Ultrasound of Perpheral Nerves - HD

Introduction

Hi, I'm Tom Grant.

I'm director of ultrasound at Northwestern Memorial Hospital.

I'm professor of radiology at Northwestern Medical School and I'm from Chicago.

Today I'm gonna be talking about ultrasound of the peripheral nerves, both the upper and lower extremity.

I'm gonna be talking about the normal anatomy, in addition to injuries, traumatic congenital anomalies, as well as compression neuropathies of these nerves.

I hope you enjoy the talk and hope you find it interesting.

Thank you.

Normal Anatomy of Nerves

I'd like to start by talking about the normal anatomy of nerves.

Nerves are composed of fibers called fales that are invested in a connective tissue called the endoneurium.

The size and number of these fales contained in a nerve is very variable.

Obviously, large nerves like the sciatic nerve have the same appearance on ultrasound as smaller nerves such as the median nerve in the carpal tunnel.

The ultrasound appearance of peripheral nerves correlates closely with the histology.

Normal nerves are very echogenic tubular structures due to the surrounding connective tissue.

The nerve vesicles are hypo coic, while they connective tissue surrounding them is hyper coic.

The size of the peripheral nerve decreased from proximal to distal due to branches exiting from the main nerves.

The normal peripheral nerve, this is very important, has no internal color doppler flow.

However, injured or stretched nerves over a long period of time will contain abnormal doppler flow.

This is a normal nerve.

This patient had an injury and they wanted to make sure that the median nerve in this case was intact.

So you can see some soft tissue edema and thickening of the subcutaneous tissues, but the normal appearance of the nerve, both on the sagittal and transverse scan, is clearly seen.

It's much easier to identify a nerve on a transverse scan than it is on a longitudinal one, and it has this typical honeycomb appearance.

Ultrasound in the Evaluation of Peripheral Neuropathology

Now ultrasound has become the imaging procedure of choice in the evaluation of peripheral neuropathology.

This is primarily due to new developments using high resolution transducers with broadband technology that gives ultrasound a much higher resolution than MRI.

The ultrasound transducer can be easily moved from one anatomic segment to another, and therefore ultrasound is the preferred method for imaging a long anatomic segment.

For instance, we not infrequently will look at the median nerve from the midar all the way down to the proximal palm.

Now the best method, as I mentioned earlier, is to look at axial imaging.

Longitudinal images are only obtained after an abnormality suspected, but it is valuable when that abnormality is found.

Peripheral Nerve Injuries and Anomalies

This is the case that may be become in interested in peripheral nerve injuries.

This is a 45-year-old yoga instructor who could not do one of the primary techniques in yoga, a down dog technique, and we can follow the sagittal ulnar nerve at the level of the hamate that would be in the region of guillen's canal.

As we go distally, we can see compression on the ulnar nerve by a small mass, which I marked m and you can also see the hypo thenar muscles on this scan on the right.

And you can see this nerve measures one millimeter in diameter, something that cannot be identified in MRI.

This mass was resected and the patient returned to normal.

The mass was a small lipoma, which directly compressed the ulnar nerve causing the patient's symptoms.

Etiologies of Peripheral Nerve Disorders

Now, there are a number of etiologies for peripheral nerve disorders.

The most common are entrapment neuropathies, and these may be related to compression or stretching of these peripheral nerves After a long period of time, high pressure on these peripheral nerves can alter their morphology and function causing irreversible damage.

Chronic nerve compression changes the size of the nerve.

It's attenuated at the site of compression and swollen just proximal to the site of compression.

Other causes of peripheral nerve injuries besides entrapment neuropathies in neuropathies include congenital anomalies, trauma masses, pathologic changes seen in charcoal Marie tooth disease and neurofibromatosis.

Congenital Anomalies

This is one of the unusual anomalies of the median nerve, which c has an increased association with carpal tunnel syndrome.

This is a bifid median nerve and we can see on the scan on the left that there are actually two peripheral nerves within the carpal tunnel and it's separated by a median artery.

This is important for the hand surgeon in the case of a decompression for carpal tunnel syndrome to make sure that he does not damage that median artery because it can cause significant longstanding injury.

