Objective To observe the origin， branching patterns， and trajectory distribution of the intercostobrachial

nerve （ICBN） during minimally invasive （robot-assisted and endoscopic） axillary lymph node dissection （ALND）， and to provide anatomical evidence for intraoperative nerve preservation. Methods A retrospective analysis was conducted on surgical videos of 72 breast cancer patients who underwent minimally invasive axillary lymph node dissection （ALND） from September 2023 to April 2025. Under the magnified view of minimally invasive surgery， the ICBN was identified and recorded intraoperatively. Observation indicators included the origin of ICBN （T1/T2/T3/common trunk）， branching patterns （single trunk without branches/single trunk with two branches/single trunk with multiple branches/double trunks）， and the trajectory of each branch （medial arm/axilla， mammary tail， lateral chest wall）. Results The ICBN was identified in all 72 patients （identification rate 100%）， and a total of 170 ICBN nerve trunks were recorded. The most common origin was T2（67 cases，

93.1%）， followed by T1（58 cases，80.6%） and T3（36 cases，50.0%）， with common trunk observed in 5 cases （6.9%）. Regarding branching patterns， single trunk without branches （53.4%） and single trunk with two branches （40.9%） were the most prevalent types. Stratified analysis revealed that T2 was predominantly of the single trunk with two branches type  （73.1%）， while T1 and T3 were mainly of the single trunk without branches type （70.6% and 88.9%， respectively）. Regarding trajectory distribution， T1 mainly traveled to the medial arm/axilla （79.7%）， while T2 and T3 predominantly traveled to the lateral chest wall （83.3% and 90.5%， respectively）. Branches traveling to the mammary tail （anterior chest wall） were mainly derived from T2（69.6%）. Conclusion The origin， branching patterns， and trajectory variations of the ICBN can be clearly visualized under the magnified view of minimally invasive surgery. The observed branching types and trajectories may provide an anatomical reference for ICBN identification and preservation during ALND.

Intercostobrachial nerve, Axillary lymph node dissection, Minimally invasive surgery, Anatomical variation