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Cranial Synostosis

Cranial synostosis. So here we first want to show you what the major sutures are. As you can see, here is the metopic suture, there is the coronal one going across, sagittal and the lambdoid, and there’s the anterior fontanelle. So growth occurs at right angles to any suture cranial synostosis. So any time you have synostosis where the suture fuses prematurely.

You will grow tangential. I’ll show you, for instance, how brachycephaly develops. Here’s someone where there is coronal synostosis. The arrows show the growth that is orthogonal to this line, that is 90 degrees perpendicular, is limited and compensatory growth occurs tangential to the suture.

So what will happen if you have difficulty with a sagittal suture? You won’t be able to grow this way, you’ll grow that way. You’ll get a long boat-head. So it turns out that’s why we call it scaphocephaly. Boat-head. This is commonly encountered cranial synostosis, 40-50% of all cranial synostosis are sagittal. Coronal is brachycephaly, meaning short-head. Lambdoid will cause flat back, like plagiocephaly. When all the sutures are affected you get oxycephaly. I don’t have a good picture of it. What oxycephaly looks like, it looks like a tower-head. See, you can’t grow this way, you can’t grow this way, so you grow straight up. It’s not a very good-looking sight. You can get cranial synostoses in many congenital syndromes, like Cruzon’s syndrome, Apert’s syndrome, Carpenter syndrome, etc. A lot of these kids, again, you probably don’t see them in your continuity clinic in your program, however if you go to the craniofacial clinic, usually run by head and neck surgery and neurosurgery.

Anencephaly is relatively common. It’s slightly less than 1:1,000 in the United States and the recurrence rate is 3-5%. As you know probably, it can be monitored with alpha fetoprotein. Then there are encephaloceles. These are herniations of meninges with or without brain parenchyma, usually through a bony defect. Three out of four are occipital, and in the Orient there is an association with hypertelorism and short stature, and frontal encephaloceles. This illustration is there in your handout on the right side, and what it is, is to schematically show.

One is called a meningocele where the meninges are herniating. The space would be of course CSF filled and in a meningo and encephalocele there is actually some extrusion or herniation of brain parenchyma, right down here. Neural tube closure defects will continue by briefly mentioning that there is a condition called diastematomyelia. As you know, anything with myelia pertains to spinal cord. And this is a failure of fusion with some persistence of mesodermal elements where the cord actually looks like a doublet. It’s a split cord. Then there is hydromyelia which is an enlarged central canal. Then there are syringomyelia and syringobulbia. Syrinx in Greek means tube. So these are somewhat like hydromyelia in the sense that it is a central cavity, however this can occur either in the spinal cord per se or more rosterally in the brain stem, in which case we call it syringobulbia. And it can be due to tumor. It may be due to tumor following resection, it can be from an infarction, and it can present with spasticity, depending on its size, and there can be very distinct sensory findings that I will demonstrate to you momentarily. But the combination; sometimes these patients are mistaken to have multiple sclerosis or some other disease. In this day and age it is not at all difficult to see these because of the availability of magnetic resonance imaging.

The sensory findings have to do with the anatomy. We told you in the morning, neurologists tend to be very interested in anatomic correlations. These are patients in whom you will get a very distinctive sensory examination. You will find that they have some deficiency in sensation to pain or temperature and yet seem to be capable of perception of vibratory sense and, in an old enough and mature enough child, you may be able to test them for graphesthesia and so on. And you may wonder, how can this be possible? They can barely feel the hot or cold tuning fork, and yet they know the vibration. It has to do with the fact that this is the dorsal root ganglion on this side where pain temperature fibers enter the segment and they cross and go to the lateral spinal.

Holoprosencephaly is a condition where you don’t have cerebral hemispheres. This is because the telencephalic vesicles never formed. Basically you end up with one cavity and there may be arrhinencephaly and there is cleft lip, again a midline defect. And these patients have severe mental retardation and motor deficits, seizures. Lissencephaly is another migrational error. It is often called by different names. Most commonly it would be called agyria.

Chiari malformations. Type I Chiari is one where there is herniation of the cerebellar tonsils. That’s a very classic type of description, many of you probably recall. Frequently Chiari’s are asymptomatic until later. Not everyone presents with major symptoms right away. Type II includes what’s said in type I, but there is an association of other anomalies. There is an elongation of caudal medulla, which is an important finding, and there is a kinking of the cervical medullary junction and type II always implies also a lumbosacral meningomyelocele.

Polymicrogyria is often due to some sort of acquired insult where the brain has a few too many neurons and there are too many gyri that are very very small. And it usually results in pretty severe seizure disorders. There is schizencephaly where there is a gray matter line cleft that may extend clear across the brain, from the pial lining to the ependymal lining.