Aortic Aneurysm — Thoracic and Abdominal

• Medial degeneration and smooth muscle cell apoptosis: Chronic hemodynamic stress and inflammatory cytokines (TNF-α, IL-6, IL-8) promote programmed death of vascular smooth muscle cells (VSMCs), reducing the contractile and structural support within the medial layer. This process is particularly prominent in degenerative TAA and accounts for the progressive nature of aneurysm expansion. Loss of VSMCs paradoxically increases wall tension according to Laplace's law (T = Pr), where pressure (P) and radius (r) create positive feedback: as the vessel expands, wall stress increases exponentially, further promoting smooth muscle death and continued dilatation.

• Extracellular matrix degradation and elastin/collagen disruption: Matrix metalloproteinases (MMPs, particularly MMP-2 and MMP-9) are aberrantly upregulated in aneurysmal tissue and directly cleave elastin fibers and collagen cross-links that provide elastic recoil and tensile strength. This process is mediated by inflammatory macrophages and activated VSMCs responding to chronic hypoxia, oxidative stress, and shear forces. Tissue inhibitors of metalloproteinases (TIMPs) are simultaneously downregulated, favoring net protease activity. The loss of elastin is particularly critical because elastin provides up to 90% of the elastic recoil in the thoracic aorta; once degraded, collagen becomes the primary structural support but cannot match elastin's mechanical properties, predisposing to rupture.

• Chronic inflammatory infiltration and oxidative stress: Immune cell infiltration (CD4+ and CD8+ T cells, macrophages) in response to both infectious triggers and autoimmune pathology generates pro-inflammatory cytokines and reactive oxygen species (ROS). In degenerative AAA, this inflammation is primarily atherosclerosis-associated; in TAA related to connective tissue disease or vasculitis, inflammation is more prominent. Oxidative stress inactivates nitric oxide (NO), reducing endothelium-derived vasodilation and promoting endothelial dysfunction, which further perpetuates inflammation through increased expression of adhesion molecules and chemokines.

Degenerative (atherosclerotic-related) — most common

• Advanced age (peak incidence 65-80 years)
• Chronic hypertension (present in 60-80% of AAA cases; primary driver in TAA)
• Smoking (single strongest modifiable risk factor; 5-10 fold increased risk for AAA)
• Male gender (5-10:1 male predominance for AAA; 2-3:1 for TAA)
• Hyperlipidemia and metabolic syndrome

Connective tissue disorders and genetic syndromes

• Marfan syndrome (FBN1 mutation affecting fibrillin-1): accounts for 5-10% of TAA; presents with ascending aorta and aortic root dilatation with associated aortic regurgitation; typical presentation includes family history, lens dislocation, skeletal features
• Ehlers-Danlos syndrome (Types IV [vascular EDS] most aorta-relevant; defects in type III collagen): vascular EDS carries extreme rupture risk even with modest aneurysm diameter due to tissue fragility
• Loeys-Dietz syndrome (TGF-β receptor mutation): presents with ascending aorta aneurysm, tortuosity, hypertelorism, bifid uvula
• Turner syndrome: increased risk of ascending aortic aneurysm, aortic dissection; associated with bicuspid aortic valve

Inflammatory aortopathies

• Takayasu arteritis: large-vessel vasculitis predominantly affecting young women; causes aortic root and ascending aorta involvement with secondary aortic regurgitation
• Giant cell (temporal) arteritis: primarily affects descending thoracic and abdominal aorta; presents in patients >50 years with constitutional symptoms and temporal headache
• Syphilis (tertiary): chronic infection causes endarteritis obliterans of the vasa vasorum; produces ascending aorta and aortic arch aneurysms with characteristic "tree-barking" appearance
• Behçet disease: multisystem vasculitis with aortic involvement
• Ankylosing spondylitis and other seronegative spondyloarthropathies: associated with ascending aorta aneurysm and aortic regurgitation

