Final answer:
A hematoma after a psa nerve block is likely due to the solution being deposited into a blood vessel or the needle penetrating the pterygoid plexus of veins, both of which can cause significant bleeding and subsequent hematoma formation.
Step-by-step explanation:
The formation of a hematoma after a psa nerve block could likely be caused by one of several factors. One potential cause is if the solution was deposited into a blood vessel, which may cause bleeding and hematoma. Another possibility is if the needle penetrated the pterygoid plexus of veins, which is a network of veins that could also lead to significant bleeding and the formation of a hematoma. Lastly, penetration of the parotid gland could potentially cause bleeding, although it is less likely to result in a hematoma compared to vascular injury. It is less likely that irritation of the muscles of the cheek would result in a hematoma quickly appearing after a psa nerve block.