 Hi, my name is Dr. Ankit Shah and I'm a radiologist practicing at Wille Parle West at Grace Kill Imaging and Eclat Poly Clinic. My specialty is Muscular Skeletal Imaging and thank you for listening in. My name is Dr. Ankit Shah and I will be talking on ultrasound evaluation of carpal tunnel syndrome. Carpal tunnel syndrome or median nerve entrapment and the level of carpal tunnel typically presents with pain and parasthesias in the thumb, the index finger, the middle finger and radial half of the ring finger. Presence of night pains is one of the most characteristic features of carpal tunnel syndrome. This is because the patient sleeps on their affected hand or in that particular position for a prolonged period of time and suddenly they wake up in the night having numbness along the distribution of the median nerve. Advanced disease results in reduced grip as well as tenor muscle atrophy. The most important risk factors are hypothyroidism, diabetes mellitus and pregnancy. Now on the right side what we see is this considerable atrophy of the tenor musculature. The black arrow points towards the wasting that we see to compare that to the unaffected tenor eminence which is pretty smooth. Now let me tell you that by the time the patient comes to you for an ultrasound scan the diagnosis of carpal tunnel syndrome has already been made. Most of the times or maybe more than 85% of the times physical examination as well as history they are quite specific. So nobody is going to send the patient to you to make the diagnosis of carpal tunnel syndrome. What you are expected to do is comment on the nerve or any other pathologies which might result in compression of the median nerve. Nerve conduction studies and EMG is known to be the gold standard. However there are pitfalls because what happens is that nerve conduction studies evaluate only the large myelinated nerve fibres and the results are often normal in cases of early compression when only small unmyelinated fibres are affected. So that's where ultrasound really has an important role to play. So coming to the carpal tunnel anatomy it's typically a fibrocious tunnel whose floor is formed by the proximal and distal rows of the carpal bones and the roof is formed by a transverse carpal ligament or the flexor retinaculum. The transverse carpal ligament typically attaches to the paciform and the scaphoid proximally whereas distally it attaches to the hook of hammock as well as a trapezium tubercle. So the most important content of the carpal tunnel is obviously the median nerve and apart from that the other contents are the flexor tendons which are your flexor digitorum superficialis the flexor digitorum profundus tendons as well as the flexor polisus longus tendon. So if you have to remember the bony anatomy I would suggest that you remember the paciform as well as the hook of hammock as an important ocious landmarks we need to remember while we are scanning the carpal tunnel. As far as the surface anatomy of the carpal tunnel goes you have to remember that the distal pama gris forms the proximal edge of the carpal tunnel whereas the distal edge of the carpal tunnel is formed approximately at the level of the first web space. So what we see over here this yellow area marks the surface anatomy of the carpal tunnel. The primary pathology in carpal tunnel syndrome is a reduction in the volume of the carpal tunnel. Irrespective of the underlying cause reduction in the overall volumes of the carpal tunnel results in markedly increased pressures within the carpal tunnel. This can be regarded as compartment syndrome in C2. Alternatively there is another theory which says that the most common entrapment neuropathies are secondary to microtrauma to the nerves as it travels the osteofibrous tunnels. The carpal tunnel syndrome is divided into two main categories. One is an idiopathic form and the other is a secondary form. In the idiopathic form whenever the clinical features the nerve conduction studies or the ultrasound features a suggestive of median nerve entrapment but we don't find an obvious cause that's when we label it as idiopathic carpal tunnel syndrome. Whenever we see an extrinsic pathology causing compression of the median nerve or a space occupying lesion within the carpal tunnel such as a ganglion, accessory muscle, flexitin and dinocynovitis or even a lipoma we label it as secondary carpal tunnel syndrome. Irrespective of the nerve being involved in primary or secondary carpal tunnel syndrome all entrapment neuropathies undergo a series of changes. The earliest changes in paired venous flow which results in increased intranural edema. Chronic increased intranural edema results in ischemia and chronic ischemia results in internal fibrosis. Now mind you internal fibrosis is an irreversible change. Once the fibrosis sets in there's myelin sheath and axonal degeneration and this results in motor impairment wherein you get significant muscle weakness along with loss of muscle volume. The goal of imaging is to detect median nerve entrapment as early as possible because once internal fibrosis sets in the post-operative outcomes might not be that favorable. It is difficult to really differentiate between