Angiography & Vascular Radiology

Vascular radiology spans catheter-based diagnostic angiography (DSA) and modern cross-sectional CT/MR angiography. For NEET PG, the high-yield zone is DSA principles, CT angiography of aortic dissection, pulmonary embolism, and aneurysm sizing — image-based questions are increasingly common.

Digital Subtraction Angiography (DSA) — principles

DSA remains the gold standard for luminal vascular imaging because of its high spatial and temporal resolution. The core trick is subtraction: a pre-contrast image (the mask) is digitally subtracted from the post-contrast image, so that bone and soft-tissue background disappear and only the contrast-filled vessel remains.

Workflow: Mask image acquired → iodinated contrast injected via catheter → serial images captured → mask subtracted pixel-by-pixel → vessel highlighted against a clean background.

Key technical facts:

• Logarithmic amplification is applied so that subtraction reflects iodine concentration linearly.
• The biggest artefact is misregistration — caused by patient/bowel/respiratory motion between mask and contrast frames. Corrected by pixel shifting or re-masking.
• Temporal subtraction (mask before contrast) is the standard; energy/dual-energy subtraction uses two kVp exposures.
• Contrast: low/iso-osmolar non-ionic iodinated agents (e.g. iohexol, iodixanol). CO₂ is used as a negative contrast agent in patients with renal failure or iodine allergy — but CO₂ is contraindicated above the diaphragm (risk of cerebral/coronary gas embolism).

High-yield: The fundamental principle of DSA is removal of the bony and soft-tissue background by subtracting a pre-contrast mask image; the commonest artefact is patient motion (misregistration), corrected by pixel shifting.

Seldinger technique

Vascular access for angiography uses the Seldinger technique (1953):

Needle puncture → guidewire passed through needle → needle removed → catheter advanced over guidewire → guidewire removed.

The common femoral artery (over the femoral head, below the inguinal ligament) is the classic access site; radial and brachial access are increasingly used. Puncture below the femoral head risks pseudoaneurysm and retroperitoneal haemorrhage if too high.

Contrast media & safety

Feature	Ionic high-osmolar	Non-ionic low/iso-osmolar
Osmolality	Very high (~1500 mOsm/kg)	Low/iso (~290–800)
Adverse reactions	More frequent	Fewer
Cost	Cheap	Costly
Current use	Largely abandoned	Standard of care

• Contrast-induced nephropathy (CIN): rise in serum creatinine ≥0.5 mg/dL or ≥25% within 48–72 h. Prevent with hydration; metformin is withheld for 48 h after contrast in renal impairment.
• Anaphylactoid reactions: managed with adrenaline (IM 0.5 mg of 1:1000 for severe reactions), oxygen, antihistamines, steroids.
• eGFR <30 is the major threshold for caution with gadolinium (risk of nephrogenic systemic fibrosis with older linear agents).

High-yield: Withhold metformin for 48 hours after iodinated contrast in renal impairment; treat severe contrast anaphylaxis with IM adrenaline 1:1000.

CT Angiography — general

CTA uses a timed bolus of iodinated contrast with bolus tracking (a region of interest in the aorta triggers scanning when attenuation reaches a threshold, typically ~100–150 HU). MDCT allows isotropic 3D reconstructions (MIP, volume rendering, curved planar reformats).

Aortic Dissection

A tear in the intima allows blood to track into the media, creating a false lumen separated from the true lumen by an intimal flap.

Risk factors: hypertension (commonest), Marfan syndrome, Ehlers-Danlos, bicuspid aortic valve, coarctation, pregnancy, cocaine, trauma.

Classification

System	Type	Extent
Stanford	A	Involves ascending aorta (± arch/descending)
	B	Distal to left subclavian; ascending spared
DeBakey	I	Ascending + arch + descending (entire)
	II	Ascending only
	IIIa	Descending, above diaphragm
	IIIb	Descending, below diaphragm

Memory bridge: Stanford A = DeBakey I + II (anything involving the Ascending). Stanford B = DeBakey III.

