A spinal cord hemisection describes an incomplete spinal cord injury where damage occurs predominantly on one side, either the left or right, of the spinal cord. This pattern of injury affects communication pathways between the brain and body in a distinct manner. The disruption of these pathways leads to a unique set of neurological deficits below the level of the injury, affecting motor function, sensation, and the ability to perceive pain and temperature.
The Anatomy of a Hemisection
The spinal cord houses various nerve pathways, known as tracts, each specialized in carrying distinct types of information. Understanding three primary tracts helps explain the specific symptoms of a hemisection. The corticospinal tract transmits signals from the brain that control voluntary movements. This tract descends from the brain and crosses over to the opposite side of the body high up in the brainstem before reaching the spinal cord.
Another significant pathway is the dorsal columns, which relay sensory information related to fine touch, vibration, and proprioception—our awareness of body position and movement. Similar to the corticospinal tract, nerve fibers within the dorsal columns ascend and cross over in the brainstem. This means sensory information from one side of the body travels up the spinal cord on the same side before crossing at a higher level.
In contrast, the spinothalamic tract carries signals for pain and temperature sensations. Upon entering the spinal cord, these nerve fibers quickly cross over to the opposite side, typically within one or two segments. This immediate crossover accounts for the distinctive sensory losses observed in a spinal cord hemisection.
Resulting Symptoms and Brown-Séquard Syndrome
The neurological deficits that arise from a spinal cord hemisection are clinically termed Brown-Séquard syndrome. This syndrome presents a characteristic pattern of symptoms below the level of the injury, directly resulting from the specific affected pathways and their crossing patterns. On the same side of the body as the spinal cord injury, individuals typically experience a loss of voluntary motor function, ranging from weakness to complete paralysis.
This ipsilateral motor deficit occurs because the corticospinal tract, which controls movement, has already crossed over in the brainstem and is descending on the same side of the spinal cord as the injury. Accompanying the motor weakness on the injured side is a loss of fine touch, vibration, and proprioception. This sensory loss is also ipsilateral to the injury, as the dorsal columns ascend on the same side before crossing higher up in the brainstem.
Conversely, on the side of the body opposite to the spinal cord injury, individuals experience a loss of pain and temperature sensation. This contralateral sensory deficit is a hallmark of Brown-Séquard syndrome. The spinothalamic tract crosses over to the opposite side of the spinal cord almost immediately after entering. An injury to one side of the spinal cord will interrupt these crossed fibers, leading to a loss of pain and temperature sensation on the opposite side of the body below the injury level. For example, an injury to the right side of the spinal cord would result in weakness and loss of fine touch on the right side of the body, while pain and temperature sensation would be lost on the left side.
Causes and Diagnosis
Spinal cord hemisection can result from various causes, including direct trauma or localized compression of the spinal cord. Penetrating injuries, such as stab wounds or gunshot wounds, are a common cause, as they can directly sever or damage one side of the spinal cord. Other less frequent causes include spinal tumors that grow and compress one side of the cord, or vascular problems such as a spinal cord stroke (ischemia) that affects blood flow to a specific region of the cord. Inflammatory conditions, though rare, can also lead to localized damage mimicking a hemisection.
Diagnosing a spinal cord hemisection begins with a comprehensive neurological examination. During this examination, the doctor meticulously assesses the patient’s sensory and motor functions to map the specific areas of loss. This detailed evaluation helps to pinpoint the level of the injury and differentiate between the ipsilateral motor and proprioceptive deficits and the contralateral pain and temperature losses characteristic of Brown-Séquard syndrome.
Following the clinical examination, medical imaging is used to confirm the diagnosis and visualize the extent of the damage. Magnetic Resonance Imaging (MRI) is the preferred imaging modality for spinal cord injuries. An MRI scan provides detailed images of the spinal cord, allowing clinicians to identify the precise location of the injury and confirm that the damage is primarily confined to one side of the cord. This imaging also helps to identify the underlying cause, whether it be a foreign object, a tumor, or signs of a vascular event.
Medical Management and Rehabilitation
Immediate medical management focuses on stabilizing the patient and preventing further spinal cord damage. This may involve immobilizing the spine with a brace or collar to ensure stability, particularly in traumatic injuries. Surgical intervention might be necessary to remove any foreign objects, decompress the spinal cord if there is excessive pressure from a tumor or bone fragment, or stabilize a fractured spine. Medications, such as corticosteroids, may be administered in the acute phase to reduce swelling around the injured area and minimize secondary damage, although their effectiveness is debated.
Long-term recovery relies on a comprehensive rehabilitation process, which begins as soon as the patient’s medical condition stabilizes. Physical therapy (PT) plays a central role, aiming to improve muscle strength, range of motion, and overall mobility. Therapists guide patients through targeted exercises to re-educate muscles, improve balance, and, for many, work towards regaining the ability to walk. This structured approach helps to maximize functional recovery and adapt to any persistent weaknesses.
Occupational therapy (OT) is another integral component of rehabilitation, focusing on helping patients regain independence in activities of daily living (ADLs). Occupational therapists work with individuals to relearn tasks such as dressing, bathing, and eating, adapting techniques and recommending assistive devices as needed. The goal of OT is to enable patients to perform everyday tasks with greater ease and independence.
The Path to Recovery
The prognosis for individuals with Brown-Séquard syndrome is generally more favorable compared to other types of incomplete spinal cord injuries. A significant percentage of individuals, often 75% to 90%, experience substantial recovery of motor function and may regain the ability to walk independently. Many also see improvements in bladder and bowel control, which significantly enhances their quality of life. The degree of recovery, however, is a highly individual process.
Several factors influence the recovery trajectory, including the initial severity of the injury, the patient’s age, and their general health status before the injury. Younger individuals and those with fewer pre-existing health conditions often demonstrate a greater capacity for recovery. The intensity and consistency of rehabilitation efforts also play a substantial role in maximizing functional outcomes.
Recovery is a prolonged journey that can span months to years, with the most significant improvements often occurring within the first six to twelve months post-injury. This recovery is largely facilitated by neuroplasticity, the brain’s remarkable ability to reorganize and form new neural connections. Through targeted therapy, the nervous system can adapt and reroute signals around damaged areas, enabling some degree of functional restoration and helping individuals regain lost abilities.