Fungi

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Fungi (singular fungus) 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)
Zygomycota (zygomycosis);
more specific
Mucorales (mucormycosis)
Fungi ? Branching hyphae with variable width ? Granulomata assoc. Diabetes, immunodeficient [4]
 
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)
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. (WC)
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 - 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

www:

Coccidioidomycosis

General

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

Microscopic

Features:

  • Forms spherules 60-80 μm in size.[8]
    • Contain endospores 1-5 μm in diameter.

Notes:

  • Spherules may be described as a "bag of marbles".

Images

www:

Pneumocystis pneumonia

  • Abbreviated PCP.
  • AKA Pneumocystis jirovecii pneumonia.

General

  • Organism: pneumocystis,
  • Specific organism: Pneumocystis jirovecii[13] (used to be called Pneumocystis carinii).
    • May be spelled Pneumocystis jiroveci.
    • 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:

  • Form frothy aggregates that take the shape of the alveoli they sit within, i.e. they form "alveolar casts".
  • "Dented ping-pong ball" appearance.[8] **Remember PCP = ping-pong.
    • Approximately 7-8 μm in size.

Images

www:

Stains

Cryptococcosis

General

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

Trivia:

  • Crypto- = hidden/invisible.[14]
    • Why the name? A. The capsule is almost invisible.

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]
  • Usually accompanied by very little inflammation.[15]

Notes:

  • May be confused with corpora amylacea in the CNS, esp. as they (like cryptococci) stain for methenamine silver, Alcian blue, and PAS.[16]

Images

www:

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

www:

Notes:

  • Cryptosporidium parvum?[17]

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.[18]

Notes:

  • May be described as "sticks and stones".

Images

www:

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.[19]
    • The interface between two separating fungi, i.e. fungi in the process of reproducing, is very large.

DDx:

Images

www:

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.
    • Rarely in immune competent individuals.[20]

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.
    • Spherical structures ~50 micrometres in diameter with radially arranged structures (like spokes of a wheel) +/- an empty centre in the plane of section.

DDx:

  • Mucormycosis - irregular width.
  • Scedosporium prolificans - in immunoincompetent individuals.[21]

Images:

Stains

  • PAS-D +ve.

Microsporidiosis

General

  • A group of (extremely) small intracellular microorganisms - classified as fungi.[23]
    • Human pathogenic organisms in this group include: Enterocytozoon bieneusi, Encephalitozoon hellem, and Encephalitozoon intestinalis.[24]
  • Important in the context of HIV/AIDS,[25] and solid organ transplant recipients.
  • May be seen in immune competent individuals.[24]

Clinical:[24]

  • Diarrhea.
  • Weight loss.
  • Abdominal pain.

Microscopic

Features:

  • Partial villus atrophy (villous blunting) and crypt hyperplasia.[24]
  • Small intracellular microorganisms ~ 1.0-4.0 μm.

Images:

EM

  • Small intracellular microorganisms ~ 1.0-4.0 μm.[23]

Image:

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. Redhead, SA.; Cushion, MT.; Frenkel, JK.; Stringer, JR.. "Pneumocystis and Trypanosoma cruzi: nomenclature and typifications.". J Eukaryot Microbiol 53 (1): 2-11. doi:10.1111/j.1550-7408.2005.00072.x. PMID 16441572.
  14. URL: http://en.wiktionary.org/wiki/crypto-. Accessed on: 12 April 2012.
  15. Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 423 Q29. ISBN 978-1416025887.
  16. URL: http://flylib.com/books/en/2.953.1.17/1/. Accessed on: 15 December 2010.
  17. http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm
  18. http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  19. 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.
  20. Sugimura, S.; Yoshida, K.; Oba, H.; Hashiguchi, K.; Nakajima, M.; Moriya, O.; Okimoto, N.; Niki, Y. et al. (Oct 1994). "[Two cases of invasive pulmonary aspergillosis in non-immunocompromised hosts].". Nihon Kyobu Shikkan Gakkai Zasshi 32 (10): 1032-7. PMID 7844909.
  21. URL: http://path.upmc.edu/cases/case290.html. Accessed on: 14 January 2012.
  22. 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.
  23. 23.0 23.1 Didier, ES. (Apr 2005). "Microsporidiosis: an emerging and opportunistic infection in humans and animals.". Acta Trop 94 (1): 61-76. doi:10.1016/j.actatropica.2005.01.010. PMID 15777637.
  24. 24.0 24.1 24.2 24.3 Didier, ES.; Weiss, LM. (Oct 2011). "Microsporidiosis: not just in AIDS patients.". Curr Opin Infect Dis 24 (5): 490-5. doi:10.1097/QCO.0b013e32834aa152. PMID 21844802.
  25. Orenstein, JM.. "Diagnostic pathology of microsporidiosis.". Ultrastruct Pathol 27 (3): 141-9. PMID 12775504.
  26. URL: http://wwwnc.cdc.gov/eid/article/18/2/11-1319_article.htm. Accessed on: 2 June 2012.