Bilateral Posterior Tibial Nerve SSEP Changes During STA to MCA Bypass
February 27, 2025
The superficial temporal artery to middle cerebral artery (STA-MCA) bypass is a specialized procedure designed to improve blood flow to the brain by redirecting blood from the extracranial carotid artery to branches of the middle cerebral artery (MCA). This surgical approach is typically employed for patients with intracranial vascular occlusions or compromised blood flow. The aim is to bypass blocked arteries and restore normal circulation. While the technique offers life-saving benefits, it also carries significant risks, including graft occlusion, hematoma, scalp necrosis, and intracranial hemorrhage. One crucial way to mitigate these risks and improve patient outcomes is through intraoperative neuromonitoring (IONM).
Patient Case Overview: Complex History and Severe Blockage
A 67-year-old male presented with left-eye blindness, mild right-sided weakness, and speech difficulties. His medical history included a previous left-sided stroke, diabetes, hypertension, tobacco use, and coronary artery disease—factors that contributed to a severe blockage in his internal carotid artery. Due to the internal carotid artery occlusion, a left STA to MCA bypass was planned to restore blood flow and prevent further neurological decline.
Given the patient’s complex medical history and the delicate nature of the procedure, meticulous neuromonitoring was necessary to ensure real-time feedback on the patient’s neural function during surgery.
The Neurophysiology Monitoring Approach
In this case, a combination of upper and lower somatosensory evoked potentials (SSEPs) and 8-channel EEG monitoring were employed throughout the procedure to track the patient’s neurological function. These neurophysiological techniques provided the surgical team with continuous, real-time data on the patient's brain perfusion, helping to detect any changes that might indicate neural compromise.
During the bypass, upper SSEPs remained stable and reproducible, signaling that sensory pathways in the upper body were unaffected by the procedure.
Instantaneous Feedback and Faster Response Times
Following the initial clamping and administration of propofol boluses, a significant drop in the cortical channels of bilateral posterior tibial nerve (PTN) SSEPs occurred. Notably, the left PTN showed a more pronounced decrease compared to the right, indicating that the neural pathways responsible for transmitting signals from the legs were being compromised.
The surgical team immediately informed the surgeon of the PTN SSEP changes. In response, the surgeon acted quickly to remove the clamps, which prevented long-term damage to the nerves. Once the bypass was complete and the EEG emerged from burst suppression, the bilateral PTN cortical channels returned to acceptable limits compared to their baseline readings.
Avoiding Potential Consequences
Without the use of neurophysiological monitoring, the surgical team might not have been alerted to the changes in the patient’s leg SSEPs during the clamping stage. This lack of awareness could have delayed the removal of the clamps, leading to leg complications from lack of blood flow to the areas in the brain controlling leg function. This could have resulted in serious postoperative complications such as weakness, pain, altered gait, and even paralysis in the lower limbs, particularly the left leg and foot.
By providing real-time feedback, neuromonitoring enabled the surgical team to act promptly and prevent irreversible damage. This case exemplifies how crucial IONM is in safeguarding patient outcomes during complex cerebrovascular surgeries like STA to MCA bypasses.
The Benefits of Intraoperative Neuromonitoring
Intraoperative neuromonitoring plays a pivotal role in preventing complications during high-risk surgeries. Modalities such as SSEPs and EEG allow surgeons to detect and respond to changes in neural activity before permanent damage is done. In STA-MCA bypass procedures, monitoring the sensory and motor pathways ensures that blood flow alterations and surgical manipulations do not harm critical neural structures.
By incorporating IONM into these surgeries, healthcare teams can optimize patient outcomes and reduce the risk of postoperative deficits. This case serves as a powerful reminder of the importance of neurophysiology in modern surgery, not just for protecting patients but for guiding surgeons to make informed, data-driven decisions in real time.
A Higher Standard of Care
STA to MCA bypass is a complex and potentially life-saving procedure, but it comes with significant risks, particularly concerning neural perfusion. The use of intraoperative neuromonitoring techniques like SSEPs and EEG can help mitigate these risks, ensuring that patients receive the highest standard of care during surgery.
For more information on the benefits of neuromonitoring and its role in enhancing patient care, please contact us or sign up for our newsletter.
