What Does the Hummingbird Sign Mean for PSP?

When you read an MRI report that mentions a “hummingbird sign” (sometimes called the “penguin sign”) and “midbrain atrophy,” it means your radiologist has spotted a specific visual pattern that is strongly associated with Progressive Supranuclear Palsy (PSP) ^[1]. Reading that a part of your brain is shrinking can be a frightening and overwhelming experience. This sign appears because a specific part of your brainstem has shrunk, while the area right next to it has stayed its normal size ^[2]. Because this unique pattern is rarely seen in other conditions, it helps doctors confirm a PSP diagnosis and distinguish it from similar diseases like Parkinson’s ^[3][4].

What is Midbrain Atrophy?

Atrophy is the medical term for shrinkage or loss of tissue. Your MRI report notes atrophy in the midbrain, which is the upper part of the brainstem connecting the brain to the spinal cord. The midbrain is like a central control station for essential functions, particularly your eye movements, balance, and posture ^[5].

While PSP can affect multiple areas of the brain over time, the midbrain is typically one of the most severely and visibly impacted on an MRI ^[6]. Because the midbrain controls these specific functions, its shrinkage directly corresponds to the hallmark symptoms of PSP, such as difficulty looking up and down (which can feel like a blurring of vision), frequent falls, and unsteadiness ^[7].

How Does it Look Like a Hummingbird?

The brainstem is made up of different sections. The midbrain sits directly on top of a larger, rounded section called the pons. In PSP, the midbrain shrinks significantly, but the pons retains its normal volume ^[1].

When a doctor looks at your MRI from a side-angle view (called a sagittal view), they see the profile of these brain structures. Because the top part (the midbrain) has flattened and shrunk, it looks like a bird’s small head and slender beak. The normal, un-shrunken pons beneath it looks like the plump, rounded body of a bird. Together, the silhouette strongly resembles a hummingbird or a penguin ^[1].

What This Means for Your Care

Seeing the hummingbird sign on an MRI is a crucial piece of the puzzle for your care team.

• High Specificity: The hummingbird sign is highly specific to PSP ^[3]. This means that if the sign is present, it is very likely the condition is PSP rather than another movement disorder ^[4].
• Measuring the Shrinkage: You might also see terms like the midbrain-to-pons ratio on your report. Radiologists sometimes measure the exact size of the midbrain and compare it to the pons to put a number on the amount of shrinkage ^[8].
• Not Always Present Early On: The hummingbird sign does not always show up in the very earliest stages of PSP ^[3]. If your MRI now shows the sign, it simply means enough structural change has occurred to visually confirm the disease. It does not automatically mean you are in the final stages of the illness.

This structural confirmation provides clarity for your doctors—ideally including a movement disorder specialist—allowing them to tailor your care plan specifically for PSP. For instance, knowing that the midbrain damage is causing your eye and balance issues, your doctor can refer you to a neuro-ophthalmologist for specialized vision care, or to a physical therapist trained in fall prevention strategies.

During your next appointment, consider asking your doctor to pull up the MRI and point the hummingbird sign out to you. Many patients find that visually understanding what is happening in their brain is empowering and helps demystify their symptoms.