Colon non tumor
Infectious colitis (specific microorganisms)

Author: Lili Lee, M.D. (see Authors page)

Revised: 4 January 2017, last major update November 2013

Copyright: (c) 2003-2017,, Inc.

PubMed Search: Histoplasmosis of colon
Cite this page: Histoplasmosis . website. Accessed July 21st, 2017.
Definition / general
  • Pulmonary fungal infection which may disseminate to other organs (disseminated histoplasmosis)
  • Cave disease, Darling's disease, Ohio valley disease, reticuloendotheliosis, spelunker’s lung
  • Caused by inhaling the microconidia (spores) formed by the environmental mold
  • Mostly encountered in endemic areas of Mississippi River Valley and Ohio River Valley
  • Classically associated with bird feces, bat guano, spelunking
  • Common infection among immunocompromised patients
  • Pulmonary infection, sclerosing/fibrosing mediastinitis, disseminated form affects multiple organs including GIl tract
  • Yeast forms are phagocytized by pulmonary macrophages and may disseminate to other organs
  • Healthy individuals are usually asymptomatic
  • Immunocompromised patients may develop progressive disseminated infection
Clinical features
  • Flu-like symptoms, abdominal pain, diarrhea
  • Early diagnosis and treatment avoids bowel perforation and hemorrhage
  • Miscroscopy, Histoplasma capsulatum antigen in urine or serum by enzyme immunoassay (EIA), culture (slow, may take 4-6 weeks)
Radiology description
  • Bowel wall thickening or mass-like lesions
Case reports
  • Amphotericin B and itraconazole
Clinical images

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Large, polypoid, ulcerated, malignant-appearing tumor

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Ulcer in the sigmoid colon

Gross description
  • May cause gastrointestinal mucosal ulceration and form polypoid lesions, strictures or a mass, grossly simulating carcinoma
Microscopic (histologic) description
  • Yeast forms (2-5 um) with basophilic crescent-shaped nucleus seen within macrophages, often with a pericellular halo
  • Organism are most easily found within necrotizing granulomas
Microscopic (histologic) images

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Numerous yeast forms

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Small rounded intracytoplasmic organisms

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Fig 2/3-H&E, 4-GMS

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Cytology description
  • Numerous vacuolated single cells suspicious for signet ring cell carcinoma; oval histiocytes with intracellular yeasts (Acta Cytol 1996;40:989)
Positive stains
Differential diagnosis
  • Cryptococcus: rare in colon; variably sized organisms (3 - 10 um)
  • Leishmania: rare in colon; GMS-, Histoplasma lacks kinetoplasts