Update on the Use of Ultrasound in the Diagnosis of Carpal Tunnel Syndrome   First of all, I would like to thank the organizing committee for the invitation   to participate in the fourth international conference of orthopedics and rheumatology.   The issue that I will address relates to the use of ultrasound for the diagnosis of Carpal tunnel syndrome. Renato A. Sernik, MD, PhD

Carpal Tunnel Syndrome Common compressive neuropathy. Initially, pain and sensitivity changes in the median nerve territory. Advanced stages – weakness and atrophy of the thenar muscles. t Flexor retinaculum median nerve carpal tunnel    Carpal tunnel syndrome is the most common compressive neuropathy. It is  initially characterized by pain and sensitivity changes in the median nerve territory     In advanced stages weakness and atrophy of the thenar muscles are present

Carpal Tunnel Syndrome diagnosis ultrasonography Clinical examination electromyography   Diagnosis is based on  the clinical examination   aided by complementary exams, such as electromyography   and more recently   by ultrasound

Ultrasonography - useful as a screening test, reducing the cost of diagnosis of carpal tunnel syndrome. According to some recent articles, ultrasound can be used as a screening test for the diagnosis of carpal tunnel syndrome, therefore avoiding the use of electromyography in many cases. However, in order to obtain good results, the exam must be performed by a trained radiologista, using suitable equipment   Fowler JR, Maltenfort MG, Ilyas AM. Ultrasound as a first-line test in the diagnosis of carpal tunnel syndrome: a cost-effectiveness analysis. Clin Orthop Relat Res. 2013 Mar;471(3):932-7.

Linear transducers: 12 –18 MHz. High resolution. Ultrasound equipment must have linear transducers with a frequency of between 12-18 megahertz which ensures the evaluation of small structures in a high resolution.

PERIPHERAL NERVE ANATOMY Basically what we assess by ultrasound, in the carpal tunnel syndrome, are the changes of the median nerve which makes it crucial to understand the anatomy of the peripheral nerve

nerve fascicle fiber perineurium Peripheral nerves are composed of the fibers and a supporting tissue.    Neural fibers come together to form the fascicles that are separated by the perineurium composed of collagen and vascular structures, whose main function is to promote their nutrition. perineurium

In an ultrasound, on the axial plane, neural fascicles are seen as hypoechoic rounded images surrounded by perineurium. These are represented by hyperechoic linear images, giving the nerve a bunch of grapes or honeycomb like appearance.   On the longitudinal plane, The neural fascicles   appear as parallel tubular images  giving a fascicular aspect to the nerve, unlike the flexor tendons that show a fibrilar structure.

Carpal Tunnel pisiform trapezium hamate flexor retinaculum scaphoid pisiform trapezium hamate flexor retinaculum The median nerve is assessed through its path inside the carpal tunnel.

a u fu * PIS pisiform scaphoid CARPAL TUNNEL * a n scaphoid pisiform In the proximal region, where the scaphoid and pisiform bonés can be seen, the median nerve appears with an oval shape.   PIS

hamate trapezium In the distal carpal tunnel, where the trapezium and the hamate bones are identified, the nerve presents as more tapered. trapezium hamate

Median Nerve Evaluation ULTRASONOGRAPHY Median Nerve Evaluation Qualitative Quantitative Qualitative and quantitative changes of the median nerve are evaluated  

Qualitative Evaluation - shape echogenicity structure In the qualitative exam,   three characteristics of the nerve  are checked:  the shape, echogenicity and structure  

Echogenicity / structures The most frequent change of the median nerve relates to the reduction of their echogenicity. Depending on the intensity of edema, the usual nerve fascicular appearance may be altered. In this image the perineurium can not be identified. The honeycombs like appearrance has disappeared.

Sometimes, nerve fascicles are replaced by areas of fibrosis and demyelination, represented by hyperechoic images poorly defined on the nerve, as in this case.  

Shape COMPRESSION EDEMA HOURGLASS SHAPE median nerve carpal tunnel The shape of the median nerve is altered due to compression determined by the retinaculum and the intraneural edema that is often present These changes may lead to the nerve looking like an hourglass.