Here's another patient with a very large median and ulnar nerve.

In fact, these nerves are probably eight to 10 times larger than normal.

This happened to be a patient with unilateral plexiform neurofibromatosis markedly abnormal median nerves that could be easily palpated.

Traumatic Injuries

Now traumatic. Her injuries can be seen with a variety of trauma.

There can be direct puncture, stretching, repetitive trauma or overuse ultrasound of minor trauma.

You usually get very minimal loss of the vesicular nerve architecture and sometimes positive color Doppler flow ultrasound of major trauma.

It's very important because ultrasound will predict the level of injury and the extent of separation of the cut ends of the nerve, and it's very helpful for the attending physician who happens to who may be a hand surgeon or a plastic surgeon to know exactly if this is a damaged nerve or is it a severed nerve and the earlier it's treated, the better function the patient will have.

Ultrasound also gives reliable postoperative information about the continuity of the nerve in a patient who has had surgery, but still may have some symptoms.

This is an example of a patient who would developed who's had wrist pain for three months after a repair of his triangular fibrocartilage.

And it was troubling because all of the other exams were absolutely normal and we can trace the dorsal branch of the ulnar nerve over the medial aspect of the distal ulna and we can see focal enlargement of that nerve secondary to a traumatic neuroma.

This eventually improved but didn't and did not require surgery, but they wanted to differentiate between a severed nerve and a traumatic stretch injury as was seen in this case.

Brachial plexus is also easily identified in the neck as well as certain portions of the upper arm.

The nerve can be compressed in the rectal pectoralis space as we see here, but in this particular space, ultrasound is not very helpful because of the injury because of the overlying bone.

However, most of the nerve in the brachial plexus can be easily identified using ultrasound.

This is an example of a 72-year-old, turns out to be a physician who after open heart surgery had a developed an injury.

Nobody seems to know the cause in the radial nerve distribution of his upper right arm, and we can see on this coronal ultrasound that there is hypoechoic appearance of the radial nerve branch of the brachial plexus that is swollen and thickened.

This eventually receded, but the patient did have significant symptoms for several months after the initial surgery and injury.

Another injury that's significant are patients who develop spiral fractures of the mid and proximal shaft of the humerus.

Now the radial nerve arises from C five through eight and supplies the muscles of the upper limb.

The nerve rhymes around the posterior and lateral shaft of the humerus adjacent to the brachial artery and vein.

The nerve is fixed when it is fixed in position adjacent to the bone.

So any type of fracture or injury makes the nerve very prone to significant motor loss and also wrist drop.

The ultrasound findings may show that the nerve is either swollen, compressed, or even severed.

This is an example of a normal radial nerve in the spiral groove posterior to the mid shaft of the humerus, and we can see the normal appearance of the brachial artery, the lateral and medial triceps muscles and the nerve in this arrow and the arrow head demonstrates the radial nerve.

Now if you look at the scan to the right and bottom of the image, excuse me, the left and bottom of the image, you can see mild compression of the radial nerve in the spiral groove and you can see the fracture deformity as noted by the arrowhead.

Patient had intermittent pain every time he moved his arm, but after fixation did not require surgery.

We also have an interesting kind of a sport at Chicago.

We have an amateur Circus act and people who are interested in this can go and learn how to be acrobats.

And we had a patient about a year ago who developed symptoms in the region of the median nerve secondary to a stretching injury created by the acrobatic Act, and this is known as the pronator syn syndrome, pain in the proximal forearm or paraesthesia in the distribution of the nerve.

The etiology is in this particular case was trauma, trauma stretch, a stretch injury and ultrasound can show either hypertrophy of the pronator Terry's muscle or flattening or thickening of the median nerve, and we can see the normal nerve on the left separated by the humeral and ulnar heads of the pronator muscle and the abnormal nerve best demonstrated on this transverse image.

On the lower right, we can see that the nerve is flattened, hypoechoic and mildly thickened between the humeral and ulnar heads of the pronator muscle.

The patient, again, it's nice to know that the patient didn't sever the nerve and the nerve was intact and eventually it recovered.

