Fungi

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Fungi are microorganisms that are occasionally seen by pathologists.

Overview

  • There are lots of 'em. Below are a few of 'em.

Terminology:[1]

  • Hyphae = microscopic filamentous growth (of fungi) -- single cell.
  • Mycelial = filamentous network of hyphae.
  • Septae/septation = hyphae may be subdivided by septae -- if they aren't they are one mass of protoplasm. (?)
  • Dimorphism = exist in two forms; e.g. single cell (yeast) and mycelial growth.
  • Pseudohyphae = looks like hyphae --but branching pattern is created by separate cells.[2]

Tissue invasive fungi

Typically:[3]

Summary table

Name (disease) Kingdom Size Shape Stains Other (microscopic) Clinical References Image
Aspergillus (aspergillosis) Fungi ? Hyphae that branching
with 45 degrees angle
PAS-D Fruiting heads when aerobic ? Immunosuppression [4] Aspergillus (WC), Aspergillus cytology (WC)
Zygomycota (zygomycosis);
more specific
Mucorales (mucormycosis)
Fungi ? Branching hyphae with variable width ? Granulomata assoc. Diabetes, immunodeficient [4] Mucormycosis (homestead.com), Zygomycosis (WC)
Coccidioides, usually C. immitis
(coccidioidomycosis)
Fungi Large - 20-60 micrometers,
endospores 1-5 micrometers
Spherules Stains? Other? Immunodeficient [4] Coccidioidomycosis (med.sc.edu) C. immitis (WC) (webpathology.com)
Histoplasma (histoplasmosis) Fungi 2-5 micrometers Spherical GMS Intracellular (unlike candida), granulomata Source: soil with bird droppings [4] Histoplasmosis (WC)
Blastomyces (blastomycosis) Fungi 5-15 micrometres Spherical (yeast) Stains? Granulomas, broad-based budding yeast Habitat: Northeast America, Africa [4][5] Blastomyces
Paracoccidioides (paracoccidioidomycosis) Fungi 6-60 micrometres Spherical (yeast) Stains? Multiple budding "steering wheel" appearance Clinical??? [4] P. brasiliensis (WC).
Pneumocystis jirovecii (pneumocystis carinii pneumonia; abbrev. PCP) Fungi (previously thought to be a protozoan) 7-8 micrometres "Dented ping-pong ball" GMS Usually in clusters of alveolar casts with a honeycomb appearance HIV/AIDS associated [6] PCP (WC)
Cryptococcus (cryptococcosis) Fungi 5-15 micrometres Yeast GMS Prominent (i.e. thick polysaccharide) capsule HIV/AIDS associated, most common CNS fungus [4] Crytococcosis - methenamine silver (WC), Crytococcosis - mucicarmine (WC).

Notes:

  • Bold text = key features.

Specific fungi

Histoplasmosis

General

  • Organism: Histoplasma.
  • Specific organism: Histoplasma capulatum.
  • Typical location: lung.

Microscopic

Features:

  • Often in yeast form in tissue 2-5 micrometres.[7]
    • Nice bright red on PAS-D.
      • Have a "central dot".[8]

Images:

Coccidioidomycosis

General

  • Organism: Coccidioides.
  • Specific organism: Coccidioides immitis.
    • Usu. from soil.
  • Typical locations: lung, oral cavity.[9]

Microscopic

Features:

  • Forms spherules 60-80 micrometres in size.[7]

Images:

Pneumocystis pneumonia

  • Abbreviated PCP.
  • AKA Pneumocystis jiroveci pneumonia.

General

  • Organism: pneumocystis,
  • Specific organism: Pneumocystis jirovecii (used to be called Pneumocystis carinii).
    • Fungus... used to be considered a parasite.
  • Typical location: lung.

Clinical:

  • Opportunistic infection - typically in HIV +ve individuals.
  • May have subtle findings on chest X-ray.

