At the Viewbox: Mycobacterium Avium-intracellulare Complex Enteritis

Why did this 30-year-old man with AIDS present with abdominal pain and diarrhea? Axial (A) and coronal (B) CT images demonstrate bowel wall thickening throughout the duodenum, jejunum, and ileum (black arrows) with hypodense mesenteric lymphadenopathy (white arrow). The coronal image (B) also demonstrates splenomegaly with multiple splenic infarcts (curved arrows). Differential diagnosis for such a presentation includes opportunistic infections, such as Mycobacterium avium-intracellulare complex (MAC), tuberculosis, cytomegalovirus, and cryptosporidium vs. lymphoma. Biopsy of the ileum confirmed the diagnosis of MAC.

MAC is the most common systemic bacterial infection in AIDS patients, affecting up to 25%.¹ It primarily involves the gastrointestinal tract in patients with a CD4 < 50.¹ Presentation typically consists of malabsorptive watery diarrhea. CT characteristically shows thickened loops of small bowel, lymphadenopathy, and hepatosplenomegaly.² Jejunal thickening is common but the entire small bowel may be involved. Lymphadenopathy often involves mesenteric, periportal, and retroperitoneal nodes. Nodes are more often small and noncaseating as compared to tuberculosis. However, as CD4 count rises above 100 with treatment, nodes often become larger and hypodense secondary to immune-mediated caseous necrosis.¹ Biopsy with a positive acid fast stain may be necessary to exclude lymphoma.

1. Macari M. Imaging of intestinal manifestations of AIDS. In: Dionisio D, ed. Textbook-atlas of intestinal infections in AIDS. Milano: Springer-Verlag Italia; 2003:263-270.
2. Ha HK, Park SH, Lee SH, et al. Gastrointestinal tract. In: Haaga JR, Dorga VS, Forsting M, Gilkeson RC, Ha HK, Sundaram S, eds. CT and MRI of the whole body, 5th ed. Philadelphia: Mosby Elsevier; 2009:1213-1372.