Cubital Tunnel Syndrome

Cubital tunnel is another interesting syndrome.

It's very common. We can see pain in the distribution of the median nerve.

It's usually caused by a compression of the median nerve within the within the tarsal, within the cubital tunnel.

And there could be a number of entities that cause this including ganglion cyst or fracture fragments that compress the nerve.

But a lot of these cases are idiopathic and we can see in the images on the right upper and the left lower that the nerve is markedly thickened in hypo coic within the cubital tunnel.

And if you look at the dynamic images when the patient flexes the elbow, we can see the abnormal median nerve being sliding over the medial epicondyle and that loss of the rec ulu was probably the cause of this patient's significant cubital tunnel syndrome.

We have another patient with a snapping triceps tendon and neuropathy and there were two palpable SMA snaps.

One was secondary to compression and on the ulnar nerve by the nerve being compressed over the medial epicon.

And the second was an accessory muscle from the triceps also crossed over the medial epicondyle causing significant symptoms in this patient.

So if you ever have a patient who has two palpable snaps in the distribution of the ulnar nerve at the cubital tunnel, this is probably gonna be the etiology.

Posterior Interosseous Nerve

Another entity I'd like to discuss is posterior interosseous nerve.

And this is a difficult injury in the sense that it's not detected by the usual standard methods of finding abnormalities of the nerve that is EMG.

And I found in my experience, and I've probably seen about 10 of these cases now, as the nerve, as it's, as it bifurcates from the main radial nerve at the level of the elbow joint becomes swollen at the level of the Arcata Roche, which is a fibrous band just before the nerve goes between the two supinator muscles.

And it because by a number of entities symptoms vary, patients could present with finger drop, limited finger extension and most commonly, at least in my experience, lateral epicondylitis, the nerve is usually swollen as it passes into the supinator muscle.

This is another example of what the nerve looks like normally, and you can see the main radial nerve is demarcated with an R where it branches into a superficial branch overlying the supinator muscle and the posterior interosseous nerve going between the two supinator muscles.

We can also see nicely an ultrasound as the nerve passes to a light slight degree of compression at the level of the arcade of Roche and can be traced approximately five centimeters distal to that point.

This is happens to be a patient with a with no symptoms, but had a very nice scan of the normal posterior neuro osseous nerve.

This is a patient who presented with symptoms of non-specific symptoms of tingling finger drop, but most marked was significant pain in the region of the lateral epicondyle.

And we can see the normal nerve dip down on the left, but the abnormal nerve on the opposite side have a area of increased echogenicity as pointed to by the middle arrow and on the transfer scan also a echogenic focus within the nerve suggesting a long standing injury.

And when the this nerve is involved, it symptoms can, as I said before, not on commonly simulate lateral epicondylitis.

This is a patient, a very unusual patient because she had a palpable mass and this is a radial bici radial bursitis causing posterior interosseous nerve symptoms.

And we can see the posterior interosseous nerve immediately adjacent to this large bursa collection and we decided to aspirate this collection and once we aspirated the collection, the symptoms totally resolved.

And as far as I know, the symptoms have remained absent for over a year.

Penetrating Injuries

Now, I'd like to also talk a little bit about these penetrating injuries.

This happened to be a carpenter who was almost had his nerve almost severed by a nail, but we can see on the two images, one a transverse image on the left and a longitudinal image on the right that the nerve was mildly compressed by this penetrating injury due to the nail, but was intact even though the patient was having symptoms.

Upper Extremity Compression Neuropathies

Carpal Tunnel Syndrome

Very important entity is the median nerve as it traverses the carpal tunnel and the nerve is in a relatively tight spot because there are eight flexor tendons within this relatively small carpal tunnel and it's located between the carpal bones obviously and the transverse carpal ligament.

There are a number of normal variants which can lead to carpal tunnel syndrome.

These include accessory muscles duplicated median nerve, which I demonstrated before, and a persistent median artery guillen's canal lies between the piece of form bone and the hook of the hamate and the transverse carpal ligament.

The contents of guillen's canal include the ulnar nerve, ulnar artery and vein.

