Pulvinar sign | Radiology Signs

Answer:

The pulvinar sign is symmetric hyperintensity of the pulvinar nuclei of the posterior thalami that is brighter than the signal of the anterior putamen, seen on FLAIR, proton-density and diffusion-weighted images. In the appropriate clinical setting it is highly suggestive of variant Creutzfeldt-Jakob disease, in which large series of neuropathologically confirmed cases found it in the great majority of patients, giving a sensitivity of about 80 to 90 per cent and high specificity against other rapidly progressive dementias. The comparison with the anterior putamen matters, because mild pulvinar hyperintensity can be a normal finding; the sign requires the pulvinar to be the brightest structure. Diffusion-weighted imaging is the most sensitive sequence and should always be reviewed, since restricted diffusion in the thalami, and in sporadic disease in the cortex and striatum, may be the only abnormality. The differential for symmetric thalamic hyperintensity is wide and must be worked through: Wernicke encephalopathy, which also involves the mamillary bodies and periaqueductal grey, deep cerebral venous thrombosis, which shows the dense internal cerebral veins, Japanese encephalitis and other flaviviruses, osmotic demyelination, hypoxic-ischaemic injury, Fabry disease and post-infectious encephalitis. Confirmation of prion disease uses cerebrospinal fluid real-time quaking-induced conversion, 14-3-3 and total tau, the electroencephalogram and, definitively, neuropathology.

Why is it called so?

The sign is named for the pulvinar, the posterior nucleus of the thalamus that lights up bilaterally.

Pathophysiology

In variant Creutzfeldt-Jakob disease the misfolded prion protein reaches the brain from lymphoreticular tissue after oral exposure and propagates along neural pathways. It accumulates preferentially in the posterior thalamus, where spongiform change, neuronal loss, astrocytic gliosis and microglial activation increase tissue water and restrict extracellular diffusion, producing the FLAIR and diffusion signal change. The reason for the pulvinar predilection is not fully explained but is thought to relate to the thalamic connectivity of the pathways along which the agent spreads. The associated involvement of the dorsomedial nuclei produces the hockey stick appearance, and in sporadic disease the same pathology is distributed cortically and striatally instead, which is why the imaging patterns of the two forms differ.

Alternative names: Pulvinar hyperintensity; posterior thalamic sign

Other associated named signs: Hockey stick sign of combined pulvinar and dorsomedial thalamic involvement and the cortical ribboning of sporadic Creutzfeldt-Jakob disease

References

1. Collie DA, Summers DM, Sellar RJ, Ironside JW, Cooper S, Zeidler M, et al. Diagnosing variant Creutzfeldt-Jakob disease with the pulvinar sign: MR imaging findings in 86 neuropathologically confirmed cases. AJNR Am J Neuroradiol. 2003;24(8):1560-9. PMID: 13679271.