What is a Posterior Fossa Lesion?
A posterior fossa lesion is an abnormal growth or area of damage located in the back, lower part of your skull where critical brain structures sit—specifically the cerebellum (which controls balance and coordination), the brainstem (which controls breathing, heart rate, and consciousness), and important nerves and blood vessels. 1, 2
Location and Anatomy
The posterior fossa is essentially a compartment at the base of your skull, behind your ears and at the back of your head. Think of it as a "basement" area of the brain that houses:
- The cerebellum: Your brain's balance and coordination center 3, 4
- The brainstem: The connection between your brain and spinal cord that controls automatic functions like breathing 3
- Cranial nerves: Nerves that control facial movement, hearing, swallowing, and eye movement 3
- Major blood vessels: Arteries that supply blood to these vital structures 3
What Can Go Wrong
Lesions in this area can be:
- Tumors (both cancerous and non-cancerous): Including metastases (spread from other cancers), schwannomas (nerve tumors), meningiomas (membrane tumors), and various brain tumors 3, 1, 5
- Infections: Such as abscesses or parasitic infections like neurocysticercosis 1, 2, 5
- Strokes or bleeding: From blocked or ruptured blood vessels 3, 6
- Cysts: Fluid-filled sacs that can be present from birth or develop later 1, 2
- Inflammatory conditions: Such as multiple sclerosis plaques 3
How They Affect You
Because this area is so tightly packed with vital structures, even small lesions can cause significant problems. Common symptoms include:
- Balance and coordination problems (ataxia): Difficulty walking, stumbling, or feeling unsteady 3, 4
- Headaches: Often worse in the morning or when lying down 1, 4
- Hearing loss or ringing in the ears (tinnitus): Particularly with nerve tumors 3, 4
- Dizziness and vertigo: A spinning sensation 3, 4
- Nausea and vomiting: From increased pressure in the skull 3, 4
- Facial weakness or numbness: From nerve involvement 3
- Double vision or eye movement problems: From cranial nerve compression 3
Why This Location is Particularly Concerning
Lesions larger than 3 cm in the posterior fossa, or those causing swelling and pressure, require urgent surgical consideration because they can rapidly lead to life-threatening complications. 3, 1 The confined space means that swelling can quickly compress the brainstem (affecting breathing and consciousness) or block the flow of spinal fluid, causing hydrocephalus (fluid buildup in the brain), which occurs in approximately 60% of cases with certain posterior fossa lesions 1, 2.
Diagnosis
MRI with and without contrast is the preferred imaging method for evaluating posterior fossa lesions, as it provides far superior visualization compared to CT scans. 3, 1, 2 CT scans have limitations in this area due to bone artifacts that obscure the view, though they remain useful for detecting bleeding or calcifications 2, 7.
The Bottom Line
A posterior fossa lesion is essentially any abnormality in the "basement" of your brain—a critical area where damage can affect balance, coordination, consciousness, and vital life functions. The symptoms often develop gradually (like progressive hearing loss) but can become serious quickly if the lesion grows or causes swelling, making prompt evaluation and treatment essential 4.