Imaging Features of Neurosarcoidosis in FDG PET/CT

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A 62-year-old male presented with clinical features and nerve conduction study suggestive of trigeminal neuropathy and demyelinating axonal polyneuropathy. Upon evaluation, his S. angiotensin-converting enzyme (ACE) level was 64.9U/ml. ¹⁸F fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) was suggested due to the clinical suspicion of neurosarcoidosis [Figure 1]. (a) FDG PET/CT Maximum intensity projection (MIP) image demonstrates FDG avid foci in the bilateral middle cranial fossa, in bilateral parotid gland, in bilateral hilar and mediastinal nodes, and in the upper lumbar paraspinal region on the right side. (b-d) Image shows FDG uptake along bilateral Meckel’s cave with subtle dural enhancement. (e) and (f) Image shows multiple enlarged bilateral hilar and mediastinal nodes. (g) and (h) Image shows focal area of increased FDG uptake along neural foramina of L2 vertebra on the right side. Apart from these, increased FDG uptake was seen along neural foraminae of few other cervical, dorsal, and lumbar vertebrae. FDG avidity in Meckel’s canal and neural foramina, explained the cranial neuropathy and radiculopathy symptoms. In view of raised S.ACE levels and PET/CT findings, we raised a possibility of sarcoidosis with neurological involvement and suggested biopsy correlation from the enlarged subcarinal node. (i) Image demonstrates histopathology section showing lymphoid tissue studded with several well-formed nonnecrotizing granulomas composed of epithelioid cells, lymphohistiocytic cells, and surrounding multinucleated giant cells, which were negative on acid-fast bacillus staining suggestive of sarcoidosis. Sarcoidosis is a systemic immune-mediated disease with no specific bio or imaging markers. Neurosarcoidosis can present with a myriad of symptoms including parenchymal, cranial neuropathic, meningeal, and myelopathy symptoms.[12] Tissue biopsy is the only reliable modality for the diagnosis. FDG PET/CT is often used in sarcoidosis for assessing the extent of disease involvement and for identifying a site amenable for biopsy. Neurosarcoidosis lacks a typical conventional or radionuclide imaging pattern. Although magnetic resonance imaging is the preferred imaging modality, FDG PET/CT findings in suspected neurosarcoidosis have been described in various case reports or short communications.[3] To our knowledge, there are not many literature with FDG PET/CT detected cranial neuropathy and radiculopathy findings in neurosarcoidosis. This article aims to familiarize the clinicians with the various patterns of FDG uptake in neurosarcoidosis.

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Figure 1 62 year old male with clinical suspicion of Neurosarcoidosis, ¹⁸F FDG PET/CT was done for disease evaluation. (a) FDG PET/CT MIP image demonstrates FDG avid foci in bilateral middle cranial fossa, in bilateral parotid gland, in bilateral hilar and mediastinal nodes and in upper lumbar paraspinal region on right side. (b), (c) and (d) show FDG uptake along bilateral Meckel’s cave with subtle dural enhancement. (e) and (f) show multiple enlarged bilateral hilar and mediastinal nodes. (g) and (h) show focal area of increased FDG uptake along neural foramina of L2 vertebra on right side. (i) demonstrates histopathology section showing lymphoid tissue studded with several well-formed non-necrotizing granulomas composed of epithelioid cells, lympho-histiocytic cells and surrounding multinucleated giant cells, which were negative on AFB staining- suggestive of Sarcoidosis.

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