Iliofemoral Venous Stenosis Complicating Large-Bore Access for Balloon Mitral Valvotomy, Unmasking Incidental May-Thurner Anatomy

BACKGROUND: Large-bore transvenous access for balloon mitral valvotomy (BMV) can be complicated by unrecognized iliofemoral venous disease, occasionally unmasking a congenital variant. CASE SUMMARY: A 51-year-old woman with rheumatic mitral stenosis and NYHA functional class III-IV dyspnea, on acenocoumarol for atrial fibrillation, was scheduled for BMV. After right femoral venous access and transseptal puncture, hardware >8-F could not be advanced; venography showed a tight, recoiling right external iliac vein stenosis, not responding to intravenous nitroglycerine, treated with angioplasty and stenting, and BMV was deferred. Computed tomography venogram 14 days later confirmed stent patency and incidentally revealed left common iliac vein compression by the right common iliac artery, consistent with asymptomatic May-Thurner anatomy rather than syndrome. Acenocoumarol was continued after stenting, held 3 days before reattempt, and BMV was then completed successfully via the same route. DISCUSSION: Comprehensive venous evaluation during difficult large-bore access can uncover clinically silent iliocaval anatomic variants and guide individualized, staged management.