Introduction
slow-flow malformations, vascular malformation, slow-flow vascular malformations, arteriovenous malformations, abnormal lymph-filled cysts, Vascular malformations, VMs, LMs, CM, macrocystic, phleboliths
INFILTRATE
Vascular malformations result from defects in vasculogenesis, angiogenesis, and lymphangiogenesis. They are divided based on blood flow velocity into slow-flow malformations (capillary, CM; venous, VM; lymphatic, LM), fast-flow malformations (arteriovenous malformations), and combined malformations. VMs and LMs are the most common slow-flow malformations. They can be well localized or extensive. VMs can affect any tissue or organ; they are easily detected on the skin. They are usually blue-colored, soft, and compressible, and intralesional phleboliths are common. Histologically, they are characterized by enlarged venous-like channels with relative lack of smooth muscle cells. LMs consist of multiple abnormal lymph-filled cysts, which are covered by a single layer of lymphatic endothelial cells. Two subtypes are recognized: LMs with large cysts (macrocystic) and lesions that infiltrate tissues (microcystic) (Excessive activation of the phosphoinositol-3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) cascade is frequently observed in slow-flow vascular malformations, resulting in locally uncontrolled development of blood vessels (The efficacy of the mTOR inhibitor sirolimus for the treatment of slow-flow vascular malformations was prospectively evaluated in a small number of phase II trials, all having inherent limitations in terms of patient number, patient population (mostly children, vascular malformation types, absence of genomic studies), and design (undefined treatment time duration versus 12 months) (