RESUMEN
CASE: We reported a dynamic neurogenic left thoracic outlet syndrome (TOS) with a permanent abduction of the fifth left finger. Preoperative magnetic resonance imaging (MRI) assessed the presence of subclavius posticus muscle (SPM). Because of a nonoperative treatment failure, we performed a brachial plexus neurolysis and SPM resection. Immediate postoperative assessment showed an immediate disappearance of the Wartenberg sign. CONCLUSION: SPM constitutes an underestimated cause of TOS. A careful MRI reading is necessary to make correct diagnosis. Nonoperative treatment includes physiotherapy and can be proposed in first instance. When nonoperative treatment fails, brachial plexus exploration with release of the SPM may result in resolution of symptoms.