Purpose

To assess the potential correlation of the rectus capitis posterior minor muscle and nuchal ligament, two components of myodural bridge via suboccipital zone using 3D MR imaging.

Introduction

Previous literature revealed the existence of some fibrous fascial tissue bridges extending from the suboccipital structures to the cervical dura mater, which is named as myodural bridges. The RCPmi was the first reported component of MDB. Additionally, NL had been shown to attach to the cervical dura mater. Whether these two structures work collectively or independently is unknown. A previous study showed some muscular or fibrous tissues from RCPmi terminated into NL. In anatomical MR images, fibrous or muscular tissues were identified as low signal intensity band, and a potential correlation may exist connecting them. The current study aimed to identify whether the RCPmi and NL form a complex composition in the MDB in vivo.

Materials and Methods

This retrospective study was approved by the institutional review board and the informed consent was waived. Three hundred and twenty subjects underwent 3D T₂WI CUBE MR imaging of the suboccipital muscles and NL. Sagittal T₂ CUBE MR imaging sequences (TR: 2500ms; TE: 70 ms; slice thickness: 0.6 mm) were obtained on a 1.5 T or 3.0 T MRI scanner (GE Signa HDxt, USA) with a spinal phase-array coil. The parasagittal reformatted images of the RCPmi and NL were analyzed using the Functool post-processing software equipped on the Advantage Workstation (GE, AW4.6, USA). Thereafter, the subjects were classified into positive and negative groups according to connection observed between RCPmi and NL. The positive group indicated hypo-intense band or strip from RCPmi to NL while the negative group demonstrated no connection between them (Figure 1). The major axis of cross-sectional area (maCSA) of left and right RCPmi was measured with a 30°deviation from the oblique plane that passed through the mid-posterior arch of atlas (Figure 2). The body mass index (BMI) and gender distributions in these two groups were compared with Spearman analysis. Two experienced radiologists measured all the maCSAs separately and the inter-examiner agreement was tested by means of the repeated measures ANOVA intraclass correlation coefficient (ICC). The differences of maCSAs between positive and negative groups were compared using the paired Student’s t-test. A P-value＜0.05 was considered to be statistically significant.

Results and discussion

A total of 624 RCPmis were observed in 316 subjects with 311 on the left side and 313 on the right side. Hypo-intense bands or strips from RCPmis to NLs were identified in positive group including 123 RCPmis with 61 on the left side and 62 on the right side. There were 501 RCPmis in negative group. Representative images of the positive and negative groups are shown in Fig.1. The BMI and gender showed no correlation between these two groups (r=0.053, 0.045). The inter-examiner repeatability of MRI measurements (ICC) for RCPmis’ maCSA were 0.891, suggesting a good agreement. The measurement method is shown in fig.2. The mean maCSAs of positive group was significantly smaller than that of negative group (55.95±26.76 mm² vs. 64.78±30.07 mm², P=0.003) .

Conclusions

The current study indicated that RCPmi connected with NL by hypo-intense fibrous or muscular tissue correlating with smaller RCPmis. This may indicate that RCPmi and NL work together as a myodural bridge complex.

Acknowledgements

The authors wish to acknowledge the department of radiology and Mrs. Xu Bin, Ms. Libao and Ms. Li Si-yao for their contribution to this work.