A Rare Coexistence of Arteria Lusoria, Truncus Bicaroticus, and Klippel-Feil Syndrome: A Five-Year Follow-Up and Procedural Considerations.

Arteria lusoria, an aberrant right subclavian artery (ARSA) arising as the most distal branch of the aortic arch, is the most common congenital aortic arch anomaly, yet it is clinically silent in over 90% of individuals and is usually discovered incidentally. We report the incidental identification of ARSA together with a truncus bicaroticus and Klippel-Feil syndrome (KFS) in a 32-year-old man investigated for intermittent pretracheal pressure. Contrast-enhanced MRI of the neck demonstrated a retro-oesophageal ARSA with mild oesophageal compression and revealed congenital fusion of the C2-C3 and C6-C7 vertebrae, consistent with KFS, together with suspected canal stenosis at C4-C5. Thoracic MR angiography confirmed ARSA with proximal ectasia at its origin, absence of a Kommerell's diverticulum (KD), and a truncus bicaroticus, alongside congenital right-sided latissimus dorsi and serratus anterior atrophy. Serial MR angiography over five years demonstrated no significant interval progression, and a conservative surveillance strategy was adopted in line with current guidelines. The coexistence of ARSA, truncus bicaroticus, and KFS in this patient raises the possibility of a shared developmental basis. Previously described embryological mechanisms, including the subclavian artery supply disruption sequence (SASDS), provide a plausible framework linking abnormalities of pharyngeal arch development and cervical somite segmentation during weeks 4-8 of gestation; however, such a relationship cannot be established from a single case. Beyond surveillance, the principal clinical message is procedural: unrecognised ARSA carries potentially avoidable risks during right transradial catheterisation, thyroid and anterior cervical surgery (through its association with a non-recurrent laryngeal nerve), and oesophageal, mediastinal, and thoracic procedures. Recognition of one component of this constellation may therefore warrant consideration of associated congenital anomalies and targeted vascular imaging, particularly when invasive cardiac, cervical, or thoracic procedures are planned.