Nervous System Infections and Meningitis Review

Comprehensive vocabulary terms and definitions covering nervous system infections, routes of transmission, meningitis subtypes, specific viral and fungal pathogens, and clinical pathology based on lecture notes.

Direct Injury (Nervous System)

Mechanical or cellular damage occurring when infectious agents directly injure neurons or glia.

Indirect Injury (Nervous System)

Damage caused by microbial toxins or the body's own destructive inflammatory response to an infection.

Hematogenous Spread

The most common route of CNS infection where microbes enter via arterial circulation or retrograde venous spread.

Direct Implantation

Pathogen entry caused by open trauma, penetrating trauma, or congenital malformations like meningomyelocele.

Transplacental Spread

Perinatal infection route across the placenta or during childbirth, often caused by $Toxoplasma$ or $Cytomegalovirus$ ($CMV$).

PNS Transport

A route of infection where viruses like Rabies or Herpes Zoster hijack nerves to travel into the central nervous system.

Meningitis

An inflammatory process involving the leptomeninges within the subarachnoid space.

Meningoencephalitis

An infection that has spread past the meninges into the underlying functional brain tissue.

Chemical Meningitis

A noninfectious inflammatory response in the subarachnoid space triggered by an irritant, such as debris from a ruptured epidermoid cyst.

Carcinomatous Meningitis

Inflammation in the subarachnoid space caused by the infiltration and spread of metastatic cancer cells.

Acute Pyogenic Meningitis

Bacterial meningitis characterized by rapid onset and the production of a purulent exudate (pus).

Neonatal Meningitis Pathogens

The most likely bacterial causes are $Escherichia\,coli$ and Group B Streptococci.

Adolescent/Young Adult Meningitis Pathogens

The most common bacterial cause is $Neisseria\,meningitidis$.

Older Adult Meningitis Pathogens

The most common bacterial causes are $Streptococcus\,pneumoniae$ and $Listeria\,monocytogenes$.

Nuchal Rigidity

Neck stiffness that serves as a clinical sign of meningeal irritation.

Photophobia

Sensitivity to light, often observed in patients with meningeal inflammation.

Acute Pyogenic CSF Profile

Increased opening pressure, abundant neutrophils, elevated protein, and reduced glucose.

Leptomeningeal Fibrosis

A late-stage complication of healed meningitis that can obstruct CSF flow and lead to hydrocephalus.

Aseptic Meningitis

A clinical term for meningitis where no organisms are detectable by standard bacterial culture; 80% of identified cases are caused by enteroviruses.

Aseptic Meningitis CSF Profile

Lymphocytic pleocytosis (elevated lymphocytes), moderately elevated protein, and normal glucose levels.

Tuberculous Meningitis Morphological Signature

Dense arachnoid fibrosis, particularly at the base of the brain, and the potential formation of tuberculomas.

Meningovascular Neurosyphilis

A pattern of neurosyphilis featuring chronic meningitis at the brain base and obliterative endarteritis rich in plasma cells and lymphocytes.

Paretic Neurosyphilis

Direct invasion of the brain parenchyma by spirochetes ($Treponema\,pallidum$) causing neuronal loss, dementia, and delusions of grandeur.

Tabes Dorsalis

Damage to sensory nerves in the dorsal roots resulting in loss of joint position sense, ataxia, and lightning pains.

Neuroborreliosis

CNS involvement of Lyme disease ($Borrelia\,burgdorferi$), often manifesting as aseptic meningitis or facial nerve ($CN\,VII$) palsies.

Soap Bubble Lesions

A distinct visual pattern in brain tissue caused by $Cryptococcus$ organisms proliferating within and expanding the Virchow-Robin spaces.

Brain Abscess

A localized focus of liquefactive necrosis surrounded by intense inflammation and vasogenic edema, typically due to bacterial infection.

Brain Abscess CSF Profile

High white cell count, increased protein concentration, and normal glucose concentration.