Aortic valve pathology and hemodynamic stress

• Bicuspid aortic valve: present in 1-2% of population; associated with ascending aortic root aneurysm independent of stenosis or regurgitation severity; abnormal flow mechanics promote medial degeneration
• Chronic aortic regurgitation: chronic volume overload increases wall stress; can cause progressive aortic root and ascending aorta dilatation

Infectious causes (rare)

• Bacterial aortitis (secondary to endocarditis, bacteremia, contiguous infection): Staphylococcus aureus, Salmonella, Mycobacterium tuberculosis
• Fungal aortitis: Histoplasma, Cryptococcus, Aspergillus (primarily in immunocompromised hosts)
• Treponema pallidum (tertiary syphilis)

Post-traumatic

• Aortic injury from motor vehicle accident, penetrating trauma, or high-speed deceleration
• Pseudoaneurysm formation from intimal tear with contained rupture

Iatrogenic

• Aortic cannulation during cardiac surgery
• Endovascular procedures with arterial access-related complications

Other risk factors

• Chronic kidney disease (uremia-associated inflammation and medial calcification)
• Obstructive sleep apnea (hypoxia-induced oxidative stress)
• Cocaine abuse (acute hypertensive surges and vasospasm)

Asymptomatic aneurysms (often detected incidentally)

• Often found on imaging obtained for unrelated reasons
• Prevalence increases with age and smoking history
• Majority of AAA >5 cm and TAA >5.5 cm eventually cause symptoms without intervention

Symptomatic thoracic aortic aneurysm

• Anterior chest pain: typically deep, substernal, may radiate to back or interscapular region; often constant and severe
• Back pain or interscapular pain: particularly prominent in descending thoracic aorta aneurysms
• Hoarseness and stridor: from recurrent laryngeal nerve compression (left-sided descending aorta or arch lesions)
• Dyspnea and cough: from compression of left main bronchus or pulmonary vessels
• Dysphagia: from esophageal compression (descending aorta)
• Superior vena cava syndrome: from compression of superior vena cava (right-sided ascending aorta or arch involvement)
• Aortic regurgitation murmur: early diastolic decrescendo murmur at left sternal border if aortic root involved; may progress to signs of acute heart failure (orthopnea, peripheral edema, rales)
• Arm blood pressure differential: >20 mmHg discrepancy between arms suggests aortic arch involvement or brachiocephalic artery compression
• Horner syndrome: from lateral mediastinal involvement affecting sympathetic chain (ptosis, miosis, anhidrosis)

Symptomatic abdominal aortic aneurysm

• Abdominal or flank pain: deep, constant pain in periumbilical or lateral abdomen; not colicky; may radiate to groin, buttocks, or thighs
• Pulsatile abdominal mass: visible or palpable expansile mass on abdominal exam, transmitted from aortic pulsation (distinguish from transmitted pulsation by observing outward motion of examining hands)
• Back pain: particularly lower lumbar region; may suggest contained rupture with retroperitoneal involvement
• Lower extremity ischemia: cool extremities, absent pulses, claudication from iliac artery involvement
• Gastrointestinal bleeding: rare presenting symptom; suggests aortoenteric fistula (most commonly aortointestinal, particularly second and third portions of duodenum)

Signs of rupture or contained rupture (medical emergency)

• Sudden, severe, "tearing" or "ripping" pain in chest (TAA) or abdomen/flank (AAA)
• Hemodynamic instability: hypotension, tachycardia, shock
• Syncope or altered mental status
• Abdominal distension with rigid abdomen
• Groin or inguinal ecchymosis (Grey Turner sign variant for AAA rupture into retroperitoneum)
• Pulsatile abdominal mass with sudden expansion
• Signs of acute heart failure (if aortic regurgitation acute)

