Introduction:
Central nervous system (CNS) tuberculosis is one of the most severe forms of extrapulmonary TB, particularly affecting immunocompromised patients and children. It includes a spectrum of manifestations such as tuberculous meningitis (TBM), tuberculomas, tubercular abscess, miliary TB, and spinal arachnoiditis. Imaging plays a crucial role in diagnosis, assessment of extent, complications, and treatment monitoring.
Common CNS TB Manifestations on Imaging:
1. Tuberculous Meningitis (TBM):
MRI Findings (Best modality):
- Basal cisternal enhancement (interpeduncular, suprasellar, prepontine) on post-contrast T1-weighted images.
- Leptomeningeal enhancement, often thick and nodular.
- Hydrocephalus – communicating type, due to CSF pathway obstruction.
- Cerebral infarcts – especially in basal ganglia and internal capsule, due to vasculitis.
- Cranial nerve involvement, especially optic and oculomotor nerves.
CT Findings:
- May show basal cisternal hyperdensities.
- Hydrocephalus is well seen.
- Basal exudates may be visualized as hyperdense areas.
2. Tuberculomas:
MRI Findings:
- Can be non-caseating or caseating (solid/liquefied).
- T1W: Iso to hypointense lesions.
- T2W:
- Non-caseating: Hyperintense.
- Caseating solid: Hypointense core.
- Caseating liquefied: Hyperintense center.
- Post-contrast: Ring or nodular enhancement.
- MR Spectroscopy: Shows lipid-lactate peak (helpful in differentiating from neurocysticercosis).
CT Findings:
- Well-defined hypodense lesions with ring enhancement.
- May show central calcification.
3. Tuberculous Abscess:
- Larger than tuberculoma, often >3 cm.
- T2W MRI: Hyperintense center.
- Post-contrast: Thick irregular ring enhancement.
- Restricted diffusion on DWI (unlike liquefied tuberculomas).
- Surrounding vasogenic edema and mass effect.
4. Miliary CNS TB:
- Multiple small (1–2 mm) tubercles scattered throughout brain parenchyma.
- Seen as tiny enhancing nodules on post-contrast MRI.
- Often associated with miliary pulmonary TB.
5. Spinal TB (Tuberculous arachnoiditis / spinal meningitis):
- Clumping of nerve roots in cauda equina region.
- Thickening and enhancement of meninges.
- Dural enhancement in the spinal canal.
- Can lead to CSF loculations, spinal cord atrophy, and radiculopathy.
Imaging Modality of Choice:
- MRI with contrast is the investigation of choice for CNS TB.
- CT is helpful in detecting calcifications, hydrocephalus, and mass effect.
Differential Diagnoses:
- Pyogenic abscess
- Neurocysticercosis
- Metastases
- Fungal infections
- Primary brain tumors (e.g., gliomas)
Complications Seen on Imaging:
- Hydrocephalus
- Vasculitic infarcts
- Optochiasmatic arachnoiditis
- Seizures due to cortical tuberculomas
Summary / Key Points:
- MRI with contrast is essential for evaluating the spectrum of CNS TB.
- Basal meningeal enhancement, ring-enhancing lesions, and hydrocephalus are key findings.
- MR spectroscopy and DWI help differentiate tuberculomas from other ring-enhancing lesions.
- Early diagnosis can help reduce neurological sequelae and morbidity.
