Wyburn-Mason syndrome is an extremely rare nonhereditary disorder that is present at birth (congenital). Affected infants have arteriovenous malformations (AVMs), which are developmental abnormalities affecting the blood vessels, specifically the arteries, veins and capillaries. Arteries typically carry oxygen-rich blood from the heart to body cells, while veins transport oxygen-deficient blood to the heart and lungs for the exchange of oxygen and carbon dioxide. The network of very tiny blood vessels (capillaries) that normally connects arteries and veins may be absent and the arteries and veins may be directly linked together. Larger AVMs may consist of a tangled mass of abnormal or malformed blood vessels. AVMs associated with Wyburn-Mason syndrome are usually found in the eyes and midbrain. The exact cause of Wyburn-Mason syndrome is unknown.

The symptoms associated with Wyburn-Mason syndrome vary greatly among affected individuals based upon the specific number and location(s) of associated arteriovenous malformations. Affected infants may have abnormalities affecting the eyes, central nervous system and, in rare cases, the skin.

In Wyburn-Mason syndrome, AVMs may range from absence of the capillaries to the presence of large masses of widened, twisted, tangled blood vessels known as a racemose hemangioma. Absence of capillaries results in the abnormal, direct connection of the arteries to the veins. This abnormal connection can result in excessive blood flow and subsequently inadequate blood flow (ischemia) further downstream.

AVMs in Wyburn-Mason syndrome often affect the thin layer of nerve cells that lines the back of the eyes (retina). In some cases, an AVM may extend into the eye socket (orbit) or brain. The specific symptoms associated with an ocular AVM vary depending upon the exact location and extent the abnormality. Small AVMs affecting tiny blood vessels may not cause any symptoms (asymptomatic) and may be difficult to detect. Large AVMs such as a racemose hemangioma may cause significant loss of vision, usually from lack of blood flow to the retina (retinal ischemia).

Additional Eye abnormalities may occur in some individuals with Wyburn-Mason syndrome including pressure on the eyeball so that the eyes bulge forward (proptosis), drooping of the upper eyelid (blepharoptosis), difficulty moving the eyes (ocular motility disorders), abnormally widened (dilated) blood vessels of the thin membrane that covers the outer surface of the eye (conjunctiva), and nerve Paralysis (palsies).

AVMs of the central nervous system may not cause any symptoms (asymptomatic) or can cause severe symptoms. Although AVMs are present at birth, in many cases they may not cause symptoms until the second or third decade of life or even later. Neurological symptoms associated with Wyburn-Mason syndrome include severe headaches, vomiting, seizures, Paralysis (palsy) of various cranial nerves and neck Stiffness (nuchal rigidity). Spontaneous bleeding (hemorrhaging) of these Lesions can lead to the sudden onset of symptoms. If the bleeding is severe, it can cause partial or full Paralysis of one side of the body (hemiparesis or hemiplegia) or even death.

In rare cases, the skin may be involved in Wyburn-Mason syndrome including the formation of small bumps or clusters of blood vessels (angiomas) on the face. If the jaw bones are involved, dental procedures can lead to excessive bleeding. Other areas of the body may also develop AVMs including the lungs or the kidneys or other bones and muscles.

The exact cause of Wyburn-Mason syndrome is unknown. It is considered a developmental abnormality characterized by AVMs. No specific genetic abnormality or hereditary tendencies have been identified. The specific, underlying mechanism(s) that cause AVMs in Wyburn-Mason syndrome are not known. However, they are thought to result from abnormalities of blood vessel development during embryonic or fetal growth.

No specific treatment for Wyburn-Mason syndrome exists. Treatment is directed toward the specific symptoms that are apparent in each individual. Some AVMs may not require treatment, especially retinal lesions which usually remain stable. If lesions in the eyes cause bleeding (hemorrhaging) in the retina or the clear, jelly-like substance that fills the middle of the eye (vitreous), laser treatment or the use of extreme cold to destroy abnormal tissue (cryosurgery) may be performed in an attempt to control the bleeding. Surgical removal of the vitreous (vitrectomy) has been performed in some cases if bleeding is persistent, although surgery is controversial.