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MDCT of the Spleen: Splenic Abscess/Infection

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Infectious disease can spread systemically causing abscesses or micro abscesses. Infection of the spleen is unusual, but potentially lethal.

Abscess formation can be bacterial, parasitic or myocotic, but is typically due to pyogenic organisms including staphylococcus, streptococcus, anaerobes, and gram-negative rods such as Salmonella. The prevalence of abscess formation from pyogenic sources is 0.1-0.7%. Individuals predisposed to abscess formation includes diabetics, intravenous drug abusers, sickle cell patients, alcoholics, and the immunocompromised.

In immunocompetent hosts, infection often occurs through septic emboli in endocarditis, direct spread in pancreatitis, and via superimposed infection in trauma/infarction. 75% of these infections result from hematogeneous spread, 15% from penetrating trauma and 10% from infarction. Fungal infections prevail in immunocompromised hosts while infection in sickle cell patients is commonly the result of Salmonella.

Splenic infection can go unsuspected, however frequently presents with fever, chills, nausea and left upper quadrant pain. Occasionally infection is associated with development of a left pleural effusion. On contrast enhanced CT, abscesses appear as a focal region of decreased attenuation. The shape is typically slightly lobular with irregular, enhancing borders. When gas is present, it is specific for abscess formation, baring history of instrumentation. Debris can be present within an abscess. This CT appearance is similar to splenic cysts, cystic tumors, cystic degeneration of an infarct or hematoma. Treated/healing infection may produce further thickening or calcification of the abscess wall.

Micro abscesses are the result of widespread disease. Micro abscesses account for 26% of splenic infections and often causes splenomegaly. These lesions are typically multiple and 5-10 mm in size. This pattern occurs in immunocompromised patients often due to fungal disease, especially Candidiasis, Aspergillosis, and Cryptococcus. Other disease resulting in microabscesses include granulomatous processes such as tuberculosis or mycobacterium-avium-intracellulare, sarcoidosis, and pneomocystis carinni. Once treated these micro abscesses leave punctate calcifications heralding treated disease. The CT findings of lymphoma and leukemia simulate micro abscesses, with differentiation relying on clinical presentation and ancillary findings.

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