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.
  • Common in immunosuppressed individuals, e.g. HIV/AIDS population.
    • Extrapulmonary or disseminated histoplasmosis is considered to be AIDS-defining.[7]

Microscopic

Features:

  • Often in yeast form - in tissue, spherical, 2-5 micrometres.[8]
  • Intracellular[9] - may be within macrophages that form a granuloma.
    • Nice bright red on PAS-D.
      • Have a "central dot".[10]

Images:

Coccidioidomycosis

General

  • Organism: Coccidioides.
  • Specific organism: Coccidioides immitis.
    • Usu. from soil.
  • Typical locations: lung, oral cavity.[11]

Microscopic

Features:

  • Forms spherules 60-80 micrometres in size.[8]

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:

Stains

Cryptococcosis

General

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

Gross

Features (brain):

  • Small cystic spaces, often diffuse.
    • Known as "soap bubble brain".

Image:

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.[13]

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?[14]

Candidiasis

In the context of pap tests see: Gynecologic_cytopathology#Candida.

General

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

Microscopic

Features:

  • Dimorphic - seen in two forms:
    • Pseudohyphae[11] - collections of many C. albicans cells in a branching pattern.
    • Yeast form - single cells, 10 to 12 micrometres in diameter, gram positive.[15]

Notes:

  • May be described as "sticks and stones".

Stains

Features:

  • PAS +ve.
  • Methenamine silver +ve.

Blastomycosis

General

  • Usually Blastomyces dermatitidis - fungus.
  • May be in the oral cavity.[11]

Microscopic

Features:

  • Broad-based budding yeast -- is Blastomyces.[16]
    • The interface between two separating fungi, i.e. fungi in the process of reproducing, is very large.

DDx:

Images:

Mucormycosis

General

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

Microscopic

Features:[4]

  • Branching hyphae with variable width.
  • Granulomata associated.

Notes:

  • Not septated.
  • Branching angle typically ~90 degrees.

DDx:

Images:

Aspergillosis

General

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

Microscopic

Features:

  • Hyphae that branching with 45 degrees angle - key feature.[4]
    • Uniform width - typically ~3-5 μm.
  • Septated - often difficult to see.
  • Fruiting heads when aerobic - uncommon.

DDx:

  • Scedosporium prolificans.[17]

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. ↑ Schneider E, Whitmore S, Glynn KM, Dominguez K, Mitsch A, McKenna MT (December 2008). "Revised surveillance case definitions for HIV infection among adults, adolescents, and children aged <18 months and for HIV infection and AIDS among children aged 18 months to <13 years--United States, 2008". MMWR Recomm Rep 57 (RR-10): 1–12. PMID 19052530. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5710a1.htm.
  8. ↑ 8.0 8.1 8.2 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.
  9. ↑ Gorocica, P.; Taylor, ML.; Alvarado-Vásquez, N.; Pérez-Torres, A.; Lascurain, R.; Zenteno, E. (May 2009). "The interaction between Histoplasma capsulatum cell wall carbohydrates and host components: relevance in the immunomodulatory role of histoplasmosis.". Mem Inst Oswaldo Cruz 104 (3): 492-6. PMID 19547878.
  10. ↑ 10.0 10.1 URL: http://moon.ouhsc.edu/kfung/jty1/opaq/PathQuiz/A6I001-PQ01-M.htm. Accessed on: 19 October 2010
  11. ↑ 11.0 11.1 11.2 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.
  12. ↑ URL: http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/pufrm.html. Accessed on: 4 December 2011.
  13. ↑ URL: http://flylib.com/books/en/2.953.1.17/1/. Accessed on: 15 December 2010.
  14. ↑ http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm
  15. ↑ http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  16. ↑ 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.
  17. ↑ URL: http://path.upmc.edu/cases/case290.html. Accessed on: 14 January 2012.
  18. ↑ URL: http://www.ispub.com/journal/the-internet-journal-of-otorhinolaryngology/volume-6-number-1/maxillary-sinus-mycetoma-due-to-aspergillus-niger.html. Accessed on: 27 February 2012.
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