54-year-old female with symptoms suggestive of right-sided median nerve compression. Clinical symptoms may include nocturnal paresthesia, tingling in digits 1–3 and the radial side of digit 4, sensory disturbance, loss of grip strength, or thenar weakness.
Ultrasound examination of the right wrist demonstrates enlargement of the median nerve at the level of the carpal tunnel. The cross-sectional area of the median nerve at this level measures 0.15 cm², corresponding to 15 mm². The nerve appears hypoechoic.
Using the protocol in which the median nerve cross-sectional area at the carpal tunnel is compared with the cross-sectional area proximally at the level of the pronator quadratus muscle, the median nerve measures 0.07 cm², corresponding to 7 mm², at the proximal reference level.
The delta cross-sectional area is therefore 8 mm². This is clearly above the commonly used threshold of approximately 2 mm² and supports the diagnosis of carpal tunnel syndrome. The transverse findings are confirmed in the longitudinal plane. Doppler examination shows no intraneural neovascularization.
1. Final diagnosis
Right-sided carpal tunnel syndrome, with clear swelling and hypoechogenicity of the median nerve at the level of the carpal tunnel. The pathological delta-CSA of 8 mm² strongly supports focal median nerve compression at the wrist.
2. Differential diagnosis
The primary diagnosis is compressive neuropathy of the median nerve at the carpal tunnel. Depending on the clinical presentation, differential diagnoses include flexor tendon tenosynovitis with secondary nerve compression, a space-occupying lesion within the carpal tunnel, diabetes-related or other polyneuropathy, cervical radiculopathy, or a proximal median neuropathy such as pronator teres syndrome. Given the clear focal swelling at the carpal tunnel, carpal tunnel syndrome is the most likely diagnosis.
3. Teaching points
Ultrasound can support the diagnosis of carpal tunnel syndrome by demonstrating focal enlargement and hypoechogenicity of the median nerve at the carpal tunnel. Comparing the median nerve cross-sectional area at the carpal tunnel with a proximal reference level, such as the pronator quadratus level, may increase diagnostic confidence. In this case, the delta-CSA of 8 mm² is clearly abnormal.
4. Injury/disease information
Carpal tunnel syndrome is caused by compression of the median nerve within the carpal tunnel. It commonly presents with nocturnal paresthesia, tingling or numbness in the median nerve distribution, hand weakness, and in more advanced cases thenar muscle involvement. Ultrasound can assess nerve swelling, echotexture, dynamic changes, and possible secondary causes such as tenosynovitis or space-occupying lesions. Clinical correlation and, when indicated, nerve conduction studies are useful for grading severity or planning further treatment.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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