Aortic Aneurysm

A focal, permanent dilatation of the aorta to >1.5 times its expected normal diameter, involving all three layers of the vessel wall (a "true" aneurysm). Abdominal aortic aneurysm (AAA) is the commonest and the highest-yield for NEET PG, but thoracic aneurysms, the EVAR-versus-open debate, and the catastrophe of rupture are all repeatedly tested.

Definition & classification

An aneurysm is a localised dilatation exceeding 1.5× the normal diameter of the segment. For the infrarenal aorta (normal ≈ 2.0 cm), the threshold for the label "aneurysm" is conventionally a diameter ≥ 3.0 cm.

True vs false aneurysm

Feature	True aneurysm	False (pseudo) aneurysm
Wall	All 3 layers (intima, media, adventitia)	Contained by adventitia/surrounding tissue only; a pulsatile haematoma
Cause	Atherosclerosis, degenerative, connective-tissue	Trauma, anastomotic leak, post-catheterisation (femoral)
Example	Infrarenal AAA	Post-angiography femoral pseudoaneurysm

Morphology: Fusiform (uniform circumferential dilatation — commonest in AAA) vs Saccular (eccentric outpouching of one wall — more often mycotic/post-traumatic).

By location: abdominal (90% infrarenal), thoracic (ascending, arch, descending), and thoraco-abdominal. Thoraco-abdominal aneurysms are graded by the Crawford classification (types I–IV), important because the extent dictates the risk of paraplegia from spinal cord ischaemia during repair.

High-yield: "True" aneurysm = all three layers; "false"/pseudoaneurysm = a contained leak walled off by adventitia or peri-vascular tissue. A femoral pulsatile swelling after coronary angiography is the classic pseudoaneurysm.

Etiology & pathophysiology

The dominant mechanism is degeneration of the medial elastin and collagen with increased matrix metalloproteinase (MMP-2, MMP-9) activity and chronic transmural inflammation, leading to wall weakening. Atherosclerosis is strongly associated but is now regarded as a contributor rather than the sole cause.

Risk factors (AAA):

• Smoking — the single strongest modifiable risk factor (and the strongest driver of expansion and rupture).
• Male sex (M:F ≈ 4–6:1), age > 65 years.
• Family history (first-degree relative roughly doubles risk).
• Hypertension, COPD, hyperlipidaemia, atherosclerosis.

Protective association: Diabetes mellitus is paradoxically associated with a lower incidence and slower expansion of AAA — a favourite exam point.

Connective-tissue & inherited causes (especially thoracic / younger patients):

• Marfan syndrome (fibrillin-1, FBN1) → ascending aortic root dilatation, annuloaortic ectasia.
• Loeys–Dietz syndrome (TGF-β receptor) → aggressive, early aortic dissection.
• Ehlers–Danlos type IV (vascular type, COL3A1) → arterial rupture.
• Bicuspid aortic valve → ascending aorta dilatation.

Other causes: Infective/mycotic (Salmonella, Staphylococcus; classically saccular and rapidly expanding), syphilitic (tertiary — ascending aorta, "tree-bark" intima), Takayasu and giant-cell arteritis, and post-traumatic (aortic isthmus just distal to left subclavian — deceleration injury).

High-yield: Smoking is the strongest modifiable risk factor for AAA; diabetes is protective. Syphilitic aneurysms classically affect the ascending aorta and arch, whereas atherosclerotic AAA is infrarenal.

Laplace's law explains progression: wall tension ∝ (pressure × radius). As the aneurysm dilates, radius rises → tension rises → further dilatation → eventual rupture. This is why larger aneurysms grow and rupture faster.

Clinical features

Most AAAs are asymptomatic and found incidentally (USG, CT, or a palpable expansile mass on routine examination). When symptomatic:

• Pulsatile, expansile abdominal mass above the umbilicus (expansile = fingers pushed apart, distinguishing it from a transmitted pulsation).
• Vague central abdominal or back pain.
• Compression/embolic phenomena: "trash foot" (distal microembolism with blue toes despite palpable pulses), ureteric obstruction, early satiety.

Thoracic aortic aneurysm (TAA): often silent; may cause hoarseness (left recurrent laryngeal nerve stretch — Ortner syndrome), dysphagia, stridor, SVC obstruction, or chest/back pain.

Ruptured AAA — the classic triad:

1. Sudden severe abdominal/back/flank pain →
2. Hypotension/shock →
3. Pulsatile abdominal mass.

Rupture is usually retroperitoneal (posterolateral, often left), which may temporarily tamponade the bleed and allow survival to reach hospital; intraperitoneal (anterior) rupture is rapidly fatal. Retroperitoneal tracking of blood can produce Grey Turner sign (flank bruising) and Cullen sign (periumbilical bruising) — the same signs seen in haemorrhagic pancreatitis.

