Face of the giant panda | Radiology Signs

Answer:

The face of the giant panda is the appearance of the axial midbrain on T2-weighted MRI when the tegmentum becomes diffusely hyperintense while the red nuclei, the superior colliculi and the substantia nigra pars reticulata remain relatively low in signal. The preserved red nuclei form the eyes, the spared substantia nigra the ears and the superior colliculus the muzzle of a panda’s face. It is the classic, though not universal or entirely specific, finding of Wilson disease, and variants such as a bright-eye pattern are described. In the pons an analogous appearance formed by the central tegmental tracts and the medial lemnisci is called the face of the miniature panda, and the two together constitute the double panda sign, which is also reported in Leigh disease. The full Wilson MRI pattern includes symmetric T2 hyperintensity of the putamen, caudate and thalamus, often with T1 shortening in the globus pallidus from associated hepatic dysfunction, and central pontine and extrapontine myelinolysis-like change. Diagnosis rests on a low serum caeruloplasmin, raised 24-hour urinary copper, Kayser-Fleischer rings on slit-lamp examination and ATP7B testing, with liver biopsy copper quantification where doubt remains, because early treatment with chelation or zinc reverses much of the neurological and imaging abnormality.

Why is it called so?

The pattern of spared and affected midbrain nuclei on the axial image reproduces the black and white markings of a giant panda’s face.

Pathophysiology

Wilson disease is an autosomal recessive defect of the copper-transporting ATPase ATP7B, which impairs biliary copper excretion and incorporation of copper into caeruloplasmin. Copper accumulates first in the liver and then, once hepatic capacity is exceeded, is released into the circulation and deposited in the basal ganglia, midbrain and cornea. Free copper generates reactive oxygen species and causes neuronal loss, spongiform degeneration and gliosis, all of which increase tissue water and produce T2 hyperintensity. Structures with a high iron content, notably the red nucleus and the substantia nigra pars reticulata, retain their intrinsically low T2 signal, and it is this contrast between the affected tegmentum and the iron-rich spared nuclei that draws the panda face.

Alternative names: Giant panda sign; panda face of the midbrain

Other associated named signs: Face of the miniature panda in the pons and the combined double panda sign

References

1. Srinivasan S, Paul A, Sahitya J, Mulupuru S, Sakinala EK. Expanding the spectrum of the giant panda sign: a bright-eye variant in Wilson disease. Radiol Case Rep. 2026;21(10):4414-4418. PMID: 42438777.