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CNS infections - Coggle Diagram
CNS infections
- Subdural and Epidural Infections
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- Extension from infection in paranasal sinuses or mastoid air spaces
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- Subdural: Spreads widely (can form Subdural Empyema / acute purulent inflammation)
- Localized form of acute suppurative inflammation surrounded by fibrous tissue
- Mostly direct extension of bacterial infection (e.g., sinusitis, mastoiditis)
- Septic emboli from infective endocarditis
- Cyanotic Congenital Heart Disease (R-to-L shunt bypasses pulmonary filtration of organisms)
- Bronchiectasis (dilated bronchi with accumulated mucus -> risk of chronic bacterial infection/bacteremia)
- Mostly due to viruses (HSV-1 / Herpes, CMV)
- Almost always accompanied by meningitis (Meningoencephalitis)
- Microscopy hallmark: Perivascular cuffing
meningitis
acute meningitis
- Acute Bacterial (Septic) Meningitis
- Microscopy: Abundant neutrophils, congested blood vessels, fibrin & granulation tissue formation (new vessels, macrophages/microglia, reactive astrocytes)
- CSF Findings: Turbid; markedly elevated neutrophils; high protein; low glucose
- Gross: Dull, opaque meninges; congested blood vessels; pus in subarachnoid space
- Common Pathogens: N. meningitidis, S. pneumoniae, H. influenzae, GBS, Listeria
- Acute Viral (Aseptic) Meningitis
- Presentation: Not purulent
- CSF Findings: Elevated lymphocytes; normal to mildly elevated protein; normal glucose
- Rare Parasitic Meningitis
- Naegleria fowleri (Primary Amebic Meningoencephalitis)
- Etiology: Bacteria (Tuberculosis) and Fungi (Cryptococcus neoformans)
- Gross: Opaque, thick, and dull leptomeninges with exudate in subarachnoid spaces (cheesy-like exudate)
- Microscopy: Chronic inflammatory cells (lymphocytes); endarteritis obliterans of subarachnoid arteries; granuloma formation
- Granuloma Features: Central caseous necrosis; surrounded by epithelioid macrophages, lymphocytes, and multinucleated giant cells (Langhans giant cells in TB)
- Complications of Meningitis
- Complications Due to Spread
- Direct spread: Ventriculitis (to ventricles), subdural & epidural empyema
- Venous spread: Leptomeningeal thrombophlebitis -> impaired venous return -> congestion & rupture -> hemorrhagic red infarction (liquefactive necrosis)
- Hematogenous spread (Most Dangerous): Septicemia, DIC, Waterhouse-Friderichsen syndrome (hemorrhagic adrenalitis), distant spread to joints (septic arthritis) & heart (pericarditis, endocarditis)
- Complications Due to Healing & Fibrosis
- Arachnoid / subarachnoid fibrosis: Impairs CSF reabsorption into superior sagittal sinus -> Communicating Hydrocephalus
- Perivascular fibrosis / gliosis: Compresses cranial nerves -> Cranial Nerve Palsies
- Arterial compression / Endarteritis obliterans: Obliterates end-arteries without collaterals -> cerebral ischemia -> pale/white ischemic infarction (liquefactive necrosis)
- Related Neuropathology Pearls
- Types of Necrosis & Infarctions
- Liquefactive necrosis: Brain infarcts, brain abscesses, and pancreatitis
- Caseous necrosis: TB granulomas
- Red (Hemorrhagic) Infarction: Venous occlusion / obstructed venous drainage
- White (Pale / Ischemic) Infarction: Arterial occlusion / endarteritis obliterans
- Immunodeficiency Associations
- Neisseria pyogenic meningitis with Type III hypersensitivity (immune complexes): Classical complement pathway deficiency (C1, C2, C4)
- Progressive Multifocal Leukoencephalopathy (PML): Reactivation of dormant JC polyomavirus in immunosuppressed host -> infects oligodendrocytes -> patchy demyelinating lesions in cerebral white matter -> glial replacement
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