18F-Fluorodeoxyglucose Positron Emission Tomography–Computed Tomography/Magnetic Resonance Imaging in Neurosarcoidosis

A 41-year-old lady presented with headache and ophthalmoplegia of the left eye for 1 week. Magnetic resonance imaging (MRI) of the brain with contrast showed homogenously enhancing nodular thickening of meninges in the left anterior and middle cranial fossa with white matter edema of adjacent left frontotemporal lobes, suggestive of hypertrophic pachymeningitis. As hypertrophic pachymeningitis has different etiopathologies, including neoplastic diseases, whole-body 18F-fluorodeoxyglucose positron emission tomography–computed tomography (18F-FDG PET/CT), including PET/CT brain, was done to rule out other diagnostic possibilities and to look for optimal biopsy site. 18F-FDG PET/CT [Figure 1] revealed 18F-FDG avid brain lesions (SUVmax 18.5) in the anterior and middle cranial fossa with significant perilesional white matter edema with 18F-FDG avid peribronchial thickening, more in the bilateral hilar regions with 18F-FDG avid subpleural and perifissural bilateral pulmonary nodules (SUVmax 7.8) with multiple 18F-FDG avid mediastinal and abdomino-pelvic lymph nodes, few with amorphous calcifications. The findings were highly suggestive of disseminated sarcoidosis with other differential of lympho-proliferative disorder. Biopsy from the right inguinal lymph node showed noncaseating granulomas. In addition, her laboratory investigation revealed raised serum ACE levels of 224 U/L (12–68 U/L) and raised cerebrospinal fluid protein at 180 mg/dL (15–45 mg/dL) with no leukocytes. Coregistration of 18F-FDG PET brain images with contrast-enhanced volumetric T1-weighted (T1W) MRI sequence [Figure 2] was done for better characterization and delineation of the brain lesions. On dedicated PET/CT images of brain, it was difficult to determine the origin of FDG avid lesions, i.e. parenchymal or meningeal, due to inherent poor spatial resolution of CT scan. In this case, 18F-FDG PET/CT helped in determining the extent of the disease, in narrowing down the differentials, and in deciding the biopsy site.

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Figure 1 Whole-body FDG PET/CT maximum intensity projection image (a) showing disseminated FDG avid disease involving the bilateral lungs with 18F-FDG avid peribronchial thickening, predominantly in the bilateral hilar regions with 18F-FDG avid (SUVmax 7.8) bilateral subpleural and perifissural pulmonary nodules with multiple 18F-FDG avid mediastinal, abdomino-pelvic, and bilateral inguinal lymph nodes, few with amorphous calcifications (b-g)

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Figure 2 Axial and coronal MRI with gadolinium-enhanced T1 sequence (a-c), corresponding axial and coronal 18F-FDG PET images (d-f), and fused PET/MRI images (g-i) showing enhancing nodular thickening of meninges in the left anterior and middle cranial fossa with perilesional white matter edema of the left fronto-temporal lobes with increased 18F-FDG uptake

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Neurosarcoidosis has been reported in 5%–25% cases of sarcoidosis.[123] MRI is the imaging modality of choice to diagnose neurosarcoidosis; however, imaging findings are nonspecific due to involvement of any portion of the central nervous system (CNS). The typical imaging finding is the meningeal thickening and enhancement, especially around the base of the non-enhancing brain. Parenchymal involvement may present as non-enhancing periventricular white matter lesions or enhancing masses at the hypothalamus, brainstem, cerebral or cerebellar hemispheres, hypothalamus, pituitary stalk, and optic chiasm.[123] Neurosarcoidosis with dural involvement may present as focal dural masses or diffuse dural thickening. These lesions show homogenous enhancement on contrast-enhanced T1W images and appear dark on T2W images; this pattern of appearance on MRI is not specific, however, this can serve as a clue to the diagnosis; similar appearance on MRI can be also seen in calcified meningiomas, very cellular dural metastases, lymphoma, and idiopathic hypertrophic cranial pachymeningitis.[1] Clinically, patients who have dural involvement by neurosarcoidosis present with headache or cranial nerve compression as was in our case. Currently, there are no pathognomonic neurodiagnostic tests available for neurosarcoidosis.[45] Intense 18F-FDG uptake is noted at sites of active sarcoidosis.[2] As CT has limited value in demonstrating the meninges, dural-based lesions are difficult to visualize on 18F-FDG PET/CT, especially if they present as dural thickening; however, coregistration of 18F-FDG PET with MRI provides better structural and functional information which improves the lesion identification.[2] Early diagnosis of neurosarcoidosis may prevent the extension of granulomatous intraparenchymal involvement which can result in irreversible neurologic deficit. Therefore, accurate knowledge on the extent of disease with whole-body 18F-FDG PET in patients of sarcoidosis with CNS manifestation can help significantly in their therapeutic management.