Re: HAEMATOMA

Most common cases of hematoma are seen in psa blocks due to involvement of pterygoid plexus
The pterygoid plexus is a venous plexus of considerable size, and is situated between the temporalis muscle and lateral pterygoid muscle, and partly between the two pterygoid muscles.
It receives tributaries corresponding with the branches of the maxillary artery.

Thus it receives the following veins:

* sphenopalatine
* middle meningeal
* deep temporal (anterior & posterior)
* pterygoid
* masseteric
* buccinator
* alveolar
* some palatine veins (palatine vein which divides into the greater and lesser palatine v.)
* a branch which communicates with the ophthalmic vein through the inferior orbital fissure
* infraorbital vein

Relations

This plexus communicates freely with the anterior facial vein; it also communicates with the cavernous sinus, by branches through the foramen Vesalii, foramen ovale, and foramen lacerum. Due to its communication with the cavernous sinus, infection of the superficial face may spread to the cavernous sinus, causing cavernous sinus syndrome. Complications may include edema of the eyelids, conjunctivae of the eyes, and subsequent paralysis of cranial nerves which course through the cavernous sinus.

The pterygoid plexus of veins becomes the maxillary vein. The maxillary vein and the superficial temporal vein later join to become the retromandibular vein. The posterior branch of the retromandibular vein and posterior auricular vein then form the external jugular vein, which empties into the subclavian vein