nerve ischemia versus intranural fibrosis on imaging alone. So the patient has been diagnosed with carpal tunnel syndrome. The nerve conduction studies have been done. Where does ultrasound fit in? Ultrasound will tell you about the median nerve morphology. It will tell you how significant is the nerve compression. How much is the intranural edema? Is the nerve just a single trunk or is it a biped median nerve? What is the anatomic location of the lesion? Is the nerve thickening proximal to the carpal tunnel or is it distal to the carpal tunnel? Are the branches of the nerve involved? What is the relationship of the median nerve to the surrounding soft tissues? We just discussed about secondary carpal tunnel syndrome. Areas which are difficult to assess with electro diagnostic testing can be easily seen on ultrasound and we already mentioned that ultrasound helps to identify peripheral nerve lesions which might not be that apparent on electro diagnostic testing. So we should all know that imaging gives an anatomical perspective to peripheral neuropathy which so far was just considered as functional pathologies which were evaluated on nerve conduction studies. Thankfully there is a lot of good literature coming up in recent times which actually supports the role of ultrasound in the diagnosis of carpal tunnel syndrome. So this is a very good article which got published last year in the American Society for Surgery of the Hand which says that if there is a dilemma of carpal tunnel syndrome they do recommend ultrasound to be used rather than nerve conduction studies. So from the concept diagrams we move into the real life ultrasound images. Here is a transfer section at the level of the proximal carpal tunnel which is obtained by placing the probe over the distal pama crease. Remember we spoke about the distal pama crease which forms the proximal edge of the carpal tunnel. The tautious landmark is a PC-formed bone at this site because the cross-sectional area of the median nerve is measured at this level. The red markers show the flexoretinaculum. The yellow arrow shows the median nerve which shows this honeycombed pattern and the structure marked FCR is a flexor copy radialis tendon. This tendon lies outside the tunnel. The significance of FCR is that during dynamic examinations movement of the median nerve is seen or calculated with respect to the flexor copy radialis tendon. Now moving in a little bit more we look at the flexor tendons more closely. They typically have an ecogenic appearance compared to the median nerve. However, as a beginner you might find it a little bit difficult to differentiate the median nerve from the flexor tendons of the wrist. However, how to differentiate between the two will come to that in a little bit later. Coming to the ultrasound microstructure of the nerve, you should know that all the axons are grouped together into bundles and they are arranged into fascicles. Now these multiple fascicles are grouped together and they are bound by the perineurium. Now this perineurium is this thick structure housing all the elastic fibres and the blood vessels and this perineurium is surrounded by the epineurium. This epineurium is also a active tissue with blends into the adjacent fat. What it does is it provides a cushioning to the nerve and prevents external compression. This epineurium is especially abundant around the nerves as they cross through the osteofibre tunnels. So once we've seen the concept of the cross section of the nerve, let's move on and see how the nerve looks on ultrasound and on the cross section. So on the cross section, your fascicles typically appear hypoechoic. Your perineurium looks ecogenic and even your epineurium looks significantly ecogenic and it almost blends into the surrounding fat. However, if you want to look at the epineurium properly, make sure that you look at them at the level of the osteofibre tunnels because that's where they're really significant. Typically, the nerve has a honeycomb structure. It looks like a honeycomb or if you want to call it a cut cable appearance. It's like if you cut a cable, you will see these multiple wires on the short axis. So that's what it looks like. On the long axis, the nerve typically has a filamentous pattern and may often resemble a tendon. So this is what the fascicle looks like. It's hypoechoic. Again, just the perineurium looks slightly ecogenic and the epineurium has a maximum ecogenicity. And if you look at the median nerve, it has almost a parallel course. This is a proximal end and as it enters the carpal tunnel, it still has this parallel appearance over here without any deformity. So how do we differentiate between a nerve and a tendon? What we do is we place our probe transversely over the carpal tunnel and what you do is you do this gentle rocking of the probe. So this is what I've shown over here. That's the carpal tunnel and I gently rock my probe back and forth. Now the tendons what they do is they show anisotropy. So if you see whenever there's anisotropy, the tendons become dark whereas the nerve remains more or less same. So this is how we differentiate tendons from the nerve. So okay, if you're not really comfortable with