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Nervous System Disorders

= slowly dividing facultative intracellular pathogen

Prevalence: 5% (15% with immunodeficiency)

Worldwide: 1.7 million deaths per year; latent infection in 2 billion persons → 10% lifetime risk for active symptomatic tuberculosis

Transmission: through respiratory droplets → active infection usually begins as Ghon focus

Cranial Tuberculous Meningitis!!navigator!!

◊Most common cause of chronic meningitis!

Pathophysiology:

  • rupture of initial subependymal / subpial tubercle (Rich focus) into subarachnoid space (after earlier hematogenous dissemination) into CSF → thick gelatinous inflammatory exudate settles at base of brain along cisterns + sylvian fissure + along traversing blood vessels

Predisposed: in AIDS patients + infants + small children (part of generalized miliary tuberculosis / primary tuberculous infection)

Location: basal cisterns (around M1 segment of MCA and sylvian fissure) >sulci >cerebral convexities, interhemispheric fissure

  • characteristic thick / nodular enhancement in basal cisterns

DDx:

  1. other granulomatous disease: fungus, sarcoid
  2. neoplastic disease: carcinoma, lymphoma

CT:

  • iso- / hyperattenuating meninges relative to basal cisterns
  • often homogeneous contrast enhancement of meninges

MR:

  • normal at unenhanced SE (in early stage)
  • distention of affected subarachnoid spaces with mild shortening of T1 + T2 relaxation times compared with CSF

CEMR:

  • abnormal meningeal enhancement on gadolinium-enhanced T1WI (corresponds to gelatinous exudate)
  • abnormal enhancement of choroid plexus + ependymal lining (rare)

Cx:

  1. Communicating hydrocephalus (most common) ← blockage of basal cisterns by inflammatory exudate
  2. Obstructive hydrocephalus (rare) ← mass effect of tuberculoma causing obstruction of CSF flow
  3. Ischemic infarction (20–41%) in basal ganglia and internal capsule ← vasospasm of penetrating vessels / vascular compression / occlusive panarteritis (mostly in MCA distribution)
  4. Cranial neuropathy (17–70%): CN2, CN3, CN4, CN7 ← extension of cisternal inflammation along traversing cranial nerves
  5. Pachymeningitis (rare) ← seeding to bone / dura

DDx: infection (nontuberculous bacteria, virus, fungus, parasite), inflammatory disease (rheumatoid disease, sarcoidosis), neoplasia (meningiomatosis, CSF-seeding neoplasm)

Parenchymal Tuberculosis!!navigator!!

Tuberculoma of Brain 70%

= tuberculous granuloma formation within cerebrum as most common parenchymal form of tuberculosis

Incidence: 0.15% of intracranial masses in Western countries; 30% in underdeveloped countries

Age: infant, small child, young adult

Associated with: tuberculous meningitis in 50%

  • history of previous extracranial TB (in 60%)

Location: more common in posterior fossa (62%), cerebellar hemispheres (frontal + parietal lobes)

  • solitary lesion; may be multiloculated

Progression: noncaseating → caseating → solid → liquid center

NECT:

  • hypo- / iso- (72%) / hyperdense round / lobulated lesion of 0.5–4 cm in diameter with mass effect (93%)
  • moderate surrounding edema (72%) less marked than in pyogenic abscess
  • central calcification (29%)

CECT:

  • homogeneously enhancing parenchymal tuberculoma
  • homogeneous blush in tuberculoma en plaque along dural plane (6%) (DDx: meningioma en plaque)
  • ring blush (nearly all) with smooth / slightly shaggy margins + thick irregular wall around an isodense center (DDx: pyogenic abscess less thick + more regular)
  • “target” sign (⅓) = central calcification in isodense lesion with ring-blush HIGHLY SUGGESTIVE (DDx: giant aneurysm)

MR:

  • single / multiple well-defined T2 hypointensities
  • solid / ringlike enhancement
  • varying central T2 hyperintensity depending on extent of liquefaction / caseation
  • “target” sign = small focal area of calcification / enhancement in center of ring-enhancing mass

MR spectroscopy:

  • lipid level peaks at 0.9 ppm, 1.3 ppm, 2.0 ppm, 2.8 ppm
  • NO amino acid resonance at 0.9 ppm

DDx: other CNS infection (esp. toxoplasmosis, cysticercosis, fungus), lymphoma, atypical meningioma, radiation necrosis

Tuberculous Abscess of Brain (rare)

Histo: numerous tubercle bacilli in the absence of tubercular granulomatous formation

  • early rapid clinical deterioration favors abscess
  • hypointense lesion core on T1WI
  • hyperintense lesion core on T2WI
  • peripheral hypointense rim (= capsule)

Miliary Tuberculosis of CNS 30–60%

Usually associated with: tuberculous meningitis

  • multiple tiny <2 mm T2-hyperintense foci with homogeneous enhancement

Spinal Tuberculous Meningitis!!navigator!!

MR:

  • cerebrospinal fluid loculations with cord compression
  • obliteration of spinal subarachnoid space:
    • loss of outline of spinal cord in cervicothoracic spine
    • matting of nerve roots in lumbar region
  • nodular thick linear intradural enhancement of meninges

Cx: syringomyelia, syringobulbia

Tuberculous Vasculitis!!navigator!!

= infectious vasculitis of small and medium-sized cerebral aa. in subarachnoid space

Location: lenticulostriate arteries, posterior cerebral branches, thalamoperforating arteries

Cx: small infarctions in basal ganglia and deep white matter (in up to 41%)

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