My 6 month old has a bulging fontanel. all tests (mri, ct scan, bloodwork, etc) have come back negative. what else should i push for. ?

Be patient: Sounds like your physician(s) have aggressively looked for possible causes, specifically, increased spinal fluid. If your child is developing fine, reaching all of his/her milestones, sometimes the best thing to do is be patient. If anything changes, neurologically or developmentally, let your physician know.

Ask the Doctor....: ....Could it be pseudotumor cerebrii ( also called ideopathic increased intracranial pressure )? This is a condition where the pressure inside the brain is increased it may not, i think, show up on the listed tests. Otherwise i agree with dr. Cunnar's response.

Depends: A bulging fontanel can be normal depending on the position the child is in when it is evaluated. A crying child who is lying down will almost always have a bulging fontanel. A bulge indicates an increase in pressure - either in the skull itself, or within the superior sagittal sinus (the giant vein which lies just beneath the fontanel). A spinal tap is warranted to check the intracranial pressure.

Measure csf pressure: The only approach that I can consider is to measure the cerebral spinal fluid pressure in consideration of pseudotumor cerebri.