Page 203 - AIDSBK23C

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SPLEEN IN AIDS

Splenomegaly is a common clinical finding in patients with AIDS, and it is present at
autopsy in about one third of AIDS cases. Opportunistic infections or neoplasms are more likely
to be present when the splenic weight is greater than 400 g. Weights of up to 1 kg can
occur.[837] The most frequent splenic findings at autopsy are M avium complex (MAC), M
tuberculosis (MTB), cryptococcosis, cytomegalovirus, Kaposi's sarcoma, and malignant
lymphomas (Table 5).
Gross pathologic lesions consist of a prominent follicular pattern in about half of AIDS
cases and a miliary granulomatous pattern in about 10%.[837] Sepsis may lead to a soft, almost
liquid splenic parenchyma. Splenic infarcts may occur with embolization from non-bacterial
thrombotic endocarditis or infectious endocarditis involving mitral or aortic valves.

OPPORTUNISTIC INFECTIONS.-- Either MAC or MTB can be associated with the
appearance of granulomas. Mycobacterium avium complex is more likely to produce a myriad
of small 0.1 to 0.5 cm soft tan miliary granulomas, while MTB often presents with fewer
scattered and variably sized granulomas that are tan to white and firm. Microscopically, MAC
granulomas are predominantly composed of macrophages filled with numerous mycobacteria.
Mycobacterium tuberculosis produces a more typical histopathologic appearance with necrosis,
epithelioid cells, lymphocytes, occasional Langhans' giant cells, and scattered mycobacteria.
Cytomegalovirus and Candida are infrequent and difficult to diagnose in spleen. They
may be found within small foci of inflammation or necrosis that are not grossly evident and seen
microscopically only with careful searching at high magnification, aided by methenamine silver
or PAS stains.
The dimorphic fungi C neoformans, H capsulatum, and C immitis may also produce
visible granulomas but they are never as numerous as the granulomas seen in mycobacterial
infections. The fungal organisms are usually distributed throughout the red pulp and are often
accompanied by proliferations of macrophages. Diagnosis is facilitated by use of methenamine
silver or PAS stains.
Disseminated P jiroveci (carinii) infection may involve the spleen. By computed
tomographic scan, multiple nonenhancing, low-density masses with necrosis, hemorrhage, or
peripheral calcification may be seen. Grossly, these are large, soft, friable, tan nodules, which
can have focal hemorrhage. The same foamy pink exudate seen in pulmonary alveoli is seen
microscopically, but Gomori methenamine silver staining will demonstrate the cysts, though
immunoperoxidase staining with monoclonal antibody to P jiroveci (carinii) can be helpful when
cysts are not readily identified.[416]

NEOPLASMS.-- AIDS-associated neoplasms involve the spleen less frequently than
lymph nodes. Kaposi's sarcoma can be difficult to diagnose in the spleen because both grossly
and microscopically, KS can resemble splenic red pulp, and a mass lesion may not be apparent.
Spindle cells with atypia in a definable nodule or subcapsular infiltrate help to distinguish KS.
Malignant lymphomas occur in the spleen only one fifth of the time when they are present and
appear either as nodular masses in regions of white pulp or as infiltrates in red or white pulp.
The monomorphous nature of lymphomatous infiltrates with large cells is a helpful feature.
Immunohistochemical staining may be necessary to confirm the diagnosis.