Histologic and ultrastructural characteristics of temporal arteritis. The value of the temporal artery biopsy.

Temporal artery biopsy is an easily performed procedure of low morbidity that produces valuable information in establishing a diagnosis and guiding therapy as well as providing tissue for further pathologic and immunologic research aimed at understanding and ultimately controlling this disease. The pathogenesis of temporal arteritis remains unresolved. In an effort to clarify this question, 19 temporal arteries demonstrating typical arteritic changes by light microscopy were also examined by transmission electron microscopy. At the light microscopic level, a granulomatous inflammation, often containing giant cells, was found in all layers of the vessel but most commonly concentrated within the internal or external border of the muscular media. The internal elastic lamina was usually fragmented and surrounded by inflammatory cells. Segmented subintimal fibromuscular hyperplasia and lymphocytic and plasma cell infiltration of the adventitia were nondiagnostic but suggestive findings commonly observed. Ultrastructural alterations were most striking in the muscular media. Degenerating smooth muscle cells with elongated mitochondria, dilated rough endoplasmic reticulum, and autophagic vacuoles containing electron-dense material were observed. Macrophages and giant cells contained degenerated smooth muscle cell basement membrane within phagocytic vacuoles, and macrophages were found within smooth muscle. Although frequently found in the vicinity of macrophages and giant cells, disrupted elastic lamina was not demonstrated in phagocytic cells.