A 63–year–old man with a history of end stage renal disease status post deceased donor renal transplant and small bowel carcinoid status post excision presented with fevers. Infectious work–up was negative, and a CT scan of the abdomen showed mural thickening and fat stranding around his small bowel anastomosis and mesenteric lymphadenopathy. This raised concern for an infectious or inflammatory process or post–transplant lymphoproliferative disorder. The lymph nodes were not amenable to percutaneous biopsy by interventional radiology, and thus a biopsy was not pursued. His fevers eventually resolved with empiric antibiotics and he was discharged. On outpatient follow–up, an acid fast urine culture from his hospitalization grew mycobacterium avium complex (MAC). He was prescribed azithromycin and ethambutol. The patient returned to the hospital several weeks later with left–sided abdominal pain and fever. A CT scan of the abdomen showed a small bowel obstruction along with interval enlargement of the retroperitoneal lymph nodes seen on prior CT scan. The patient underwent an exploratory laparotomy where a tumor was found in the mesentery at the site of the obstruction. This tumor was excised along with surrounding lymph nodes and the involved segment of small bowel. There was initial concern for recurrence of his carcinoid tumor or a lymphoma, however surgical pathology and culture identified the mass as a mycobacterial spindle cell pseudotumor secondary to his MAC infection. The patient’s small bowel obstruction and fevers resolved after his surgery and he was discharged on a two–year course of azithromycin and ethambutol.
Mycobacterial spindle cell pseudotumor (MSP) is an exceedingly rare tumor–like lesion characterized by spindle–cell and histiocyte proliferation secondary to Mycobacterium tuberculosis or non–tuberculosis mycobacterial infection. It usually affects immunosuppressed patients with or without AIDS and in most cases occurs in lymph nodes. Less than 30 cases have been reported in the literature since 1985, when MSP was first described. To our knowledge, this is the first reported case of MSP causing a small bowel obstruction. Histologically, MSP has been described as an “exuberant spindle cell lesion” that “resembles a mesenchymal neoplasm”, including Kaposi’s sarcoma. Because of their shared histologic features, proper identification is important as the two diseases have distinct prognoses and treatments.
We present a case of Mycobacterium avium–complex that manifested as a mycobacterial spindle cell pseudotumor causing a small bowel obstruction. Although rare, this entity should be on the differential in an immunosuppressed patient with unexplained lymphadenopathy. In addition, since pseudotumor histologically resembles Kaposi’s sarcoma, differentiation is critical for treatment and prognostication purposes.
Figure 1Gross specimen of the resected bowel and tumor.
Figure 2AFB stain demonstrates numerous acid–fast bacilli in both the cytoplasm of the spindle cells as well as within the cytoplasmic vacuoles of the histiocytes.