Open questions — thoracic aortic aneurysm¶

Last curated: 2026-08-27. This is the repository's research frontier: concrete, answerable questions the assembled literature exposes, each with the evidence showing why it is open and what would close it. Questions carry stable IDs (OQ-n) so curation sessions can reference, sharpen, or close them; when one is answered, move it to a "Closed" section with the closing citation rather than deleting it. Supporting PMIDs/NCTs were verified during the sessions that wrote them (CONVENTIONS §1).

How to read priority¶

Tier 1 = answering it would change practice or reorder the field; a study design is conceivable today. Tier 2 = important, but blocked on tools, cohorts, or a Tier-1 answer. Tiers are curator judgment, not consensus — argue with them.

Dots not yet connected¶

A different lens on the same frontier: places where two bodies of evidence both exist in this knowledge base but no study has ever joined them. These are synthesis opportunities — often cheaper than new data collection, because the dots are already on the page.

#	Dot A	Dot B	The missing junction	Powers
D1	~130 GWAS loci for aortic diameter (PMID 34837083, 35902171)	21 GWAS loci for aortic dissection/aneurysm disease (PMID 37308786)	No formal reconciliation — are "genetics of size" and "genetics of failure" the same trait?	OQ-6
D2	Circulating biomarker discovery cohorts (cross-sectional; PMID 23312977, 30373522)	Surveillance cohorts with serial imaging and events	No study has ever banked baseline plasma in a surveillance cohort and read markers against subsequent growth	OQ-7
D3	Within-patient WSS→wall-degradation mapping in BAV (PMID 26293758)	BAV heritability ~89% (PMID 15234422)	No design separates the inherited wall defect from the flow-imposed one (e.g., discordant-flow longitudinal cohorts)	OQ-17, OQ-11
D4	Ex vivo biomechanical rupture indices from resected tissue (PMID 25979384, 35894942)	Prospective clinical outcomes in surveillance patients	Every rupture metric is derivation-only; none has met a prospective event	OQ-2
D5	Polygenic scores that predict diameter (PMID 37662232)	The clinic, where diameter is already measured	Incremental event prediction conditional on known diameter — the only deployment scenario — has never been tested	OQ-18
D6	Mouse TGF-β/ARB rescue (PMID 16601194)	Human trial near-null (PMID 36049495)	No back-translation study explains the divergence (dose? timing? surrogate validity? species biology?)	OQ-4, OQ-19
D7	Sex-difference data — smaller-diameter dissection, faster growth, higher mortality (PMID 15197151, 30571545)	Threshold-setting analyses (all sex-neutral)	No sex-stratified threshold derivation or validation exists	OQ-3
D8	Patient-reported priorities: exercise guidance, surveillance anxiety, decision support (PMID 32340520, 26769698)	TAA trial endpoint design	Zero TAA trials carry patient-reported outcomes; no validated instrument even exists	OQ-35, OQ-37, OQ-38
D9	IRAD referral-registry mortality trends (PMID 26205591)	Validated national registry data (PMID 36321467)	Never reconciled — is type A mortality improving or flat?	OQ-27
D10	Diabetes inversely associated with aneurysm disease (PMID 30052821)	TAA mechanism/therapeutic pipeline	The protective mechanism has never been studied in thoracic disease; all interventional tests are abdominal-only	OQ-14
D11	Aortic length/tortuosity as dissection markers (PMID 31526537)	Guideline intervention criteria (diameter-only)	No multi-center prospective validation to carry length into criteria	OQ-24
D12	Guideline thresholds resting on Yale single-center natural history (PMID 11834007)	Population imaging biobanks now large enough to replicate	The replication has simply never been run	OQ-26

When a junction study appears in the literature, connect the dot: cite it here, and usually a question above sharpens or closes with it.

Tier 1 — highest-value directions¶

OQ-1. Does elective repair at 5.0–5.4 cm beat surveillance?¶

The central clinical question of the field. Guidelines permit 5.0 cm at experienced centers (Class 2a) on purely observational grounds; 59% of type A dissections occur below 5.5 cm, yet absolute risk in the 4.0–5.5 cm band is ~0.1%/patient-year — so earlier surgery could either save lives or mostly expose low-risk patients to operative mortality. First randomized evidence ever: TITAN:SvS (NCT03536312, n=610, readout ~2035). Until then, every threshold argument is denominator arithmetic. (PMID 36322642, 17709637, 25997607) → wiki: risk stratification, trials

