Specific Imaging Findings

MRI is the imaging modality of choice for neurosarcoidosis with the typical imaging feature of thickened and enhancing leptomeninges, primarily along the base of the brain with suprasellar and cranial nerve involvement. The leptomeningeal lesions are typically patchy, thick, and somewhat nodular, while smooth and diffuse enhancement is relatively rare. Infiltrating extension of the leptomeningeal enhancement along the surface of the brain (and/or spinal cord) into the parenchyma (along the perivascular spaces) is a relatively characteristic feature. Intra-axial, dural, and intraosseus granulomas may also be present, sometimes without associated leptomeningeal involvement. Granulomas are homogenous and without necrotic portions, enhance with contrast and are of characteristically low T2 signal. As with other inflammatory and infectious processes, perfusion studies show low cerebral blood volume of these lesions. FDG-PET may reveal other locations of the disease, primarily in the mediastinum, even with negative chest CT scans.

Pertinent Clinical Information

Neurosarcoidosis is a diagnostic challenge, especially in the absence of systemic involvement. Symptoms, when present, may be subtle and resemble those of other diseases. On the other hand, sarcoid-related imaging abnormalities are frequently not associated with correlating symptoms. The most common manifestations are cranial neuropathies, primarily affecting optic and facial nerves. Encephalopathy, seizures, diabetes insipidus and other endocrine manifestations may be encountered. The diagnosis is commonly established through a combination of chest imaging (CT), nuclear medicine scans (Gallium and FDG-PET), and laboratory findings: CSF analysis and serum angiotensin-converting enzyme (ACE) level.