this, what you can do is you can take the nerve and trace it all the way approximately. You will see that the tendons they end into muscles or the muscular tendons is junctions whereas the nerve you can trace all the way up towards the elbow through the end of muscular fat planes. So that's going to be really helpful. A lot of ultrasound imaging findings and criteria have been described for ultrasound imaging of carpal tunnel syndrome. However, there are only a handful of findings that are of practical use and are clinically relevant. The hallmark of median nerve entrapment and the level of carpal tunnel is hypoequate enlargement of the median nerve, act and proximal to the level of entrapment. So what we see over here is the long axis view of the median nerve at the level of carpal tunnel. As the median nerve dips into the carpal tunnel, we see this waist formation or if you want to call it the notch sign. This is the area where there is deformity occurring within the nerve contours and this arrow shows this mild enlargement and eddy matters appearance of the nerve with typical loss of this fibrillary pattern. So this is a classic sign. So if you get this one image and if there are presence of symptoms, typical symptoms of carpal tunnel, you already have a diagnosis. So once you've seen the nerve on the long axis, you've seen this notch sign and you've seen this hypoequate enlargement of the nerve, what we try and look on the short axis is we try and look for intranural edema. We look for the nerve aquatexture. Now in this patient who already was critically diagnosed to have carpal tunnel syndrome, what we see that the nerve is enlarged as loss of typical honeycombed appearance. And the next thing what we do is we try and quantify it by measuring its cross-sectional area. Another patient with carpal tunnel syndrome, what we see is that as the nerve dips down, we see that there's a definite change in the contours which is shown by these markers. There's this subtle waist formation and just proximal to that, the nerve appears hypoequate with loss of this typical filamentous pattern and this is because of nerve edema. So I have evaluated the nerve on the grayscale image on the long axis. Now what I do is I turn on my power Doppler and what I see is hyperemia. Presence of hyperemia within the nerve is associated with nerve entrapment or nerve pathology. So there are these two or three findings which I have already seen and once again when I want to quantify what I do is I look at the nerve on the short axis. I measure the cross-sectional area at the level of the PC form bone and in this nerve the cross-sectional area measured almost 24 millimeters square. Now you know somebody would ask me when do I call that the nerve is big? Okay, there's so many criteria which are there. These are the two references which I have which I found really helpful. So what we do is we measure the cross-sectional area at the level of the PC form bone. When the cross-sectional area is less than 9 millimeters square it's definitely normal. If the cross-sectional area is between 9 to 12 millimeters square it's borderline. So it's at your discretion. You have a look at the patient if the findings are significant if the patient's complaints are significant yes it would fit into carpal tunnel syndrome and if it's more than 12 millimeters square it's definitely abnormal. Having said that if the patient is asymptomatic all right if the patient has no complaints then there's really no point in labeling the patient as carpal tunnel syndrome. What you can do is you mention it in the report that 12 millimeters square is high but since the patient has no symptoms it would be worthwhile to clinically evaluate the patient to rule out an underlying median of compression. So that's what I would do. Now another scenario when patient is typically symptomatic but you're not seeing those classical signs the nerve is not edematous you don't have a notch formation. The cross-sectional area is equivocal all right not fitting into anyway. So what do you do? This is something really important this is what I practice in my day to day ultrasound imaging practice. So what we do is we measure the cross-sectional area of the median nerve at two levels. One is in the distal forearm which is at the level of the pronator quadratus and the next level again I come to the PC form bone and I measure the cross-sectional area of the median nerve at this level. If the difference between the two cross-sectional areas is more than 2 millimeters square then it is considered as significant. Now this finding has almost a 99% sensitivity as well as 100% specificity. Coming back to looking at the nerve morphology you have to mention in your report is it a single nerve or is it a bifid nerve? A bifid median nerve is an anatomical variant wherein there are two nerve trunks you know just before it comes to the distal forearm it kind of splits into two trunks and this anatomical variant may or may not have a persistent median artery between the two trunks so it is very essential that you mention this in your report because when you mention this if the surgeon is planning to do an endoscopic carpal tunnel release they might