Which local anesthetic block can lead to severe swelling and extraoral bruising due to nicking a blood vessel?

The greater palatine block is associated with a risk of severe swelling and extraoral bruising primarily due to the proximity of the maxillary artery and the pterygoid plexus. When implementing the posterior superior alveolar (PSA) block, the needle is advanced into the area where these vascular structures are located. If a blood vessel is inadvertently nicked during injection, it can result in hematoma formation, which manifests as swelling and bruising around the area.

The PSA block is particularly noteworthy because it anesthetizes the maxillary molars and their associated buccal tissues, but it also carries a higher risk of vascular injury compared to some other local anesthetic techniques. This is due to the location of the maxillary artery in relation to the injection site, which is why practitioners need to exercise caution and awareness of anatomical landmarks when performing this procedure.

Other blocks mentioned typically pose lower risks related to blood vessels in their respective areas. Hence, the PSA block is the one most commonly associated with this adverse effect.