A neurological MRI menagerie

The advent of non-invasive imaging has revolutionised in vivo diagnosis of many medical conditions. This is exemplified by the use of MR scanning of the brain in the investigation of neurological disease. Historically, many pathological conditions have been described in terms of their resemblance to foods, for example: sago spleen (amyloid deposition); nutmeg liver (chronic venous congestion); anchovy sauce liver (amoebic abscess); popcorn cell (Hodgkin’s disease); and strawberry gall bladder (cholesterolosis).1 The imaging revolution appears however to have heralded a metaphorical change, with an increasing tendency to describe scan appearances in terms of animate objects. There is now it seems a “neurological MRI menagerie”, and it is expanding.

PROGRESSIVE SUPRANUCLEAR PALSY: THE HUMMINGBIRD OR PENGUIN SIGN, AND THE MICKEY MOUSE SIGN

Progressive supranuclear palsy (PSP), an atypical parkinsonian syndrome previously known as the Steele-Richardson-Olszewski syndrome, has a prevalence of ~5/100,000. Characteristic features include the insidious development in middle age of early postural instability leading to falls; a vertical supranuclear gaze palsy; axial rigidity; staring facies with a reduced blink rate; and a frontal dysexecutive syndrome.2 At the moment, the diagnosis remains clinical, and differentiating PSP from Parkinson’s disease and other neurodegenerative disorders including multiple system atrophy may not be straightforward. However, certain MRI features may provide support for the diagnosis: on mid-sagittal MRI views, atrophy of the mid-brain tegmentum with relative preservation of the pons leads to an appearance that has, perhaps reflecting a degree of zoological controversy, been described both as the “hummingbird sign”3 and the “penguin sign”4 (fig 1A). On axial MRI views, the “Mickey Mouse sign” similarly reflects fairly selective atrophy of the midbrain tegmentum, with relative preservation of the tectum and cerebral peduncles (fig 1B).