Various histopathologic patterns can be observed on endomyocardial biopsy specimens from patients with cardiac sarcoidosis. These include the classic noncaseating granuloma-tous inflammation, lymphocytic myocarditis, dilated cardiomyopathy, and in some cases normal myocardium (Fig. 14-13; see color plate 33). Diffuse myocardial involvement progresses to myocyte hypertrophy and interstitial fibrosis resembling dilated cardiomy-opathy; in a minority of cases a restrictive profile is observed. The classic granulomatous pattern is characterized by firm white nodules forming discrete masses within the inter-ventricular septum, left ventricular free wall, or papillary muscle (Fig. 14-14 A; see color plate 34). These may be confused with metastatic deposits or fibrous tumors. The histopathologic features are similar to extracardiac lesions and consist of noncaseating, well-formed (so-called hard) granulomas composed of epithelioid histiocytes and multinucleated giant cells arranged in round or oval aggregates. These can be found as isolated lesions or may coalesce to form larger zones within the myocardium. Endocardial and pericardial involvement are observed in some cases. Scattered around and within the granulomas are mature lymphocytes, but eosinophils are absent or sparse. Mature collagenous fibrosis is present and surrounds the granulomas (Fig. 14-13 D), but active myocyte necrosis is uncommon.
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