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Ultrasonography of the ulnar nerve loop in relation to the flexor carpi ulnaris tendon

Marco Becciolini

Marco Becciolini

  • Department of Ultrasound, Misericordia di PistoiaPistoia, Italy
  • Scuola Siumb di Ecografia Muscolo-ScheletricaPisa, Italy
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Becciolini, Marco
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Christopher Pivec

Christopher Pivec

Department of Ultrasound, PUC – Private Ultrasound Center ViennaVienna, Austria
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Georg Riegler

Georg Riegler

  • Department of Ultrasound, PUC – Private Ultrasound Center GrazLassnitzhoehe, Austria
  • Department of Biomedical Imaging and Image-Guided Therapy, Medical University ViennaVienna, Austria
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Riegler, Georg
  
30 nov 2024
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Categoria dell'articolo: Research Paper
Pubblicato online: 30 nov 2024
Pagine: 1 - 5
Ricevuto: 24 dic 2023
Accettato: 13 feb 2023
DOI: https://doi.org/10.15557/jou.2024.0027
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© 2024 Marco Becciolini1 et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1.

Case 1. A–C. Axial sonograms from proximal (A) to distal (C) at the distal third of the forearm and wrist in a patient with paresthesia of the 4th and 5th fingers. In A, the UN is indicated by the white arrow. An aberrant branch (white arrowhead) had detached from the DCBUN (open arrowhead). The FCU is composed of two tendons (1, 2). B. At the entrance of the Guyon’s canal, the aberrant branch (black arrowhead) is thickened between the proximal pole of the pisiform bone (PIS) and the two tendons of the FCU. In C, slightly distal, the branch forms a loop (curved dotted arrow) over the radial tendon of the FCU (2) to rejoin the UN. D. Correspondent long-axis of the aberrant branch, clearly confirming its thickening. E. Schematic CT-3D drawing of the variant. Probe position of the axial images is indicated. CDN 4th indicates the common digital nerve of the 4th space; DBUN – deep branch of the ulnar nerve; fcum – flexor carpi ulnaris muscle; PDN 5th – proper digital nerve of the little finger; pq – pronator quadratus; ua – ulnar artery; v – vein
Case 1. A–C. Axial sonograms from proximal (A) to distal (C) at the distal third of the forearm and wrist in a patient with paresthesia of the 4th and 5th fingers. In A, the UN is indicated by the white arrow. An aberrant branch (white arrowhead) had detached from the DCBUN (open arrowhead). The FCU is composed of two tendons (1, 2). B. At the entrance of the Guyon’s canal, the aberrant branch (black arrowhead) is thickened between the proximal pole of the pisiform bone (PIS) and the two tendons of the FCU. In C, slightly distal, the branch forms a loop (curved dotted arrow) over the radial tendon of the FCU (2) to rejoin the UN. D. Correspondent long-axis of the aberrant branch, clearly confirming its thickening. E. Schematic CT-3D drawing of the variant. Probe position of the axial images is indicated. CDN 4th indicates the common digital nerve of the 4th space; DBUN – deep branch of the ulnar nerve; fcum – flexor carpi ulnaris muscle; PDN 5th – proper digital nerve of the little finger; pq – pronator quadratus; ua – ulnar artery; v – vein

Fig. 2.

