Actinomyces species are agents of low pathogenicity and require disruption of the mucosal barrier to cause disease. Actinomycosis usually occurs in immunocompetent persons but may afflict persons with diminished host defenses. Oral and cervicofacial diseases commonly are associated with dental caries and extractions, gingivitis and gingival trauma, infection in erupting secondary teeth, chronic tonsillitis, otitis or mastoiditis, diabetes mellitus, immunosuppression, malnutrition, and local tissue damage caused by surgery, neoplastic disease, or irradiation. Pulmonary infections usually arise after aspiration of oropharyngeal or gastrointestinal secretions. Gastrointestinal infection frequently follows loss of mucosal integrity, such as with surgery, appendicitis, diverticulitis, trauma, or foreign bodies (1). The use of intrauterine contraceptive devices (IUDs) was linked to the development of actinomycosis of the female genital tract. The presence of a foreign body in this setting appears to trigger infection. Other predisposing factors are steroid use, immunosuppression, and human immunodeficiency viral infections (2).
Other bacterial species that often are co-pathogens to Actinomyces species may assist in the spread of infection by inhibiting host defenses and reducing local oxygen tension. Once the organism is established locally, it spreads to surrounding tissues that ignore tissue planes in a progressive manner, leading to a chronic, indurated, suppurative infection often with draining sinuses and fibrosis, especially in pelvic and abdominal infection. The fibrotic walls of the mass prior to suppuration are "wooden" in nature, and may be confused with a neoplasm. Hematogenous spread can be fulminant, but is rare.
The infection tendency is to spread without regard for anatomical barriers, including fascial planes and lymphatic channels. Actinomyces grow in microscopic or macroscopic clusters of tangled filaments surrounded by neutrophils. Plasma cells and multinucleated giant cells often are observed with lesions, as may be large macrophages with foamy cytoplasm around purulent centers. When visible, these clusters are pale yellow and exude through sinus tracts; they are called "sulfur granules" (originally called "drusen"). These granules (1 to 2 mm in diameter) are made of aggregates of organisms and contain calcium phosphate. A central purulent loculation surrounds the granules. Their centers have a basophilic staining property, with eosinophilic rays terminating in pear-shaped "clubs." One to six granules can be present per loculation, and up to 50 loculations can be present in a lesion.
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