Role of Multiparametric Magnetic Resonance Imaging of the Brain in Differentiating Neurocysticercosis From Tuberculoma

Abstract

Introduction: The two most common infectious causes of ring-enhancing lesions are neurocysticercosis (NCC) and tuberculoma. It is a challenge to differentiate NCC and tuberculomas radiologically since they show the same imaging findings on computed tomography (CT). Hence, this study was performed to assess the role of magnetic resonance imaging (MRI) as an additional advanced modality to aptly characterize the lesion. Conventional MRI with additional advanced imaging sequences like diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), magnetic resonance spectroscopy (MRS), and post-contrast T1-weighted imaging (T1WI) aids in characterizing the lesion and helps in differentiating NCC and tuberculomas.

Objectives: To compare the findings of DWI, ADC cut-off values, spectroscopy, and contrast-enhanced MRI in differentiating NCC from tuberculoma.

Materials and methods: Individuals who matched the inclusion criterion underwent an MRI of the brain (plain and contrast) in a 1.5 Tesla, 18-channel, magnetic resonance scanner (Magnetom Avanto®, Siemens Healthineers, Erlangen, Germany). The following imaging sequences were included: T1WI (axial and sagittal), T2-weighted imaging (axial and coronal), fluid-attenuated inversion recovery, DWI at 0, 500, and 1000 mm²/s b-values with corresponding ADC values, and single-voxel MRS. Based on MRI features such as number, size, location, margins of lesions, scolex, surrounding edema, DWI features with corresponding ADC values, enhancement pattern of lesions, and spectroscopy findings, we evaluated and differentiated the lesions as NCC or tuberculoma. Radiological diagnoses were correlated in terms of clinical symptoms and response to treatment.

Results: In our study, 42 subjects were included, of which the total number of NCC cases was 25 (59.52%) and tuberculoma was 17 (40.47%). The mean age of patients included was 42.85 ± 14.76 years (21 to 78 years). On post-contrast imaging, all 25 cases of NCC (100%) showed thin ring enhancement whereas the majority of tuberculomas (64.7%) showed thick irregular ring enhancement. On MRS, all 25 cases (100%) of NCC showed an amino acid peak and all 17 cases (100%) of tuberculoma showed a lipid lactate peak. On DWI, out of 25 NCC cases, restriction of diffusion was absent in the majority of cases (88%) and out of 17 cases of tuberculoma, restriction of diffusion was present in 12 cases (70.5%) (T2 hyperintense tuberculoma, indicative of caseating tuberculoma with central liquefaction) and was absent in the rest. In our study, the mean ADC value of NCC lesions (1.30 ± 0.137 x 10^-3 mm²/s) was found to be greater than that of tuberculoma (0.74 ± 0.090 x 10^-3 mm²/s). ADC value of 1.2 x 10^-3 was obtained as a cut-off to differentiate NCC and tuberculoma. The ADC cut-off value of 1.2 x 10^-3 mm²/s showed a sensitivity of 92% and specificity of 94.1% in differentiating NCC from tuberculoma.

Conclusions: Conventional MRI with additional advanced imaging sequences like DWI, ADC, MRS, and post-contrast T1WI aids in characterizing the lesion and thereby helps in differentiating NCC and tuberculomas. Hence, multiparametric MRI assessment is useful in making a prompt diagnosis and eliminating the need for a biopsy.

Keywords: adc values; apparent diffusion coefficient; diffusion-weighted imaging; magnetic resonance spectroscopy; neurocysticercosis; tuberculoma.

Figure 1. MRI images demonstrating the number of lesions in our study cases

(A) MRI axial T2-weighted imaging (T2WI): A single lesion (orange arrow) was noted in the right frontal lobe - a case of neurocysticercosis. (B) MRI axial fluid-attenuated inversion recovery (FLAIR): Multiple lesions (orange arrows) in the bilateral cerebellar hemisphere and left temporal lobe - a case of tuberculoma. (C) MRI axial T2WI: Conglomerate lesion (orange arrow) in left high parietal lobe - a case of tuberculoma.

Figure 2. MRI fluid-attenuated inversion recovery (FLAIR) images showing degrees of edema surrounding lesions

(A) Case of neurocysticercosis: Lesion in the right occipital lobe (orange arrow) with mild perilesional edema. (B) Case of tuberculoma: Lesion in the left temporal lobe (orange arrow) with moderate perilesional edema. (C) Case of tuberculoma: Lesion in the left high frontal lobe (orange arrow) with severe perilesional edema.

