Morphology of fibromuscular dysplasia of the renal artery in renovascular hypertension

The arterial pathology in sixty-six cases of renovascular hypertension due to idiopathic, nonatherosclerotic disruptive and hyperplastic lesions predominantly of the media of renal arteries has been designated under the general category of fibromuscular dysplasia. These lesions usually affected young adults, although their ages ranged from six to seventy-two years (average thirty-eight years). Women were affected more often than men (3 to 1). In most patients hypertension was relieved or ameliorated by surgical treatment. Histopathology and renal arteriography were used in assessing the arterial morphology. Arteriographically, the lesions presented focal (eleven cases), multifocal (thirty-five cases) or tubular (twenty cases) stenoses, which usually involved the distal two-thirds of the artery, and in fifty-eight per cent extended to the trifurcation or major branches. The right renal artery was the site of stenosis in 44 per cent, the left in 18 per cent; lesions were bilateral in 38 per cent of the cases. Histopathologically, the stenoses were predominantly due to medial thickening in forty-four cases, perimural fibrosis in sixteen cases and dissecting aneurysm in six cases. Multifocal stenoses due to medial thickening and multiple mural aneurysms were the most frequent type and produced a beaded appearance in the arteriogram. Contraction of disrupted segments contributes to the appearance of medial thickening and increases the degree of stenosis. Saccular or fusiform aneurysms developed apparently from mural aneurysms in nine cases. Mural aneurysms occurred in six cases and saccular or fusiform aneurysms in three cases of perimural fibrosis. Dissecting aneurysms involving both the main artery and its branches produced tubular stenosis of the lumen and acute hypertension in all six cases; renal infarcts were found in all six cases. Related disease in vessels other than the renal arteries was rare. Although the basic cause is uncertain, the vasa vasorum may have some role in the production of or the variations in the morphology of this unusual arterial disease. In the individual case of renovascular hypertension due to fibromuscular dysplasia, descriptive diagnosis still remains the most useful tactic and should include a description of the type of stenosis—whether focal, multifocal or tubular—the association with mural, saccular fusiform or dissecting aneurysm, and its distribution in the arterial tree.