These images represent the carpal tunnel on the longitudinal plane. The entry and exit points of tne median nerve in the carpal tunnel are thicker than the inside point, thus resembling an hourglass form. On the axial plane, the nerve is swollen and hypoechoic in the proximal carpal tunnel, unlike the distal region where it is shown as compressed and hyperechoic.   proximal distal

Quantitative Evaluation

Carpal Tunnel Syndrome In 1991, Buchberger et al. proposed 3 criteria for sonographic diagnosis of the carpal tunnel syndrome: - increase in cross-sectional area of the median nerve, proximal to the compression. - thinning of the median nerve at the site of the compression, measured by the ratio of two diameters of the nerve. - bulging of the flexor retinaculum. As regards the quantitative evaluation the first paper mentioning the use of ultrasound in patients with carpal tunnel syndrome was published by Buchberger et al in 1991. three diagnostic criteria were proposed: - an increase in the cross-sectional area of the median nerve. - a thinning of the median nerve at the site of the compression, measured by the ratio of two transverse diameters of the nerve. - a bulging of the flexor retinaculum.

Carpal Tunnel Syndrome In 1991, Buchberger et al. proposed 3 criteria for sonographic diagnosis of the carpal tunnel syndrome: - increase in cross-sectional area of the median nerve, proximal to the compression. - thinning of the median nerve at the site of the compression, measured by the ratio of two diameters of the nerve. - bulging of the flexor retinaculum. Of the three criteria, the increase in cross-sectional area of the median nerve proved to be the most reproducible according to studies done after this report.  

Quantitative Evaluation Median Nerve Área  The measurement of the area must be made where it is greater   The measurement must be made where the area is greater. Usually this point is located in the carpal tunnel entrance or in the proximal carpal tunnel. At the entrance carpal tunnel or in the proximal carpal tunnel

The ideal cutoff of the cross-sectional area of the median nerve to differentiate individuals without the disease from those with carpal tunnel syndrome is controversial.   Tai TW, Wu CY, Su FC, Chern TC, Jou IM. Ultrasonography for diagnosing carpal tunnel syndrome: a meta-analysis of diagnostic test accuracy. Ultrasound Med Biol. 2012 Jul;38(7):1121-8. Fowler JR, Gaughan JP, Ilyas AM. The sensitivity and specificity of ultrasound for the diagnosis of carpal tunnel syndrome: a meta-analysis. Clin Orthop Relat Res. 2011 Apr;469(4):1089-94.

Carpal Tunnel Syndrome Ultrasonography in Carpal Tunnel Syndrome increase the area of ​​the median nerve  used as  diagnostic criteria. Cutoff 9 -11mm². - sensitivity 77.6% and specificity 86.8%. According to recent reports in ultrasonography studies, the best cutoff value of the median nerve area is between 9 and 11 square millimeters. Tai TW, Wu CY, Su FC, Chern TC, Jou IM. Ultrasonography for diagnosing carpal tunnel syndrome: a meta-analysis of diagnostic test accuracy. Ultrasound Med Biol. 2012 Jul;38(7):1121-8. Fowler JR, Gaughan JP, Ilyas AM. The sensitivity and specificity of ultrasound for the diagnosis of carpal tunnel syndrome: a meta-analysis. Clin Orthop Relat Res. 2011 Apr;469(4):1089-94. Mhoon JT, Juel VC, Hobson-Webb LD. Median nerve ultrasound as a screening tool in carpal tunnel syndrome: correlation of cross-sectional area measures with electrodiagnostic abnormality. Muscle Nerve. 2012 Dec;46(6):871-8. Fowler JR, Maltenfort MG, Ilyas AM. Ultrasound as a first-line test in the diagnosis of carpal tunnel syndrome: a cost-effectiveness analysis. Clin Orthop Relat Res. 2013 Mar;471(3):932-7.

Cutoff- 10 mm2 sensitivity – 85.0% specificity – 92.1% accuracy – 89.3% Tai TW, Wu CY, Su FC, Chern TC, Jou IM. Ultrasonography for diagnosing carpal tunnel syndrome: a meta-analysis of diagnostic test accuracy. Ultrasound Med Biol. 2012 Jul;38(7):1121-8. In our institution, we use a cut-off value of 10 square millimeters based on our studies pubished in 2008. A median nerve cross-sectional area of 10 square millimeters had a sensitivity of 85 percent, specificity of 92% and accuracy of 89%. The result was greater than observed in the meta-analysis studies using cutoff values between 9 and 11 square millimeters.

