Infectious Neuropathology
What You'll Learn
- Bacterial meningitis and abscess — the exudate, the stages, and the stains that confirm the organism
- Viral encephalitis by signature inclusion and location (HSV, CMV, rabies, HIV)
- Granulomatous & fungal CNS infection — TB, cryptococcus, and the angioinvasive molds
- Parasitic disease — toxoplasma, neurocysticercosis, cerebral malaria
The neuropathology view — tissue findings and confirmatory stains. Clinical CNS-infection workup lives in the Infectious / Neuro-ID notes.
- HSV-1 encephalitis = hemorrhagic necrosis of the inferomedial temporal lobes & limbic system; Cowdry type A intranuclear inclusions.
- CMV = “owl-eye” intranuclear + granular cytoplasmic inclusions, periventricular ventriculitis, immunocompromised.
- Cryptococcus = “soap-bubble” cysts in basal ganglia; capsule stains with mucicarmine (India ink on CSF).
- Aspergillus: septate hyphae, acute-angle branching. Mucor: broad, pauciseptate, ribbon-like, right-angle branching. Both angioinvasive → hemorrhagic infarct.
- Toxoplasma = necrotizing abscesses with tachyzoites + bradyzoite cysts; ring-enhancing lesions in AIDS (vs CNS lymphoma).
Bacterial Meningitis & Abscess
| Entity | Pathology | Confirm |
|---|
| Acute pyogenic meningitis | Neutrophilic exudate in subarachnoid space (convexities in pneumococcus; base in H. influenzae/TB); vascular congestion; risk of vasculitis, infarct, hydrocephalus | Gram stain + CSF culture (organism by age) |
| Cerebritis → abscess | Early cerebritis → central liquefactive necrosis → collagen/gliotic capsule (thinner on ventricular side → rupture risk) | Gram / GMS / AFB + culture; MRI restricted diffusion |
Viral Encephalitis
| Virus | Location / gross | Signature |
|---|
| HSV-1 | Hemorrhagic necrosis, inferomedial temporal & orbitofrontal / limbic | Cowdry A intranuclear inclusions; IHC/PCR |
| CMV | Periventricular necrosis / ventriculitis (immunosuppressed, congenital) | Owl-eye intranuclear + cytoplasmic inclusions; cytomegaly |
| Rabies | Brainstem, hippocampus, Purkinje cells | Negri bodies (eosinophilic cytoplasmic inclusions) |
| HIV encephalitis | Deep white matter/basal ganglia | Microglial nodules + multinucleated giant cells |
| SSPE (measles) | Cortex + white matter, years after measles | Cowdry A intranuclear inclusions; neurofibrillary change |
Granulomatous & Spirochetal
| Entity | Pathology | Stain |
|---|
| Tuberculosis | Basilar meningitis; caseating granulomas with Langhans giant cells; tuberculoma; endarteritis → infarct | Acid-fast (Ziehl-Neelsen); culture/PCR |
| Neurosyphilis | General paresis (cortical atrophy, rod-cell microgliosis, spirochetes); tabes dorsalis (dorsal-column/root degeneration); gummas; meningovascular | Warthin-Starry / IHC for T. pallidum |
| Neurosarcoid | Non-caseating granulomas, basal leptomeninges, cranial nerves | Exclusion (stains negative for organisms) |
Fungal Infection
| Fungus | Pathology | Stain / clue |
|---|
| Cryptococcus | “Soap-bubble” gelatinous cysts in basal ganglia/perivascular spaces; minimal inflammation | Mucicarmine capsule; India ink; narrow-based budding |
| Aspergillus | Angioinvasive → hemorrhagic infarct/abscess | Septate hyphae, acute-angle branching; GMS |
| Mucormycosis | Rhino-orbital-cerebral, diabetic ketoacidosis; angioinvasion, tissue necrosis | Broad, pauciseptate, right-angle hyphae; GMS |
| Candida | Microabscesses (disseminated) | Yeast + pseudohyphae; GMS/PAS |
Parasitic Infection
| Parasite | Pathology | Signature |
|---|
| Toxoplasma | Necrotizing abscesses (grey-white junction, basal ganglia); ring-enhancing in AIDS | Tachyzoites (free) + bradyzoite cysts; IHC |
| Neurocysticercosis | Taenia solium cysts; degenerating cyst → inflammation, edema, calcification | Scolex with hooklets/suckers |
| Cerebral malaria | P. falciparum; sequestration of parasitized RBCs in capillaries | Ring hemorrhages, Dürck granulomas |
| Naegleria fowleri | Acute primary amebic meningoencephalitis (PAM); hemorrhagic necrotizing, olfactory-route | Trophozoites only in tissue (no cysts) |
| Acanthamoeba / Balamuthia | Granulomatous amebic encephalitis (GAE); subacute, immunocompromised | Trophozoites and cysts in tissue |
| Finding | Diagnosis |
|---|
| Hemorrhagic temporal-lobe necrosis | HSV-1 encephalitis |
| Owl-eye inclusions, ventriculitis | CMV |
| Negri bodies | Rabies |
| Microglial nodules + giant cells | HIV encephalitis |
| Langhans giant cells + caseation, AFB+ | CNS tuberculosis |
| Mucicarmine+ soap-bubble cysts | Cryptococcus |
| Broad right-angle nonseptate hyphae | Mucormycosis |
| Bradyzoite cysts + tachyzoites | Toxoplasmosis |
References
- Love S, et al. Greenfield's Neuropathology. 9th ed. 2015.
- Ellison D, et al. Neuropathology. 3rd ed. 2013.
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