I will talk about Ultrasound-guided cervical extraforaminal peri-radicular steroid injection
I want to describe it as a hydrodissection with a steroid mixture
because it is not a simple injection.
For chronic cervical radicular pain, we have two guiding image modalities.
One is ultrasound, and the other is C arm. Which one do you prefer?
Some doctors prefer only ultrasound and hate a C-arm.
Other doctors stick to the c-arm guidance.
I like both, but I have a simple principle to apply each tool.
If the radicular pain is caused by the paracentral protrusion of the disc, which one do you prefer?
Usually, I choose C -arm guidance in this situation.
In case of Central stenosis or Type 1 Modic change with discitis,
I prefer c-arm guidance.
The oblique sagittal MRI image shows foraminal stenosis and black disc protrusion.
I prefer ultrasound-guided peri-radicular steroid injection.
In addition to central stenosis or discogenic pain,
I prefer c -arm guided interlaminar epidural steroid injection
in cases of central protrusion and intractable pain to the ultrasound-guided procedures.
Please keep in mind!!, we must undergo all the ultrasound-guided procedures in an aseptic condition.
Let me talk details about ultrasound-guided peri-radicular steroid injection.
I will start from the target
The C-arm target of transforaminal injection is the
internal aspect of bony intervertebral foramina.
It aims to spread the contrast media into the epidural space.
How about the ultrasound-guided nerve root block.
Is the target of US-guided needle placement the same as the C-arm guided needle placement?
The C-arm image showed that their needle tip seemed to be very close to the radiologic target.
The authors reported that their needle tip was within 5 mm of the radiologic target.
I repeated the same experiment with their protocol.
It is the needle tip in AP and oblique view.
The contrast media spread proximally and centrally from the needle tip.
Let me show their c-arm image one more.
Again, the contrast media spread 1 level above the needle tip.
What is the reason?
Let’s consider the anatomy of the intervertebral foramina.
It looks like the internal part of the intervertebral foramina is
in the same plane as the external orifice in this axial section.
Because of the inferior oblique orientation of the intervertebral foramen,
the external orifice of the intervertebral foramen is located
in 1 segment level below the internal orifice.
When we consider the ultrasound target point as an inter-tubercular groove
between anterior-posterior tubercle like this red arrow,
the US target point is closer to the 1 level inferior C-arm target.
It is easy to misunderstand that the US target is very close to the C-arm target.
US target is an extraforaminal perineural space, not the bony intervertebral space.
It is inevitable because there is a physical limitation of
ultrasound transmission and image-producing technology.
Where is the ultrasound-guided nerve root block target?
I wondered the reason for the hypoechoic echotexture of the nerve root in 2005.
So, I harvested cervical nerve root specimen from the fresh cadaver
and put it into the saline to compare the echotexture with the real one.
Let's watch the histology of the cervical nerve root specimen,
ultrasound demonstration of live and saline immersed nerve root.
Let's watch the histology of the cervical nerve root specimen.
The nerve root consists of several large round fascicles.
It is very homogeneous and contains abundant water contents.
It is the nerve root on real-time scanning.
The echotexture of the nerve root consists of several round hypoechoic structures.
I asked many experts about the reason 15 years ago,
and they answered it was an anisotropy.
My experiment shows saline immersed nerve root looks the same echotexture
as the real-time image, and the echotexture revealed the histologic characteristic, not the anisotropy.
The reflection and anisotropy is the most significantly influencing artifact
that hinders the ultrasound-guided needle approach into the bony foraminal space.
Reflection in ultrasound refers to the return of the sound wave energy back to the transducer.
The tissue interface with a larger difference in acoustic impedance, such as the bony cortex,
will result in a larger sound reflection and can not penetrate further.
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25 ноя 2021