High-yield: Stanford A dissection is a surgical emergency; Stanford B (uncomplicated) is managed medically with aggressive impulse control (beta-blockers first to reduce dP/dt, e.g. IV labetalol/esmolol, then vasodilators).

Investigation of choice

• CT angiography is the investigation of choice in haemodynamically stable patients (fast, sensitive ~100%).
• Transoesophageal echo (TEE) is preferred for unstable patients and intra-operatively.
• MRA is most sensitive overall but slow — used for stable follow-up.

CTA signs: intimal flap, true vs false lumen, "beak sign" (acute angle of false lumen), spider-web sign of false lumen. The false lumen is usually larger, with delayed/slower opacification and surrounds the true lumen. Differentiate from intramural haematoma (no flap, crescentic high attenuation) and penetrating atherosclerotic ulcer.

Complications: aortic rupture, cardiac tamponade (commonest cause of death in type A), coronary occlusion, aortic regurgitation, stroke, malperfusion of mesenteric/renal/limb vessels.

Aortic Aneurysm

A true aneurysm dilates all three vessel-wall layers; a false (pseudo)aneurysm is a contained rupture with blood held by adventitia/surrounding tissue. Defined as >1.5× normal diameter.

Sizing thresholds (abdominal aortic aneurysm, AAA):

Diameter	Action
<3.0 cm	Normal aorta
3.0–3.9 cm	Surveillance every 2–3 yrs (USG)
4.0–5.4 cm	Surveillance 6–12 monthly
≥5.5 cm (men) / ≥5.0 cm (women)	Elective repair
Growth >0.5 cm in 6 mo / >1 cm yr	Repair regardless
Symptomatic / rupturing	Emergency repair

• USG is the screening and surveillance modality of choice (cheap, no radiation).
• CT angiography is the modality for pre-operative planning (sizing for EVAR — endovascular aneurysm repair).
• Most AAAs are infrarenal and fusiform; degenerative/atherosclerotic is the commonest aetiology.

High-yield: Repair an AAA when it reaches ≥5.5 cm (≥5.0 cm in women), grows >1 cm/year, or becomes symptomatic. One-time USG screening is recommended for men 65–75 who ever smoked.

Rupture sign: retroperitoneal haematoma, "draped aorta sign", and the "hyperattenuating crescent sign" (crescent of high attenuation within the mural thrombus = impending rupture).

Pulmonary Embolism (PE)

Thromboembolism (usually from lower-limb DVT) lodging in the pulmonary arteries. A saddle embolus straddles the bifurcation of the main pulmonary artery — high-yield image.

Diagnostic pathway

Clinical pretest probability (Wells score) → D-dimer if low/intermediate → CT pulmonary angiography (CTPA) if D-dimer positive or high probability.

• CTPA is the investigation of choice for PE (direct visualisation of intraluminal filling defects).
• V/Q scan is preferred in pregnancy, renal failure, or contrast allergy — shows mismatched (ventilation normal, perfusion absent) defects.
• Conventional pulmonary DSA is the historic gold standard, now reserved for intervention.

Classic radiographic signs (chest X-ray — usually normal, but eponyms are tested)

Sign	Description
Hampton's hump	Wedge-shaped, pleura-based opacity (pulmonary infarct), apex toward hilum
Westermark sign	Focal oligaemia distal to the embolus (regional lucency)
Fleischner sign	Enlarged/prominent central pulmonary artery
Palla sign	Enlarged right descending pulmonary artery

High-yield: CTPA = investigation of choice for PE; switch to V/Q scan in pregnancy / renal failure / contrast allergy. Memorise Hampton's hump (infarct), Westermark sign (oligaemia), Fleischner sign (big PA).

CTPA findings: intraluminal filling defect, "polo-mint sign" (central defect on axial), "railway-track sign" (longitudinal), saddle embolus at bifurcation. RV/LV ratio >1 indicates right-heart strain (poor prognosis).

