Pathogenesis and Etiology.
Conditions that predispose to splenic abscess formation are necrosis, infarcts, and hematoma within the spleen. These splenic lesions may be infected with bacteria that reach the spleen by several different routes. The most common route is by hematogenous seeding of organisms from a remote site via the splenic artery. In about 75% of patients with infection of the spleen, multiple abscesses are found in other organs ( Simson, 1980 ), including the liver, brain, and kidneys. Splenic abscess can also occur by direct invasion of bacteria from a subphrenic abscess.
Splenic abscesses are often polymicrobial and may be caused by aerobic or anaerobic bacteria alone or by a mixture of aerobic and anaerobic bacteria. Anaerobic bacteria isolated from splenic abscess include Peptostreptococcus species, Bacteroides species, Fusobacterium species, and Clostridium species; aerobic and facultative bacteria include E. coli, P. mirabilis, Streptococcus group D, K. pneumoniae, S. aureus, viridans streptococci, and Citrobacter freundii ( Brook and Frazier, 1998 ; Green, 2001 ). Salmonella species can cause splenic abscesses in patients with diseases that predispose to splenic infarction (such as sickle-cell anemia) and decreased phagocytic and opsonizing ability. M. tuberculosis reaches the spleen during the initial lymphohematogenous spread. In children with hematologic malignancies, fungi such as Candida and Aspergillus species may enter the spleen during periods of fungemia, resulting in microabscesses. Bacteria in splenic abscesses that result from extension of a subphrenic abscess will reflect the aerobic and anaerobic organisms found in that abscess. Rarely, splenic abscesses can be caused by Brucella species