Surgical pathology of cranial arteritis and polymyalgia rheumatica.

In both clinical and histological terms cranial arteritis is one of the most distinctive of all vascular disorders. The dense granulomatous inflammatory infiltrates which characterize the acute stages of the disease resemble those of Takayasu's arteritis or granulomatous angiitis of the central nervous system, but the clinicopathological features in patients with positive temporal artery biopsies are diagnostic. Well over a third of patients with classical signs and symptoms of cranial arteritis have negative temporal artery biopsies, and focal involvement of arteries of the head and neck is the probable explanation for this. Pathologists should be aware of the wide spectrum of histological changes that occur in muscular arteries as part of normal ageing and must not interpret these as evidence of healed arteritis. The histological changes of healed arteritis include medial chronic inflammation with ingrowth of new blood vessels, focal medial scarring and a bizarre pattern of intimal fibrosis. Although ultrastructural and immunohistochemical studies have provided some insight into the underlying pathological changes, they have not contributed directly to the diagnosis of cranial arteritis. Between 15 and 55% of patients with polymyalgia rheumatica have positive temporal artery biopsies, but apart from an elevated ESR there are no other laboratory investigations or biopsy procedures that contribute to diagnosis.