Hello---I thought I needed to reply to this forum for two reasons. First, my wife and I went through this with our son. Second, I am a doctor, and I did a lot of looking up in the medical literature about this. So hopefully somebody out there finds my perspective useful.
My son also had a difficult labor---failed vacuum. Had a small caput (skin swelling) when he was born, but then it resolved. At 5.5 weeks, he started developing a flowing collection in his scalp, which by 7 weeks got VERY big (the size of half his head). We obviously freaked out. He had two separate ED visits, an ultrasound, an MRI, and a neurosurgeon appointment. Shockingly, very few doctors--even the pediatric neurosurgeon at a huge children's medical center-knew what was going on---everybody felt like it was "probably nothing," but was using logic, as opposed to data.
I am an adult doctor, not a kid's doctor, so I started looking this up. Found two articles in the medical literature about it. This is a subgaleal fluid collection, which is benign (goes away on its own), associated with instrumented deliveries (vacuum), and of unclear physiologic origin. It may represent an evolution of blood products related to the birth trauma; one article found evidence that this may be cerebrospinal fluid that has temporary connection with the scalp.
Regardless, both articles mention that this is self limiting, goes away on its own, intervention (i.e. drainage) probably has more complications than help (small risk of infection).
By reading this article, I honestly felt that I had become my city's expert on the situation. The pediatric neurosurgeon, high risk obstetrician, pedi ER guys---none of them knew about this...I think it is likely that doctors don't know about it because it is benign---i.e. if it has no clinical significance, it does not get studied extensively.
By 9 weeks our son's collection was getting smaller, and by 13-14 weeks it was gone. He is growing and happy, now approaching 5 months old.
My recommendations:
1. Don't freak out.
2. See a doctor. Get an ultrasound to make sure this is fluid and not something else. Get an MRI to make sure it is solely in the scalp.
3. Do whatever you can to avoid a CT---radiation is a real downside.
4. If this is a fluid collection, in the scalp only, try to relax---the medical literature does discuss this, and it does get better on its own.
5. Don't blame your doctor for not knowing about it---honestly, this is subject is obscure--not covered in textbooks or the major journals. Just ask your doctor to look up "subgaleal fluid collections" in the medical literature---this will reassure your doctor.
Hope this helps---please reply if you have any questions...