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Cardiovascular

Vascular Anatomy

The thoracoabdominal vascular system comprises the aorta and its named branches, the systemic and portal venous systems, and the pulmonary circulation, forming the roadmap for interpreting CT and MR angiography. Accurate assessment requires knowledge of normal caliber, branching patterns, and the many clinically important variants. Vascular imaging is central to the diagnosis of aneurysm, dissection, occlusive disease, thromboembolism, and to procedural planning.

Key Structures

  • Aorta: ascending, arch giving brachiocephalic, left common carotid, and left subclavian arteries, then descending thoracic and abdominal segments; bifurcates at ~L4
  • Visceral branches: celiac axis (T12), superior mesenteric (L1), paired renal arteries (~L1-L2), inferior mesenteric artery (L3)
  • Iliac system: common iliac arteries dividing into internal (hypogastric) and external iliac at the pelvic brim
  • Systemic veins: SVC from brachiocephalic confluence, IVC from common iliac veins ascending to the right atrium
  • Portal venous system: splenic and superior mesenteric veins forming the portal vein, with hepatic veins draining to the IVC
  • Pulmonary circulation: main pulmonary artery bifurcating into right and left, with pulmonary veins returning to the left atrium
  • Coronary ostia arising from the aortic sinuses just above the aortic valve

Imaging Planes & Modalities

  • CT angiography with bolus-tracked arterial-phase acquisition and thin sections provides the reference standard for aneurysm, dissection, and occlusive disease; MIP, MPR, and volume-rendered reconstructions aid interpretation
  • Multiphase CT (arterial, portal-venous, delayed) distinguishes arterial from venous structures and detects endoleaks and active extravasation
  • MR angiography (contrast-enhanced or non-contrast time-of-flight/phase-contrast/SSFP) is used in renal impairment and for flow assessment
  • Doppler ultrasound quantifies stenosis, flow direction, and portal/hepatic venous patency without contrast or radiation
  • Catheter angiography (DSA) remains the gold standard for detailed roadmapping and endovascular intervention
  • ECG-gated CTA reduces pulsation artifact for the aortic root and coronary arteries

Landmarks & Normal Values

  • Normal ascending aorta <3.5-4 cm, descending thoracic aorta <3 cm, infrarenal abdominal aorta typically <2 cm (aneurysm ≥3 cm)
  • Celiac origin at T12, SMA at L1, renal arteries L1-L2, IMA at L3, aortic bifurcation at L4
  • Main pulmonary artery diameter >29 mm (or PA:ascending aorta ratio >1) suggests pulmonary hypertension
  • IVC diameter and respiratory collapsibility reflect volume status; SVC drains into the upper right atrium
  • Portal vein main diameter typically <13 mm; hepatopetal flow is normal

Anatomical Variants

  • Aortic arch variants: bovine arch (common origin of brachiocephalic and left common carotid) and aberrant right subclavian artery (arteria lusoria)
  • Replaced or accessory hepatic arteries—replaced right from the SMA, replaced left from the left gastric artery (relevant to surgery and embolization)
  • Accessory/multiple renal arteries and early renal artery branching, important before transplant or endovascular repair
  • Left-sided or duplicated IVC, circumaortic and retroaortic left renal vein
  • Persistent left SVC draining to the coronary sinus; azygos continuation of the IVC with interrupted intrahepatic segment
  • Celiacomesenteric trunk and median arcuate ligament impression on the celiac origin

Pathology Correlation

  • Aortic dissection: intimal flap with true and false lumens; Stanford A (ascending) requires surgery, type B managed medically/endovascularly
  • Aneurysm rupture risk rises with diameter; periaortic stranding, hyperdense crescent, and draping over vertebra signal instability
  • Acute pulmonary embolism: filling defects with right-heart strain (RV:LV ratio >1, septal bowing)
  • Atherosclerotic and thromboembolic occlusion—renal, mesenteric, or peripheral—causing infarction or ischemia
  • Portal hypertension produces varices, recanalized paraumbilical vein, and splenomegaly; portal vein thrombosis shows expansion and cavernous transformation
  • Endoleaks after EVAR classified I-V on delayed-phase CTA; median arcuate ligament syndrome from celiac compression

Pitfalls & Mimics

  • Pulsation and motion artifact at the aortic root can mimic dissection—confirm with ECG-gating or a second phase
  • Mistiming the bolus causes pseudo-filling defects (transient interruption of contrast) that mimic PE or thrombus
  • Flow-related and mixing artifacts in the IVC, portal vein, and pulmonary arteries simulate thrombus
  • Do not overlook variant vascular anatomy before surgery or embolization—missed replaced hepatic or accessory renal arteries cause complications
  • Slow-flow or in-plane vessels cause signal loss on TOF MRA, overestimating stenosis
  • Mural thrombus and atheroma can be mistaken for dissection or true-lumen narrowing

References

  • Kadir S. Atlas of Normal and Variant Angiographic Anatomy. Saunders
  • Uflacker R. Atlas of Vascular Anatomy: An Angiographic Approach. Lippincott Williams & Wilkins
  • Rumack CM, Levine D. Diagnostic Ultrasound. Elsevier
  • Webb WR, Higgins CB. Thoracic Imaging: Pulmonary and Cardiovascular Radiology. Wolters Kluwer

⚕️ Educational reference — correlate with clinical context and confirm with a qualified radiologist.