American Journal of Neuroradiology

Case of the Month

Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO

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June 2021

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Tuberculous Meningitis with Lumbar Arachnoiditis and Leptomeningeal Tuberculomas

Background:
- CNS tuberculosis is rare (1% of cases), but is the most severe form of tuberculosis, with very high morbidity and mortality rates.
- Tuberculous meningitis (TBM) is the most frequent form of CNS involvement. It is caused by lymphatic or hematogenous dissemination of the bacillus Mycobacterium tuberculosis from the lungs to the meninges. The immune system tries to contain the infection via cell immunity, with caseating granulomas formation, called tuberculomas. When liquefactive tuberculomas rupture into the subarachnoid space, a gelatinous exudate (hallmark of the disease) accumulates within the basal cisterns of the brain or the spinal subarachnoid space, causing arachnoiditis.
Clinical Presentation:
- TBM often presents with fever, headache, meningismus, abnormal mental status, and cranial nerve palsies due to arachnoiditis of the basal cisterns.
- Spinal arachnoiditis causes radiculomyelopathy and manifests as subacute areflexic paraparesis, root pain, paraesthesias, and cauda equina syndromes, although sometimes it may be asymptomatic.
- As with other space-occupying lesions, intracranial tuberculomas may produce focal neurologic deficits, seizures, headache, vomiting, or papilledema.
- The most typical spinal tuberculoma clinical manifestations are progressive paraplegia, sensory deficits, and bladder dysfunction.
Key Diagnostic Features:
- Diagnosis is based on clinical, imaging, and laboratory findings. Identification of the acid-fast bacilli in the CSF through smear or culture techniques is the most important method to diagnose CNS tuberculosis.
- The most frequent imaging feature of TBM is basal meningeal enhancement. Hydrocephalus occurs in up to two-thirds of cases due to exudative obstruction to CSF flow. Vasculitis due to vessel involvement in the subarachnoid space can lead to infarctions, especially in the middle cerebral and basilar arteries' perforating territories.
- In spinal arachnoiditis, inflammatory exudate causes changes in CSF signal due to inflammation, enlargement, and diffuse cauda equina nerve root enhancement, as well as clumping and irregular distribution within the thecal sac, due to adhesions and fibrin deposition along the nerve sheaths. Late spinal cord changes include cord atrophy, syringomyelia, myelomalacia, or spinal cavitation.
- Tuberculomas are well defined and nodular or oval-shaped intra- or extra-axial lesions. Imaging characteristics depend on the stage. In the early phase, noncaseating lesions are hypointense on T1WI and hyperintense on T2WI, with homogeneous enhancement. Caseating lesions with a solid center show iso- to hypointense signal intensity on T1WI and T2WI, while those with a liquefacted center show hypointense signal intensity on T1WI and hyperintense signal intensity on T2WI, both with peripheral enhancement. Central calcification of the tuberculoma is known as the target sign.
Differential Diagnoses
- Leptomeningeal carcinomatosis and lymphomatosis commonly manifest in different clinical contexts. Diffuse and nodular leptomeningeal enhancement, and sometimes masses, can be found.
- In neurosarcoidosis, nodular or linear leptomeningeal and perivascular enhancement are frequent. Noncaseating sarcoid granulomas are intraparenchymal and usually smaller than tuberculomas, with no hypointense T2 macroscopic nodules described.
- Certain fungal meningitis, such as paracoccidioidomycosis, might develop hypointense spinal cord or cerebral granulomas, although leptomeningeal and cauda equina involvement are less frequent and symptomatic.
Treatment:
- Antitubercular drugs are the mainstay of treatment for tuberculous meningitis, with a 2-month course of isoniazid, rifampicin, pyrazinamide, and streptomycin or ethambutol, followed by a 6-month or 10-month course of isoniazid and rifampicin.
- Adjunctive corticosteroids are essential, as they seem to improve overall survival.
- Tuberculomas may require surgical resection to resolve mass effects.