Chylous Reflux in Pediatric Primary Lymphedema of the Lower Limbs and Genitalia: A Retrospective Study of 167 Patients.

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Background: Chylous reflux (CR) in primary lymphedema (PL) of the lower extremities is rare and requires particular diagnostic procedures. This study aimed to determine clinical and lymphoscintigraphic traits for efficient screening. Methods and Results: Pediatric patients with PL of lower extremities treated in our institution between January 2020 and December 2023 were reviewed. The medical history, lymphoscintigraphy, non-contrast MR lymphography, and direct lymphangiography were analyzed. Lymphoscintigraphic visual patterns were classified to detect CR. Patients with CR showed significantly higher proportions of childhood symptom onset (65.63% vs. 25.19%, p < 0.01), genital lymphedema (62.50% vs. 19.26%, p < 0.01), and proximal-to-distal swelling (31.25% vs. 8.89%, p < 0.01). Eight patients without skin lesions had milk discharge after acupuncture or skin breakdown. Pattern 4 shows diffused dermal backflow of the leg and an absence of superficial lymphatic drainage, or normal initial cephalad flow with subsequent reflux of tracer into the affected limb. CR showed significantly higher percentages of pattern 4 (87.50% vs. 12.59%, p < 0.01), normal/widened iliac lymphatics (78.13% vs. 11.11%, p < 0.01), and thigh/calf outlining (87.50% vs. 29.63%, p < 0.01). Genital swelling preceding limb swelling and genital radioactivity were more common in the CR group. Conclusions: CR tends to occur in childhood initially, begin centrally and progress distally, and involve genitals prior to lower extremities. Milk discharge after acupuncture or skin breakdown is important for screening CR without chylous vesicles. The patterns with typical "profiling of the leg" and normal or widened iliac lymphatic trunks strongly correlate with CR. Genital lymphedema with increased radioactivity indicates CR.