Neck Lymph Node Boundary Sublevel IA

**Semantic type:** Finding

**Definition:** The following anatomical structures define the neck lymph node boundary for sublevel IA: Superior: symphysis of the mandible; inferior: body of the hyoid; anterior (medial): anterior belly of the contralateral digastric muscle; posterior (lateral): anterior belly of the ipsilateral digastric muscle. (AJCC 8th ed.)