Sensory innervation of breast

The breast parenchyma and overlying skin are innervated by the anterior and lateral cutaneous branches of intercostal nerves T3 to T6. The lateral cutaneous branch of the second intercostal nerve (T2) crosses the axilla to innervate the upper medial arm and the anterolateral chest wall, such that numbness or pain in the axilla and upper inner arm can be combined with pain over the upper lateral breast quadrant, and that pain in the breast can be caused by arm movements, hence the term "intercostobrachial nerve." The intercostobrachial nerve is most frequently injured during axillary dissection, which is a major risk factor for postmastectomy pain syndrome.