MudPhud20XX

5+ Year Member
Nov 26, 2013
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Medical Student
Kaplan micro explains that the early onset of Listeria monocytogenes in neonate is characterized by disseminated granulomas with central necrosis.

So I have some questions:
1. What is the significance of the word "disseminated" granulomas instead of just granulomas?

2. Pathoma explains that the difference between noncaseating and caseating granulomas is whether it exhibits "central necrosis" or not. If there is an absence of central necrosis, then it is noncaseating and if there is central necrosis, then it is defined as caseating granulomas.

So would you considered disseminated granulomas with central necrosis equivalent to caseating granulomas?

3. Also, can anyone explain what is going on in granulomas? I get that granulomas = epithelioid histiocytes = macrophages abundant with pick cytoplasm, but I am not sure what they really means in plain English. (I could have googled it and try to digest in my own words, but I would appreciate any insights from you guys....)

Many thanks in advance
 

Myxedema

5+ Year Member
Aug 14, 2012
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Non-Student
A granuloma is the collection of epithelial-like macrophages (epitheloid histiocytes) and giant cells (formed by the fusion of epitheloid cells), surrounded by a rim of monocytes and lymphocytes. As you can see, this is a microscopic description. Now imagine looking at a tissue section under a microscope and you see granulomas surrounding an area of necrosis. If this is a TB infection, this central area of necrosis would be characterized as "caseous necrosis". This is not because of its microscopic appearance, but macroscopically, the necrotic area is white and soft, and the hungry hungry pathologists (as they often tend to do) describe it in a food term: cheese-like "caseous" necrosis.

Are necrotic areas seen in Listeria infections? Apparently, yes (I had to check it up in Robbins PBOD, those who like to read it, please refer to Chapter 8). According to Robbins, there is "necrotic amorphous basophilic tissue debris." However, it is not termed as "caseous". Why? No clear answer is given, but I'm going to speculate as the abscesses in Listeria infections are called as "microabscesses", perhaps such necrosis is simply not big enough to create the cheese-like morphology in the gross appearance.

Long story short: Caseous = TB. Necrosis does not necessarily mean caseous.
 
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