Not for myself, for my 6 month old daughter Anwen. Forgive me this break in 'Fish Fortnight' to bring you a very personal post. I don't know why major events happen every time I try to run a theme on Dracovenator.I will throw in a bit of science so that I can keep my
uber-nerd status. Plus knowing about a problem always helps me come to terms with it.
When Anwen was born she had a tiny lump in front of her fontanelle (where the frontal and two parietal bones of the infant skull fail to meet). I paid it no mind as it was virtually invisible amongst the lumpy irregualrities of a new-born's head. However it didn't straighten itself out, instead it got bigger. By this time it was obvious that it was a soft tissue structure of some sort. We showed it to the doctor who thought it was a benign cyst of some sort and that it posed no real problem because it appeared to be in front of the fontanelle. We went about getting an appointment for a general surgeon to remove it. The surgeon was a little leery of operating so close to a babies fontanelle and ordered MRI images of the lump. And what a sensible move that was. The MRI images show a tumor (probably a benign dermoid cyst)that rests largely IN the fontanelle. And therin lies the big problem.
But first a little about dermoid cysts and why they are classically located on the midline of a person.
It all comes down to early development of the embryo. Anwen, like all chordates, has a dorsal nerve chord formed by a process called neurulation. In neurulation a stripe of cells from the outer layer (the ectoderm), that runs down the back of the embryo, thickens, curls over and eventually pinches off to form a tube. This tub is what becomes the brain and spinal chord. You can see the process nicely in this diagram (of an amphibian - but the process is more or less the same in humans) which I nicked from Pharyngula. Incidentally
Pharyngula has a much more detailed post about neurulation if you want to know more.
What happened in Anwen's case is that a few cells thay were supposed to stay in the ectodermal layer above the neural tube and go on to form the skin (the white tissue in the diagram above) became trapped under the ectodermis when the neural tube closed over. Thus stuck out of place but already set on the path to skin-hood they grow into a little sac of skin-like cells that we call a dermoid cyst. Normally these present no problem at all and can be removed with the minimum of fuss. However in Anwen's case the position is a real bummer. The cyst is not surrounded by fatty tissue as they often are and as a result the lower surface is in contact with the structure underneath. This just happens to be the sagittal sinus. This sinus is a space bounded by the dural membranes that runs between the hemispheres of the brain and collects the venous blood and returns it back to the heart. Several veins that drain the brain enter into the sinus in the vicinity of Anwen's cyst (or at least if I understand the surgeon correctly). These veins are not robust structures like the ones you find in your limbs, they are delicate membranous structures that are easily torn. Such a tear can have catastrophic even fatal consequences.
So there you have it. Anwen has a tumor on her head that if left will grow larger, impede skull development and probably eventually constrict venous bloodflow from the brain. To remove it is a tricky operation with the risk of tearing a dural vein which may lead to her death. We have the services of a skilled neurosurgeon of high repute but we are still understandably frightened. Its not an easy decision for a parent to expose their child to risk, even if small and for her greater benefit in the long run. Nonetheless the operation must go ahead and will probably happen next week. I'll let you know how it goes.
Anwen and her pesky little bump
