Bump on scalp. Of anterior fontanelle -?

My 6 month old kid has a bump on his head. It was (bump) small when he was 2 weeks old and now it has grown proportionally. MRI scan done as suggested by a pediatrician and he has suggested to consult a neurosurgeon. I have read that the bump would disappear in few months, but for my kid even after 6 month it still exists. I am bit worried now. The report says- A 2.2 X 1.2 cm sized cystic lesion is seen deep to the scalp in the region of fontanelle. The contents are homogeneously hypointense on T1 weighted images and hyperintense on T2 weighted images (similar to CSF). No evidence of intracranial extension. Impression: No focal lesion brain parenchyma. No evidence of intracranial space occupying lesion. A cystic lesion deep to the scalp in the region of anterior fontanelle - ? Subgaleal fluid collection. Advises/suggestions are much appreciated. Thank you very much in advance.