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In this study an analysis of identified ICG lymphography features of the superficial lymphatics of the lower extremity was undertaken [Table 2.2]. The absence or presence and extent of the superficial lymphatics in the limb with LLLE was assessed to identify if any of these features or combination of features were significantly associated with particular diagnostic groups of primary or secondary cancer related or secondary non-cancer related LLLE. ICG lymphography studies undertaken by the researcher (submitted for publication) had identified two compensatory lymph drainage regions, the contralateral inguinal and axillo-inguinal nodal regions, associated with secondary cancer related LLLE which were not seen or very rarely seen in clinically diagnosed primary LLLE and less so in secondary non-cancer related LLLE. Conversely, retrograde flow in lymph vessels demonstrated during the ICG lymphography procedure was not seen in secondary cancer related LLLE. These observations provided a background rationale to exploring the diagnostic capacity of ICG lymphography in LLLE. One purpose of this study was to explore the feasibility of using ICG lymphography features as a diagnostic tool. It was hoped that identified ICG lymphographic features would allow the individual presenting with persistent leg swelling of unknown causation to be able to be advised that their condition is most likely a secondary non cancer related LLLE rather than an adult onset primary LE and therefore be possibly less likely to progress or deteriorate. This may potentially provide better prognostic information and improve individualised therapeutic plans of management and support compliance (Pigott, 2021). The aim of Part A of this study was to identify the prevalence and characteristics of ICG lymphography features of the lymph vessels, position and extent of DBF and drainage patterns. In addition, Part B of this study was to explore whether using the ALERT standardised ICG lymphography technique and a structured analysis of ICG lymphography features could be translated into a simple score to distinguish the ICG pattern of adult onset primary LLLE from secondary non-cancer related LLLE.