The clinical significance of bifid median nerve. Evaluation with ultrasonography

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1 The clinical significance of bifid median nerve. Evaluation with ultrasonography Poster No.: C-3364 Congress: ECR 2010 Type: Topic: Scientific Exhibit Musculoskeletal Authors: D. Papoutsi, E. Andipa, A. Karatasiou, A. Tsikkini, C. Kominis, M. Tsouroulas; Athens/GR Keywords: DOI: carpal tunnel syndrome, bifid median nerve, median artery /ecr2010/C-3364 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 14

2 Purpose Several anatomic variations of the median nerve have been reported, some of which are of surgical or clinical importance [1, 2, 3]. The early proximal division of the median nerve in the forearm, before its entrance to the carpal tunnel described as Group 3 in Lanz's study [4], is called bifid MN. The purpose of this study is to evaluate the potential clinical significance of bifid MN in cases of carpal tunnel syndrome (CTS) and to define how ultrasound findings should be interpreted. Methods and Materials Our study was performed on patients with clinical evidence of CTS and on a control group. The control group consisted of 53 healthy volunteers, whose both wrists were examined. There were 32 female and 21 male, (29-62 years old) with a mean age of 48,2years. The patients were 121, consisting of 72 women and 49 men, with 214 wrists, with typical pattern of CTS symptoms, (30-77 years old) with a mean age of 52,2years. The clinical evidence of CTS included typical sensory symptoms in the median nerve distribution area and abnormal physical examination, which included Tinel's and Phalen's test, sensory testing by two-point discrimination, muscle testing and examination of thenar atrophy. All of the afore-mentioned wrists were imaged with ultrasound using a high frequency 5-17MHz linear-array transducer. The examination was performed with longitudinal and transverse scans of the wrists, evaluating morphology and size of the MN at the level of the carpal tunnel, bounded anteriorly by the flexor retinaculum, posteriorly by the capitate and laterally by the scaphoid and the pisiform (figure 1) on page 3. The wrists in which bifid MN was encountered at sonographic examination (figure 2) on page 4 underwent Electromyography (EMG), as well. Page 2 of 14

3 In transverse images of the carpal tunnel, anteroposterior and transverse dimensions of the MN trunks were measured. Using the equation of the ellipse (area=#(d1xd2)/4) [5] we evaluated the areas of each MN trunk and then summed them up in order to estimate the whole cross-sectional area of the bifid MN (figure 3) on page 5, given the importance of MN size in the diagnosis of CTS. According to Lee et al [5] the mean cross-sectional area of normal median nerve is 8.3mm 2 in men and 9.3mm 2 in woman. A cross-sectional area measurement greater than 15mm 2 correlates well with moderateto-severe CTS, whereas the in-between measurements (8.3/9.3-15mm 2 ) correlate well with normal-to-mild level [5]. The electrophysiologic criteria used for the diagnosis of CTS in this study were focused on the median distal motor latency and median sensory nerve conduction velocity across the carpal tunnel. Images for this section: Page 3 of 14

4 Fig. 1: Normal anatomy of the carpal tunnel. Axial scan. The carpal tunnel is bounded anteriorly by the flexor retinaculum, marked with yellow arrows, posteriorly and laterally by the carpal bones, mentioned at the figure.the structure surrounded by the calipers is the axial scan of the median nerve, which is demonstrated markedly enlarged (25mm2), which is compatible with severe carpal tunnel syndrome. Page 4 of 14

5 Fig. 2: Axial image of bifid median nerve within the carpal tunnel,found in a volunteer's wrist. Yellow arrows point the MN trunks. The total cross-sectional area of the two trunks (9mm2) is not indicative of carpal tunnel syndrome. Ulnar artery (U) is used as a landmark. Page 5 of 14

6 Fig. 3: Axial image of a bifid MN. Anteroposterior and transverse dimensions are measured in each trunk, in order to calculate the total cross-sectional area of the nerve (11mm2), which is indicative of mild carpal tunnel syndrome. Page 6 of 14

7 Results Three (3) wrists of the 106 of the control group (2.8%) appeared bifid MN. On the contrary bifid MN was found in 27 wrists of the 214 abnormal wrists, elevating the prevalence of the variant to 12.6% (figure 1) on page 7, (figure 2) on page 8. This increased occurrence is statistically significant (p=0.004). In one case early trifurcation of the MN took place in the carpal tunnel (figure 3) on page 9. Four of the 27 wrists (15%) presented concomitant persistent median artery (figure 4) on page 10, (figure 5) on page 11, a well established variation found in cases of bifid MN [ 1, 4, 6]. No aberrant muscle was identified ultrasonographically in association with bifid MN, in our population. In CTS patients the cross-sectional area of the bifid MN ranged from 5.2mm 2 to 23mm 2, with a mean area of 15,9mm 2, though in the control group the mean cross-sectional area was 7.6 mm 2 (ranging from 7.5 mm 2 to 7.8 mm 2 ). EMG of the 27 clinically CTS wrists with bifid MN revealed 22 cases with abnormal EMG findings (82%). Images for this section: Page 7 of 14

