Thermography mapping patterns in temporal lobe epilepsy surgery

Abstract

Background: In several epilepsy etiologies, the macroscopic appearance of the epileptogenic tissue is identical to the normal, which makes it hard to balance between how much cytoreduction or disconnection and brain tissue preservation must be done. A strategy to tackle this situation is by evaluating brain metabolism during surgery using infrared thermography mapping (IrTM).

Methods: In 12 epilepsy surgery cases that involved the temporal lobe, we correlated the IrTM, electrocorticography, and neuropathology results.

Results: Irritative zones (IZ) had a lower temperature in comparison to the surrounding cortex with normal electric activity (difference in temperature (ΔT) from 1.2 to 7.1, mean 3.40°C standard deviation ± 1.61). The coldest zones correlated exactly with IZ in 9/10 cortical dysplasia (CD) cases. In case 3, the coldest area was at 1 cm away from the IZ. In 10/10 dysplasia cases (cases 1-4, 6-11), there was a radial heating pattern originating from the coldest cortical point. In 2/2 neoplasia cases, the temporal lobe cortical temperature was more homogeneous than in the CD cases, with no radial heating pattern, and there were no IZ detected. In case 8, we found the coldest IrTM recording in the hippocampus, which correlated to the maximal irritative activity recorded by strip electrodes. The ΔT is inversely proportional to epilepsy chronicity.

Conclusion: IrTM could be useful in detecting hypothermic IZ in CD cases. As the ΔT is inversely proportional to epilepsy chronicity, this variable could affect the metabolic thermic patterns of the human brain.

Keywords: Cortical dysplasia; Electrocorticography; Epilepsy surgery; Functional mapping; Hypothermic irritative zone; Infrared thermography brain mapping; Refractory epilepsy; Thermography patterns.

Figure 1:

(a) Infrared thermography grid placed over the electrocorticography (ECoG) grid in the left temporal lobe and infrared thermography grid placement in the frontal lobe. Note that, the infrared thermography grid has the same size as the electrocorticography grid designed to have a very precise anatomical correlation. (b) The final position of both infrared thermography mapping grids in left frontal and temporal lobes, after removing the ECoG grid.

Figure 2:

Cases numbers and graphic representation of the temperature lectures as recorded in °C. The infrared thermography mapping grid lectures show a color representation using the thermographic palette, where deep blue represents the lowest and yellow the highest temperature. Note the radial heating pattern indicated with black arrows where the coldest temperature lecture is in the hypothermic irritative zones (HIZ) in 90% or at 1 cm of distance to the HIZ in 10% of the dysplasia cases. The temperature in italics surrounded by a red oval corresponds to the IZ detected by electrocorticography.

Figure 3:

Picture numbers correspond to case numbers. The red letter F is placed over the frontal lobe and T over the temporal pole. The values are similar to the temperature recorded using the infrared thermographic laser pointer thermometer.

Graph 1:

(a) Error graphs of registered temperatures. Averages and dispersions are observed where values with the lowest recorded temperatures were in irritative zones (IZ). (b) Dispersion between the IZ temperature and the maximal brain temperature. It is observed that by increasing the temperature in the IZ, the maximal brain temperature is also increased.

Graph 2:

(a) Trivariable histogram between age, age of onset, and meningeal temperature: it is observed that at an older age, the temperature tends to stabilize. (b) Trivariate analysis between age, start age, and ΔT: it is observed that at the increase of the epilepsy chronicity, it decreases the value of ΔT.

Graph 3:

The median difference between registered temperatures. It is observed that from the age of 26 to 56 years old, the medians of the recorded temperatures decrease.