OQ-2. Who below threshold dissects? (individualized risk beyond diameter)¶

Diameter is the only variable in guidelines, yet most dissections happen below its action point, and the population reservoir of 4.0–5.4 cm aortas is enormous. Candidate discriminators exist in silos — indexed size (ASI/AHI), aortic length (11 cm hinge), wall stress/strength metrics, 4D-flow WSS, polygenic scores — but none has prospective validation against events: every biomechanical rupture index derives from tissue resected at elective surgery, every biomarker cohort is cross-sectional, and no analysis shows a polygenic score adds prediction conditional on measured diameter. The unifying study (multi-modal baseline → longitudinal events) has never been run. (PMID 17709637, 16368358, 29395211, 31526537, 25979384, 35894942, 37662232) → wiki: risk stratification, hemodynamics, biomarkers

OQ-3. Should women have lower thresholds?¶

Women are diagnosed older, dissect and rupture at smaller absolute diameters, contribute 79% of ruptures in population data, grow faster in some series (2×), and carry higher adjusted dissection mortality (OR ~1.4) — yet every major guideline's primary threshold is sex-neutral (body-size indexing is a partial patch, not a validated sex-specific criterion). No trial or even large prospective cohort has tested sex-stratified action points. (PMID 15197151, 9851478, 30571545, 36322642) → wiki: risk stratification, epidemiology

OQ-4. Is elevated TGF-β signalling causal, compensatory, or epiphenomenal?¶

The field's oldest mechanistic dispute, and it underwrites drug strategy. Loss-of-function mutations in TGF-β receptors/ligands paradoxically increase tissue TGF-β signalling; TGF-β antagonism rescues mouse Marfan aortopathy, yet receptor deletion in SMCs worsens disease and Tgfb2 haploinsufficiency aggravates Fbn1 mice. No experiment has separated the cell type, compartment, and time window in which TGF-β harms from those in which it protects. Resolving this would explain why losartan underdelivered clinically and what to target instead. (PMID 12598898, 16601194, 24401272, 22772368, 28119285) → wiki: pathophysiology, medical therapy

OQ-5. Can any drug slow degenerative (non-syndromic) TAA — and is such a trial even powerable?¶

No RCT shows any drug slows growth or prevents dissection in the degenerative majority; recommendations reduce to blood-pressure control. Worse, the trial mathematics are hostile: typical growth (~0.1 cm/yr) sits below inter-scan measurement error (±2.4–5.2 mm), and the only accepted hard endpoints are rare. A validated growth/risk surrogate (OQ-2, OQ-7) is the unlock; until then the "medical therapy of TAA" literature is a Marfan literature. (PMID 11834007, 22864960, 36049495, 36322642) → wiki: medical therapy

OQ-6. What explains the ~75% of familial TAAD with no identified gene?¶

Gene discovery by family exome sequencing is saturating — each large effort returns fewer new large-effect genes — implying the residual architecture is oligogenic, non-coding, or polygenic; meanwhile the two GWAS families (aortic diameter loci, ~100+, vs dissection/aneurysm disease loci, 21) have never been formally reconciled, so "genetics of size" and "genetics of failure" may be different questions. Both the missing-heritability hunt and the reconciliation are tractable with existing biobanks. (PMID 26838787, 34837083, 35902171, 37308786) → wiki: genetics, omics

OQ-7. Can a circulating biomarker predict growth or dissection prospectively?¶

Every candidate (MMPs, TGF-β, D-dimer variants, miRNAs) was validated by discriminating operated aneurysms from normal aortas cross-sectionally — a design that cannot support surveillance use. No study has banked baseline plasma in a surveillance cohort and read markers against subsequent growth/events. This is a fixable design failure, not (yet) a demonstrated biology failure. (PMID 23312977, 30373522, 31409059) → wiki: biomarkers

OQ-8. Are gene-specific surgical thresholds correct, or only plausible?¶

Genotype-adjusted thresholds (e.g., TGFBR2 at 4.5 cm, lower with risk modifiers) rest on registry observations as thin as 6 dissections below 45 mm among 441 carriers; no prospective comparison of threshold strategies exists, so number-needed-to-operate per genotype is unknown. As panel testing spreads, miscalibrated thresholds scale their errors with it. (PMID 27879313, 36322642) → wiki: genetics, guidelines

