An infratentorial lesion is any area of abnormal tissue in the lower portion of the brain, located beneath a membrane called the tentorium cerebelli. The term “lesion” refers to tissue that has been damaged or has undergone abnormal changes, appearing on imaging scans as areas that look different from healthy brain tissue. While the term may sound concerning, lesions can vary greatly in their cause and significance.
The Infratentorial Region of the Brain
The infratentorial region, also called the posterior fossa, is a compact area at the base of the skull housing the cerebellum and the brainstem. The cerebellum, at the back of the head, is responsible for coordinating voluntary muscle movements, maintaining posture, and ensuring balance. It is the brain’s center for fine-tuning motor skills for smooth, precise actions.
The brainstem connects the upper brain to the spinal cord and is composed of the midbrain, pons, and medulla oblongata. This structure acts as a relay station for nerve signals and governs automatic functions like breathing, heart rate, blood pressure, and consciousness. The pons is involved in eye and face movements, while the medulla contains control centers for the heart and lungs.
Causes and Types of Lesions
Infratentorial lesions have diverse causes. One is the growth of a tumor, which is an abnormal cluster of cells. These can be non-cancerous (benign), such as some meningiomas, or cancerous (malignant), like medulloblastomas. Another type of tumor in this area is an acoustic neuroma, which develops on the nerve for hearing and balance.
Vascular events are another cause. An ischemic stroke occurs when a blood clot blocks an artery, while a hemorrhagic stroke involves a ruptured blood vessel. Infections can lead to an abscess, a collection of pus and inflamed tissue. Inflammatory conditions like multiple sclerosis cause lesions by damaging the protective myelin sheath around nerve cells, and traumatic brain injuries can also damage these structures.
Recognizing the Symptoms
When a lesion impacts the cerebellum, a person may experience problems with coordination and balance. This can manifest as ataxia, a loss of coordinated movement that makes walking difficult and unsteady. Other cerebellar-related symptoms include vertigo, which is a sensation of spinning, and nystagmus, which involves involuntary, rapid eye movements.
If a lesion affects the brainstem, symptoms can be more widespread. Problems with the cranial nerves are common, leading to facial weakness, difficulty swallowing (dysphagia), slurred speech (dysarthria), and double vision. Since the brainstem controls consciousness and vital signs, a lesion here can cause changes in alertness, breathing, and heart rate. Headaches, nausea, and vomiting may also occur due to increased pressure within the skull.
Diagnosis and Treatment Approaches
Diagnosis begins with a neurological exam to assess motor skills, balance, reflexes, and sensory functions. Medical imaging is then used to view the brain. Magnetic resonance imaging (MRI) is preferred for its detailed images of soft tissues, allowing doctors to see the lesion’s size, location, and characteristics. Computed tomography (CT) scans may also be used, especially in emergencies, to detect bleeding or fractures.
Treatment depends on the lesion’s cause, size, and location. If the lesion is a tumor, surgery may be performed to remove it. Malignant tumors often require follow-up radiation or chemotherapy. For an infection like an abscess, antibiotics are the primary treatment, while inflammatory conditions like multiple sclerosis are managed with immune-system medications. Corticosteroids may be prescribed to reduce swelling and pressure within the brain.