Intro to Meningitis Pathology

Question 1

What does acute bacterial meningitis look like grossly?

Answer 1

• Pus, many neutrophils collect over surface, collects more near veins
• Engorged meningeal veins
• Exudate (or pus) over hemispheres

Question 2

Where might pus collect at base of brain?

Answer 2

In the cisterna magna!

Question 3

Where do different bacteria collect in meningitis?

Answer 3

H. infleunzae, TB, Cryptococcus –> Basal (coats borrom of brain)
S. pneumoniae –> Cortical (cortex) or Basal

Question 4

What can happen to the pus of acute bacterial meningitis later in disease course?

Answer 4

Pus will start to organize, almost has fibrinous look, looks like there are strings between brainstem

Question 5

What is found in acute bacterial meningitis microscopically?

Answer 5

• Neutrophils in subarachnoid space (very busy looking, Mickey mouse hats)
• Gram stain may be positive (but likely negative if treated)
• Tons of neutrophils in subarachnoid space
• Sometimes you can see neutrophils plugging vessels up (phlebitis) –> can make it difficult for blood to flow through (acts like thrombus)

Question 6

What can happen if acute bacterial meningitis is fulminating?

Answer 6

• Phlebitis

- Superficial Cerebritis

Question 7

What is Phlebitis?

Answer 7

Neutrophils in vessels or in walls of vessels

Question 8

What is Superficial Cerebritis?

Answer 8

Neutrophils extending into the brain itself

Question 9

What causes hydrocephalus in meningitis?

Answer 9

Exudate covering the brain becomes organized and fibrous. This fibrous material makes it difficult for resorption through arachnoid granulations

Question 10

How is TB meningitis different?

Answer 10

• Brain infection comes on in a more chronic fashion (ongoing, takes weeks
• May be cranial nerve symptoms (very common in meningitis), difficult to diagnose clinically (and in lab!)
• Looks different on brain: exudate in basal location that may block cisterns, encase cranial nerves
• Rarely see tuberculomas (look like neoplasm)

Question 11

How does TB exudate look different?

Answer 11

More gelatinous, more translucent

• Looks more organized, stringy connections between brain areas - adhesions
• May see more space between structures

Question 12

Tuberculoma

Answer 12

Mass of TB organisms

-Organisms are no longer in subarachnoid space, they are forming a mass in the brain

Question 13

What does TB meningitis look like microscopically?

Question 14

What is obliterative endarteritis?

Answer 14

• Granulomas can become so abundant that they get in the way of/fill up arteries
• Can impede blood flow to brain

Question 15

What does a caseating granuloma look like on a slide?

Answer 15

• Massive inflammatory infiltrate in center
• Then caseous debris is in center = bunch of necrotic debris and broken down cell nuclei
• Histocytes surround necrotic debris
• Lymphocytes are through out

Question 16

What does Acute Viral Meningitis look like?

Answer 16

• Brain may be swollen
• No microscopic findings (or very mild lymphocytic infiltration of meninges)
• You usually wouldn’t see in autopsy
• Won’t see neutrophils
• May see lymphocytes in meninges
• Lymphocytes/mononuclear cells on slide look very small, dense, dark, probably infiltrating subarachnoid space