Lung - nontumor
Infections
Histoplasma capsulatum

Author: Elliot Weisenberg, M.D. (see Authors page)

Revised: 24 February 2017, last major update September 2011

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

PubMed search: Histoplasma capsulatum [title] pulmonary

Cite this page: Histoplasma capsulatum. PathologyOutlines.com website. http://pathologyoutlines.com/topic/lungnontumorhistoplasma.html. Accessed May 28th, 2017.
Clinical features
  • Deep fungal infection indigenous to Ohio and Missouri River valleys and the Caribbean basin (eMedicine)
  • See also Skin - nontumor topic
  • Fungi are thermally dimorphic; spore producing hyphae outside body, but yeast at body temperature
  • Infection due to inhaling dust or soil particles contaminated with bird or bat droppings
  • "Capsulatum" is incorrect - no capsule is present
  • In immunocompetent, generally causes a self limited or latent infection, but chronic pneumonia preferentially involving lung apices associated with systemic symptoms and cough can occur; localized lung lesions, with or without lymph node involvement, are common; also localized lesions, often calcified, in adrenal, lymph nodes, liver, spleen, meninges; resembles tuberculosis with epitheliod granulomas with caseous necrosis; necrotic foci may coalesce to produce large areas of necrosis; with drug therapy or endogenous control, fibrosis and calcification occur, causing "tree bark" lesion
  • In immunocompromised, disease is often virulent and widely disseminated
  • If necessary, microbiologic studies, serology, or molecular studies are confirmatory
Pathophysiology
  • Infection is incompletely understood, but is usually controlled by helper T cells and heat shock protein that activate macrophages to kill yeast
Gross description
  • Resembles tuberculosis, may see "tree bark" appearance (due to fibrosis and calcification) or coin lesion
Gross images

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Cut surface of fibrocaseous nodule

Microscopic (histologic) description
  • Diagnosis based on identifying small, budding, intracellular yeast in tissue, 2 - 5 microns
  • Yeasts usually visible with H&E, but may need special stains; GMS more sensitive than PAS, but microcalcifications may create false positives
  • No / minimal granulomas in immunosuppressed or neonates; yeasts fill histiocytes and are widely disseminated
Microscopic (histologic) images

Images hosted on PathOut server:

Left images: H&E; right images: GMS - contributed by Dr. Jamie Shutter, Florida



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GMS staining

Negative stains