Physical examination findings

• Hypertension: typically present in majority of patients; may be severe acutely
• Asymmetric blood pressures: difference between upper extremities suggests aortic arch involvement or subclavian artery compression
• Pulse deficits: diminished or absent radial, femoral, or lower extremity pulses depending on aneurysm location; suggest significant stenosis or dissection
• New aortic regurgitation murmur: high-pitched early diastolic decrescendo at left sternal border, accentuated with patient sitting forward; indicates aortic root involvement
• Bruits: abdominal bruit may be heard with AAA, particularly if stenotic component
• Palpable pulsatile mass: in thin patients with AAA; not reliably detected in obese patients
• Signs of chronic aortic regurgitation: wide pulse pressure, bounding pulses, prominent carotid pulsations, Quincke pulses (nail bed pulsations), pistol-shot femorals (Korotkoff sounds heard over femoral artery with stethoscope)

Laboratory studies

• Complete blood count: obtain baseline hemoglobin/hematocrit for surgical planning; anemia from chronic disease common
• Comprehensive metabolic panel: assess renal function (critical for surgical risk stratification and contrast considerations); assess for electrolyte abnormalities from acute complications
• Coagulation studies (PT/INR, PTT): baseline for surgical candidates; particularly important if considering perioperative anticoagulation interruption
• Biomarkers (D-dimer, troponin): elevated D-dimer supports diagnosis of aortic syndrome (dissection, aneurysm with dissection) but lacks specificity; troponin elevation suggests myocardial involvement or ischemia from involvement of coronary ostia
• Inflammatory markers (ESR, CRP): helpful in suspecting inflammatory aortopathy (Takayasu, giant cell arteritis, syphilis)
• Serologic testing for syphilis (RPR/VDRL, FTA-ABS): indicated for ascending aorta and arch aneurysms, particularly in elderly or with characteristic imaging findings

Imaging — modalities and findings

• Widened mediastinum: mediastinal width >8 cm at level of aortic knob suggests TAA; can also be seen with mediastinal masses or hemorrhage
• Displaced trachea: rightward displacement suggests left-sided mass/aneurysm
• Abnormal aortic contour: loss of normal concavity of aortic knob (straightening or convexity) suggests aneurysm
• Pleural effusion: left-sided effusion common with descending aorta involvement; may suggest contained rupture if acute
• Limited sensitivity and specificity: normal CXR does not exclude significant aneurysm; used primarily to narrow differential diagnosis

• Technique: thin-slice (≤2mm) helical CT with IV contrast administration synchronized to aortic bolus (arterial phase optimal); arterial phase imaging (8-10 seconds post-injection) best visualizes aorta; venous phase not necessary for aneurysm characterization
• Measurement protocol: measure outer-wall-to-outer-wall diameter perpendicular to long axis of aorta at level of maximum diameter; aneurysm defined as ≥1.5× normal diameter at that location (normal ascending aorta 3-3.5 cm, descending thoracic 2.5-3.5 cm, infrarenal aorta 2-3 cm)
• Advantages: excellent spatial resolution; rapidly acquired; allows assessment of aneurysm extent, involvement of branch vessels, presence of thrombus, complications (rupture, dissection); shows relationships to surrounding structures; superior for surgical planning
• Ascending aorta findings: dilatation, involvement of sinuses of Valsalva, potential involvement of aortic valve and coronary ostia
• Arch findings: extent of involvement, relationship to head and neck vessels, potential for subclavian artery compromise
• Descending aorta findings: relationship to esophagus, bronchi, spinal canal
• AAA findings: infrarenal aorta dilatation, involvement of iliac arteries, relationship to renal arteries and mesenteric vessels, presence of intimal flap (dissection), eccentric thrombus, periaortic stranding (contained rupture)
• Signs of rupture: extravasation of contrast, active bleeding, loss of aortic wall integrity, high-density fluid in periaortic space or retroperitoneum
• Limitations: requires renal function adequate for IV contrast (eGFR typically >30 required); radiation exposure; contrast allergy risk

