Thoracic outlet syndrome (TOS) represents a complex neurovascular compression disorder with varied clinical presentations. This study investigates the relationship between anatomical variations of the brachial plexus and the development of TOS through morphometric analysis. We conducted a prospective study of 128 patients (76 with confirmed TOS and 52 controls) who underwent high-resolution MRI neurography. Morphometric analysis revealed significant differences in brachial plexus configuration between TOS patients and controls, with higher prevalence of prefixed plexus (21.1% vs 7.7%, p<0.01) and supraclavicular branching variations (37.5% vs 13.5%, p<0.001). Abnormal scalene muscle attachments were observed in 63.2% of TOS patients versus 19.2% of controls (p<0.001). Quantitative measurements showed reduced interscalene triangle areas (mean difference: 27.4 mm², p<0.01) and increased neural angulation at compression points in TOS patients. Surgical outcomes in 48 patients demonstrated that preoperative identification of anatomical variants significantly improved symptom resolution rates (88.5% vs 63.6%, p<0.05). This research establishes specific brachial plexus variations as independent risk factors for TOS development and highlights the importance of detailed preoperative anatomical assessment for surgical planning. Recognition of these variations can guide targeted surgical decompression strategies and improve clinical outcomes.