Saturday, June 15, 2024
HomeRadiologyCarpal Tunnel Syndrome Imaging

Carpal Tunnel Syndrome Imaging

Practice Essentials

Carpal tunnel syndrome (CTS) is the most common peripheral compressive neuropathy, accounting for 90% of all compressive neuropathies.
It is defined as the impairment of motor and/or sensory function of the median nerve as it traverses through the carpal tunnel. (See the images below.) It is caused either by intrinsic swelling of the median nerve or by extrinsic compression of the median nerve by one of the many surrounding structures of the wrist.

Carpal tunnel syndrome. Carpal and Guyon tunnels.

Carpal tunnel syndrome. Carpal and Guyon tunnels. Drawing showing the proximal level of the carpal tunnel delimited by the pisiform (P) and the scaphoid (S). The flexor retinaculum (medium gray region) forms the roof of the carpal tunnel and the floor of the Guyon tunnel. The palmar carpal ligament (dark gray region) forms the volar boundary of the Guyon tunnel. * = flexor pollicis longus tendon, * = flexor carpi radialis tendon. From Martinoli C, Bianchi S, et al. US of nerve entrapments in osteofibrous tunnels of the upper and lower limbs. Radiographics 2000; 20:S199-S217. Used by permission of the authors and RSNA.

View Media Gallery

Carpal tunnel syndrome. Carpal and Guyon tunnels.

Carpal tunnel syndrome. Carpal and Guyon tunnels. Drawing showing the distal level of the carpal tunnel delimited by the hook of the hamate (H) and the tubercle of the trapezium (T). The flexor retinaculum (medium gray region) forms the roof of the carpal tunnel. From Martinoli C, Bianchi S, et al. US of nerve entrapments in osteofibrous tunnels of the upper and lower limbs. Radiographics 2000; 20:S199-S217. Used by permission of the authors and RSNA.

View Media Gallery

Carpal tunnel syndrome. Axial fast spin-echo T2-we

Carpal tunnel syndrome. Axial fast spin-echo T2-weighted MRI with fat saturation. Note the increased T2-weighted signal within the median nerve (arrow). A slightly increased cross sectional area of the nerve is noted but the nerve architecture is preserved, consistent with early or mild inflammation.

View Media Gallery

Preferred examination

Electrodiagnostic tests such as electromyography (EMG) and nerve conduction studies are 85-90% accurate in patients with carpal tunnel syndrome, with a false-negative rate of 10-25%, especially for early CTS; results may be normal in up to one third of patients with mild CTS.
Therefore, in cases of clinically symptomatic carpal tunnel syndrome with normal EMG and conduction findings, radiology studies can have a strong complementary role in diagnosis.

Of radiologic imaging methods, magnetic resonance imaging (MRI) has consistently shown the greatest sensitivity and specificity in the diagnosis and evaluation of carpal tunnel syndrome.
 Advances in ultrasonography (US) have improved its image quality as well as affordability, leading to an increased adaptation of US evaluation of CTS.
 Ultrasonography can be useful in the evaluation of soft tissues of the carpal tunnel and the median nerve. An increasing number of studies have supported early suggestions that measurement of the cross-sectional area and morphology of the median nerve with high-resolution sonography compares favorably with physical examination alone. Additionally, ultrasound may prove to be a beneficial adjunct in the conservative treatment of carpal tunnel syndrome.

Plain radiographs have no role in the evaluation of carpal tunnel syndrome except for their ability to show the anatomic relationship of the carpal bones and evidence of severe prior trauma or fractures. Helical computed tomography (CT) scanning is more sensitive than plain radiography in revealing subtle bony trauma and misalignments and can be used to measure the cross-sectional area of the carpal tunnel.

Limitations of techniques

Plain radiographs usually do not reveal ligamentous or soft tissue abnormalities but may be useful to exclude frank fractures or chronic degenerative/posttraumatic morphologic abnormalities.

CT scanning does not reveal ligamentous or soft tissue abnormalities to any degree. Axial scanners are even more limited, since they do not allow adequate multiplanar or 3-dimensional (3D) reconstructions.

Ultrasonography is operator and equipment dependent. Although musculoskeletal ultrasonography using high-frequency transducers is widely used in Europe, familiarity with and training in the performance and interpretation of carpal tunnel ultrasonography is still variable, more so in the United States.

High-frequency gray scale ultrasonography (US) can clearly show the median nerve (MN) and surrounding structures, which provides valuable information for clinical treatment. Generally, an increased nerve cross-sectional area (CSA) is the main objective criterion for diagnosis of CTS on US. However, the cut-off value for CSA varies among published reports from 8.5 to 15 mm2, and the uncertainty of the diagnosis criterion affects its value. In addition, sensitivity is low for diagnosis using CSA alone.

MRI is useful for the evaluation of all of the intrinsic structures of the wrist (including the carpal bones) but may not be widely available, is technique and equipment dependent, can require up to 45 minutes to complete an examination, and has a number of contraindications (eg, cardiac pacemakers, older aneurysm clips, new stents or aortic valves, ferromagnetic ocular fragments).

Differential diagnosis

A number of clinical processes can create symptoms similar to carpal tunnel syndrome, originating more proximally in the neural pathway of the median nerve. These include multiple sclerosis, cervical radiculopathy, Pancoast tumor, brachial plexitis or brachial plexopathy, pronator syndrome, ulnar or radial neuropathy, generalized neuropathy, and median nerve contusion.

Although the appearance of carpal tunnel syndrome is fairly distinctive on MRI, differential possibilities include contusion and lipofibromatous hamartoma of the median nerve. A clinical history of recent trauma or a longstanding mass often allows the exclusion or inclusion of these etiologies in the differential.

Previous articleNightmare Disorder
Next articlePetrosal Sinus Sampling
RELATED ARTICLES
- Advertisment -

Most Popular