There are a number of causes of carpal tunnel and guillen's canal syndrome.

Most commonly it's a tenino synovitis of the flexor tendons either due to microtrauma or rheumatoid arthritis.

There are also, occasionally you'll see patients with ganglion s or nerve sheath tumors, amyloid deposits in patients with chronic renal disease or even anomalous muscles in guillen's canal.

It's often a sports or work-related injury.

And not uncommonly not uncommon to have a mass or pseudo aneurysm from the ulnar artery compressing the nerve.

This is a typical example of a patient with severe carpal tunnel syndrome.

We can see the schematic above.

We can see the markedly enlarged median nerve, and also the appearance of abnormal color doppler flow within the abnormal nerve.

As I said before, color doppler flow is never normally seen within a nerve.

So, what we like to do is, and I find it very helpful, is to measure the median nerve, do a circumference around the nerve, both in the distal arm, distal form and in the carpal tunnel.

And as you know, all nerves get smaller as they go from proximal to distal.

So if this cross-sectional measurement gets significantly larger in the region of the carpal tunnel, we're almost certainly dealing with a patient with carpal tunnel syndrome.

This study was originally shown by Klauser and a group from Vienna.

It was published in radiology in 2009 and we found it very beneficial in determining what patients may require surgery and which patients don't.

This is the measurement we obtain.

The two images on the top are images of the median nerve in the distal forearm and in the carpal tunnel.

The two images on the bottom are the same, but we take a circumference around the nerve and compare them and you can see the circumference of the nerve in the distal forearm.

It's very much smaller than it is in the carpal tunnel.

And the patient had a classic clinical picture of carpal tunnel syndrome patients with guillen's canal.

Guillain's Canal Syndrome

Uh, compression as we see here with all modern day ultrasound is very easy to see the ulnar nerve from the arm to the thenar or in hypo thenar eminence.

And we can see in the proximal portion of the guillen canal, we can see the normal ulnar nerve and the ulnar artery.

On the opposite side, we can see a thickened enlarged ulnar nerve and we can see the reason was is the patient had an old fracture and there was a fibrous scar compressing the ulnar nerve in Yen's canal, which is a very small space.

The surgeon, the hand surgeon did a decompression and all of the symptoms didn't come back.

There was a significant improvement due and he knew exactly where to do the surgery on the basis of what we found on the ultrasound image.

Another interesting patient we saw in the spring this year, a 24-year-old professional hockey player slammed his hand on was slammed by a hockey stick in the region of the hypo thenar eminence.

And sometimes you'll see this entity is called hypo thena hammer syndrome and we can see that the ulnar nerve was being compressed by this pseudo aneurysm that we see nicely on the ultrasound as well as the MRA and once the pseudo aneurysm was treated, the patient did recover function that resulted in this hypo thena or hammer syndrome.

Palmar Cutaneous Nerve and Digital Nerves

Now there's a nerve which under normal circumstances really usually doesn't cause problems.

However, sometimes in a patient who's had carpal tunnel repair, the palmar cutaneous nerve can be damaged and this nerve is always seen normally with high resolution ultrasound image becoming arising from the median nerve in the distal forearm and extending between the median nerve and the flexor car radiologist tendon.

And the nerve is normal on the top, but on the bottom we can see a very well circumscribed hypo coic mass secondary to a traumatic neuroma of the Palmer cutaneous nerve after carpal tunnel syndrome.

And this example shows you the benefits of high resolution ultrasound.

This nerve will not be seen by any other imaging method and these nerves are as small as a millimeter in size but easily detected on ultrasound as long as you know where to look.

Digital nerves are also clearly seen, and since these are sensory nerves and patients who have penetrating injuries can present with significant sensory loss, it's very helpful to know is there a severed nerve which has to be repaired or is it just compressed and damaged that will come back.

The sooner a severed nerve is repaired, the better the patient will do.

And we can see on this diagram the normal digital nerve.

This happens to be the third long finger and we can see it extending adjacent to the digital artery and vein and we also can see a longitudinal image on the bottom right ultrasound scan.