8 Fig. 1: Axial image of an enlarged left bifid MN at the level of pisiform, of a patient suffering from CTS. The radial trunk (yellow arrow) is markedly greater than the ulnar trunk (green arrow). The total cross-sectional area in this case was measured 23mm2, which is compatible with severe carpal tunnel syndrome. Page 8 of 14

9 Fig. 2: Axial image of a bifid median nerve (MN) at the pisiform-level. In this case the MN trunks (white arrows) are of equal size and the total cross-sectional area is 13mm2, which is indicative of mild carpal tunnel syndrome. Blue arrow points the ulnar artery. Page 9 of 14

10 Fig. 3: Axial image of a patient's carpal tunnel. Median nerve (MN) is trifurcated (yellow arrows)and it's total cross-sectional area was measured 13mm2, which is indicative of mild carpal tunnel syndrome. Page 10 of 14

11 Fig. 4: Axial image of a bifid median nerve(mn), pointed with yellow arrows, and a persistent median artery (red arrow), between the two trunks. The total cross-sectional area in this case was 11mm2, which is compatible with mild carpal tunnel syndrome. U:ulnar artery. Page 11 of 14

12 Fig. 5: Axial image of a bifid median nerve (yellow arrows). A persistent median artery with concomitant two median veins are depicted between the two nerve trunks. The total cross-sectional area of these nerves is 8.2mm2, not indicative of carpal tunnel syndrome. U:ulnar artery. Page 12 of 14

13 Conclusion Several variations of the median nerve have been reported, mainly in surgical studies, and classified, by Lanz, into four groups, including variations of the thenar branch course (group 1), accessory branches at the distal portion of the carpal tunnel (group 2), high division of the median nerve (MN) (group 3), accessory branches proximal to the carpal tunnel (group 4) [4]. After a brief review of the literature bifid MN appears with a wide range of prevalence in surgical (0.9%-3.3%) [1, 2, 4, 7] and radiology (2%-24%) [3, 8, 9, 10] studies. The median artery, when it does not regress, after the 8 th week of gestation, remains as a persistent median artery throughout the entire life. In our study the prevelance of persistent median artery in combination with bifid MN correlates well with the latest report of these two entities, studied with MRI [10]. There are few reports in the literature [3, 8, 9] to relate the presence of CTS with the area of bifid MN. We used the sum of each MN trunk area to determine the total MN size. Although it is still not known whether the size criteria for MN enlargement on sonography can be applied to bifid MN [3, 8, 9] our results comply with the diagnostic criteria for CTS [5, 11]. The total cross sectional area proved to be in accordance with EMG findings, in most of the cases, indicating the clinical significance of bifid MN, since EMG still remains the gold standard for the CTS diagnosis [5]. Patients with bifid median nerve are prone to develop carpal tunnel syndrome. The increased sum of the area of the bifid nerve is well correlated with abnormal EMG findings. Ultrasound is an ideal diagnostic technique for the study of bifid MN, an anomaly which is important to know when surgical decompression of the carpal tunnel is performed. References Page 13 of 14

14 1. Lindley SG, Kleinert JM. Prevalence of anatomic variations encountered in elective carpal tunnel release. J Hand Surg Am 2003 Sep;28(5): Tountas CP, Bihrle DM, MacDonald CJ, Bergman RA. (1987) Variations of the median nerve in the carpal canal. J Hand Surg 12(5 Pt 1): Propeck T, Quinn TJ, Jacobson JA, Paulino AFG, Habra G, Darian VB. Sonography and MR Imaging of Bifid Median Nerve with Anatomic and Histologic Correlation. AJR 2000; 175: Lanz U. Anatomical variations of the median nerve in the carpal tunnel. J Hand Surg [Am] 1977;2A: Lee D, Van Holsbeeck MT, Janevski PK, Doreen LG, Ditmars MD, Darian BV. Diagnosis of Carpal tunnel syndrome. The Radiologic Clinics of North America. Musculoskeletal ultrasound. (July 1999)37(4): Toranto IR. Aneurysm of the median artery causing recurrent carpal tunnel syndrome and anatomic review. Plast Reconstr Surg Sep;84(3): Amadio PC (1988) Anatomic variations of the median nerve within carpal tunnel. Clin Anat 1: Iannicelli E, Chianta AG, Salvini V, Almberger M, Monacelli G, Passariello R. Evaluation of bifid median nerve with sonography and MR imaging. J Ultrasound Med 2000;19: Bayrak IK, Bayrak AO, Kale M, Turker H, Diren B (2008) Bifid median nerve in patients with carpal tunnel syndrome. J Ultrasound Med 27(8): Pierre-Jerome C, Smitson Dr, Shah RK, Moncayo V, Abdelnoor M, Terk MR. MRI of the median nerve and median artery in the carpal tunnel: prevalence of their anatomical variations and clinical significance. Surg Radiol Anat. DOI /s Duncan I, Sullivan P, Lomas F. Sonography in the diagnosis of carpal tunnel syndrome. AJR 1999;173: Personal Information Page 14 of 14