Sinotubular junction
STJ · PLAX, end-diastole, leading-edge to leading-edge, at the ridge where sinuses meet tubular aorta
Normal range & thresholds
Men 29 ± 3 mm · Women 26 ± 3 mm.[1] Normally the STJ is 10–15% narrower than the sinuses; loss of that waist (‘effacement’) is abnormal even when the absolute diameter is still within range.
Pathophysiology
The STJ anchors the three commissures. Dilating it pulls the commissural posts radially outward, so the free edges of the cusps can no longer coapt centrally — producing a central jet of aortic regurgitation with structurally normal leaflets. This is why STJ geometry, not cusp pathology, decides whether a valve can be spared: restoring STJ diameter alone abolishes the regurgitation.[18]
Raised by
- Annuloaortic ectasia with effacement — Marfan, Loeys-Dietz (the classic ‘loss of the waist’)
- Ascending aortic aneurysm extending proximally, especially BAV ascending phenotype
- Chronic severe AR with progressive root remodelling
- Aortitis and post-dissection false-lumen remodelling
- Age and hypertension (modest)
Lowered by
- Supravalvular aortic stenosis — Williams-Beuren syndrome, familial elastin (ELN) variants: an hourglass narrowing exactly at the STJ
- Post-surgical: after a Yacoub/David procedure, or a snug graft anastomosis
- Prior aortic dissection with a compressive false lumen
Technique & pitfalls
- Same frame and convention as the sinuses (end-diastole, leading-edge to leading-edge).
- Identify it anatomically as the ridge where the sinus contour straightens, not by a fixed distance from the annulus.
- Always report the sinus:STJ ratio — effacement is the surgically relevant finding and is invisible if only absolute numbers are given.
- In supravalvular AS, use continuous-wave Doppler above the valve: the gradient arises at the STJ, not at the cusps.
- Colour Doppler in PLAX: a central AR jet with normal cusps points straight to the STJ.
Pseudo-change & artefact
- Measuring too high (in the tubular aorta) or too low (in the sinus) — the commonest error, and it manufactures or hides effacement.
- Poor lateral resolution at depth blurs the ridge; move to a high left parasternal window.
- In a heavily calcified root, acoustic shadowing hides the far wall and the diameter is guessed.
Treatment thresholds
- No stand-alone surgical threshold — the STJ is a feasibility and technique variable.
- STJ effacement with structurally normal cusps → the patient is a candidate for valve-sparing root replacement; STJ diameter determines graft size and whether reimplantation (David) or remodelling (Yacoub) is chosen.[9,10]
- STJ diameter and cusp effective height guide the choice between repair and replacement in the aortic-valve-repair setting.
- Supravalvular AS: surgical relief when mean gradient ≥50 mmHg or peak ≥70 mmHg, or at lower gradients with symptoms, LVH or coronary ostial involvement.[25]
Next step
- Next: characterise the AR jet direction — central jet plus effaced STJ is a repairable combination; eccentric jet implies cusp prolapse or perforation.
- Then: gated CTA/CMR for the full root geometry, and TOE for cusp effective height and coaptation depth.
- Then: if supravalvular narrowing, screen for Williams syndrome and image the pulmonary arteries and coronary ostia.
Drugs
- No drug alters STJ diameter.
- Afterload reduction and heart-rate control are supportive only, as for the sinuses.
Reversibility
0% medically. Effacement is mechanical and permanent. It is, however, one of the most surgically correctable abnormalities in the whole of this document: restoring a normal STJ during valve-sparing root replacement abolishes central AR in the large majority of patients with anatomically normal cusps, with durable freedom from significant AR at 10 years.[9,10]