Infrared thermography mapping plus neuronavigation target location in an eloquent area cavernoma resection

INTRODUCTION

Accuracy in neurosurgery is mandatory. Neuronavigation (NN) systems are useful surgical guiding systems, but they have well known limitations. In many surgical scenarios, NN can misguide to false locations mainly due to the brain shift phenomenon and deformation.[2,6,8,12,15] To perform safer and more efficient surgeries, particularly in surgery in eloquent areas, it is necessary to add in vivo information to increase the accuracy in locating surgical targets (computed tomography [CT], brain mapping, magnetic resonance [MR], ultrasound, and trans-operatory fluorescence angiography, among others).

Cavernomas make up approximately 8–15% of all intracranial vascular malformations, and the most common presenting symptom is seizures.[13] They can be located near the cortical surface in silent regions or in more challenging subcortical locations near eloquent areas.

Since the first documented inflammation description by Aulus Cornelius Celsus (25 AC–50 AD) in De Medicina, it is known that inflammation causes hyperthermia. The thermic radiation evaluation of the brain could be useful trans-operatory information, as thermographic cameras, thermometers, and qualitative thermosensitive materials can measure brain metabolism by its caloric radiation. They have been used for studying the brain temperature in different pathophysiological processes[11] and they allow for real-time evaluation of cerebral blood flow in vascular neurosurgery.[7,14] Neoplasms and normal tissue produce and transfer heat in a different manner due to a decreased metabolic rate of the tissues surrounding and superimposed by the perilesional edema and low tumor microvessel density due to concomitant ischemia.[10] Glial tumors are hypothermic and brain metastases are hyperthermic in comparison with healthy brain tissue, and infrared thermography mapping (ITM) can improve the accuracy of their resection.[3] ITM in neurosurgery has been used with good results to monitor cerebral blood flow after the resection of an arteriovenous malformation, to observe patency of bypass and to prevent irreversible damage due to ischemia during surgery, in temporary occlusion of brain arteries, among other scenarios.[1,5,7,9,10,14,16] Intraoperative IT is becoming a promising new real-time diagnostic method because it is non-invasive, radiation free, avoids exposing the patient to drugs or contrast media and it has no known side effects.

MATERIALS AND METHODS

RESULTS

Description of the procedure and results

Under entropy-monitored general intravenous anesthesia, we performed a conventional frontoparietotemporal left craniotomy guided by NN (Medtronic® optical neuronavigation system). Anesthetic profundity measured by entropy was 46, inspired fraction of oxygen was 60%, oxygen saturation was 100%, hemoglobin (14.3 g), hematocrit (42%), and carbon dioxide (32.3) by arterial blood gas. Corporal temperature was 35.2°C and the operating room temperature was 20°C, with a relative humidity of 40% during the ITM. Immediately after the dura incision, we performed a panoramic ITM of the exposed brain surface using a professional handheld thermal imaging camera that combines the functions of surface temperature and real-time thermal imaging that can turn a thermal image into a visible image [Figure 1] with the center of the record over the supramarginal gyrus. It evaluates the different thermal gradients of the brain and it can also blend the visible and infrared images (Kmoon Handheld thermal imaging camera, temperature range −20–+300°C, measuring accuracy ±2% or ±2°C). Immediately after taking the panoramic ITM photograph, we placed a sterile acetate grid with coordinates to record the cortical temperature using an infrared pointer thermometer (Floureon −50–+380°C). Cortical temperature went from 23.8°C to 33.9°C, where the hottest point was in the supramarginal gyrus [Table 1].

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Figure 1:: Panoramic thermographic photograph of the craniotomy, where the left frontal, parietal, and occipital lobes are exposed. The black arrow shows the hottest point of the exposed brain cortex, located in the supramarginal gyrus. The blue arrow shows the intraparietal sulcus.

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Table 1:: ITM recordings using the sterile acetate grid with coordinates. The hottest point (coordinate B1) was in the supramarginal gyrus. Each color has an interval of 2.5°C.

Using the NN, we located the shortest cortex entry zone to the lesion [Figure 2]. Using a trans-sulcal approach, we began the white matter dissection, realizing that the lesion was located about 10 mm toward the vertex and the resection was completed [Figure 3]. The closure was closed with standard techniques and materials. The patient was discharged on the ^5th postoperative day with a similar preoperative documented aphasia and anomia, without any added morbidity. The speech difficulties were absent 3 months after the surgery and the patient has no focal language seizures.

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Figure 2:: Neuronavigation location of the target.

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Figure 3:: (a) Neuronavigation system localization of the target (blue circle); (b) Grid placement for the pointer thermographic recording where the yellow circle represents the hottest thermographic recording [coordinate B1 of Table 1] over the supramarginal gyrus; (c) A trans- sulcal access was performed in the point where the neuronavigation system located the lesion (dotted blue circle). The yellow circle represents the real subcortical localization of the cavernous angioma. The proximity of the hottest thermographic recording to the real localization of the lesion is evident.

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DISCUSSION

Watson et al. observed that changes in blood temperature are related to changes in brain blood flow, whereas cortical brain temperature is determined by cerebral blood flow-metabolism coupling and the infrared image could be sufficiently sensitive to detect ischemia.[3,9] Arterial blood and core temperatures are higher than that of the exposed surface of the brain since they descend due to evaporation and exposure to the environment. Therefore, local microvascular blood flow self-regulation of the brain can be used for monitoring thermal contrast with ITM of the cerebral cortex during surgery. Gorbach et al. showed immediate and significant temperature decrease in the artery distal to the occlusion and the tissue perfused by it.[3,5] Intra-operatory surveillance using thermography in neurosurgery has been described in the resection of tumors and in the monitoring of patency of bypass in arteriovenous malformations, in which it demonstrated adequate correlation compared with such conventional methods as postoperative CT, MR imaging (MRI), Doppler and angiography, and its potential use for 2D-3D image fusion with preoperative MRI.[4] ITM is a safe, efficient, and real-time non-invasive method that requires no manipulation of the tissues nor does it requires the use of contrasts or filters.

Based on the previously described evidence that establishes the efficacy of ITM for detecting even subtle blood flow changes, we describe a case where a subcortical cavernoma below the supramarginal gyrus was the surgical target. The NN system located an entry point that was approximately 10 mm misplaced due to the brain shift, as was demonstrated later during the surgery. Before the trans-sulcal approach was performed, using a thermographic camera and thermographic thermometer, we detected a hotter cortical point (difference in temperature between the hottest and coldest cortical recording was 10.1°C) in the supramarginal gyrus surface at approximately 4 mm dorsal to the shortest cortical distance to the reallocation of the cavernoma. Two different technologies acted together to improve the target location accuracy in this case. The patient stayed within stable physiological hemodynamic parameters during the surgical procedure to maintain cerebral self-regulation.

CONCLUSION

More studies are needed to understand and predict the thermic behavior of the brain in physiological and in different pathological conditions, to incorporate temperature measurement devices, such as thermographic thermometers, cameras, or qualitative thermographic devices in daily neurosurgical procedures, but we believe that this is a promising avenue to explore. It could be useful to incorporate more than one device to improve target location accuracy in neurosurgery.