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A Small Bowel Obstruction Caused by Mycobacterial Spindle Cell Pseudotumor
Author: Sajan Patel, MD, Michael Pfeffer, MD
Last Revised: Sat, 23-Nov-2013
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A Small Bowel Obstruction Caused by Mycobacterial Spindle Cell Pseudotumor

Sajan Patel, MD*
Michael Pfeffer, MD*
*David Geffen School of Medicine at the University of California, Los Angeles


Mycobacterial spindle cell pseudotumor (MSP) is an exceedingly rare tumor-like lesion characterized by spindle-cell and histiocyte proliferation secondary to mycobacterial infection. It usually affects immunocompromised patients and in most cases occurs in lymph nodes. We present a case of MSP manifesting as a small bowel obstruction.

Case Report

A 63 year-old man with a history of end-stage renal disease status post renal transplant and small bowel carcinoid status post excision presented with fevers. Infectious work-up was negative, however a CT scan of the abdomen showed mural thickening and fat stranding around his small bowel anastomosis along with 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, and his fevers eventually resolved with empiric antibiotics and he was discharged.

On outpatient follow-up, an acid-fast bacilli 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 fevers.  CT scan of the abdomen showed a small bowel obstruction along with interval enlargement of the retroperitoneal lymph nodes seen on prior imaging. Given the severity of the obstruction, 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 MAC infection. The patient’s small bowel obstruction and fevers resolved after his surgery and he was discharged on an indefinite course of azithromycin and ethambutol


Mycobacterial spindle cell pseudotumor (MSP) is a rare presentation of mycobacterial infection usually seen in AIDS patients with CD4 counts less than 60/ml and those with solid organ transplants, as in our patient1,2.  It can be caused by both M. tuberculosis and nontuberculosis mycobacterium.  Less than 30 cases have been reported in the literature since 1985, when MSP was first described3.  It has been described as occurring in the skin, spleen, appendix, bone marrow, brain, and most recently the lung4,5.  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,” characterized by histiocytes containing acid-fast mycobacteria.  It is also described as resembling a mesenchymal neoplasm, including Kaposi’s sarcoma.  Because of their shared histologic features and predilection for immunosuppressed hosts, proper identification is important as the two diseases have distinct prognoses and treatments1.

Given its rarity, there are no set guidelines for treatment of MSP.  Treatment is usually guided by the mycobacterium species identified.  Patients with MSP secondary to MAC can be treated with clarithromycin and ethambutol. Duration is usually life-long in patients without immune reconstitution.  Anti-retroviral therapy is indicated in patients with AIDS-associated MSP. 


  1. Chen KT. Mycobacterial spindle cell pseudotumor of lymph nodes. Am J Surg Pathol. 1992 Mar;16(3):276-81. PubMed PMID: 1309172.
  2. Sekosan M, Cleto M, Senseng C, Farolan M, Sekosan J. Spindle cell pseudotumors in the lungs due to Mycobacterium tuberculosis in a transplant patient. Am J Surg Pathol. 1994 Oct;18(10):1065-8. PubMed PMID: 8092397.
  3. Wood C, Nickoloff BJ, Todes-Taylor NR. Pseudotumor resulting from atypical mycobacterial infection: a "histoid" variety of Mycobacterium Avium-intracellulare complex infection. Am J Clin Pathol. 1985 Apr;83(4):524-7. PubMed PMID: 2984921.
  4. Jarzembowski JA, Young MB. Nontuberculous mycobacterial infections. Arch Pathol Lab Med. 2008 Aug;132(8):1333-41. doi: 10.1043/1543-2165(2008)132[1333:NMI]2.0.CO;2. Review. PubMed PMID: 18684037.
  5. Philip J, Beasley MB, Dua S. Mycobacterial spindle cell pseudotumor of the lung. Chest. 2012 Sep;142(3):783-4. doi: 10.1378/chest.11-2503. PubMed PMID: 22948583.

Submitted on July 28, 2013

A Small Bowel Obstruction Caused by Mycobacterial Spindle Cell Pseudotumor
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