Temporal muscle stimulation for post-craniotomy brain edema reduction: can it be feasible?

Dear Editor, Traumatic brain edema is one of the common complications seen in traumatic brain-injured patients due to various lesions such as contusions, hemorrhages, hematomas, and diffuse axonal injury. Traumatic brain edema can progress variably according to the type of primary injury and associated conditions such as ischemia or hypotension. Thereby, traumatic brain edema may be divided, depending on the mode of its propagation and distribution, into two main types: focal/perifocal and diffuse, with different clinical features and prognosis. In such cases, the central area of the lesion in traumatic brain injury consists of a low perfusion necrotic center, while the tissue surrounding the lesion, the peripheral tissue, it also shows significant reductions in perfusion. Cellular and cytotoxic contributors to cerebral edema, mechanisms influencing disruption of the blood-brain barrier, and vasogenic edema all play a central role in the pathophysiology of traumatic brain injury and worsen its outcomes. The management of traumatic brain edema tends to be a challenge because the pathophysiological mechanisms behind this condition are complex. Treatment is usually based on the symptoms rather than the causes of the edema. Therapeutic strategies include general measures that optimize intracranial venous flow, fluid therapy, controlled hyperventilation, decompressive surgery, osmotherapy, barbiturates, and appropriate pain and sedation management (Moscote-Salazar et al., 2016). Understanding the underlying mechanisms and developing more targeted treatments remains an active area of research in clinical neuroscience. Transcranial electrical stimulation has been shown to have some effects on brain edema after traumatic brain injury by modulating blood-brain barrier permeability and cerebral blood flow (Ren et al., 2024). Other possible effects regarding muscle stimulation, particularly around the craniectomy area, could have an indirect effect on the cerebrospinal fluid (CSF) circulation, potentially promoting better drainage from the subdural space. Transcutaneous electrical nerve stimulation has been used for pain management with promising results and clinical applicability (Sluka and Walsh, 2003). However, the use of electrical stimulation for muscle activation has been less explored, with only a few case reports (Ingves and Power, 2014; Das et al., 2021; Senin-Camargo et al., 2022). It has also been applied to limb musculature for the promotion of venous blood flow as a treatment for leg edema and to prevent venous thrombosis. Considering its potential application in neuro-surgical conditions, a question arises: could temporal muscle stimulation be used for managing edema associated with severe brain trauma? This is particularly relevant given that the temporal muscle is often exposed in neurosurgery and may come into direct contact with patients undergoing decompressive craniectomy or large traumatic craniotomies. In this brief discussion, we will explain why and how temporal muscle stimulation could be useful for managing traumatic brain edema. Through indirect effects on cranial dynamics at the physiological level, the potential mechanism of modulation for the temporal muscle stimulation includes modulation of cranial compliance, and the temporalis muscle may indirectly influence the compliance of the cranium with an increase in the venous outflow or CSF circulation. Repeated stimulation could alleviate brain edema by affecting adjacent structures. Stimulation of the temporalis muscle may further promote the flow of venous blood in surrounding veins, such as the superficial temporal vein, through the reduction of venous stasis and intracranial congestion. Rhythmic extracranial muscle contractions may have a “pumping effect” on the improvement of CSF flow to drain interstitial brain fluid. Lastly, extracranial muscle activity can promote the glymphatic system by facilitating an increase in brain fluid clearance. Temporalis muscle stimulation may be a supportive factor (Figure 1). Some studies suggest that stimulation should be applied to a muscle group rather than a small muscle fiber. Physiologically, effectiveness is achieved through the stimulation of large muscle groups. On the other hand, the glymphatic system plays a key role in CSF circulation and the clearance of interstitial fluid from the brain. While direct muscular temporal stimulation has not been studied extensively, it is hypothesized that muscle contractions (even extracranial) may influence the glymphatic system, which is crucial in managing brain edema. The current concept would suggest that temporal muscle stimulation may improve brain edema through enhancement of lymphatic drainage, venous congestion, and improvement in cerebrovascular dynamics. The technique can utilize a device with an internally placed component having electrodes mounted on the temporal muscle coupled to an external stimulator that can modulate the effect with precision, thus constituting a potentially therapeutic invention for neuromuscular interventions (Figure 2). Therefore, this modality warrants further studies to establish a new frontier in neurostimulation and neurotrauma.Figure 1: Hypothetical mechanism of action in the mitigation of brain edema by temporal muscle stimulation.Note: This schematic diagram presents how the stimulation of the temporal muscle may influence the intracranial dynamics to increase lymphatic drainage and diminish venous congestion, thereby relieving the edema of the brain. Created with BioRender.com. CSF: Cerebrospinal fluid.Figure 2: Schematic representation of the device placement on the temporal muscle.Note: The illustration demonstrates the positioning of the generator, connecting wires, and electrodes fixed within the temporal muscle. Created with BioRender.com.