High-yield: A ruptured AAA can be misdiagnosed as renal colic, MI, diverticulitis, or pancreatitis. Any elderly male smoker with sudden flank/back pain + hypotension = ruptured AAA until proven otherwise. Do not delay for imaging if the patient is unstable.

Diagnosis & investigation of choice

Modality	Role
Ultrasonography (USG)	Screening + surveillance investigation of choice. Cheap, no radiation, accurate for diameter. Used in national screening programmes.
CT angiography (CECT)	Investigation of choice for planning surgery and for confirming/assessing rupture in a stable patient. Defines neck length, suprarenal extent, iliac involvement.
MRI / MRA	Anatomy without radiation; surveillance in young/connective-tissue patients.
Plain X-ray	"Eggshell" curvilinear calcification of the aortic wall — incidental.
Catheter angiography	Largely replaced by CTA; used during endovascular intervention.

Decision rule by stability: Stable → CT angiogram to plan → repair. Unstable with known/suspected AAA → straight to theatre (do not wait for CT). A bedside USG (FAST-type) can confirm aneurysm in the resuscitation bay.

High-yield: USG = screening and follow-up. CT angiogram = operative planning and the test of choice in a haemodynamically stable patient with suspected rupture. An unstable patient with a known AAA goes directly to the operating room.

Screening: A single abdominal USG is recommended for men aged 65–75 years who have ever smoked (one-time screen). This has reduced AAA-related mortality in large trials.

Surveillance & repair thresholds

Risk of rupture rises steeply with diameter. Surveillance intervals (USG) by size:

AAA diameter	Action
3.0–3.9 cm	USG every 2–3 years
4.0–4.9 cm	USG every 6–12 months
5.0–5.4 cm	USG every 3–6 months
≥ 5.5 cm	Refer for elective repair

Indications for elective repair:

• Diameter ≥ 5.5 cm (the single most tested cut-off; women may be offered repair at ≥ 5.0 cm as their walls rupture at smaller sizes).
• Rapid expansion > 0.5 cm in 6 months (or > 1 cm/year).
• Symptomatic aneurysm (tenderness, pain) regardless of size.
• Complications: distal embolisation, impending or actual rupture.

High-yield: The magic number is 5.5 cm. Below this in an asymptomatic patient, the risk of elective surgery outweighs the rupture risk, so surveillance, not surgery, is correct. Rapid growth (>1 cm/yr or >0.5 cm/6 months) or symptoms override the size rule.

Approximate annual rupture risk: <4 cm ≈ 0%; 4–5 cm ≈ 1%; 5–6 cm ≈ 3–10%; 6–7 cm ≈ 10–20%; >7 cm ≈ 20–40%.

Management & repair options

Medical / risk-factor optimisation (all patients, lifelong):

• Smoking cessation — the single most effective measure to slow expansion.
• Blood pressure control; statins; manage atherosclerotic risk.
• Beta-blockers were traditionally advocated to reduce shear/expansion (clearest benefit in connective-tissue TAA such as Marfan, where they slow root dilatation). In Marfan, losartan/ARBs (reducing TGF-β signalling) are also used.

Two repair strategies:

1. Open surgical repair (OSR): Laparotomy/retroperitoneal approach, cross-clamping, and replacement of the diseased segment with a prosthetic (Dacron/PTFE) tube or bifurcated graft. Durable, the gold standard for young/fit patients and unfavourable anatomy; higher peri-operative morbidity.

2. Endovascular aneurysm repair (EVAR): A stent-graft is deployed via the femoral arteries to exclude the sac from the circulation. Lower 30-day mortality, shorter stay, less physiological insult — but requires suitable "neck" anatomy and lifelong CT surveillance because of endoleaks and the need for re-intervention.

Feature	Open repair (OSR)	EVAR
Approach	Laparotomy, aortic clamp	Transfemoral stent-graft
Early (30-day) mortality	Higher	Lower
Long-term durability	Better, low re-intervention	More re-interventions; survival advantage erodes by ~2–3 yrs
Surveillance	Minimal	Lifelong CT (endoleaks)
Best for	Younger/fit patients, hostile neck, ruptured (if unstable & no EVAR setup)	Elderly/high-risk, suitable neck anatomy

Endoleak = persistent blood flow into the aneurysm sac after EVAR (the key EVAR complication):

Type	Source
I	Inadequate seal at proximal (Ia) or distal (Ib) graft attachment — needs treatment
II	Retrograde flow from branch vessels (lumbar, inferior mesenteric) — commonest; often observed
III	Defect/junctional separation between graft components — needs treatment
IV	Porosity of the graft fabric — self-limiting
V	"Endotension" — sac expansion without demonstrable leak

High-yield: Type I and Type III endoleaks are high-pressure and require intervention; Type II is the commonest and is usually managed conservatively with surveillance.