Figure 3. MRI T1-weighted axial and sagittal images showing scolex in a case of neurocysticercosis

(A) Axial T1-weighted imaging (T1WI) and (B) sagittal T1WI MRI of the brain (plain) show an oval T1 hypointense lesion in the left frontal lobe (orange arrow in both images A and B) with central T1 hyperintensity suggestive of the scolex.

Figure 4. Post-contrast magnetic resonance images of neurocysticercosis and tuberculoma cases

(A) Case of neurocysticercosis: MRI T1-weighted post-contrast image showing thin ring enhancement of the lesion in the left frontal lobe (orange arrow). (B) Case of tuberculoma: MRI T1-weighted post-contrast image showing thick irregular enhancement of the lesion in the pons (orange arrow).

Figure 5. Diffusion-weighted imaging features and corresponding apparent diffusion coefficient (ADC) values in neurocysticercosis and tuberculoma

MRI of the brain axial sections - (A) axial diffusion-weighted imaging (DWI) and (B) axial ADC map showing no restriction of diffusion (orange arrows in A and B). ADC value obtained was 1.3 x 10^-3 mm²/s - case of neurocysticercosis. MRI of the brain axial sections - (C) axial DWI and (D) axial ADC map showing patchy areas of restriction of diffusion (orange arrows in C and D). ADC value obtained was 0.73 x 10^-3 mm²/s - case of tuberculoma.

Figure 6. Tuberculoma - caseating granulomas with central liquefaction

MRI images: (A) Axial T1WI, (B) axial T2WI, (C) axial DWI, (D) axial ADC map, and (E) axial T1-weighted post-contrast. These images show few, variable-sized, T1 iso and T2 hyperintense lesions with T2 hypointense rim (blue arrows) and moderate perilesional edema in bilateral cerebellar hemispheres and right temporal lobe with restricted diffusion on DWI. The ADC value obtained was 0.9 x 10^-3 mm²/s. On post-contrast, the lesions show thick irregular ring enhancement. T1WI: T1-weighted imaging; T2WI: T2-weighted imaging; DWI: diffusion-weighted imaging; ADC: apparent diffusion coefficient.

Figure 7. Tuberculoma - caseating granulomas without central liquefaction

MRI images: (A) Axial T1WI, (B) axial T2WI, (C) axial DWI, (D) axial ADC map, and (E) axial T1-weighted post-contrast. These images show few, variable-sized, T1 iso and T2 hypointense lesions with T2 hypointense rim (blue arrows) and moderate perilesional edema in bilateral high parietal lobes with no restricted diffusion on DWI. The ADC value obtained was 1.1 x 10^-3 mm²/s. On post-contrast, the lesions show thick ring enhancement. T1WI: T1-weighted imaging; T2WI: T2-weighted imaging; DWI: diffusion-weighted imaging; ADC: apparent diffusion coefficient.

Figure 8. ROC analysis of predictive validity of ADC to differentiate neurocysticercosis from tuberculoma

ROC: receiver operating characteristic; ADC: apparent diffusion coefficient.

Figure 9. Magnetic resonance spectroscopy peaks in neurocysticercosis and tuberculoma

(A) Case of neurocysticercosis: Single voxel magnetic resonance spectroscopy shows an acetate peak at 1.9 ppm (orange arrow). (B) Case of tuberculoma: Single voxel magnetic resonance spectroscopy shows lipid lactate peak at 1.3 ppm (orange arrow).

Figure 10. Stages of neurocysticercosis

(A-B) Vesicular stage of neurocysticercosis. (A) Axial T1WI and (B) axial T2WI. These images show a well-defined, CSF intensity lesion (orange arrow) demonstrating a central T1 hyperintense dot sign in the left frontal lobe. (C-D) Colloidal vesicular stage of neurocysticercosis. (C) Axial FLAIR and (D) axial T1-weighted post-contrast images. These images show a well-defined T2 hypointense focus (measuring 6 mm) (blue arrows) in the right frontal lobe with mild perilesional edema. The lesion shows ring enhancement in the post-contrast study. (E-F) Granular nodular stage of neurocysticercosis. (E) Axial FLAIR and (F) axial T1-weighted post-contrast images. These images show a FLAIR hypointense lesion with minimal perilesional edema (blue arrows) noted in the right parietal lobe demonstrating peripheral rim enhancement in the post-contrast study. T1WI: T1-weighted imaging; T2WI: T2-weighted imaging; FLAIR: fluid-attenuated inversion recovery.