Group III includes malformations characterized by markedly convoluted, dilated, and tortuous retinal vessels extending throughout the entire fundus, making it virtually impossible to differentiate between arterial and venous components. These eyes usually are severely vision impaired, which generally leads to earlier diagnosis in childhood. Patients in this group are at higher risk for systemic vascular involvement. It is possible that the preponderance of patients with more advanced retinal lesions in the Wyburn-Mason study made associated CNS lesions more common. Intracranial and retinal AV malformations occasionally are accompanied by vascular malformations in the skin, oronasopharnyx, orbit, lung, and spine.
Orbital involvement can present as mild proptosis, which usually is nonpulsatile.
Although facial nevi initially were described in the original Wyburn-Mason paper, this association is infrequent. Etiology of this syndrome is unknown. A histopathologic report of a patient with retinal and intracranial AV malformations demonstrated that the retinal vessels had a fibromuscular media of varying thickness with wide fibrohyaline adventitial coats. Arteries and veins were indistinguishable, and, in some cases, they were so large as to occupy the entire thickness of the retina. Because of the stability of the retinal lesions, treatment from an ophthalmologist usually is not necessary beyond routine, periodic ophthalmic examination.