A 45-year-old woman with poorly controlled HIV/AIDS (CD4 count 4/µL) presented with worsening abdominal pain. CT abdomen showed extensive bulky retroperitoneal, periportal, and mesenteric lymphadenopathy with mesenteric infiltration and near-complete compression of the superior mesenteric vein, raising concern for lymphoma or an atypical infection. Hematoxylin and eosin (H&E) stained sections from an abdominal lymph node biopsy demonstrated diffuse proliferation of spindle-shaped histiocytes filled with innumerable rod-shaped ghost-like clear spaces (image A, H&E, 20x). The spindle cells were positive for CD68 and negative for cytokeratin AE1/AE3, SOX10, S100, cyclin D1, CD3, CD20, CD138, CD21, CD23, and HHV-8. Numerous intracellular acid-fast bacilli were identified by Ziehl-Neelsen (image B, ZN, 20x) and Fite stains and were also highlighted by Periodic acid–Schiff (image C, PAS, 20x) and, to a lesser extent, by Grocott's methenamine silver (image D, GMS, 20x). Flow cytometry was limited by low cellularity and viability but showed no clonal B-cell population. Blood and urine cultures subsequently grew Mycobacterium avium complex (MAC), confirming a disseminated MAC infection. The overall findings were diagnostic of mycobacterial spindle cell pseudotumor, a rare mass-forming histiocytic response to mycobacterial infection that may closely mimic a spindle-cell neoplasm or lymphoma in immunocompromised patients.