Sturge–Weber syndrome, sometimes referred to as encephalotrigeminal angiomatosis, is a rare congenital neurological and skin disorder. It is one of the phakomatoses and is often associated with port-wine stains of the face, glaucoma, seizures, intellectual disability, and ipsilateral leptomeningeal angioma (cerebral malformations and tumors). Sturge–Weber syndrome can be classified into three different types. Type 1 includes facial and leptomeningeal angiomas as well as the possibility of glaucoma or choroidal lesions. Normally, only one side of the brain is affected. This type is the most common. Type 2 involvement includes a facial angioma (port wine stain) with a possibility of glaucoma developing. There is no evidence of brain involvement. Symptoms can show at any time beyond the initial diagnosis of the facial angioma. The symptoms can include glaucoma, cerebral blood flow abnormalities and headaches. More research is needed on this type of Sturge–Weber syndrome. Type 3 has leptomeningeal angioma involvement exclusively. The facial angioma is absent and glaucoma rarely occurs. This type is only diagnosed via brain scan.

Sturge–Weber is an embryonal developmental anomaly resulting from errors in mesodermal and ectodermal development. Unlike other neurocutaneous disorders (phakomatoses), Sturge–Weber occurs sporadically (i.e., does not have a hereditary cause). It is caused by a mosaic, somatic activating mutation occurring in the GNAQ gene. Imaging findings may include tram track calcifications on CT, pial angiomatosis, and hemicerebral atrophy.