Abstract: Gynecomastia excision is commonly performed under general anesthesia, but thoracic segmental spinal anesthesia (TSSA) offers a focused thoracic block that can avoid airway instrumentation and reduce opioid exposure. An 18-year-old man American Society of Anesthesiologists I (ASA I) with unilateral left gynecomastia chose regional anesthesia, unilateral TSSA without an erector spinae plane block produced a rapid-onset unilateral sensory block on the operative side within 6 minutes while preserving motor function in the lower limbs and contralateral upper limb, with comfort maintained using dexmedetomidine sedation at 0.5 µg/kg/h.