Microorganisms

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Microorganisms show-up every once in a while. It is essential to know 'em.

Microorganisms

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 [1] Aspergillus (WC), Aspergillus cytology (WC)
Zygomycota (zygomycosis);
more specific
Mucorales (mucormycosis) 		Fungi ? Branching hyphae with variable width ? Granulomata assoc. Diabetes, immunodeficient [1] Mucormycosis (homestead.com), Zygomycosis (WC)
Coccidioides, usually C. immitis
(coccidioidomycosis) 		Fungi Large - 20-60 micrometers,
endospores 1-5 micrometers 		Spherules Stains? Other? Immunodeficient [1] Coccidioidomycosis (med.sc.edu) C. immitis (WC)
Histoplasma (histoplasmosis) Fungi 2-5 micrometers Spherical GMS Intracellular (unlike candida), granulomata Source: soil with bird droppings [1] Histoplasmosis (WC)
Blastomyces (Blastomycosis) Fungi 5-15 micrometres Spherical (yeast) Stains? Granulomas, broad-based budding yeast Habitat: Northeast America, Africa [1][2] Blastomyces
Paracoccidioides (Paracoccidioidomycosis) Fungi 6-60 micrometres Spherical (yeast) Stains? Multiple budding "steering wheel" appearance Clinical??? [1] 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 [3] PCP (WC)
Cryptococcosis Fungi 5-15 micrometres Yeast GMS Prominent (i.e. thick polysaccharide) capsule HIV/AIDS associated, most common CNS fungus [1] Crytococcosis - methenamine silver (WC), Crytococcosis - mucicarmine (WC).

Notes:

  • Bold text = key features.

Fungi

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

Terminology:[4]

  • 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.[5]

Tissue invasive fungi

Typically:[6]

  • Mucor
  • Aspergillus

Histoplasmosis

Coccidiomycosis

Pneumocystis pneumonia (PCP)

  • Pneumocystis jirovecii (used to be called Pneumocystis carinii) - fungus (that used to be considered a parasite), typical location: lung.
    • Clinical: Opportunistic infection. May have subtle finding on chest x-ray.
    • "Dented ping-pong ball" appearance;[7] - remember PCP = ping-pong.
    • Approximately 7-8 micrometres in size - PCP (WP). Several images are here (WC).

Cryptococcus

  • Usually C. neoformans, fungus - opportunistic infection, typical location: lung.
  • Most common fungus seen in CSF specimens.[1]

Appearance:

  • Yeast:
    • Round/ovoid 5-15 micrometres (may resemble Histoplasma or Candida -- but often larger).
    • Thick mucopolysacchardie capsule + refractile centre.[1]
    • "Tear drop-shapped" budding pattern (useful to differentiate from Blastomyces, Histoplasma).[1]

Images:

Notes:

  • May be confused with corpora amylacea in the CNS, esp. as they (like cryptococci) stain for methenamine silver, Alcian blue, and PAS.[10]

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?[11]

Candidiasis

Blastomycosis


Mucormycosis

General

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

Histology

Features:[1]

  • Branching hyphae variable width.
  • Granulomata associated.

Image:

Worms & stuff

Schistosoma

See Urine cytopathology.
  • Associated with squamous cell carcinoma of the bladder.

Microscopic

Features of ova:

  • Elliptical ~80 micrometres max dimension.
  • S. haematobium has a "spike" approx. the size of a PMN.

Image:

Toxoplasma

General

  • Common CNS infection.

Microscopic

General:

  • Dependent on location in body.

Lymph node

LN features:[14]

  • Reactive germinal centers (pale areas - larger than usual).
    • Often poorly demarcated - due to loose epithelioid cell clusters at germinal center edge - key feature.
  • Epithelioid cells - perifollicular & intrafollicular.
    • Loose aggregates of histiocytes (do not form round granulomas):
      • Abundant pale cytoplasm.
      • Nucleoli.
  • Monocytoid cells (monocyte-like cells) - in cortex & paracortex.
    • Large cells in islands/sheets key feature with:
      • Abundant pale cytoplasm - important.
      • Well-defined cell border - important.
      • Singular nucleus.
    • Cell clusters usually have interspersed neutrophils.

