A lesion is an area of tissue damaged by injury or disease, appearing as an abnormality on diagnostic imaging scans. Infratentorial lesions (ILs) are abnormalities specifically located in the lower, posterior region of the skull. This area houses structures responsible for fundamental life-sustaining functions. Because this space is confined, even small abnormalities can quickly lead to severe or life-threatening neurological consequences.
The Infratentorial Compartment
The location of an infratentorial lesion is defined by the tentorium cerebelli, a tough, sheet-like fold of the dura mater. This structure acts as a physical partition, separating the cerebrum (the large upper portion of the brain) from the lower region. The compartment below this partition is the infratentorial space, commonly referred to as the posterior fossa.
Within this small, dense area are two major, functionally distinct structures: the cerebellum and the brainstem. The brainstem, which is composed of the midbrain, pons, and medulla oblongata, serves as the primary relay center connecting the cerebrum and spinal cord. It is also the control center for involuntary functions such as breathing, heart rate, and consciousness.
The cerebellum occupies the largest part of the posterior fossa. Its role involves the coordination of voluntary movements, motor learning, posture, and balance. Because the brainstem and cerebellum are packed tightly, any expanding lesion, such as a tumor or collection of blood, can rapidly compress these structures. This explains why infratentorial lesions often present with sudden, profound symptoms reflecting the disruption of these control systems.
Primary Causes of Lesions
Infratentorial lesions arise from a diverse set of medical conditions, which can be broadly categorized by their origin, including abnormal cell growth, interruptions in blood flow, or inflammatory processes. Neoplastic causes, involving the growth of tumors, represent a major group, and these lesions can be either benign or malignant.
In children, 60 to 70 percent of brain tumors originate in the posterior fossa. Common tumors include medulloblastomas and ependymomas, which often arise near the fourth ventricle, and various types of astrocytomas. In adults, frequently observed tumors include meningiomas (arising from the meninges) and acoustic neuromas (tumors of the eighth cranial nerve). Tumors in this region often differ in cell type and behavior compared to those found in the upper brain.
Vascular events, collectively known as strokes, are another frequent cause of damage to the infratentorial compartment. These can be ischemic, resulting from a blockage of blood flow to the brain tissue, or hemorrhagic, caused by bleeding into the brain. The posterior circulation, which supplies the brainstem and cerebellum, is susceptible to these events, leading to a condition known as infratentorial infarction.
A third major category involves infectious or inflammatory processes that create areas of damaged tissue. A brain abscess, a localized collection of pus and inflamed tissue, can form following an infection elsewhere in the body. Demyelinating diseases, such as multiple sclerosis, also frequently cause lesions in the infratentorial region, specifically in the brainstem and cerebellum.
How Lesions Affect Neurological Function
The clinical presentation of an infratentorial lesion is highly dependent on which specific structure within the posterior fossa is compressed or damaged. Since the area is so tightly packed, many patients experience a combination of symptoms related to both the cerebellum and the brainstem. A common and potentially life-threatening complication is the development of hydrocephalus, which is an excessive accumulation of cerebrospinal fluid (CSF).
Lesions can obstruct the flow of CSF out of the fourth ventricle, leading to a rapid rise in pressure inside the skull. This increased intracranial pressure (ICP) often causes symptoms like persistent headaches, nausea, and vomiting. Headaches are often worse in the morning or when lying down, a characteristic sign of pressure buildup.
When the lesion affects the brainstem, patients may experience deficits related to the cranial nerves, which control functions of the head and neck. Damage here can lead to double vision, facial weakness or numbness, and difficulty swallowing (dysphagia) or speaking (dysarthria). Furthermore, brainstem involvement can compromise the centers controlling respiration and heart rate, leading to serious medical emergencies.
Damage to the cerebellum primarily results in problems with coordination and balance, collectively known as ataxia. Patients may present with an unsteady or clumsy gait, often walking as if they are intoxicated. Lesions in the cerebellar hemispheres tend to cause clumsiness in the limbs on one side of the body, while midline lesions cause instability of the trunk. Other cerebellar symptoms include vertigo (a sensation of spinning) and nystagmus (a repetitive, involuntary movement of the eyes).
Diagnosis and Management Strategies
The initial step in evaluating a suspected infratentorial lesion involves a thorough neurological examination to pinpoint the location of the damage based on symptoms. Diagnostic imaging is then utilized to visualize the abnormality and determine its underlying cause. Magnetic Resonance Imaging (MRI) is the preferred method for imaging the posterior fossa due to its superior resolution of soft tissues like the brainstem and cerebellum.
MRI scans, particularly those enhanced with a contrast agent like gadolinium, provide detailed pictures that help differentiate between various types of lesions, such as tumors, abscesses, or demyelinating plaques. Computed Tomography (CT) scans are also frequently used, especially in emergency settings because they are fast and readily available. CT is particularly effective at identifying acute hemorrhage, calcifications within a tumor, or any associated bone abnormalities.
Management of an infratentorial lesion depends on the specific cause, size, and location of the abnormality. For many tumors, surgical intervention to remove the mass (resection) is the preferred course of action, aiming for the greatest possible removal while preserving neurological function. If hydrocephalus is present, a neurosurgeon may place a shunt, a tube that drains excess CSF to relieve pressure.
Non-surgical treatments are often employed either as an alternative or as an adjunct to surgery. Radiation therapy and chemotherapy may be used to treat malignant tumors, such as medulloblastoma, either before or after surgical resection. Lesions caused by inflammatory conditions, like multiple sclerosis, are managed with medications that suppress the immune system and control inflammation. Vascular lesions, such as strokes, are managed medically to prevent recurrence, often involving blood thinners or risk factor modification.