Microscopic

Features:

Cryptococcosis

General

  • Organism: Cryptococcus.
  • Specific organism: C. neoformans.
  • Opportunistic infection.
  • Typical location: lung.
    • Most common fungus seen in CSF specimens.[4]

Microscopic

Features:

  • Yeast:
    • Round/ovoid 5-15 micrometres (may resemble Histoplasma or Candida -- but often larger).
    • Thick mucopolysacchardie capsule + refractile centre.[4]
    • "Tear drop-shapped" budding pattern (useful to differentiate from Blastomyces, Histoplasma).[4]

Notes:

  • May be confused with corpora amylacea in the CNS, esp. as they (like cryptococci) stain for methenamine silver, Alcian blue, and PAS.[11]

Images:

Cryptosporidiosis

General

  • Caused by cryptosporidium.
  • Fecal-oral transmission.
  • Usu. in immunoincompetent individuals, e.g. HIV/AIDS.

Microscopic

Features:

  • Uniform spherical nodules 2-4 micrometres in diameter, typical location - GI tract brush border.
    • Bluish staining of brush border key feature - low power.

Images:

Notes:

  • Cryptosporidium parvum?[12]

Candidiasis

General

  • Commonly Candida albicans.
  • Yeast forms.
  • Locations: oral cavity, vagina.

Microscopic

Features:

  • Dimorphic - seen in two forms:
    • Pseudohyphae[9] - collections of many C. albicans cells in a branching pattern.
    • Yeast form - single cells, 10 to 12 micrometres in diameter, gram positive.[13]

Stains

Features:

  • PAS +ve.
  • Methenamine silver +ve.

Blastomycosis

General

  • Usually Blastomyces dermatitidis - fungus.
  • May be in the oral cavity.[9]

Microscopic

Features:

  • Broad-based budding yeast -- is Blastomyces.[14]
    • The interface between two separating fungi, i.e. fungi in the process of reproducing, is very large.

Images:

Mucormycosis

General

  • Causative organism: Mucorales.
    • Kingdom: Fungi.
    • AKA Zygomycota (zygomycosis).
  • Assoc. with diabetes, immunodeficiency.

Microscopic

Features:[4]

  • Branching hyphae variable width.
  • Granulomata associated.

Image:

Aspergillosis

General

  • Due to Aspergillus.
  • Fungus.
  • Associated with immunosuppression/immunodeficiency. (???)

Microscopic

Features:

  • Hyphae that branching with 45 degrees angle - key feature.[4]
  • Fruiting heads when aerobic.

DDx:

  • Scedosporium prolificans.[15]

Images:

Stains

  • PAS-D +ve.

See also

References

  1. http://www.fungionline.org.uk/1intro/3growth_forms.html
  2. http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  3. CM 17 Apr 2009.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 682. ISBN 978-1416025887.
  5. http://pathmicro.med.sc.edu/mycology/mycology-6.htm
  6. Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 684. ISBN 978-1416025887.
  7. 7.0 7.1 7.2 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 103. ISBN 978-0781765275.
  8. 8.0 8.1 URL: http://moon.ouhsc.edu/kfung/jty1/opaq/PathQuiz/A6I001-PQ01-M.htm. Accessed on: 19 October 2010
  9. 9.0 9.1 9.2 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 3. ISBN 978-0781765275.
  10. URL: http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/pufrm.html. Accessed on: 4 December 2011.
  11. URL: http://flylib.com/books/en/2.953.1.17/1/. Accessed on: 15 December 2010.
  12. http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm
  13. http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  14. Veligandla, SR.; Hinrichs, SH.; Rupp, ME.; Lien, EA.; Neff, JR.; Iwen, PC. (Oct 2002). "Delayed diagnosis of osseous blastomycosis in two patients following environmental exposure in nonendemic areas.". Am J Clin Pathol 118 (4): 536-41. doi:10.1309/JEJ0-3N98-C3G8-21DE. PMID 12375640.
  15. URL: http://path.upmc.edu/cases/case290.html. Accessed on: 14 January 2012.