Krasnoyarsk; What is an AVM, anyway?

As expected, Dr. Ahn told us Christopher needed a cerebral angiogram to know for certain what kind of tangle was in his brain.  But first he showed us what they were seeing in his MRI and what it meant.  In the very top layer of his brain, you see a few tiny black circles in the middle, just to the left, kind of like swiss cheese.  The next layer down—nothing.  

Image 1--View of the AVM in the top layer of Christopher's brain.  I added the labels.  Note that since the AVM is located in the right side of his brain, any deficits would occur on the left side of his body.  Also note that it is straddling the central sulcus, but in this view, appears to mostly be located in the pre-central gyrus, aka, the motor strip.

Dr. Ahn said those black circles could mean one of three things:  

1. A benign tangle of blood vessels that will never cause harm.
2. A true, but mild, arteriovenous malformation (AVM), where the arteries are hooked up directly to the veins without any intervening capillaries.  They’d monitor it yearly.
3. A true AVM that is deemed dangerous enough to remove.

Why are AVMs dangerous?  First, veins aren’t intended to take the pulsile flow of an artery, but since the blood flow slows WAAAAY down in the capillary beds, that isn’t an issue in normally wired blood vessels.  Second, the arteries in an AVM are missing a structural layer that causes the whole thing to wind up like a tangled ball of yarn.  

 Figure 1--Okay, so this is two figures I pulled off the braingletangle blog, but I like the visualization of an AVM compared to a normal artery--capillary bed--vein connection.

He also felt, based on what he saw on the MRI image of Christopher’s brain, that an AVM diagnosis would be physically inoperable and would require gamma knife surgery to remove.  Why?  Because they thought his AVM is in an area of the brain called the motor strip.  When you decide you want to move one of your skeletal muscles, the motor strip is responsible for sending that message down your spinal cord to the muscles required.  In the world of vascular neurosurgeons, it makes it “eloquent tissue”; to the layman, it’s “prime real estate”.  Just behind the motor strip is the sensory strip, which, as the name implies, is responsible for receiving the sensory input from various areas of the body.  Where the regions of the motor strip learn early which parts of the body to control and display little plasticity for taking on new roles later in life, the sensory strip is much more flexible.  Lying immediately between the two regions is a line called the central sulcus.

Figure 2--The pre-central gyrus, also known as the primary motor cortex or motor strip, is the area just in front of the central sulcus in this diagram.  The post-central gyrus, also known as the primary somatosensory cortex or sensory strip, is located immediately behind the central sulcus.  Image Courtesy of The Aneurysm and AVM Foundation.

Christopher's biggest concern about the angiogram, as usual, was whether or not he’d need an IV.  As soon as he heard the words “gamma irradiation”, however, he was all atwitter with questions about the nature and safety of the therapy.  Luckily, Dr. Ahn is a pediatric neurosurgeon and appeared more than happy to answer those questions.  He was also ready to explain how gamma irradiation shreds the DNA inside the targeted tissues, but since I spent several years in graduate school studying the DNA damage repair cycles, we were able to focus on Christopher’s questions.

With that information, we chose the first available date for a cerebral angiogram and awaited our arrival at the next station.