Multiple sections of the right and left ventricles and interventricular septum demonstrated geographic foci of myocardial necrosis and focal fibrosis (Images 01 and 02). There was a prominent inflammatory infiltrate of eosinophils, neutrophils and lymphocytes (predominantly T cells). In addition, there were a variable number of Touton type giant cells in the absence of well formed granulomata (Images 03 and 04). The giant cells were randomly distributed, some adjacent to necrotic myocytes (Image 03). The atria were involved with a similar process, although to a lesser extent.
Immunohistochemical evidence of a histiocytic origin of the giant cells was confirmed by immunoreactivity with KP-1 (CD 68) (Images 05 and 06), and a lack of staining with muscle markers, pan-actin and desmin. There was minimal inflammation of the epicardium, with no giant cells identified beyond the myocardium (Image 07). Myocyte hypertrophy was also noted.
Special stains for fungal and acid fast organisms were negative and there were no interstitial Aschoff bodies identified.