Location of emotional corticobulbar tract in the internal capsule

Emotional facial paresis (EFP) is a rare neurological symptom with intact volitional facial movement. The exact location of emotional corticobulbar tract remains unclear. EFP was frequently recognized following the surgery of stereotactic radiofrequency thermocoagulation for hypothalamic hamartoma in 84.5% of 58 patients. To examine our hypothesis that EFP might be caused by stereotactic trajectories passing through an area including the internal capsule (IC), topographical locations of trajectories were analyzed and compared between the EFP-positive group (n = 41) and the EFP-negative group (n = 8). In the EFP-positive group, multiple (2 to 5) trajectories focused within the genu of the IC in 31 (75.6%) cases, whereas a single trajectory passed through the genu in 8 (19.5%) cases. In the EFP-negative group, 6 (75.0%) of 8 patients had a single trajectory and only one patient had two trajectories passing through the genu of the IC. The ratio between multiple trajectories and a single trajectory relevant to the genu differed significantly between two groups (p < 0.01). The multiple trajectories focusing in the genu have high risks of EFP, whereas a single trajectory seemed to incidentally cause EFP. The results proved our hypothesis and provided a high probability that the emotional corticobulbar tract passes through the genu rather than anterior or posterior limbs of the IC. The location of the emotional corticobulbar tract is in the genu of the IC.