The surgical pathology of pulmonary infarcts: diagnostic confusion with granulomatous disease, vasculitis, and neoplasia

Twenty-three cases of surgically resected pulmonary infarcts sent in consultation were reviewed to evaluate their morphology and to assess reasons for consultation. The morphology of these infarcts demonstrated that only a minority had the classical triangular shape at low magnification (26%) whereas the majority were either spherical (17%) or had a geographic pattern of necrosis (35%). The margin of the infarcted tissue often had a pseudogranulomatous appearance due to palisaded histiocytes, foam cells, or perpendicularly oriented proliferations of fibroblasts and myofibroblasts (74%) and occasional cholesterol-and hemosiderin-laden giant cells. Basophilic granular karyorrhectic necrosis was seen focally (52%) as was vascular inflammation (56%) raising the differential diagnosis of Wegener's granulomatosis or infectious granulomas. These nonclassical features combined with a low incidence of clinical hemoptysis, chest pain and pleurisy, and a primary radiographic diagnosis of 'nodule r/o malignancy' highlight the need to consider thromboembolic pulmonary infarcts in the differential diagnosis of necrotic lung nodules with a histiocytic and fibroproliferative rim. Modern Pathology (2009) 22, 679-685; doi: 10.1038/modpathol.2009.20; published online 13 March 2009