SP54. Are Venous Malformations a Distinct Clinical Entity? Evidence of Lymphatic Involvement In “Venous Malformations”

PURPOSE: Vascular malformations are classified according to flow characteristics and vessel subtype. Slow-flow vascular malformations consist of malformations of capillaries, veins (VMs), lymphatics (LMs), or a combination thereof. Both VMs and LMs can cause severe morbidities and even mortality. The diagnosis of a VM or LM is made by patient history, clinical exam, and imaging studies. In the skin and subcutaneous tissues, VMs are blue or violaceous while LMs are colorless. Ultrasound with Doppler flow studies (USG Doppler) demonstrate slow-flow in dilated vascular channels in VMs but not LMs. Despite clinical differences, VMs and LMs share similar pathogenic genetic variants (phenotypic heterogeneity). As lymphatic endothelial cells (ECs) are derived from venous ECs, we hypothesize that there are no pure VMs, and they should be re-classified as lymphaticovenous malformations (LVMs). METHODS: Patients who underwent resection of a clinically diagnosed VM were included in this study. VM clinical appearance and ultrasound flow characteristics were recorded. Paraffin-embedded tissues were stained for the nuclear lymphatic marker PROX1. ECs were isolated from resected VMs (VM-ECs) using the progenitor EC marker CD133. These VM-ECs were characterized by fluorescent-activated cell sorting (FACS) for established pan-EC markers (CD31 and VEGFR3) and lymphatic EC marker podoplanin (D2-40). Human umbilical venous endothelial cells (HUVECs) and human dermal lymphatic endothelial cells (HDLECs) were used as controls. RESULTS: A total of 11 VM samples and 1 LVM sample were available for analysis. All patients were clinically diagnosed as having a VM with blue and/or violaceous appearing lesions. USG Doppler confirmed slow flow in all patients. There were 7 tissue samples (including 1 LVM); 2 tissue samples also had corresponding isolated VM-ECs. VM-ECs (n=7) were successfully isolated. Four tissue specimens (3 VMs, 1 LVM) demonstrated PROX1 staining. FACS analysis revealed 2 VM-ECs were CD31+/VEGFR3+, 2 VM-ECs were CD31+/VEGFR3− and 1 VM-EC was CD31−/VEGFR3+. In summary, 4/7 VM-ECs expressed CD31 on the cell surface and 3/7 expressed VEGFR3 on the cell surface. By contrast, 6/7 VM-ECs expressed podoplanin on the cell surface. CONCLUSIONS: Most clinically diagnosed “pure VMs” with blood flow by USG Doppler express lymphatic EC markers. Our study suggests pure VMs are rare, complicating the VM-LM differentiation process by clinical examination and imaging studies alone. Our findings may also explain why VMs and LMs have similar genetic variants. Rather than being distinct diseases, our results suggest that VMs and LMs may belong on the spectrum of lymphaticovenous pathologies. We recommend that when resecting clinical “VMs”, the clinician should request podoplanin (D2-40) staining by pathology, to further separate true, pure VMs from LVMs.