Right-heart strain on CT → consider thrombolysis in massive PE (haemodynamic instability/hypotension). Anticoagulation is the mainstay; IVC filter if anticoagulation contraindicated or recurrent PE despite therapy.

Other vascular interventions (exam-relevant snapshots)

• TIPS (transjugular intrahepatic portosystemic shunt): for variceal bleeding / refractory ascites; connects hepatic vein to portal vein. Complication: hepatic encephalopathy.
• Uterine artery embolisation: for symptomatic fibroids and post-partum haemorrhage.
• Bronchial artery embolisation: for massive haemoptysis.
• Embolic agents: coils, gelfoam (temporary), PVA particles, glue (NBCA), Onyx.
• Stroke thrombectomy: mechanical clot retrieval for large-vessel occlusion within the time window.

Renal artery stenosis & FMD

• Atherosclerotic RAS: ostial/proximal, elderly — commonest cause overall.
• Fibromuscular dysplasia (FMD): young women, mid/distal renal artery, classic "string of beads" appearance on angiography. Treated by angioplasty (stenting usually not needed).

High-yield: "String of beads" on renal angiography = fibromuscular dysplasia, typically a young hypertensive woman, treated with balloon angioplasty.

Key differentials & look-alikes

Entity	Key distinguishing feature
Aortic dissection	Intimal flap, two lumina
Intramural haematoma	Crescentic high-attenuation wall, no flap
Penetrating ulcer	Focal contrast outpouching through intima
Aneurysm	Dilatation >1.5× without flap
PE (acute)	Acute-angle, central filling defect, vessel expanded
Chronic PE	Eccentric, web/band, calcified, vessel narrowed

Recently asked / exam angle

• Image-based: "Saddle embolus" CTPA, "string of beads" renal angiogram, intimal flap on CT — identify the diagnosis.
• Classification matching: Stanford A vs DeBakey I/II; "which dissection needs surgery?" (answer: type A / ascending involvement).
• IOC questions: IOC for stable aortic dissection (CTA); IOC for PE (CTPA); PE imaging in pregnancy (V/Q scan); AAA screening/surveillance (USG).
• Cut-offs: AAA repair at 5.5 cm; aneurysm = >1.5× normal.
• Principle question: what does DSA subtract? (background bone/soft tissue via a mask image).
• Eponym recall: Hampton's hump = infarct; Westermark = oligaemia; Fleischner = enlarged PA.
• Safety: withhold metformin 48 h post-contrast; CO₂ angiography contraindicated above the diaphragm.

Rapid revision

1. DSA removes background by subtracting a pre-contrast mask; commonest artefact = motion (misregistration), fixed by pixel shifting.
2. Seldinger technique = needle → guidewire → catheter; classic access = common femoral artery over femoral head.
3. Stanford A (ascending) = surgical emergency; Stanford B = medical (impulse control with beta-blockers first).
4. DeBakey: I = whole aorta, II = ascending only, III = descending (a above / b below diaphragm).
5. IOC for stable dissection = CT angiography; unstable = TEE.
6. AAA repair at ≥5.5 cm men / ≥5.0 cm women, or growth >1 cm/yr, or symptomatic.
7. USG = AAA screening/surveillance; CTA = EVAR planning. Hyperattenuating crescent = impending rupture.
8. CTPA = IOC for PE; use V/Q scan in pregnancy / renal failure / contrast allergy.
9. Saddle embolus straddles the main PA bifurcation; RV/LV >1 = right-heart strain.
10. Hampton's hump = infarct; Westermark = oligaemia; Fleischner = enlarged central PA.
11. "String of beads" renal artery = fibromuscular dysplasia in a young woman → angioplasty.
12. CO₂ contrast for renal failure/iodine allergy but never above the diaphragm; withhold metformin 48 h post iodinated contrast.