want to change their surgical planning or maybe they would keep that little bit of information at the back of their mind so it is essential to do that. So coming to secondary carpal tunnel syndrome once you've really evaluated the median nerve what you do is you look for the rest of the structures in the carpal tunnel so if they are causing any compression. This was one 32 year old female with vague pain and parasthesias only along the tenor eminence there was a clinical suspicion of carpal tunnel syndrome so the median nerve we evaluated it was somewhere around 9.2 millimeters square but what we see over here is that we see a ganglion cyst right below the flexopolisis longest tendon on the short axis we see a typical anechoic appearance of the ganglion and long axis it has a similar finding this was one 47 year old female with night pains in the hand along the median nerve distribution she was a known case of rheumatoid arthritis so what we see over here is that there's hypoechoic soft tissue surrounding the echogenic tendons so this was typically flexor tendon tenor cyanobitis and what we see that the median nerve is pushed more along the volar surface so this one was secondary carpal tunnel syndrome because of flexor tendon tenor cyanobitis these are intra-op picture showing active panacea within the flexor tendon sheath this was a 56 year old male with carpal tunnel syndrome if you look at the cross sectional area of the median nerve it's around 7 millimeters square so pretty much normal however when you increase your depth you're done looking at the median nerve what we see is this soft tissue deep to the flexor tendons so this turned out to be low grade of flexor tenor cyanobitis which was subsequently turned out to be tuberculosis a lot of us are used to using high res hockey stick probes after you're done with evaluating the median nerve with the hockey stick probe it's a good idea to drop your depth and have a look at the base of the carpal tunnels just so that you don't miss out on any space occupying lesion or low grade tenor cyanobitis this was 60 year old female with a vague swelling over the volar aspect of the wrist and typical pain along the median nerve distribution so what we see over here on the transverse image there's this figure A that the nerve is enlarged see this echogenic soft tissue kind of causing separation of the nerve fibrils and color Doppler really doesn't show much vascularity on the long axis we see that there's separation of the fibrils with indefined echogenic soft tissue along the course of the nerve so we gave this as a infiltrative lipoma of the median nerve this is what the T1 weighted actual MR looks like and ultimately it turned out to be a fibril lipomata somatoma of the median nerve this is an interop picture wherein we see that the transverse carpal ligament is causing this indentation of the nerve that we see over here and this was this entire nerve which was significantly thicker so you've looked at the median nerve you've looked at the carpal tunnel it's a good idea to look at the end organ ultimately the tenor muscles because tenor muscle atrophy corresponds to disease severity so they say that atrophy of the abductive polycystic brevis is associated with poor outcome even in the post surgical period so it helps in counseling the patient and helps in treatment planning the median nerve looks normal at the level of the wrist is that the only reason is that the only reason for this pain so that's where I mentioned that the patient has to be diagnosed clinically first so your patient might be normal, your scan might be normal but then have other pathologies being ruled out like multiple sclerosis of bats, of apple disc disease, syringomylia, peripheral nerve sheath tumors once in a while you might see something like this brachial plexus neuritis and thoracic outlet syndrome so you should know when to alert the clinician that okay fine your scan is normal maybe he should look up for something else you know get an MR done so this is my last slide so this is my checklist for ultrasound evaluation of carpal tunnel syndrome I look at the median nerve ecogenicity and morphology I look it in the long as well as the short axis when I say morphology again is this a single trunk? is this a bifid median nerve? does it have a persistent median artery? I look for waist formation or the not sign on the long axis cross sectional area at the levels of PC form bone and the pronator quadratus alright if the difference is more than 2 millimeters squared it's significant I look out for secondary causes of carpal tunnel syndrome look out for you know tino sinovitis, ganglions lipomas, accessory muscles it's not always necessary to label what kind of a muscle is it as long as you identify it you know that should be good enough tenor muscle, equatexture and volume look at that as well and if you can try and look at the path of the pama cutaneous branch of the median nerve with respect to the flexor retinaculum sometimes some of the surgeons would like to know this because inadvertently if they injure that nerve the patient can have postoperative symptoms so with that we're done and thank you so much for listening again