sturge–weber syndrome is usually manifested at birth by a port-wine stain on the forehead and upper eyelid of one side of the face, or the whole face. the birthmark can vary in color from light pink to deep purple and is caused by an overabundance of capillaries around the ophthalmic branch of the trigeminal nerve, just under the surface of the face. there is also malformation of blood vessels in the pia mater overlying the brain on the same side of the head as the birthmark. this causes calcification of tissue and loss of nerve cells in the cerebral cortex.