Images (lymph node):

CNS

CNS features:[15]

  • "Ball with granular skin"

Image (CNS):

IHC

  • IHC for toxoplasma.[16]

Strongyloidiasis

General

  • Causes by worm Strongyloides stercoralis.
  • High case mortality rate ~ 70%.[17]
  • May present after years of latency due to immune suppression.[18]

Location:

  • Lung. (???)

Microscopic

Features:

  • Long worms.
  • ~10-15 micrometers wide.

Images:

Echinococcus

  • Echinococcus granulosus.
  • Causes hydatid disease in the liver.

Features:

  • Hooklets.
  • Scoleces - knoblike anterior end of a tapeworm.[19]

Enterobius vermicularis

  • AKA pinworm.

Features:[20]

  • Ovoid eggs - double walled shells, one side flat.

Images:

Trichinella

General

  • Causes Trichinosis.
    • Classically associated with uncooked pork.[21]
  • Several types; most due to T. spiralis.[21]

Microscopic

Features:

  • Worm.

Image:

Cysticercosis

General

  • Caused by Taenia solium; pork tapeworm.
  • May cause epilepsy; most common parasitic CNS infection.[23]

Viruses

Main article: Viruses

This is a fairly big topic. There are about half a dozen viral inclusions (e.g. CMV, HSV, VZV, adenovirus) a decent pathologist ought to be able to identify. The virus article covers 'em.

See also

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 682. ISBN 978-1416025887.
  2. ↑ http://pathmicro.med.sc.edu/mycology/mycology-6.htm
  3. ↑ Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 684. ISBN 978-1416025887.
  4. ↑ http://www.fungionline.org.uk/1intro/3growth_forms.html
  5. ↑ http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  6. ↑ CM 17 Apr 2009.
  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. ↑ 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://flylib.com/books/en/2.953.1.17/1/. Accessed on: 15 December 2010.
  11. ↑ http://www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis.htm
  12. ↑ http://pathmicro.med.sc.edu/mycology/mycology-3.htm
  13. ↑ PMID 12375640
  14. ↑ Ioachim, Harry L; Medeiros, L. Jeffrey (2008). Ioachim's Lymph Node Pathology (4th ed.). Lippincott Williams & Wilkins. pp. 113. ISBN 978-0781775960.
  15. ↑ URL: http://moon.ouhsc.edu/kfung/jty1/opaq/PathQuiz/N0I001-PQ01-M.htm. Accessed on: 19 October 2010.
  16. ↑ URL: http://moon.ouhsc.edu/kfung/jty1/opaq/PathQuiz/N0I001-PQ01-M.htm. Accessed on: 19 October 2010.
  17. ↑ Lim, S.; Katz, K.; Krajden, S.; Fuksa, M.; Keystone, JS.; Kain, KC. (Aug 2004). "Complicated and fatal Strongyloides infection in Canadians: risk factors, diagnosis and management.". CMAJ 171 (5): 479-84. doi:10.1503/cmaj.1031698. PMID 15337730.
  18. ↑ Siddiqui, AA.; Berk, SL. (Oct 2001). "Diagnosis of Strongyloides stercoralis infection.". Clin Infect Dis 33 (7): 1040-7. doi:10.1086/322707. PMID 11528578.
  19. ↑ http://www.thefreedictionary.com/scoleces. Accessed on: 10 January 2010.
  20. ↑ Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 685. ISBN 978-1416025887.
  21. ↑ 21.0 21.1 Kaewpitoon N, Kaewpitoon SJ, Philasri C, et al. (October 2006). "Trichinosis: epidemiology in Thailand". World J. Gastroenterol. 12 (40): 6440–5. PMID 17072975. http://www.wjgnet.com/1007-9327/12/6440.asp.
  22. ↑ URL: http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/msfrm.html. Accessed on: 5 December 2010.
  23. ↑ Prasad KN, Prasad A, Verma A, Singh AK (November 2008). "Human cysticercosis and Indian scenario: a review". J. Biosci. 33 (4): 571–82. PMID 19208982.
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