Comparative Evaluation Normal Nerve: A1- A2 ≤ 2mm² Thickened Nerve: A1- A2 ≥ 2mm² carpal tunnel A1 Some radiologists, instead of performing a single measurement, prefer to compare the areas of the median nerves made at two points: in the carpal tunnel and near the proximal third of the pronator quadratus muscle. The nerve is considered to be thickened when the difference between the areas is greater than 2 square millimeters. pronador quadratus A2

A1 A2 pronador quadratus carpal tunnel In this example, the median nerve in the carpal tunnel is thicker when compared to the the median nerve in the forearm. This apparent increase in nerve size was confirmed by the measurement of the difference between the areas, whose value was 8 square millimeters. pronador quadratus A2

Palmar Cutaneus Branch(PCB) of the Median Nerve Patients with carpal tunnel syndrome may also have their symptoms related to the involvement of the palmar cutaneous branch of the median nerve, occurring in approximately 50% of cases.

median nerve median nerve FCRT palmaris longus t antebrachial fascia palmaris longus t FCRT flexor retinaculum median nerve median nerve This small nerve is the last collateral branch of the median nerve in the distal forearm. Despite its small size it is of great clinical importance. It passes radially to the median nerve below the forearm fascia. Close to the wrist, it enters a tunnel formed by the superficial and deep layers of the antebrachial fascia. At the exit of the tunnel, the branch pierces the fascia usually near the palmar crease of the wrist, reaching the subcutaneous tissue. From this point, it crosses the tubercle of the scaphoid to innervate the skin of the thenar eminence and the proximal portion of the hand.  

Palmar Cutaneus Branch of the Median Nerve Compression in the tunnel. Stretching as a consequence to reduced mobility of the median nerve. In non-operated patients, there are two hypotheses that attempt to explain the nerve involvement: 1) compression related to its passage in the tunnel formed by the superficial and deep layers of the forearm fascia; 2) Stretching as a consequence of reduced mobility of the median nerve within the carpal tunnel. We must also consider the patients undergoing surgery of carpal tunnel syndrome who develop pain and hypoesthesia. These symptoms after the surgical procedure could be related not only to na incomplete section of flexors retinaculum or fibrous adhesion to the median nerve, but also the compression or the palmar cutaneous nerve injury.

FCRT PCB median nerve FCRT median nerve palmaris longus t In an ultrasound, on the axial plane, the nerve is visualized as a rounded hypoechoic fascicle with a diameter of 0.8 to 1.0 mm, between the median nerve and the flexor carpi radialis tendon. FCRT median nerve

Median nerve This patient had a history of carpal tunnel syndrome. The median nerve was thickened and hypoechoic. The palmar cutaneous branch shows a normal appearance.

median nerve median nerve In this other case, besides the changes observed in the median nerve, we notice a great focal thickening of the palmar cutaneous branch, in both axial and longitudinal planes of the volar aspect of the wrist. median nerve

Post-Operative - Carpal Tunnel Syndrome Besides assisting in the diagnosis of carpal tunnel syndrome, ultrasonography has also been used in cases of a failure in surgical treatment. In these cases, fibrosis at the surgical site may determine adhesion or even new compression on the median nerve.

Post-Operative - Carpal Tunnel Syndrome In these images fibrosis is seen as hypoechoic nodules adhered to the median nerve. In another patient, fibrosis compresses the nerve, which appears hypoechoic and thin.

median nerve median nerve In this case, 7 months after the surgery, the patient continues with paresthesia in the thenar region. In an ultrasound, in the distal region of the forearm, the palmar cutaneous branch appears with its usual aspect, surrounded by fat tissue. In the proximal carpal tunnel, we observed blurring of nerve contours due to fibrosis surrounding it, responsible for maintaining the symptoms of the patient. median nerve

CONCLUSION Ultrasound in Carpal Tunnel Syndrome The method doesn’t predict severity. useful as a screening test, reducing the cost of diagnosis of carpal tunnel syndrome. post-operative evaluation. So, in conclusion   ultrasonography despite not predicting severity, can be useful as a screening test by reducing the cost of diagnosis of carpal tunnel syndrome, therefore avoiding the use of electromyography in many borderline cases. we have also observed that ultrasound has shown to be valuable in determining the cause in many cases of operated patients who show poor results, especially when fibrosis is present.

rasernik@uol.com.br Thank you ladies and gentlemen for your attention. If you have any questions at this point,please feel free to ask. rasernik@uol.com.br