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

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

Journal of Ultrasonography
Volume 24 (2024): Issue 98 (September 2024)
By: Marco Becciolini,  Christopher Pivec and  Georg Riegler  
Open Access
|Nov 2024

Figures & Tables

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 sideAgeSexUN variationSymptomsBmax / Bprox ratio
1 Right55MA 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 canalYes2.7 / 0.5 mm 5.4
2 Right70FThe 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 absentNo0.9 / 0.6 mm 1.5
3 (bilateral) Left48MSimilar to case 1Yes2.6 / 0.7 mm 3.7
4 (bilateral) Right48MSimilar to case 1Yes3 / 0.7 mm 4.3
5 Left37MA 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 canalNo0.9 / 0.7 mm 1.3
6 Right51FDCBUN forming a loop around an accessory, deeply located small FCU tendonNo0.6 / 0.3 mm 2
DOI: https://doi.org/10.15557/jou.2024.0027 | Journal eISSN: 2451-070X | Journal ISSN: 2084-8404
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Language: English
Page range: 1 - 5
Submitted on: Dec 24, 2023
|
Accepted on: Feb 13, 2023
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Published on: Nov 30, 2024
Published by: MEDICAL COMMUNICATIONS Sp. z o.o.
In partnership with: Paradigm Publishing Services
Publication frequency: 4 issues per year
Keywords:
neuropathy,
variant,
loop,
ulnar nerve,
flexor carpi ulnaris
Related subjects:
Medicine,
Basic medical science,
Basic medical science, other

© 2024 Marco Becciolini, Christopher Pivec, Georg Riegler, published by MEDICAL COMMUNICATIONS Sp. z o.o.
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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