Patients with Wilson disease have an increase in extracellular copper, which causes oxidative stress and cell destruction. Brain changes include atrophy, cavitation, a reduction in neurons, increased cellularity, and Opalski cells.
On imaging increased T2 signal abnormalities are seen in the putamen (81%), pons (46.6%), thalami (36%), caudate nuclei (34.3%), midbrain (33.5%), and globus pallidus (15.4%). Temporal, parietal, and frontal lobes are affected less than 4% of the time, however the cerebral cortex is more frequently impaired in patients with torsion spasm. The occipital lobes and medulla oblangata are not affected.
Patients presenting younger than 10 years, show impairment of only the putamen. Patients with an age of onset between 10-14 years, often have brainstem impairment
Bilateral T1 hyperintensity may also be seen in the globus pallidus, putamen, and midbrain of children. These signal changes may be reversible with treatment, and are thought to be due to manganese deposition secondary to liver disease or porto-systemic shunting.
The "Face of the giant panda" sign on T2 MRI where there is preservation of normal signal intensity in the red nuclei and lateral portion of the pars reticulata of the substantia nigra, high signal in the tegmentum, and hypointensity of the superior colliculus.
The "Face of the miniature panda" on T2 MRI is seen within the pontine tegmentum. There is hypointensity of the medial longitudinal fasciculi and central tegmental tracts ("eyes of the panda") in contrast with the hyperintensity of the aqueduct opening into the fourth ventricule ("nose and mouth of the panda") bounded inferiorly by the superior medullary velum. The superior cerebellar peduncles form the panda's "cheeks".
References
1. MR Imaging of the brain in neurologic Wilson disease. XE Yu et al, AJNR 2019, 40(1):178-183
2. Pediatric Neuroimaging, 6th edition, AJ Barkovich
3. MR imaging of the brain in Wilson disease of childhood: Findings before and after treatment with clinical correlation. TJ Kim et al, AJNR 2006, 27(6): 1373-1378
4. The "double panda sign" in Wilson's disease. DA Jacobs et al, Neurology 2003, 61(7)