Anatomical localization of the emergence point of the accessory zygomaticotemporal nerve using the marginal tubercle for its clinical implications

Zygomaticotemporal nerve (ZTN) blocks are widely used for temporal procedures, yet incomplete anesthesia may occur when accessory ZTN branches (aZTN) are not accounted for. This study aimed to localize the emergence point of the aZTN (aEP) using the marginal tubercle (MT) as a palpable landmark and to provide in vivo ultrasound depth information relevant to safe, accurate needle placement. We dissected 36 hemifaces from 20, embalmed cadavers to identify the aZTN and measure the aEP relative to the MT and the lateral canthus (LC). In vivo ultrasonography was performed in 23 healthy volunteers to measure the depth from the skin surface to the superficial layer of the deep temporal fascia (sDTF) near the MT. The aZTN was identified in 7 of 36 hemifaces (19.4%), with the aEP clustering within a few millimeters of the MT and showing three vertical patterns (superior, same level, or inferior). Using the LC as a reference, the aEP was located 22.3 ± 2.4 mm lateral and 5.8 ± 2.7 mm superior to the LC. Ultrasonography showed a mean skin-to-sDTF depth of 5.92 ± 0.99 mm. Two specimens demonstrated a bone-emergent aZTN variant (mean MT–bony emergence distance, 4.2 ± 0.1 mm). In conclusion, MT- (and LC-) referenced mapping, combined with ultrasound-derived depth to the sDTF, provides practical anatomical guidance for localizing the aEP and may help refine future MT-centered approaches for addressing accessory ZTN pathways.