Subgaleal hemorrhage is a rare collection of fluid in the potential space of the galeal or epicranial aponeurosisand cranial periosteum. Birth trauma and forceps use typically cause it (90% of cases), and may also be present in patients with blood clotting disorders.
This condition is similar in appearance to a cephalohematoma, though the cephalohematomas are unilateral, don’t cross over cranial sutures and located within the periosteum.
Distinguishing between these two is important as cephalohematomas are self-limiting and resolve on their own, whereas subgaleal bleeds can lead to a significant amount of blood loss which may lead to anemia and hypovolemic shock. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC81073/
Sources:
http://emedicine.medscape.com/article/980112-overview
Sonographic Tendencies 