The intercostobrachial nerve (ICBN) is commonly encountered and often sacrificed during axillary dissections. Interestingly, the benefits of preserving the ICBN during surgical procedures have been observed, such as a reduction in postoperative pain, improved sensation, and reduced arm stiffness. This study aimed to provide a comprehensive overview of the detailed anatomy of ICBN for surgeons performing axillary, arm or shoulder procedures. This study was conducted on 57 axillae from formalin-fixed and fresh cadavers (29 from male cadavers and 28 from female cadavers). The ICBN was found in 54 out of 57 cases, accounting for a prevalence of 94.7%. No ICBN was observed in 3 cases (5.3%). Out of the 54 cases, the ICBN originated exclusively from the T2 intercostal nerve in 45 cases (83.3%); the ICBN originated solely from the T3 intercostal nerve in 2 cases (3.7%); the ICBN originated from both T1 and T2 in one case (1.9%); the ICBN originated from T2 and T3 in 5 cases (9.4%), and the ICBN originated from T1, T2 and T3 in one case (1.9%). After emerging from the intercostal space, the ICBN traveled across the axilla, passing anterior to the lateral thoracic vein (LTV) in 41 out of 54 cases (75.9%). It passed posterior to the LTV in 4 cases (7.4%) and wrapped around the LTV in 9 cases (16.7%). The ICBN gave cutaneous branches to the anterior and lateral parts of the axilla, as well as to the posterior and medial parts of the arm, in all cases. Additional branches were found in 14 out of 54 cases (25.9%), including a connecting branch to both the medial cutaneous nerve of arm and forearm in 1 case (1.9%), a connecting branch to the medial cutaneous nerve of arm only in 5 cases (9.3%), a branch to the pectoralis major and minor muscles in 5 cases (9.3%), and a branch to the pectoralis minor muscle only in 1 cases (1.9%). In 46 out of 54 cases (85.2%), the ICBN terminated in the upper one-third of the arm. In 6 cases (11.1%), it terminated in the middle one-third of the arm. In 1 case (1.9%), it terminated in the lower one-third of the arm, and in another 1 case (1.9%), it terminated in the forearm just below the elbow. The ICBN emerges from the second intercostal space approximately 34.3 ± 8.5 mm (mean ± SD) lateral to the mid-clavicular line. In the second intercostal space, the ICBN emerges below the lower border of the 2nd rib with a mean value of 5.2 mm, ranging from 0 to 24 mm. The mean (SD) distance between the ICBN origin and the upper border of 3rd rib is 16.1 (7.8) mm. The diameter of the ICBN is 1.97 ± 0.66 mm (mean ± SD) immediately at the point of emergence. This nerve most commonly originates from the T2 intercostal nerve but also occasionally involves T1 and T3. In the axilla, the nerve intersects the LTV and serves as an important anatomical landmark. The ICBN might probably give both sensory and motor innervation to regions of the arm and the pectoral muscles. Measurements of the ICBN could also be used as a reference in searching the ICBN by ultrasound for blockade in pain management procedures. Therefore, the knowledge obtained from this study could provide a comprehensive understanding of the ICBN’s anatomy and its variations for surgeons in optimizing surgical outcomes.
