Specific Imaging Findings. Neurodegenerative Langerhans cell histiocytosis (ND-LCH) develops years after the initial disease presentation and presents on CT as symmetric nonenhancing hypodensities in the dentate nuclei region of the cerebellum, sometimes with calcifications. On MRI, the symmetric cerebellar lesions are T2 hyperintense with hypointense and/or hyperintense signals on T1-weighted images. The abnormalities may be limited to the deep cerebellar gray matter or extend to the surrounding white matter, and can eventually result in CSF-like “holes”. T2 hyperintensities may also be found in the pontine tegmentum and/or pontine pyramidal tracts. T1 hyperintensity of the basal ganglia is another characteristic finding, which may be limited to globus pallidus. All of these lesions do not show mass effect or contrast enhancement, and are the second most frequent presentation of CNS LCH, after the extra-axial involvement of the pituitary gland and hypothalamus. Slight hyperintensity of the dentate nucleus on T1WI may be the initial finding, followed by T2 hyperintensity and subsequent slow extension of T2 hyperintensity to the cerebellar white matter. In the cerebral hemispheres, dilated perivascular spaces and white matter T2 hyperintensities may be encountered. The entire spectrum of intracranial LCH findings can be classified into four groups: (1) osseous lesions in the craniofacial bones and/or skull base with or without soft-tissue extension; (2) intracranial extra-axial disease in the hypothalamic–pituitary region, pineal gland, meninges, choroid plexus, and ependyma; (3) intra-axial degenerative disease in the gray and/or white matter with a striking symmetry of the lesions and a clear predominance in the cerebellum and basal ganglia; (4) localized or diffuse atrophy.
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