Also known as: Parasites in the brain
Addison's brother Archer has multiple parasitic cysts (eight total) in his third ventricle from eating unwashed fruit in Mexico. He initially presents with seizures during sex and undergoes a complex endoscopic surgery where Derek must carefully deflate and remove each cyst without rupturing them. He codes during surgery but is successfully resuscitated.
Also known as: Colorectal cancer
Beth's father has been secretly fighting colorectal cancer with five polyps removed over three years and radiation treatment. He presents with bowel obstruction requiring emergency surgery to remove diseased portions of bowel. He has been hiding his illness from his daughter Beth, who is Owen's ex-fiancée.
Also known as: Brain aneurysm
A pregnant woman who previously ran over her husband with her car before discovering she has a brain aneurysm. Her surgery is repeatedly delayed due to Derek being pulled into Archer's emergency case, causing her significant anxiety about the aneurysm rupturing.
Also known as: Hernia in groin
Beth's father has an inguinal hernia that is initially thought to be causing his symptoms, but it is not the source of his bowel obstruction (which is actually due to his colorectal cancer).
Also known as: PTSD
Owen is clearly struggling with PTSD after returning from Iraq. He has not told his mother he's back and feels like a ghost, unable to reconnect with his former fiancée Beth or his old life. He confides in Cristina that she's the only one who truly sees him as he is now.