This happens to be a patient with a lacerated a lacerated digital nerve in the proximal phx and we can see the two severed ends of the digital nerve above.

There is about a two millimeter separation between the proximal and distal stumps.

This patient required a nerve repair.

The patient on the bottom, although he had a significant stretch injury, did not require surgery but did develop traumatic neuromas.

In fact, two of them that were nicely seen, but there is no disruption of the nerve anytime you're looking for digital nerve injuries.

You also should think of associated vascular anomalies.

This patient not only had stretching and injury to the digital nerve, but immediately adjacent to it in the digital artery, we can see a pseudo aneurysm that was formed.

Now this did spontaneously resolve, but it's not unusual after either penetrating injury or occasionally a stretch injury for vascular injuries to be associated with this.

Usually pseudo aneurysms occasionally are rarely AV malformations.

Lower Extremity Neuropathies

Common Peroneal Neuropathy

Another entity that's I find important is the most common mono neuropathy of lower extremity.

This is a common perineal entrapment neuropathy.

Patients present with foot drop, which is characterized by weakness of the foot dorsi flexor muscles in the leg.

EMG is useful in evaluating the common peroneal function nerve function, but is limited in demonstrating the cause or the location of the nerve pathology.

The common perineal nerve arises from the sciatic and crosses laterally to wind around the fibular head.

And in this location the nerve is very prone to injury due to its fixed location around the fibular neck and there's only a small amount of fat and subcutaneous and skin making the nerve very vulnerable to external pressure.

If we can see the common perineal nerve in this diagram on the left, as we can see, it crosses from a lateral posterior approach to go around the fibular neck.

And at this point there's only skin and a small amount of fat sparing the nerve from significant compression.

We can see this patient with common perineal neuropathy has a swollen common perineal nerve and we can see the markedly abnormal colored doppler flow on this longitudinal scan within the abnormal nerve.

Another patient with common perineal neuropathy.

In this particular case that had been going on for a long period of time, we can see as the nerve goes between or adjacent to the fibular head and neck, the nerve is markedly swollen.

There's a lot of soft tissue compressing the nerve and this has been going on so long that the anterior tus muscle has totally atrophied.

As we can see in this corresponding MRI of this patient, a very common compression neuropathy.

Tarsal Tunnel Syndrome

What we see in the foot, or I shouldn't say common, but it's surely a painful one and one that needs to be discovered and diagnosed as quickly as possible is the tarsal tunnel syndrome, and this is due to entrapment of the tibial nerve or its branches in the tarsal tunnel at the an at the medial ankle.

Patients will have pain or numbness in the ankle and sole of the foot and al ultrasound is used to find these space occupying lesions.

This is a 43-year-old gentleman who was having symptoms of carpal tunnel syndrome and we can see the nerve very nicely on the left hand view, but these other structures represented large varicosities that compressed the tibial nerve causing the tarsal tunnel syndrome.

Once the cause was discovered, the patient had treatment for these varicosities in the more proximal leg and the symptoms gradually resolved.

Morton's Neuroma

Morton's is a mundane, very common abnormality.

We see it frequently in athletes, non-athletes, women primarily, and we can see the swollen plantar digital nerve in this particular location, which happens to be the third web space.

The most common is the third web space, but we can also see this in the second web space, extremely unusual in other web spaces and we can see nicely this yellow air pointed to the normal plantar nerve and the swollen bulbus mors neuroma at the spa at the web space.

The image below shows us injecting in this particular case the Mor s neuroma with some steroid.

And it's very easy to accomplish this technique under ultrasound guidance.

In some institutions, especially in Europe, absolute alcohol is given to totally destroy the Mor s and relieve symptoms most of the time.

More a more conservative approach including triamcinolone injection is helpful.

Conclusion

So in conclusion today, I would like to talk to you about the importance of ultrasound.

Ultrasound predicts the level of injury.

It distinguishes a damage from a transected nerve for six weeks before an EM MG is can distinguish these two entities and due to the better resolution of high frequency ultrasound, the nerve abnormality can be detected both with entrapment syndromes and injuries that are never shown with MRI.

Thank you for your attention.