Quantitative 0.55 T MRI of the Infraclavicular Brachial Plexus: Topography and Neurovascular Morphometry Relevant to Infraclavicular Block

Background/Objectives: Quantitative MRI data describing the infraclavicular brachial plexus cords together with both axillary vessels remain limited. This study characterized artery-centered cord topography and neurovascular morphometry on 0.55 T MRI and discussed the potential anatomical implications for infraclavicular block. Methods: This prospective cross-sectional imaging study included 100 adults undergoing clinically indicated MRI. One infraclavicular region was analyzed per participant. Within the mid-infraclavicular retropectoral region posterior to the pectoralis minor muscle, the axial T1-weighted image providing the clearest simultaneous visualization of the lateral cord (LC), medial cord (MC), posterior cord (PC), axillary artery (AA), and axillary vein (AV) was selected. The LC, MC, PC, and AV were mapped using a 12-sector clock-face model centered on the AA, and center-to-center intercord, cord-to-AA, and cord-to-AV distances were measured. Results: The LC was most frequently located at 11 o’clock (62%), the MC at 3 o’clock (41%), the PC at 6 o’clock (40%), and the AV at 2 o’clock (71.1%; n = 90). Mean intercord distances were 11.73 ± 3.17 mm (LC-MC), 11.09 ± 2.43 mm (LC-PC), and 8.13 ± 2.83 mm (MC-PC). Mean cord-to-AA distances were 6.33 ± 1.69, 7.36 ± 2.03, and 7.13 ± 1.83 mm for LC, MC, and PC, respectively. In 92 participants with complete cord-to-AV measurements, corresponding means were 17.01 ± 5.01, 9.61 ± 2.90, and 16.54 ± 3.87 mm. Conclusions: At the mid-infraclavicular retropectoral level, 0.55 T MRI demonstrated a structured but non-equidistant neurovascular arrangement. These imaging-derived data provide quantitative anatomical reference information but are not procedural safety margins or predictors of block success.