Septic Emboli

Infected blood clots, often from acute bacterial endocarditis, that can lead to multiple widespread brain abscesses.

Neuronophagia

The active destruction and phagocytosis of dying neuronal debris by clusters of microglial cells during viral encephalitis.

Microglial Nodules

Small aggregations of proliferating microglia that mark focal points of tissue injury in viral encephalitis.

Perivascular Cuffs

Dense collections of lymphocytes and plasma cells surrounding blood vessels, characteristic of viral encephalitis histopathology.

Viral Encephalitis CSF Profile

Lymphocytosis (after early neutrophilic pleocytosis), slightly elevated pressure, elevated protein, and normal glucose.

Arboviruses

Arthropod-borne viruses (e.g., West Nile virus, EEE, WEE) transmitted by mosquitoes or ticks that cause epidemic encephalitis.

HSV-1 Encephalitis

A necrotizing and often hemorrhagic infection with a preference for the temporal lobes and orbital gyri of the frontal lobes.

Cowdry Type A Inclusions

Large eosinophilic intranuclear viral inclusion bodies found in neurons and glia, diagnostic of $Herpes\,simplex\,virus$.

Postherpetic Neuralgia

A persistent, debilitating pain syndrome in a specific dermatome following the resolution of a shingles rash.

Granulomatous Arteritis ($VZV$)

Infection of cerebral blood vessels by $Varicella-Zoster\,Virus$ causing arterial wall inflammation and potential stroke.

Congenital CMV Manifestations

Severe periventricular necrosis leading to microcephaly and periventricular calcifications.

Paralytic Poliomyelitis

Infection that selectively destroys lower motor neurons in the anterior horns of the spinal cord and brainstem, causing flaccid paralysis.

Postpolio Syndrome

A syndrome of new progressive weakness and muscle atrophy occurring 25 to 35 years after the original polio infection.

Rabies Pathogenesis

Virus ascends from a wound site along peripheral nerves to the CNS; clinical signs include hydrophobia and extreme CNS excitability.

HIV-Associated Neurocognitive Disorder (HAND)

Cognitive dysfunction ranging from mild impairment to dementia, driven by microglial infection and cytokine-induced neuronal injury.

Immune Reconstitution Inflammatory Syndrome (IRIS)

A severe disorder caused by a hyper-active inflammatory response when ART is started, often presenting with cognitive impairment and cerebral edema.

Multinucleated Giant Cells (HIV)

Macrophage-derived cells that form a characteristic diagnostic component of microglial nodules in HIV encephalitis.

Progressive Multifocal Leukoencephalopathy (PML)

A demyelinating disease caused by the JC virus, which target and destroys oligodendrocytes in immunocompromised patients.

Bizarre Astrocytes (PML)

Giant astrocytes with irregular, hyperchromatic nuclei found in PML lesions that can mimic malignant tumors.

Mucormycosis (CNS)

A fungal infection associated with DKA that enters the brain through the cribriform plate via direct extension or angioinvasion.

Aspergillus fumigatus Morphology

An angioinvasive fungus that breaches vascular walls, causing localized thrombosis and septic hemorrhagic infarctions (strokes).

Toxoplasma gondii Congenital Triad

Chorioretinitis, hydrocephalus, and intracranial calcifications.

Ring-Enhancing Lesions

A neuroimaging pattern classic for $Toxoplasma$ abscesses in immunocompromised adults.

Cysticercosis

A tissue infection caused by ingesting eggs of the tapeworm $Taenia\,solium$, often presenting as space-occupying mass lesions and seizures.

Naegleria fowleri

An ameba from stagnant warm fresh water that causes Primary Amebic Meningoencephalitis (PAM), a rapidly fatal necrotizing encephalitis.

Spinal Epidural Abscess

A neurosurgical emergency where a collection of pus in the spinal epidural space can rapidly compress the spinal cord and cause paralysis.

Subdural Empyema

A collection of pus in the subdural space, often from sinusitis, that can cause mass effect and venous infarction due to thrombophlebitis.