Nerve fiber density differences in the temporal dura mater: An explanation for headache after temporal lobectomy? An anatomical study

OBJECTIVE: Patients who undergo a temporal lobectomy for drug-resistant epilepsy more frequently complain about postoperative headache compared to patients who undergo a craniotomy in any other region. The pathophysiological mechanism is not well understood. It is hypothesized that a relatively high density of sensory nerve fibers in the temporomesial dura underlies a higher sensitivity to pain upon stimulation. The objective of this study was to address this hypothesis by comparing the nerve fiber density in the temporomesial dura to that in the temporolateral dura.

METHODS: Temporomesial (n = 6) and temporolateral (n = 6) dura mater samples (2.5 × 2 cm) were dissected from the middle cranial fossa of 5 formalin fixed human cadavers. Paraffin embedded specimens were cut in a sagittal direction into 5 µm sections (temporomesial group n = 106, temporolateral group n = 113), and immunohistochemically stained for S100 as a marker of myelinated nerve fibers. The number of S100-immunoreactive nerve fiber bundles was counted in an anterior-posterior direction by a blinded observer, expressed as mean ± standard error of the mean per cm for each group, and statistically analyzed by a linear mixed-effects model. To assess potential observer bias, a randomized subset of the sections (n = 28) was evaluated by a second blinded observer and statistically analyzed by intraclass correlation coefficient (ICC).

RESULTS: The temporomesial dura expressed 4.1 ± 2.1 and the temporolateral dura displayed 1.0 ± 0.7 nerve fiber bundles per cm (β = 3.2, SE= 0.30, 95% CI [2.6, 3.8], p < 0.001). There is a significant decrease in nerve fiber bundle density in the mesial to lateral direction (mean difference -0.1, SE= 0.0, 95% CI [-0.1, -0.2], p < 0.001). The ICC was 0.69.

CONCLUSIONS: The density of myelinated nerve fiber bundles is about 4 times higher in the temporomesial dura, than in the temporolateral dura. Assuming that dural innervation primarily consists of sensory trigeminal fibers, this observation suggests that a summation of stimuli to surpass the threshold to convey pain is reached sooner in the temporomesial than in the temporolateral dura mater.