57-year-old female with hand and wrist symptoms suggestive of median nerve compression. Symptoms may include nocturnal paresthesia, numbness or pain in digits 1–3 and the radial side of digit 4, reduced fine motor function, grip weakness, or thenar symptoms. Symptom duration and severity are not provided.
Ultrasound examination demonstrates swelling of the median nerve at the level of the proximal carpal tunnel. The median nerve is clearly hypoechoic and has a cross-sectional area of 15 mm².
At the level of the pronator quadratus muscle, the cross-sectional area of the median nerve measures 9 mm². This results in a delta-CSA of 6 mm². The clearly increased difference in cross-sectional area between the carpal tunnel and the proximal reference level supports the diagnosis of carpal tunnel syndrome.
The site of compression appears to be located predominantly in the distal part of the carpal tunnel. No clear underlying secondary cause is identified. There is no space-occupying lesion, relevant flexor tendon tenosynovitis, or other local compressive structure.
Doppler examination demonstrates no intraneural or perineural neovascularization.
1. Final diagnosis
Primary carpal tunnel syndrome with clear swelling and hypoechogenicity of the median nerve at the level of the carpal tunnel. The delta-CSA between the proximal carpal tunnel and the pronator quadratus reference level measures 6 mm² and is pathologically increased. There is no intraneural neovascularization or identifiable secondary compressive cause.
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 median nerve irritation, diabetes-related or other polyneuropathy, cervical radicular irritation, and proximal median neuropathy such as pronator teres syndrome. Given the focal swelling and hypoechogenicity of the median nerve within the carpal tunnel, carpal tunnel syndrome is the most likely diagnosis.
3. Teaching points
Ultrasound assessment of suspected carpal tunnel syndrome should include evaluation of median nerve size and echotexture and comparison with a proximal reference level. The delta-CSA is calculated by subtracting the proximal median nerve cross-sectional area from the cross-sectional area at the carpal tunnel. In this case, the increase from 9 mm² at the pronator quadratus level to 15 mm² at the carpal tunnel results in a pathological delta-CSA of 6 mm². Ultrasound can also help identify secondary causes of nerve compression, such as tenosynovitis or space-occupying lesions.
4. Injury/disease information
Carpal tunnel syndrome is a compressive neuropathy of the median nerve at the wrist. Typical symptoms include nocturnal paresthesia, numbness or pain in the median nerve distribution, impaired fine motor function, and, in more advanced cases, weakness or thenar muscle atrophy. Ultrasound can demonstrate focal nerve swelling, hypoechogenicity, and caliber change and can assess for possible secondary causes. Clinical examination and, when indicated, nerve conduction studies or EMG can help determine disease severity and guide 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.
More Cases from Marc Schmitz
