A 56-year-old female presented with left medial elbow symptoms and ulnar-sided paraesthesia/numbness. Symptoms had been present for 6 months.
Ultrasound examination demonstrates enlargement of the ulnar nerve within the cubital tunnel.
At the level of maximal swelling, the nerve measures approximately 3.26 mm in thickness. The cross-sectional area is approximately 0.21 cm², corresponding to 21 mm², indicating marked nerve enlargement.
Immediately distal to this segment, there is focal reduction in nerve calibre, with a thickness of approximately 1.96 mm. The abrupt transition from proximal nerve enlargement to distal narrowing produces a sonographic notch-like appearance and suggests a focal site of entrapment.
The enlarged segment of the ulnar nerve is hypoechoic and demonstrates reduced visibility of the normal internal fascicular pattern, consistent with neuropathic change.
The combination of increased cross-sectional area, hypoechogenicity, loss of normal fascicular architecture and focal calibre change is compatible with ulnar neuropathy at the cubital tunnel.
1. Final diagnosis
Sonographic findings consistent with ulnar neuropathy at the cubital tunnel, with marked enlargement of the ulnar nerve to a cross-sectional area of approximately 21 mm². Focal calibre reduction immediately distal to the swollen segment produces a notch sign, supporting localised nerve entrapment.
2. Differential diagnosis
The findings primarily support compressive ulnar neuropathy at the cubital tunnel. In an atypical clinical setting, other causes of focal ulnar nerve enlargement should be considered, including inflammatory neuropathy, post-traumatic change or an adjacent space-occupying lesion. Correlation with the complete ultrasound examination is important to exclude an extrinsic compressive cause.
3. Teaching points
Ultrasound assessment of suspected cubital tunnel syndrome should include measurement of the ulnar nerve cross-sectional area as well as evaluation of echogenicity and fascicular architecture. A markedly enlarged, hypoechoic nerve with reduced fascicular definition supports neuropathy. Abrupt calibre change at the site of compression, with swelling proximal to a narrowed segment, may produce a characteristic notch sign and can help localise the entrapment.
4. Injury/disease information
Cubital tunnel syndrome is a compressive neuropathy of the ulnar nerve around the medial elbow. Chronic or repetitive compression can result in intraneural oedema, nerve enlargement, hypoechogenicity and progressive loss of the normal fascicular appearance. Dynamic ultrasound may additionally assess ulnar nerve mobility or subluxation during elbow flexion when clinically relevant. Electrodiagnostic testing can complement ultrasound by assessing the physiological severity and distribution of the neuropathy.
5. Reference values
Ultrasound evaluation of the ulnar nerve at the elbow is commonly based on measurement of the cross-sectional area (CSA). In healthy individuals, the CSA at the level of the cubital tunnel is generally in the range of approximately 6–9 mm², while a value exceeding approximately 10 mm² is widely regarded as suggestive of pathological nerve enlargement. In this case, the ulnar nerve CSA measures 21 mm² (0.21 cm²), representing marked enlargement. In combination with the focal calibre change, hypoechoic appearance and reduced fascicular definition, this strongly supports the sonographic diagnosis of ulnar neuropathy at the cubital tunnel.
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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