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Neuroradiology Case of the Week

Case 120

Clinical Presentation: A 31-year-old gentleman presented with history of leg weakness.

Radiological Findings: Axial T2-weighted image (Fig. 1A) shows a small round hyperintense area with hypointense center, this is associated with surrounding edema. Post-contrast T1-weighted image (Fig. 1B) of the same patient shows multiple ring-like enhancing lesions in the same area. There is also increased enhancement of the meninges along the falx cerebri. Figure 1C shows multiple enhancing tuberculomas involving bilateral cerebellar hemispheres. There is enhancement of basal meninges as well.

Discussion: Mycobacterium tuberculosis has infected humans for thousands of years. Fragments of the spinal column from Egyptian mummies from 2400 BCE have been found that show definite pathological signs of tubercular decay.
     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 [1]. Clinical diagnosis can be difficult; therefore, imaging has an important role in establishing the diagnosis.
     Clinical symptomology may include headache, fever, mental deterioration, and seizures. Early diagnosis is essential as the prognosis is dependent on early treatment. Most tuberculous infections of the central nervous system area result of hematogenous spread. Intracranial tuberculosis results in two related pathologic processes: tuberculous meningitis and intracranial tuberculomas [3]. Tuberculous meningitis is a more frequent manifestation of neuro-tuberculosis than is brain tuberculoma and is more commonly seen in children.

Meningeal Involvement
     MR imaging findings vary depending on the stage of the disease. In the early stages findings at unenhanced spin-echo imaging may be normal. In later stages there is distention of the affected subarachnoid spaces associated with mild shortening of T1 andT2 relaxation times compared with normal cerebrospinal fluid. Gadolinium-enhanced T1-weighted imaging demonstrates abnormal meningeal enhancement that is more pronounced in the basal cisterns. There may be involvement of the meninges within the sulci over the cerebral convexities and in the sylvian fissures. Abnormal enhancement of the choroid plexus and ependymal lining of the ventricular system may rarely be seen. Sequelae of tuberculous meningitis include focal areas of atrophy secondary to infarcts and hydrocephalus and, rarely, syringomyelia or syringobulbia [1,2].
     The differential diagnosis for tuberculous meningitis includes other infectious agents (nontuberculous bacteria, viruses, fungi, parasites), noninfectious inflammatory disease affecting the leptomeninges (rheumatoid disease, sarcoidosis), and primary or secondary neoplastic involvement of meningeal surfaces (meningiomatosis, neoplastic meningitis from a peripheral tumor source, cerebrospinal fluid seeding from a primary tumor of the central nervous system).

Parenchymal Involvement
     Parenchymal disease can occur with or without meningitis and usually manifests as either solitary or multiple tuberculomas.
     MR imaging findings vary depending on whether the granulomas are noncaseating, caseating with a solid center, or caseating with a necrotic center. Tuberculomas consisting of noncaseating granulomas are usually hypointense relative to the brain on T1-weighted images and hyperintense on T2-weighted images. The lesions usually demonstrate homogeneous enhancement after gadolinium administration. Caseating granulomatous lesions with a solid center appear relatively hypointense or isointense on T1-weighted images and iso- to hypointense on T2-weighted images [1,4]. They are typically associated with surrounding edema. The lesion has a hypointense rim on T2-weighted images. Caseating lesions demonstrate rim enhancement at contrast-enhanced T1-weighted MR imaging.
     Tuberculomas with a necrotic center demonstrate central hyperintensity on T2-weighted images.
     The differential diagnosis for parenchymal tuberculomas includes other granulomatous infections (e.g., cysticercosis) and fungal lesions as well as primary or metastatic neoplasms.

References:

1. Harisinghani MG, McLoud TC, Shepard J-A, Ko JP, Shroff MM, Mueller PR. Tuberculosis from head to toe. RadioGraphics 2000; 20: 449-70 [Medline].
2. Engin G, Acunas B, Acunas G, Tunaci M. Imaging of extrapulmonary tuberculosis. RadioGraphics 2000; 20: 471-88 [Medline].
3. Salgado P, Del Brutto OH, Talamas O, et al. Intracranial tuberculoma: MR imaging. Neuroradiology 1989; 31:299-302 [Medline].
4. Gupta RK, Jena A, Sharma A, et al. MR imaging of intracranial tuberculomas. J Comput Assist Tomogr 1988; 12:280-285 [Medline].