Wyburn-Mason syndrome (WMS), also known as Bonnet-Dechaume-Blanc syndrome or retinoencephalofacial angiomatosis, is a rare condition. It is considered one of the nonhereditary congenital phakomatoses and is characterized by arteriovenous malformations (AVMs) that affect the retina, visual pathways, midbrain, and facial structures. It usually is unilateral and often is asymptomatic.
An example of a retinal AVM is shown in the image below.
Although these combined vascular abnormalities were recognized prior to the reports of Bonnet (1937)  and Wyburn-Mason (1943),  this syndrome is most frequently referred to as Wyburn-Mason syndrome, to honor the initial author of the classic case series. Wyburn-Mason syndrome is considered to be a congenital, nonhereditary, sporadic disorder and without sexual or racial predilection. Other vascular malformations may be present elsewhere in the body, including facial skin. In contrast to other phakomatoses, Wyburn-Mason syndrome does not commonly cause cutaneous manifestations.
Although the precise etiology and risk factors associated with Wyburn-Mason syndrome are unknown, recent studies have suggested a role for genetic factors in the pathogenesis of retinal AVMs. Early in the gestational period, vascular dysgenesis of the embryological anterior plexus occurs, characterized by variable alterations in capillary and arteriolar networks. Small AVMs may be subtle, with only minor alterations within the capillary system. Alternatively, the large "bag-of-worms" racemose AVM lesions are characterized by direct artery-to-vein communication, without interposing capillary or arteriolar elements causing high blood flow. The timing of the insult determines the embryonic tissue that is be affected. 
Wyburn-Mason syndrome is very uncommon, with incidence and prevalence rates that remain poorly defined. To date, fewer than 100 cases have been reported in the literature.
The worldwide incidence of Wyburn-Mason syndrome is also rare but ill defined.
Wyburn-Mason syndrome has no reported racial predilection, and there is no familial form of the syndrome.
No sexual predilection is noted.
Wyburn-Mason syndrome is a congenital disorder. Larger retinal AVMs that cause visual or neurologic impairment are generally diagnosed earlier in life, whereas smaller AVMs may remain asymptomatic and may not be diagnosed until later in life.
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