Tier 2 — by theme¶

Mechanism¶

OQ-9. Which compartment drives disease — medial SMC or adventitial fibroblast — and does it differ by genotype? Marfan models show a modulated-SMC cluster; LDS tissue shows adventitial fibroblast activation without one. Model artifact or genotype-specific biology? (PMID 32698686, 40109260) → pathophysiology
OQ-10. Is the modulated-SMC state causal for wall failure or reactive to it? All human atlases are end-stage surgical snapshots; temporality is structurally unresolvable with current tissue access — needs longitudinal animal sampling or in-situ lineage/clock methods. (PMID 32698686, 36172868) → pathophysiology, omics
OQ-11. Is high or low wall shear stress the dangerous exposure? Elevated regional WSS co-localizes with elastin degradation within patients, yet low WSS correlates with degraded tissue properties elsewhere, and WSS falls as the aorta dilates. Stage-dependence vs opposing mechanisms is untested — needs serial 4D-flow with tissue endpoints. (PMID 26293758, 31331875) → hemodynamics
OQ-12. Does embryologic lineage (second heart field vs neural crest) confer differential vulnerability or only location? Disease localizes to SHF-derived outer media, but lineage markers are largely undetectable in adult human aorta, leaving the human relevance inferential. (PMID 35143327, 39697172) → pathophysiology
OQ-13. How much of the angiotensin-II mouse literature measured pseudoaneurysm rather than dissection? Careful re-phenotyping suggests endpoint misclassification in a foundational model family; a systematic re-read could reweight two decades of mechanism claims. (PMID 35132962) → animal models
OQ-14. Why does diabetes associate with less aneurysm disease? The inverse association is reproducible and mechanistically unexplained; all interventional tests (metformin) are abdominal-only and explicitly exclude TAA. A TAA-specific mechanism study would either export the protection or kill the analogy. (PMID 30052821; NCT04500756, NCT04224051, NCT03507413) → medical therapy, trials

Genetics¶

OQ-15. What determines penetrance in confirmed carriers? ACTA2 lifetime aortic-event risk is 76%, varying at codon resolution — modifiers (genetic, environmental, hemodynamic) are unidentified; no modifier study exists. (PMID 25759435) → genetics
OQ-16. How should MYLK-type disease be surveilled when it dissects without dilating? Diameter — the universal surveillance variable — is structurally uninformative here; no validated alternative (biomarker, imaging, fixed-age prophylaxis) has been proposed. (PMID 21055718) → genetics, imaging
OQ-17. Is BAV aortopathy hemodynamic, genetic, or sequential? Within-patient paired sampling shows shear-localized wall degradation (genotype held constant) while BAV heritability is ~89%; no design yet separates the intrinsic wall defect from the flow-imposed one — discordant-flow longitudinal cohorts could. (PMID 26293758, 15234422) → bicuspid aortopathy
OQ-18. Does a polygenic score add value conditional on known diameter? PRS predicts diameter well, but the deployment scenario always includes a measured aorta; incremental event prediction has never been shown. (PMID 37662232, 34837083) → omics

Therapy & trials¶

OQ-19. Is aortic root Z-score a valid surrogate for dissection? The entire Marfan drug literature rests on Z-trajectory differences (e.g., 0.07/yr) never linked to hard events; a registry-based surrogate-validation study is feasible and overdue. (PMID 36049495) → medical therapy
OQ-20. Does medical therapy prevent hard endpoints in Marfan? All randomized evidence is surrogate growth; the only event-level signal is non-randomized follow-up. (PMID 36049495, 32548624) → medical therapy
OQ-21. Is the fluoroquinolone–aorta association causal? Strong cohort signals attenuate toward null under active-comparator designs with baseline imaging; regulatory warnings may be steering therapy on confounding. A target-trial-emulation with imaging covariates would settle it. (PMID 29519881, 32897358, 32897307) → medical therapy
OQ-22. Does PEARS change outcomes versus waiting for valve-sparing root replacement? ~700 implants, zero randomized comparison. (PMID 30165980, 36094493) → surgery
OQ-23. What is the long-term cost of ascending TEVAR damping aortic pulsatility? Stent grafts stiffen the system (with effects propagating to native segments); trial endpoints (30-day) cannot see late ventricular/vascular consequences. Needs a decade of device-cohort follow-up with functional endpoints. (PMID 37144300; NCT05800743) → surgery, trials
OQ-24. Can ascending aortic length graduate from marker to intervention criterion? The 11-cm hinge and length-based risk are single-program observations; prospective multi-center validation against events is the gate to guideline entry. (PMID 31526537) → risk stratification

