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Background and Aims Locating subclavian artery (SCA) serves as an important landmark while scanning for ultrasound (US) guided supraclavicular brachial plexus block (BPB). We report a case where the SCA was not visualized in its typical position in the supraclavicular fossa during a supraclavicular BPB.

Methods A young patient was posted for fixation of distal humerus fracture. While performing scout scanning, we could identify the ‘bunch of grapes’ above the midpoint of clavicle, but the SCA was notably absent in its usual proximity. Upon medial scanning, two arteries were discerned, out of which one was identified as the carotid artery (CA) based on its association with the internal jugular vein (Figure–1a). To elucidate the course of the SCA, the infraclavicular area was scanned with the US probe aligned parallel to the clavicle, which showed SCA in its expected position. Tracing the course above the clavicle revealed that the second artery located close to the CA was the SCA. Despite the absence of the typical ‘corner pocket’ appearance, the lower trunk was successfully identified and blocked.

Results Magnetic resonance imaging (MRI) of the neck showed that the SCA was lying anterior to the anterior scalene muscle (ASM) (Image–1b). The reported incidence of SCA passing in front of the ASM is less than 1% in adults, primarily attributed to a dorsal shift in the insertion of the ASM over the 1st rib.[1,2]

Conclusions In such scenarios, it is important to identify neural targets based on their intrinsic course rather than relying solely on surrogate landmarks.

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Abstract P007 Figure 1

1A Ultrasound image of the BP in the supraclavicular fossa. Note the medial location of the SCA than its usual position. 1B: MRI of the neck showing location of the SCA anterior to the ASM Abbreviations: BP – Brachial Plexus; SCA – Subclavian Artery; ASM – Anterior Scalene Muscle; MSM – Middle Scalene Muscle