fluid sac in ear

Question
i have a 7 years old german sheppard/boxer mix.  2 days ago we noticed he had a small sac of fluid in his ear flap.  today my husband took a sterile syringe and drained the sac.  at first it was greenish in color then turned to clear with red tinge.  my dog is showing no signs of anything wrong.  hes acting completely normal. After draining the sac, my husband then fully cleaned his ears.  what could the sac be and should we worry?

Answer
This is most likely an aural hematoma.  Dogs get these from shaking their head,  It could come from an ear infection of some kind of itching causing the dog to violently shake the head.  Draining them is OK in the short term, but many of these will come back after a few days.  Surgical treatment is usually recommended.