It is not the case that all cranial hemangiomas affect the cerebrum; the common facial nevi, especially the flat midline ones and the elevated strawberry nevi, are of no neurologic significance. And a cerebral–meningeal angiomatosis may be present without skin lesions. The involvement of the upper eyelid is of greatest importance since nearly all such cases are associated with cerebral lesions (Barlow). There seems to be a close correlation between the persistence or maldevelopment of the embryonic vascular plexus of the eyelid and forehead and that of the occipitoparietal parts of the brain. When the nevus lies entirely below the upper eyelid or high on the scalp, a cerebral lesion is usually absent, although in a few instances such an angioma has been associated with a vascular malformation of the meninges overlying the brainstem and cerebellum. In angiograms, the abnormal meningeal vessels, which are largely veins, are not well seen; thus they can be distinguished from true arteriovenous malformations. These purely meningeal venous nevi are rarely the source of subarachnoid or cerebral hemorrhage and they do not enlarge to form a mass. The cortical lesion is, however, destructive of cortical tissue, which is replaced by glial tissue that calcifies. One explanation holds that diversion of blood to the meninges during seizures causes progressive ischemia of the cerebral cortex. Barlow has stated that the seizures themselves are responsible for the progressive neurologic deficits and that a special effort should be made to prevent them by carefully regulated medical therapy. Occasionally surgical excision of intractable discharging foci may be necessary, but often this may not be feasible in view of the magnitude of the cerebral lesion. Radiotherapy in the past was unsuccessful in reducing the skin blemish, though has shown promise in small studies in treating ocular choroidal hemangiomas and preserving vision. Instead, various laser techniques have been employed for the skin lesion with moderate cosmetic success. There is little literature on treating the brain vascular malformation with endovascular techniques.
Although a heredofamilial trait has long been known, it was only relatively recently that Shirley and colleagues found a polymorphism in the responsible gene, GNAQ, in almost 90 percent of individuals with the trait and in a similar number of patients with non-syndromic port-wine stains on the cranium. The variant may be of a mosaic type, being present only in affected tissues. This substitution in the gene activates extracellular signal-regulated kinase. Similar SNPs have been known to participate in other conditions that feature abnormal skin pigmentation.
A hemangioma of the spinal cord may rarely be accompanied by a vascular nevus in the corresponding dermatome, as was first pointed out by Cobb. Such nevi are most frequent on the arm and trunk. When the cutaneous lesion involves an arm or leg, there may be enlargement of the entire limb or fingers in combination with underdevelopment of certain other parts (Klippel-Trenaunay-Weber syndrome). Some of these angiomatous syndromes combine a spinal or retinal-diencephalic arteriovenous malformation (AVM) with a nevus of the trunk or face, respectively. Such cases provide a link to the common AVMs described in Chap. 33.