Histopathologic features of intracranial vascular involvement in fibromuscular dysplasia, ehlers-danlos type IV, and neurofibromatosis I.

Nonatherosclerotic cerebrovascular arteriopathies share epidemiologic and clinical features, but few studies directly compare histologic features of the intracranial vasculature. We studied 3 adult autopsy cases of fibromuscular dysplasia in patients who died of basilar artery aneurysm rupture, vertebral artery dissection, or Moyamoya syndrome. Fibromuscular dysplasia was only identified when multiple sections (optimally of the entire circle of Willis) were examined by microscopy. A fourth case of a massive subcutaneous scalp cirsoid aneurysm with classic "string-of-beads" gross appearance and microscopic medial hypertrophy was also compatible with fibromuscular dysplasia. Intracranial vascular changes were compared with those in 1 patient with Ehlers-Danlos type IV (vascular type) and in 4 patients with neurofibromatosis I. Distinct histologic features and distributions of cerebral vessel abnormalities were observed in all 3 disorders. Disordered collagen within the muscularis (identified using picrosirius red histochemistry) was confined to fibromuscular dysplasia; fibrocellular smooth muscle intimal proliferation within parenchymal cerebral arteries was confirmed using smooth muscle actin immunohistochemistry in the Moyamoya case; the patient with Ehlers-Danlos type IV showed aneurysm formation and eccentric intimal thickening of circle of Willis vessels but no obvious abnormalities of the muscularis; and neurofibromatosis I cases showed extensive leptomeningeal smaller-caliber arterial disease that particularly affected the spinal cord. Thus, cranial/intracranial artery involvement is not rare in these conditions but requires extensive sampling to identify the range of features.