Specific Imaging Findings

Progressive supranuclear palsy (PSP) causes a selective atrophy of the rostral midbrain (tegmentum and superior colliculi), with characteristic imaging findings: flattening and concavity of the normally convex superior midbrain contour and a “funnelshaped” inferior third ventricle on sagittal images; relative increase in the length of the interpeduncular fossa with decreased anteroposterior midbrain diameter on axial images. These changes are responsible for the typical appearance on midsagittal MR images that has been called the “penguin” and “hummingbird” sign, because the shape of the atrophic midbrain resembles the bill of a hummingbird or a penguin's head, and it is a distinguishing feature of PSP. Increased T2 signal of the superior colliculi and periaqueductal gray matter may also be present. A less specific high T2 signal can be observed in the lenticular nuclei, along with T2 hypointensity and increased ADC values of the putamen as well as atrophy of the insular and fronto-temporal cortex.

Pertinent Clinical Information

PSP is a clinical syndrome comprising supranuclear ophthalmoplegia (impaired downward gaze), postural instability, and mild dementia. It is seen mainly in late adult life with a peak during the sixth decade. Clinical presentation includes parkinsonism, axial rigidity, contracture of neck and facial muscles (neck hyperextension and “surprised look”), and disautonomy. ADC measurements, MRI morphometry, DTI and MRS all show abnormal findings at the level of the fronto-temporal cortex, basal ganglia, and midbrain, with limited specificity and sensitivity.