Epidemiology, statistics & data infrastructure¶

OQ-25. What is the true prevalence of silent TAA? Clinical detection (~0.16%) vs autopsy series (~0.76%) implies a large hidden reservoir; no modern population imaging-screening study has sized it — which also blocks rational screening policy. (PMID 33705940, 25609416) → epidemiology
OQ-26. Do the Yale hinge points and size-band rates replicate at population level? The numbers anchoring every guideline derive from one referral center with censoring at operation; population replication (now feasible in imaging biobanks) has never been done. (PMID 11834007, 16368358, 10391339) → epidemiology, risk stratification
OQ-27. Is type A dissection mortality actually improving? Referral-registry trends (IRAD: 31%→22%) conflict with flat validated national data (Denmark: 22% for two decades); survivorship/referral bias vs true stagnation is unresolved and determines where improvement effort should go. (PMID 26205591, 36321467) → dissection, statistics
OQ-28. How much do ICD-coded databases overstate dissection? Only 60.2% of coded dissections survived validation in Denmark; no US validation figure exists, yet NIS/WONDER studies keep publishing. (PMID 36321467) → statistics
OQ-29. What is the TAA-specific share of global aortic-aneurysm burden? GBD and national vital statistics pool thoracic+abdominal disease; the field literally does not know its own death toll. (PMID 25432126, 35711350, 41776414) → statistics
OQ-30. Is family screening cost-effective, and with what protocol? Screening first-degree relatives finds new disease in ~1/3, but predictive accuracy, interval, and cost-effectiveness are unmeasured — the evidence base is yield-only. (PMID 30371227) → epidemiology, genetics
OQ-31. What supports "1–2% per hour" untreated type A mortality? The canonical claim traces to 1958/1972 series whose internals predate modern abstracting; no contemporary estimate exists (and ethically cannot be generated directly) — deserves formal evidence-archaeology and modeling. (PMID 13577293, 4557973, 10807810) → dissection, statistics

Guidelines & care delivery¶

OQ-32. Are the three overlapping European guidelines (ESC 2024, EACTS/STS 2024, ESVS 2026) concordant with ACC/AHA 2022 — and where not, why? Documented historical conflicts (BAV thresholds needed a formal 2016 clarification; EACTS/STS defines aneurysm at >45 mm vs the 1.5× convention) make a systematic concordance audit valuable and cheap. (PMID 26637530, 38408364, 39210722, 41448425, 36322642) → guidelines, registry
OQ-33. Which dissection classification should trials and registries speak? SVS/STS 2020 vs EACTS/STS 2024 TEM ("non-A non-B") bifurcates the literature's denominators; no harmonization document exists. (PMID 32001058, 38408364) → dissection
OQ-34. Sports and exercise guidance lags two guideline generations. The governing eligibility statement dates to 2015; modern genotype-aware, imaging-aware exercise prescription in aortopathy is unstudied territory with large quality-of-life stakes. (PMID 26621648) → guidelines, patient experience

Patient-centered research¶

OQ-35. What should a validated TAA/dissection-specific patient-reported outcome measure contain? None exists, so trials cannot register patient-relevant endpoints even if they wanted to; qualitative groundwork exists to build from. (PMID 37451607, 35701761, 39789589) → patient experience
OQ-36. What is the psychological cost of surveillance, and does mental-health screening in aortic clinics change outcomes? After acute dissection, 23% screen PTSD-positive while charts document 7% — the burden is real and undercounted; no aortic clinic pathway includes systematic screening. (PMID 32340520, 40948724) → patient experience
OQ-37. Can a shared decision-making tool serve patients at threshold sizes? AAA has a randomized decision-aid trial; TAA — where the surgery-vs-surveillance dilemma is sharper (OQ-1) — has nothing. (PMID 24913683, 35501043) → patient experience, risk stratification
OQ-38. What exercise is actually safe after TAA diagnosis or repair? Restriction advice is consequential for identity and mental health, observational signals favor activity, and no trial has ever tested a prescription — patients repeatedly name this their top unanswered question. (PMID 26769698, 39352231, 34386933) → patient experience, medical therapy
OQ-39. Do awareness campaigns (THINK AORTA and kin) measurably reduce the ~34% dissection misdiagnosis rate? Campaigns scale internationally on face validity; no before/after or regional-comparison evaluation exists. (PMID 34968970, 34838743) → patient experience, dissection
OQ-40. Does organized peer support improve surveillance retention and adherence? Patient organizations run large support programs; the effect on measurable care outcomes is unstudied. (PMID 42491301, 42285644) → patient experience

Closed¶

(None yet. When a question closes, move it here with the closing citation and date.)