Case 3. Patient with bilateral symptomatic variant, similar to Case 1. Note the details with a 6–24 MHz hockey-stick transducer (A–C) and latest-generation US machine. A–B. Axial sonograms from proximal (A) to distal (B) at the entrance of the Guyon’s canal. In A, the aberrant branch (ab, indicated also by the black arrowhead) is thickened between the proximal pisiform bone and the two tendons (1,2) of the FCU. In B, slightly distal the aberrant branch rejoins the UN. Note anisotropy of the radial FCU tendon (2), which appears hypoechoic. C. Longitudinal Color Doppler sonogram confirms the non-vascular nature of the aberrant branch, thickened and hypoechoic, which distinguishes it from a small vessel (a). The course of the branch is indicated by the curved dotted arrow. D. Corresponding longitudinal sonogram obtained with a 6–15 MHz transducer. The variant is clearly easier to visualize in C than in D due to the superior quality of the hockey stick when evaluating superficial structures, related to its higher frequency. Fcum indicates the flexor carpi ulnaris muscle; tcl, transverse carpal ligament; ua, ulnar artery
Case 3. Patient with bilateral symptomatic variant, similar to Case 1. Note the details with a 6–24 MHz hockey-stick transducer (A–C) and latest-generation US machine. A–B. Axial sonograms from proximal (A) to distal (B) at the entrance of the Guyon’s canal. In A, the aberrant branch (ab, indicated also by the black arrowhead) is thickened between the proximal pisiform bone and the two tendons (1,2) of the FCU. In B, slightly distal the aberrant branch rejoins the UN. Note anisotropy of the radial FCU tendon (2), which appears hypoechoic. C. Longitudinal Color Doppler sonogram confirms the non-vascular nature of the aberrant branch, thickened and hypoechoic, which distinguishes it from a small vessel (a). The course of the branch is indicated by the curved dotted arrow. D. Corresponding longitudinal sonogram obtained with a 6–15 MHz transducer. The variant is clearly easier to visualize in C than in D due to the superior quality of the hockey stick when evaluating superficial structures, related to its higher frequency. Fcum indicates the flexor carpi ulnaris muscle; tcl, transverse carpal ligament; ua, ulnar artery

Fig. 3.

Case 6. Incidental asymptomatic variant. A. Axial sonogram at the distal forearm. The DCBUN (white arrowhead) forms a loop (small gray arrow) around an accessory tendon of the FCU (afcu). B. Sagittal sonogram demonstrates the small branch passing deep and over to the small accessory tendon due to its loop course. C. Schematic CT-3D drawing of the variant. The FCU is transparent to better show the relationship of the DCBUN with the accessory tendon. Position of the transducer in A is indicated. Fcum indicates the flexor carpi ulnaris muscle; fcut – flexor carpi ulnaris tendon; ua – ulnar artery
Case 6. Incidental asymptomatic variant. A. Axial sonogram at the distal forearm. The DCBUN (white arrowhead) forms a loop (small gray arrow) around an accessory tendon of the FCU (afcu). B. Sagittal sonogram demonstrates the small branch passing deep and over to the small accessory tendon due to its loop course. C. Schematic CT-3D drawing of the variant. The FCU is transparent to better show the relationship of the DCBUN with the accessory tendon. Position of the transducer in A is indicated. Fcum indicates the flexor carpi ulnaris muscle; fcut – flexor carpi ulnaris tendon; ua – ulnar artery

Demographic characteristics, description of the variant found, whether it was associated with nerve entrapment-related symptoms

Case side Age Sex UN variation Symptoms Bmax / Bprox ratio
1 Right 55 M A small branch detaches from the DCBUN to proceed parallel to the UN, and just proximal to the pisiform passes through a bifid FCU, rejoining the UN at the proximal Guyon’s canal Yes 2.7 / 0.5 mm 5.4
2 Right 70 F The aberrant branch detaches from the UN at the level of the usual DCBUN origin to follow a course similar to that of case 1. DCBUN is absent No 0.9 / 0.6 mm 1.5
3 (bilateral) Left 48 M Similar to case 1 Yes 2.6 / 0.7 mm 3.7
4 (bilateral) Right 48 M Similar to case 1 Yes 3 / 0.7 mm 4.3
5 Left 37 M A small branch detaches from the UN just before the pisiform to pass through a bifid FCU, and then rejoins the UN at the proximal Guyon’s canal No 0.9 / 0.7 mm 1.3
6 Right 51 F DCBUN forming a loop around an accessory, deeply located small FCU tendon No 0.6 / 0.3 mm 2
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