Pathology of CNS infections Flashcards
1
Q
Acute meningitis
A
- Acute onset (hours), fever + nonspecific sx. Headache, altered mental status, stiff neck
- Causes: viral, fungal, bacteria (viral usually self-limiting)
2
Q
Acute bacterial meningitis
A
- Overall mortality of 10-15%, with frequent and permanent complications
- Bacteria in leptomeninges causes outpouring of PMNs into subarachnoid space
- Very early hyperemia of leptomeningeal vessels and edema but no visible pus
- Pus begins to accumulate in the sulci, which can cause ocular palsies and deafness
- Eventually so much pus forms that it fills the entire subarachnoid space (pus contains dead PMNs and fibrin)
- Arteritis and phlebitis can result in vascular thrombosis (infarcts)
- Can lead to ischemic or hemorrhagic necrosis
3
Q
Acute viral meningitis
A
- Usually benign, self-limiting, resolves w/o sequelae
- Microscopically there are lymphocytes in the leptomeninges
4
Q
Chronic meningitis
A
- Classic meningitis sx that can evolve over weeks-months
- Can be normal candidates plus parasites
- Generally no sequelae
- Most common severe is form TB and cryptococcus
- Damage to CNs and blood vessels can lead to nerve palsies and infarcts
5
Q
TB chronic meningitis
A
- See abnormal enhancement of leptomeninges at base of brain in CT
- The leptomeninges look thick and fibrotic (instead of widespread purulent exudate)
- Can find multiple granulomas, containing giant cells and epithelioid cells
6
Q
Cryptococcal chronic meningitis
A
- Common in HIV and ICd pts, most common fungal infection of CNS
- Appears as a pleomorphic budding yeast, eliciting little inflammatory response
- Has a capsule (positive for mucin stain), under H&E shows a halo around the capsule
- Can produce granulomas, which appears similar to TB
- Ventricles can fill w/ gelatinous material (feels slippery)
7
Q
Bacterial cerebritis and abscess
A
- Most cerebrates and abscesses are bacterial, where the bacteria invade the brain parenchyma (viruses cause encephalitis)
- Many, but not all, CNS abscesses cause focal problems
- On CT the abscesses are ring enhancing rim around a low-density mass (also look like this: mets and GBM)
- Almost always arise from an emboli of infected tissue (not primary abscess), usually valvular vegetations form endocarditis
- The bacteria produce an abscess when the emboli occludes the vessel and causes ischemic necrosis
- Center of the abscess becomes liquified and it is walled-off
8
Q
Fungal cerebritis (aspergillus)
A
- Predominantly affects ICd pts, causing multiple hemorrhagic and necrotic lesions (w/ acute/chronic inflammation)
- Not as common in HIV b/c most common in those w/ neutropenia
- H&E shows septated hyphae (stains w/ silver)
- Has an affinity for blood vessels, destroys them causing hemorrhagic necrosis
9
Q
Parasitic cerebritis: cysticercosis
A
- Pork tapeworm (taenia solium), from ingesting the ova
- Causes seizures, mass effect, obstruction of CSF
- Elicits immune response when it dies and breaks down
- Immune response leads to granulation tissue in surrounding parenchyma
- Infection may be first symptomatic when parasite dies
10
Q
Viral encephalitis
A
- Tropism: affinity of some viruses for certain types of cells
- Latency: reactivates if immune system is compromised
- Viruses infecting CNS can present acutely, subacutely, or chronically
- Can be opportunistic
- Can infect gray or white matter, or both
- Suggestive evidence of viral encephalitis: perivascular lymphocytes, microglial acitvation/nodules and neuronophagia (killing of infected neurons by PMNs/lymphocytes)
- To find out which virus: cell types/brain regions affected, whether or not there is tissue necrosis and any viral inclusions
11
Q
Opportunistic vs non-opportunistic viruses
A
- Non: herpes (HSV), arboviruses, rabies, poli
- Op: CMV, varicella zoster
- Most dangerous viral encephalitis: HSV
12
Q
HSV encephalitis
A
- Imaging shows irregular lesions w/ edema and hemorrhage, microscopically see microglial nodules and cowdry type A viral inclusions
- Affects both gray and white matter and demonstrates latency
- Tropism for medial temporal and base of frontal lobes
13
Q
Rabies encephalitis
A
- Non-necrotizing, affects gray matter w/ some predilection for purkinje cells and medial temporal lobe including hippocampus
- Can see neuronophagia w/ little inflammation
- Inclusion body: Negri body
14
Q
Polio encephalitis
A
- When it spreads to the CNS is selectively infects motor neurons in the SC and brain stem (rarely cortex)
- Microscopically can see inflammation/neuronophagia, and microglail nodules
- Viral inclusions rarely seen
15
Q
Arbovirus encephalitis
A
- Most important cause of epidemic viral encephalitis
- Non-specific acute viral encephalitis affecting mostly gray matter and w/o viral inclusions
- Sx vary greatly: ranges form aseptic meningitis to necrotizing panencephalomyelitis
