What causes a hematoma in a PSA nerve block?

• A. Insertion of needle too far anteriorly into the maxillary sinus
• B. Insertion of needle too far posteriorly into the pterygoid plexus of veins or perforation of the maxillary artery
• C. Over-insertion into the nasal cavity
• D. Injection into the pterygopalatine fossa

Answer: (B)

During a PSA nerve block, a hematoma forms when the needle is advanced too far posteriorly into the infratemporal region and injures vascular structures. The pterygoid venous plexus sits behind the maxilla, and the maxillary artery runs nearby. Puncturing these vessels with a deep posterior approach can bleed into the soft tissues of the cheek, producing a hematoma. Misplacements that are more anterior into the maxillary sinus or nasal cavity, or injections into the pterygopalatine fossa, are less about vascular injury causing a hematoma and more about other complications or anesthesia distribution.