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Imaging in CNS Tuberculosis

Practice Essentials

Tuberculosis (TB) of the central nervous system (CNS) is a granulomatous infection caused by Mycobacterium tuberculosis. The disease predominantly involves the brain and meninges, but occasionally, it affects the spinal cord.
Clinical diagnosis can be difficult; therefore, imaging has an important role in establishing the diagnosis (see the images below).

Contrast-enhanced computed tomography (CT) scan in

Contrast-enhanced computed tomography (CT) scan in a patient with tuberculous meningitis demonstrating marked enhancement in the basal cistern and meninges, with dilatation of the ventricles.

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T1-weighted gadolinium-enhanced magnetic resonance

T1-weighted gadolinium-enhanced magnetic resonance image in a child with a tuberculous abscess in the left parietal region. Note the enhancing thick-walled abscess.

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The hallmark feature of tuberculous meningitis (TBM) is the formation of thick gelatinous exudates. Exudates are relatively more copious in the basal regions of the brain. Other characteristic pathologic changes are meningeal inflammation; vasculitis of the arteries of the circle of Willis while traversing the basilar exudates; and obstruction of the flow of cerebrospinal fluid, resulting in hydrocephalus. Multiple small intracranial and spinal tuberculoma are frequent when TBM is part of the miliary tuberculosis. When the thick inflammatory exudates of TBM surround the spinal cord, complications include tuberculous radiculomyelitis, spinal tuberculoma, myelitis, syringomyelia, vertebral tuberculosis, and very rarely spinal tuberculous abscess. Tuberculous arachnoiditis leading to myeloradiculopathy is the most characteristic spinal complication of TBM.
 Abnormal fluid-attenuated inversion recovery (FLAIR) signal changes along the cerebellar folia has also been reported.

Preferred examination

Magnetic resonance imaging (MRI) with gadolinium enhancement is the preferred method of initial investigation.
MRI is the most sensitive test for detecting the extent of leptomeningeal disease and is superior to computed tomography (CT) scanning in detecting parenchymal abnormalities, such as tuberculomas, abscesses, and infarctions. MRI also readily depicts hydrocephalus.
 CSF analysis is usually used to detect a decreased glucose level, elevated protein levels, and a slight pleocytosis. Results of CSF polymerase chain reaction (PCR) assays may be diagnostic.

Follow-up CT at 1 week and 1 month after the initial scan have been found to be of use in following the evolution of infection with early identification of complications, as well as in tracking the response to treatment, although most CT abnormalities persist beyond 6 months despite clinical improvement.

Conventional MRI may cause early meningitis and early infarcts to be missed, and no MRI findings are pathognomonic for TBM. Diffusion-weighted imaging, if available, depicts infarctions in the hyperacute stage.

Skull radiographic findings are usually normal. Rarely, in healed tuberculosis meningitis, faint parenchymal calcification is evident. Calcifications on skull radiographs in patients with healed TBM or healed tuberculomas are nonspecific findings. Skull calcification may indicate choroid plexus, pineal, and/or habenular calcification.

Single photon emission CT scanning with hexamethylpropyleneamine oxime (HMPAO) can be used to assess the degree and extent of cerebral ischemia resulting from TBM cerebral vasculitis. Findings are specific only for diminished cerebral perfusion.

In infants, brain ultrasonography can be used to detect hydrocephalus.
  A considerable proportion of patients with TBM develop intracranial vasculopathy, which can be diagnosed and monitored using transcranial Doppler ultrasonography (TCD). TCD provides accurate information on intracranial blood flow velocities and identifies areas of intracranial stenosis. TCD is a noninvasive and a relatively inexpensive test and can be performed at the bed-side, making it a valuable tool in the critically ill and ventilated patients. In addition, TCD monitoring in TBM may guide the management of elevated intracranial pressure.

Although not currently in routine use in patients with CNS TB, cerebral angiography demonstrates findings of vasculitis. These findings include vascular irregularity, vascular narrowing, and vascular occlusion. Vessels commonly affected include the terminal portions of the internal carotid arteries, as well as the proximal parts of the middle and anterior cerebral arteries. Features of vasculitis and/or vascular occlusion are detected in other inflammatory and ischemic cerebral conditions.

For excellent patient education resources, visit eMedicineHealth’s Infections Center and Brain and Nervous System Center. See also eMedicineHealth’s patient education articles Tuberculosis and Brain Infection.

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