54-year-old female with an approximately 10-year history of symptoms compatible with median nerve irritation and carpal tunnel syndrome affecting the right hand. Symptoms are severe, with persistent paraesthesia and a reported VAS score of 9–10. Multiple previous corticosteroid injections have been performed for carpal tunnel syndrome, without sustained resolution of symptoms.
Ultrasound examination demonstrates marked focal enlargement of the median nerve at the carpal tunnel.
The cross-sectional area of the median nerve within the carpal tunnel measures 25 mm².
Proximal to the carpal tunnel, at the level of the pronator quadratus muscle, the median nerve cross-sectional area measures 6 mm².
This represents an increase of 19 mm² between the proximal reference level and the carpal tunnel, indicating very pronounced focal enlargement of the median nerve.
In combination with the longstanding typical symptoms, the sonographic findings are strongly compatible with significant median nerve entrapment within the carpal tunnel.
1. Final diagnosis
Pronounced focal enlargement of the median nerve within the carpal tunnel, with a cross-sectional area of 25 mm² compared with 6 mm² proximally and an absolute difference of 19 mm². In the context of approximately 10 years of severe persistent paraesthesia and previous treatment for carpal tunnel syndrome, the findings are strongly compatible with pronounced carpal tunnel syndrome.
2. Differential diagnosis
The clinical history and marked focal median nerve enlargement strongly support carpal tunnel syndrome as the primary diagnosis. If symptoms extend beyond the expected median nerve distribution or if more proximal neurological symptoms are present, additional neurological causes such as cervical radiculopathy or more proximal median neuropathy should be considered. Clinical neurological correlation and, when necessary, electrodiagnostic assessment can help identify additional or overlapping pathology.
3. Teaching points
Ultrasound assessment of carpal tunnel syndrome can include measurement of the median nerve cross-sectional area within the carpal tunnel and comparison with a proximal reference measurement. In this case, the combination of a CSA of 25 mm² at the carpal tunnel and 6 mm² at the level of the pronator quadratus demonstrates marked focal nerve enlargement. A large proximal-to-distal difference reinforces the anatomical localisation of the abnormality to the carpal tunnel. Ultrasound findings should nevertheless be interpreted together with the clinical history and neurological examination.
4. Injury/disease information
Carpal tunnel syndrome results from compression of the median nerve within the carpal tunnel. Longstanding compression may lead to persistent sensory symptoms and, in more advanced disease, motor dysfunction and thenar weakness. In patients with severe persistent symptoms despite previous conservative treatment, specialist assessment may be appropriate to discuss decompressive treatment.
Treatment options may include conventional open carpal tunnel release, endoscopic release, and, where appropriate expertise is available and anatomy is suitable, minimally invasive ultrasound-guided carpal tunnel release. Given the longstanding symptoms and lack of durable benefit from multiple previous injections, repeated corticosteroid injection is less likely to provide a definitive long-term solution.
If uncertainty remains regarding the localisation or severity of the neuropathy, or if there is concern for additional proximal neurological pathology, neurological examination and electrodiagnostic testing with EMG and nerve conduction studies may provide complementary information before intervention.
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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