Hydrocephaly is often suggested as the cause of the unusual bulging of the bones at the rear sides (called "parietal bossing") of the Starchild Skull. Hydrocephaly, also called "water on the brain", is a condition where fluid builds up inside the skull causing pressure, which pushes the skull outwards, inflating it like a balloon. This condition is well known, readily treated with modern medicine, and easy for an expert to recognize. A study in 2004, led by Dr. Ted Robinson, concluded that the Starchild Skull did not have Hydrocephaly. 

"Dr. Bachynsky noted that there is no evidence of erosion of the inner table of the skull. Such erosion would be consistent with a diagnosis of hydrocephaly, so this condition can safely be ruled out as a cause of the abnormalities expressed. Hydrocephaly also causes a widening of the sutures, again not expressed here. There was consensus agreement to both of these observations by other experts conversant with these features."
   -  Dr. Ted Robinson, M.D. extract from Deformity and Features Study

With a little knowledge about Hydrocephaly it is easy for anyone to understand why the experts have ruled this condition out as an explanation for the Starchild Skull.

The human skull is made up of plates of hard bone. In babies these plates are held together by flexible fibrous tissue called "cranial sutures" that allow the skull to reshape so it can safely pass through the birth canal. At this stage the "sutures" are "open". As we grow, the bone plates eventually fit together like puzzle pieces knitted tightly together by the sutures, at which stage the cranial sutures are "closed." If something goes wrong and the bone plates grow together into a solid plate of bone, as happens in conditions such as Craniosynostosis, this is called a "fused" suture, and this can result in deformation of the skull.

In Hydrocephaly the pressure inside the skull pushes out, expanding the skull at the weakest point- the cranial sutures. CAT scans have shown that the Starchild's sutures were not fused, and so if there had been any internal pressure, they would have been the first place to expand.

Instead, it is the solid plates of hard bone that are expanded in the Starchild Skull, while the soft sutures are not pulled open or pushed out in any way. In fact, there is a noticable "dent" at the saggital suture.

With no internal pressure, and no abnormal fusion of the cranial sutures, there is no possible way to make Hydrocephaly fit as an explanation for the Starchild Skull.


Bulging, unusual skull shape caused by internal pressure Bulging, unusual skull shape with no internal pressure NO
Shallow eye sockets present in cases of abnormal suture fusion Shallow eye sockets without suture fusion NO
Bone may become thin and weak Bone thin, but extremely strong NO
Facial features appear disproportionately small, however are only actually smaller than statistical norm if other deformity present Facial features significantly smaller than normal human, entire skull 10 standard deviations from norm NO
Occipital (bone at rear of skull) rounded unless abnormal sutures present Flattened occipital (bone at rear of skull) with no abnormal fusion of cranial sutures NO
Normal sinus unless other deformity present Absent frontal sinus NO
Normal inoin Absent inion NO