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Nervous System Disorders

= infection of the pia mater + arachnoid + adjacent CSF

  1. Pachymeningitis: infection of dura mater
  2. Leptomeningitis: infection of pia matter / arachnoid (most common) + CSF

ROLE of CT and MR:

  1. to exclude parenchymal abscess, ventriculitis, localized empyema
  2. to evaluate paranasal sinuses / temporal bone as source of infection
  3. to monitor complications: hydrocephalus, subdural effusion, infarction

Chemical / Aseptic Meningitis!!navigator!!

= rare complication of dermoid / epidermoid cyst ← cyst rupture into subarachnoid space

MR:

  • T1-hyperintense speckles in cortical sulci
  • fat-fluid level in ventricles

Purulent / Bacterial / Acute Septic Meningitis!!navigator!!

Cause: otitis media / sinusitis

Organism:

  1. adults: Neisseria meningitidis, Diplococcus pneumoniae, Haemophilus influenzae, Meningococcus, Staphylococcus aureus
  2. children: group B Streptococcus (86%), S pneumonia (= Pneumococcus in 58%), Escherichia coli, Citrobacter

Incidence: 4100 cases annually in USA

  • fever, headache, seizures, altered consciousness, neck stiffness

Neuroimaging most useful to:

  • exclude herniation before lumbar puncture
  • to detect complications

Cross-sectional imaging is neither sensitive nor specific for detection of meningitis.

NECT:

  • often normal / falsely negative due to subtlety of findings
  • sulcal effacement
  • slightly increased density in subarachnoid space ← increased vascularity, esp. in children
  • small ventricles ← diffuse cerebral edema

CECT:

  • marked curvilinear meningeal enhancement over cerebrum (frontal + parietal lobes) and interhemispheric + sylvian fissures
  • obliteration of basal cisterns with enhancement (common)

MR (most sensitive modality):

  • no abnormality (in most cases)
  • ± hyperintense obliterated basal cisterns on FLAIR ← increased protein content (NOT specific for meningitis)
  • abnormal hyperintensity in cerebral sulci on DWI (NOT specific for meningitis) ← pyogenic (bacterial) >>lymphocytic (viral) / aseptic meningitis

CEMR (postcontrast FLAIR + delayed T1WI):

  • abnormal enhancement of pia mater + subarachnoid space (leptomeninges) ← inflammatory breakdown of blood-brain barrier (in only 50%):
    • thin linear enhancement in cerebral sulci = typical for acute pyogenic (bacterial) + lymphocytic (viral) meningitis
    • thick nodular enhancement in basal cisterns = typical of granulomatous / carcinomatous meningitis
  • leptomeningeal enhancement (in chronic infection)

Dx: CSF analysis

Cx:

  1. Cerebritis (parenchymal) / subdural infection, especially with streptococcus / staphylococcus
  2. Ventriculitis ← retrograde spread
  3. Brain atrophy
  4. Brain infarction ← arteritis, venous thrombosis (5–15% of adults, in up to 30% of neonates)
  5. Subdural effusion [sterile subdural effusion ← H. influenzae meningitis (in children) may turn into subdural empyema]
  6. Hydrocephalus ← cellular debris blocking foramen of Monro, aqueduct, 4th ventricular outlet / intraventricular septa / arachnoid adhesions
  7. Cranial nerve dysfunction

Prognosis:

  • Cerebral infarction + edema predict poor outcome
  • Enlargement of ventricles + subarachnoid spaces + subdural effusions have no predictive value

Mortality: 10% for H. influenza + meningococcus, 30% for Pneumococcus (5th commonest cause of death in children between 1 and 4 years of age)

DDx: meningeal carcinomatosis

Granulomatous Meningitis!!navigator!!

Histo: thick exudate, perivascular inflammation, granulation tissue + reactive fibrosis

  1. Tuberculous meningitis = basilar meningitis
    part of generalized miliary tuberculosis / primary tuberculous infection
  2. Sarcoidosis (in 5% of sarcoidosis cases)
    Histo: granulomatous infiltration of leptomeninges
    • nodular pattern (DDx from bacterial causes)
    • thick meningeal plaques over convexities (mimicking meningioma)
    • marked enhancement
    • may be associated with single / multiple intracerebral mass(es)

    Cx: cranial nerve palsy, hypothalamic-pituitary dysfunction, chronic meningitis
  3. Fungal meningitis: coccidioidomycosis (endemic), blastomycosis, mucormycosis (diabetics), nocardiosis, actinomycosis, aspergillosis (under chronic corticosteroid therapy)
    1. yeast = unicellular eukaryotic microorganism that reproduce by asymmetric fission:
      • Cryptococcosis
      • Candidiasis
    2. mold = multicellular filaments (hyphae) that can form into macroscopic networks (mycelia); too large for meningeal microcirculation and more likely cause invasive parenchymal CNS disease in immunocompromised patients
      • Aspergillus
      • Mucormycosis
    3. dimorphic fungus = dimorphic fungus that grows as mold (yeast) at room (body) temperature; resides in soil in endemic regions and releases conidia (spores) into the air (unicellular eukaryotes at body temperature → initially misidentified as protozoa)
      • Blastomycosis
      • Coccidioidomycosis
      • Histoplasmosis

Fungal CNS diseases are usually opportunistic infections from hematogenous dissemination in susceptible hosts at extremes of age or with immunodeficiency.

  • acute life-threatening process / chronic indolent disease

May be associated with: cerebritis, abscess formation

  • hydrocephalus

CT:

  • obliteration of basal cisterns, sylvian fissure, suprasellar cistern (isodense cisterns ← filling with debris)
  • intense contrast enhancement of gyri + involved subarachnoid spaces
  • calcification of meninges
  • decreased attenuation of white matter

MR:

  • high-signal intensity of basilar cisterns on T2WI
  • enhancement with gadopentetate dimeglumine

Cx:

  1. Hydrocephalus ← obliteration of basal cisterns, blocking of CSF flow + blocking of CSF absorption
  2. Infarction ← arteritis

Outline