Musculoskeletal (MSK) ultrasound of the extremities has recently undergone significant developments. A dedicated symposium sheds light on these advances, particularly in peripheral nerve disorders.
Colour Doppler, power Doppler and other technological advances have enabled great progress in MSK ultrasound of the hand, wrist, foot and ankle. With microvascular technology, radiologists do not need to use contrast agents, but just press a button on the machine to get detailed information about vascularity. This information can help make an early diagnosis of an injured ligament and impact on treatment pathways, explained Dr. Georgina Allen, a consultant MSK radiologist at Oxford University and director at St. Luke’s Radiology Oxford Ltd.
“Within 24 hours, an injured ligament starts to form new blood vessels. You would not see that on MRI, even with contrast enhancement. It does not have sufficient resolution,” said Allen.
In MSK imaging of the extremities, ultrasound has enabled identification of problems and some soft tissue masses perhaps better than with MR, not only thanks to its superiority in depicting microvascularity, but also because it provides much better resolution of soft tissue than MRI.
“Structures can be scanned using movement. You can see tears open up in ligaments and tendons, and you can see these structures moving abnormally. With ultrasound you can examine things very close to the skin. With MRI you get a very good global view but not such a good focus of what you are looking at. With ultrasound, the patient will be able to tell you where it hurts, so you can focus precisely on that area,” she said.
In some instances, ultrasound also has higher spatial resolution in imaging peripheral nerves, according to Carlo Martinoli, Associate Professor of Radiology at the University of Genova, who will delve into the topic during the symposium. One of the benefits of ultrasound that he describes is the depiction not only of abnormalities affecting major nerves, like the median nerve or the tibial nerve in the lower extremities, but also changes affecting small nerve branches and terminal branches.
“Using high frequency probes, we are able to identify not only the nerve bundle but also its inner architecture. Ultrasound seems to be very sensitive for identifying subtle histopathologic abnormalities affecting individual fascicles and their relationship with the epineurium, thus opening new interesting perspectives for a better definition and characterisation of nerve disorders,” he said.
Nerves are elongated, tubular structures, which makes them easy to spot on imaging. Once the nerve is identified, radiologists or sonographers can go back and forth with a probe, from distal to proximal in a few seconds, following the nerves across a long segment.
This is a major benefit over MRI, and there are others, Martinoli believes. “Ultrasound is a dynamic examination that demonstrates nerves during contraction of muscles or joint motion, identifies areas of nerve instability, and shows nerves moving over structures and bony prominences,” he said.
But ultrasound has some limitations when nerves are too deep in a location or in the presence of bony barriers. For example, there may be problems when examining the proximal root of the sciatic nerve, or the nerves in the pelvis, because they are surrounded by bony structures or are located too deep. “As soon as the nerve is exposed in the upper and lower extremity, we have a wonderful depiction of its characteristics,” Martinoli said.
Ultrasound can help characterise many diseases – not just compression neuropathies, but also congenital diseases, non-immune neuropathies and nerve traumas, extrinsic and intrinsic tumours. “It is fantastic because it can demonstrate any damage, even at fascicular level, much better than MRI, so you can understand both the level and the severity of nerve disease,” he said.
Specialised probes must be used for the examination of very superficial tissues in the extremities, to extend the examination to smaller branches.
To perform MSK ultrasound to the best of its potential for the extremities, radiologists must have a detailed knowledge of the anatomy of the region. “When you approach these areas, you need to identify the appropriate landmarks. Because you have spatial resolution that is close to 0.1mm, you need to know about even the smallest soft-tissue structures and nerve branches,” he said.
“Check your anatomy – have a book or the internet at hand to check anything you need to look up when not sure. Do not be scared to use these resources,” Allen recommended.
Hands-on technique is essential in this setting, according to Allen; users must know how to position the probe. “If you hold it in the wrong position, you might not see what you need to see. Perhaps you will also need to use a lot of gel so as not to press too hard,” she said.
It is important to listen to patients when performing the examination, as one needs to recreate the movement that triggers discomfort to better locate the injury. “Patient input is paramount,” she concluded.
State of the Art Symposium
SA 7 Musculoskeletal ultrasound of the extremities
- Tendons, ligaments and retinaculae of the wrist and hand
Marie Faruch; Toulouse/FR
- Tendons, ligaments and retinaculae of the ankle and foot
Georgina M. Allen; Oxford/UK
- Soft tissue masses
Elena E. Drakonaki; Iraklion/GR
- Peripheral nerve disorders
Carlo Martinoli; Genoa/IT
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