Ruptured AAA management (flow): Suspect rupture → two large-bore IV lines + cross-match → permissive hypotension (target systolic ≈ 70–90 mmHg / a palpable radial pulse and conscious patient — avoid aggressive fluids that "pop the clot") → stable → CT angiogram → emergency repair (open or rEVAR if anatomy & setup allow); unstable → straight to theatre.

High-yield: In ruptured AAA, practise hypotensive (permissive) resuscitation — do not over-transfuse before clamping/sealing. Over-aggressive fluid resuscitation raises pressure, dislodges the contained clot, and worsens haemorrhage.

Complications

• Rupture — the lethal complication; overall mortality of ruptured AAA approaches 80–90% (many die before reaching hospital).
• Distal embolisation / thrombosis — "trash foot," acute limb ischaemia.
• Aortocaval fistula — high-output cardiac failure, machinery abdominal bruit, leg swelling.
• Aortoenteric fistula — usually erosion into the third/fourth part of the duodenum; classically presents with a small "herald" GI bleed followed by catastrophic haemorrhage. Suspect in any patient with GI bleeding and a previous aortic graft.
• Inflammatory AAA — thick fibrotic wall, periaortic/ureteric involvement (hydronephrosis), raised inflammatory markers.
• Spinal cord ischaemia/paraplegia (thoraco-abdominal repair — artery of Adamkiewicz), renal failure, colonic ischaemia (loss of inferior mesenteric supply).

High-yield: A GI bleed in a patient with a previous aortic graft = aortoenteric fistula (graft erodes into the 3rd/4th part of duodenum) until proven otherwise.

Aneurysm vs dissection — key differential

Feature	Aneurysm	Aortic dissection
Pathology	Dilatation, all-layer	Intimal tear → false lumen in media
Pain	Dull/absent until rupture	Sudden, tearing, radiates to back
Classification	Crawford / location	Stanford A (ascending) vs B (descending); DeBakey I–III
Management	Size-based elective repair	Type A = emergency surgery; Type B = medical BP control
Investigation	USG / CT	CT angiogram (or TOE)

Other differentials: a tortuous/ectatic atherosclerotic aorta, a retroperitoneal mass with transmitted pulsation, pancreatitis (shares Grey Turner/Cullen signs), and renal/ureteric colic in the acute setting.

Recently asked / exam angle

• Repair threshold: Asymptomatic infrarenal AAA → elective repair at ≥ 5.5 cm (or >0.5 cm growth in 6 months). Repeatedly tested as a single-best-answer.
• Commonest site: Infrarenal abdominal aorta.
• Investigation logic: USG for screening/surveillance; CT angiogram for planning and for the stable suspected-rupture patient.
• Screening cohort: one-time USG in men 65–75 who ever smoked.
• Risk factors: smoking strongest; diabetes protective (counter-intuitive favourite).
• Endoleak types: Type II commonest; Types I & III need intervention.
• Ruptured AAA resuscitation: permissive hypotension; unstable patients bypass imaging and go to theatre.
• Eponyms: Grey Turner (flank), Cullen (periumbilical), Ortner (hoarseness from TAA), Crawford (thoraco-abdominal), DeBakey/Stanford (dissection — often paired with aneurysm in MCQs).
• Syphilitic aneurysm: ascending aorta, "tree-bark" intima — classic image-based question.
• Connective tissue: Marfan (FBN1) → ascending root; managed with beta-blockers ± ARBs and earlier surgical threshold.

Mnemonic for elective-repair indications — "5.5, fast, or hurts": ≥ 5.5 cm, fast growth (>0.5 cm/6 mo), or symptomatic.

Mnemonic for AAA risk — "SMOKING": Smoking, Male, Old age, Kin (family history), Increased BP, Nicotine again (the dominant one!), Genetic connective-tissue disease.

Rapid revision

1. Aneurysm = dilatation >1.5× normal; infrarenal aorta ≥ 3.0 cm qualifies.
2. True aneurysm involves all 3 layers; pseudoaneurysm is a contained leak (e.g., post-angiography femoral).
3. AAA is 90% infrarenal; smoking is the strongest risk factor; diabetes is protective.
4. Most AAAs are asymptomatic — found as an expansile pulsatile abdominal mass.
5. Ruptured AAA triad = sudden abdominal/back pain + hypotension + pulsatile mass; usually retroperitoneal.
6. Grey Turner (flank) and Cullen (periumbilical) bruising signal retroperitoneal haemorrhage.
7. USG = screening/surveillance; CT angiogram = operative planning and stable-rupture diagnosis.
8. Elective repair at ≥ 5.5 cm, >0.5 cm growth/6 months, or if symptomatic.
9. Screen men 65–75 who have ever smoked with a one-time USG.
10. EVAR = lower early mortality but lifelong CT surveillance; open repair = more durable.
11. Endoleak Type II is commonest; Types I and III need intervention.
12. Ruptured AAA → permissive hypotension; if unstable, straight to theatre — never delay for imaging.