• Technique: high-resolution ECG-gated sequences (steady-state free precession) for morphology; gadolinium-enhanced MR angiography (preferably with blood-pool agents) for vascular anatomy
• Advantages: no ionizing radiation; no iodinated contrast (safer in renal insufficiency, contrast allergy); superior soft tissue contrast; better characterization of dissection flap and branch vessel involvement; useful for surveillance of chronic aneurysms
• Disadvantages: longer acquisition time (problematic in acute, hemodynamically unstable patients); contraindicated with ferromagnetic implants (some older prosthetic valves, pacemakers without MR-conditional design); less available acutely in many centers
• Best use: surveillance imaging for known aneurysms, definitive diagnosis when CT contraindicated, assessment of chronic dissection

• Advantages: rapid bedside assessment; no radiation or contrast; can assess aortic valve function and quantify aortic regurgitation; can assess ventricular function
• Limitations: poor acoustic windows in many patients; limited assessment of distal ascending aorta and arch; cannot adequately visualize descending aorta; not appropriate as sole diagnostic modality for suspected aneurysm but can support diagnosis in acute setting
• Findings: aortic root dilatation (measured as diameter at level of sinuses of Valsalva >4 cm), loss of normal systolic closure of aortic valve, eccentric aortic regurgitation jet, ventricular dilatation with dysfunction

• Advantages: superior visualization of aortic root, ascending aorta, arch, and proximal descending aorta

Immediate stabilisation (suspected rupture — emergency)

• Two large-bore IVs, type and cross, activate massive transfusion: ruptured AAA/TAA is a surgical, not medical, diagnosis. The 2022 ACC/AHA Aortic Disease Guideline and Society for Vascular Surgery endorse permissive hypotension (accept a low-but-perfusing pressure, avoid aggressive crystalloid) to limit clot disruption at the rupture site.
• No delay for CT if hemodynamically unstable: bedside ultrasound confirming aneurysm plus shock is enough — go to the operating room.
• If pain suggests superimposed dissection: IV beta blocker (esmolol) first to lower dP/dt, then vasodilator (nitroprusside). Giving the vasodilator alone causes reflex tachycardia and increased shear stress.

Medical therapy for the stable aneurysm

• Smoking cessation: the single most effective intervention to slow expansion and reduce rupture risk.
• Antihypertensives: beta blockers (metoprolol) and ARBs (losartan) are preferred, particularly in Marfan syndrome, to reduce wall stress; ACC/AHA recommends blood pressure control in all aortopathy patients.
• Statin therapy for concomitant atherosclerotic risk, per ACC/AHA cholesterol guidance.
• Surveillance imaging: ultrasound for AAA, CT/MRA for TAA, at intervals based on diameter.

Definitive repair — size and growth thresholds (ACC/AHA 2022, SVS)

• Infrarenal AAA: repair at ≥5.5 cm in men, ≥5.0 cm in women, rapid expansion (>0.5 cm/6 months), or any symptomatic/tender aneurysm regardless of size.
• Ascending aorta/root: repair at ≥5.5 cm; lower thresholds (≈5.0 cm, or smaller in experienced centres) for Marfan, Loeys-Dietz, vascular EDS, bicuspid valve, or family history of early dissection.
• Options: EVAR (lower perioperative mortality, requires suitable neck/iliac anatomy and lifelong imaging surveillance) versus open repair (more durable, fewer reinterventions). Descending TAA → TEVAR. Root aneurysm → valve-sparing root replacement (David procedure) or composite graft (Bentall).

Avoid

• Fluoroquinolones: FDA warns against use in aneurysm/aortopathy patients (collagen degradation).
• Heavy isometric straining and stimulants (cocaine, high-dose sympathomimetics).
• Thrombolysis — never appropriate for aortic pain of aneurysmal origin.

