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Findings: CT of the abdomen was performed which showed multiple cystic lesions within the spleen diffusely.
Diagnosis: Pneumocystis carinii infection in the spleen.
Discussion: Pneumocystis carinii is a pathogen which is an important cause of pneumonia in an immunocompromised host. The natural habitat of this pathogen is in the lung. Although this pathogen typically remains confined to the lungs, extrapulmonary disease is possible. Estimates range from less than 1-3 percent of cases. Common sites of dissemination include lymph nodes, liver, bone marrow, and spleen. Splenic pneumocystis carinii infections have been described typically as low attenuation lesion which may contain internal calcifications.
One proposed mechanism for dissemination was that extensive necrosis and calcification in the lungs, atypical for PCP, may cause increased host phagocytic activity, leading to phagocystosis of live organisms and therefore dissemination of live organisms to sites other than the lung.
Additionally, increasing numbers of disseminated pneumocystis carinii cases may be secondary to the increasing number of AIDS cases and the increasing life span of these patients.
Aerosolized pentamidine is being used increasingly for PCP infections. The aerosolized form of this drug causes decreased levels of systemic pentamidine and this may also lead to dissemination of the infection.
Differential diagnosis of cystic lesions in the spleen includes post traumatic, epidermoid, epithelial and echinococcal cysts. Additionally abscess, lymphoma and metastatic lesions may also appear as regions of decreased attenuation in the spleen that may mimic cystic lesions.
References:
Cohen OJ, Stoeckle MY. Extrapulmonary Penumocystis Carinii Infections in the
Acquired Immunodeficiency Syndrome. Archives of Int. Med. June 1991, 151(6)1205-14.
Burke BA, Good RA. Pneumocystis Carinii Infection. Medicine 1973;52:23-51.
Lubat E, et al. Extrapulmonary Pneumocystis Carinii Infection in AIDS. CT Findings.
Radiology 1990;174:157-160.
Harrison's Principles of Internal Medicine. 13th edition. McGraw Hill 1994.
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