Topographic relationship between the supratrochlear nerve and corrugator supercilii muscle

Abstract

The supratrochlear nerve (STN) and supraorbital nerve (SON) are anesthetized prior to performing various surgical procedures such as nerve-block procedure and botulinum toxin type A (BTX-A) injection. However, there has been little research to determine the most effective injection point for these procedures based on the detailed anatomical structure of the frontal area. The aim of this present study was to determine the topographic relationship between the STN and corrugator supericlii muscle (CSM) in the forehead region and to classify the patterns of emergence of the STN from the orbit and its course within the CSM, thus delivering the most effective BTX-A injection point for clinical applications. Fifty-eight hemifaces from Korean and Thai cadavers were used for this study. To indicate the point where the STN enters the CSM, the midsagittal line and the line connecting both supraorbital margins were used as the vertical and horizontal reference lines, respectively. Type I, in which the STN emerged separately at the medial one-third portion of the orbit, was observed. The type Ia, in which the STN entered the CSM as a single nerve branch, was observed in 22/58 (38%) cases. And type Ib, in which the STN bifurcated prior to entering the CSM, was observed in 18/58 (31%) cases.Type II, in which the STN emerged from the orbit at the same location as the SON, was observed and as with the type II category could be further divided into two subtypes: type IIa (13 cases, 22.4%), where the STN entered the CSM as a single nerve branch, and IIb (5 cases, 8.6%), where the STN bifurcated into two branches prior to entering the CSM. The point at which the STN entered the CSM was 16.4±4 mm lateral to the midsagittal line and 2.3±3.9 mm superior to the supraorbital margin. When the STN emerged separately from the orbit, it was located 7.5±2.3 mm medial to the SON at the level

of the supraorbital margin. The STN may not only have a different exit point, but also the same exit point from the orbit. This anatomical study provides valuable clinical information for BTX-A injection designed to treat tension-type headache, local anesthesia of the periorbital region, and surgical planning to resect the CSM.