Complications of the aneurysm itself

• Rupture (emergency): wall stress rises with radius (Laplace), so risk climbs steeply above threshold diameters. Signals: abrupt tearing pain, hypotension, syncope, flank ecchymosis. Free intraperitoneal rupture is usually fatal; retroperitoneal rupture may be temporarily contained.
• Aortic dissection (emergency): intimal tear in a degenerated media; pulse deficit, arm-to-arm pressure differential, new aortic regurgitation.
• Aortoenteric fistula (emergency): erosion into the third/fourth portion of the duodenum; a herald bleed of self-limited hematemesis or melena precedes exsanguination. Most often seen years after graft placement.
• Aortocaval fistula: rupture into the IVC produces high-output heart failure, a continuous machinery murmur over the abdomen, and lower-extremity venous engorgement.
• Mural thrombus with distal embolisation: blue toe syndrome, livedo, or acute limb ischemia from an otherwise asymptomatic AAA.
• Mycotic (infected) aneurysm: saccular, rapidly enlarging aneurysm with fever and positive cultures (Salmonella, S. aureus) — high early rupture risk.
• Compressive/inflammatory sequelae: hoarseness, dysphagia; inflammatory AAA with periaortic fibrosis causing ureteral entrapment and hydronephrosis.

Complications of repair

• Perioperative myocardial infarction: the leading cause of death after open repair — reflects the shared atherosclerotic substrate; screen and optimise cardiac risk preoperatively.
• Colonic (sigmoid) ischemia (emergency): inferior mesenteric artery sacrifice or embolisation; bloody diarrhea within 48 hours of repair is the classic clue — obtain sigmoidoscopy.
• Spinal cord ischemia/paraplegia: loss of intercostal collaterals feeding the artery of Adamkiewicz during descending TAA repair or TEVAR; anterior cord syndrome with preserved proprioception. CSF drainage and permissive hypertension are used prophylactically.
• Acute kidney injury: suprarenal clamping, atheroembolism, or contrast nephropathy.
• Endoleak after EVAR: persistent perfusion of the sac; sac enlargement on surveillance CT signals ongoing rupture risk — mandates lifelong imaging follow-up.
• Graft limb occlusion, migration, anastomotic pseudoaneurysm, and graft infection: late causes of reintervention.

• Screening: USPSTF recommends a one-time abdominal ultrasound for men aged 65–75 who have ever smoked. Ultrasound — not CT — is also the surveillance modality for known AAA (no radiation, no contrast).
• Unstable patient, single best next step: hypotension + back/flank pain + pulsatile mass = ruptured AAA → to the operating room, with bedside ultrasound at most. Ordering CT angiography in a crashing patient is the classic wrong answer.
• Post-repair GI bleed: hematemesis or melena in a patient with a prior aortic graft = aortoenteric fistula at the duodenum, even if the bleed stops (herald bleed). Endoscopy/CT then urgent surgery — do not label it peptic ulcer disease.
• Bloody diarrhea within days of AAA repair: sigmoid ischemia from inferior mesenteric artery interruption; sigmoidoscopy is diagnostic.
• The association examiners love: bicuspid aortic valve → ascending aortic aneurysm independent of stenosis severity; and Marfan/Loeys-Dietz → root dilatation managed with beta blockers or losartan plus earlier surgical thresholds.
• Tertiary syphilis produces an ascending aorta/arch aneurysm with tree-bark intima from vasa vasorum endarteritis — atherosclerotic AAA, by contrast, is infrarenal.
• Drug pearl: avoid fluoroquinolones in known aneurysm or aortopathy (FDA warning).
• Common distractor: aneurysm and dissection are not interchangeable. If the stem gives a pulse/BP differential, new diastolic murmur, and a widened mediastinum with acute tearing pain, think dissection physiology — beta blocker before vasodilator.
• EVAR trade-off: lower early mortality than open repair but more reinterventions and mandatory lifelong imaging for endoleak; a patient who skips follow-up is the setup for late sac expansion and rupture.