a plateau phase ( Fig. 7.2 ). The linear pattern, longitudinal lines along the axis of the extremity, represents lymph flows of the collecting lymphatic vessels, normograde lymph flows. Damage to lymph nodes or vessels, such as by lymph node dissection, radiation, trauma, or malformation, causes lymphatic hypertension, dilatation of the collecting lymphatic vessels, lymphatic valvular insufficiency, and retrograde lymph flows. Retrograde lymph flows of the superficial collecting or the precollecting lymphatic vessels are shown as a splash pattern of tortuous lines on ICG lymphography. These dilated superficial lymphatics play as collateral lymphatic pathways. When the collateral pathways fail to compensate for lymphatic overload, further retrograde lymph flows take place, leading to vertical retrograde flows toward the dermis. These vertical retrograde lymph flows are shown as spots on ICG lymphography: the stardust pattern. Finally, the collecting and precollecting lymphatic vessels can be obstructed because of lymphosclerosis, and horizontal lymph flows of the dilated lymphatic capillaries play a major role in lymph circulation. These dilated lymphatic capillaries are shown as a diffuse pattern, diffusely enhanced on ICG lymphography.
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