Chest CT Basics and Anatomy

Overview

• Introductory lesson on chest CT: basic anatomy and a systematic reading approach.
• Covers contrast timing, mediastinal compartments, key vascular/airway anatomy, lung lobes/segments, lymph nodes, pleura, chest wall, and a stepwise search pattern.

CT Protocols and Contrast Timing

• Non-contrast CT chest: no IV contrast in heart or vessels.
• Early arterial (≈15 s): bright pulmonary arteries; CT pulmonary angiogram (CTPA) for pulmonary emboli.
• Arterial/aortic phase (≈20 s): bright aorta and arteries; CTA for aortic dissection.
• Routine venous/soft tissue phase (≈60–70 s): optimal soft tissue enhancement.
• Other protocols exist (low dose, high-resolution), not detailed here.

Thoracic Cavity Boundaries

• Thoracic inlet superiorly: bordered by first ribs and manubrium.
• Thoracic outlet inferiorly: closed by diaphragm; bordered by lower ribs and sternum.
• Contents: right and left lungs; mediastinum centrally; chest wall surrounding.

Mediastinum: Compartments and Contents

• Landmark: fibrous pericardium visible on CT; inserts on diaphragm; up to great vessel roots.
• Superior mediastinum: above pericardium, below thoracic inlet; trachea, esophagus, major vessels.
• Anterior mediastinum: anterior to pericardium; fat in adults; thymus in youth; lymph nodes; possible thyroid extension.
• Middle mediastinum: within pericardium; heart, SVC, pulmonary trunk, ascending aorta; tracheal bifurcation; nodes.
• Posterior mediastinum: posterior to pericardium; spine, paraspinal nerves, vasculature, esophagus; neurogenic tumors common.

Cardiac Anatomy on CT

• Right atrium: receives IVC and SVC; right atrial appendage; crista terminalis is normal ridge.
• Right ventricle: thinner wall; moderator band (septomarginal trabecula) may be subtle.
• Pulmonary outflow: pulmonary trunk to right and left pulmonary arteries.
• Pulmonary veins: drain lungs to left atrium posteriorly; left atrial appendage prone to thrombus and mixing artifact.
• Left ventricle: thicker wall; papillary muscles visible; outflow to aortic valve and ascending aorta.
• Left atrium normal AP dimension roughly under four centimeters.

Major Arteries

• Aorta: aortic valve, ascending aorta, arch, descending aorta.
• Coronaries: left main with LAD along septum and circumflex; right coronary from right cusp.
• Arch branches: brachiocephalic trunk → right subclavian and right common carotid; left common carotid; left subclavian.
• Subclavian branches: vertebral artery; internal thoracic artery along anterior chest wall.
• Intercostal arteries: run along inferior rib margins; key in trauma bleeds.
• Pulmonary arteries: trunk and main branches; segmental branches covered later.

Major Veins

• Jugular + subclavian → brachiocephalic veins bilaterally.
• Left and right brachiocephalic → superior vena cava to right atrium.
• Azygos vein: ascends right of aorta; arch joins SVC above right main bronchus.
• Inferior vena cava: enters right atrium inferiorly.
• Largest cardiac (coronary) vein drains posterior heart to right atrium.

Airways and Esophagus

• Trachea bifurcation (carina) into right and left main bronchi.
• Right main bronchus: shorter, more inferiorly angled; aspiration favors right.
• Esophagus: posterior mediastinum to gastroesophageal junction and stomach.

Lymph Node Stations (Key Groups)

• Supraclavicular and low cervical nodes bilaterally.
• Prevascular nodes: anterior to great vessels.
• Aortopulmonary (AP) window: between aorta and pulmonary artery.
• Paratracheal nodes: left and right; divided by left lateral tracheal border.
• Subcarinal nodes: below carina; paraesophageal nodes inferiorly/posteriorly.
• Hilar nodes: adjacent to main bronchi; then interlobar, lobar, segmental, subsegmental.
• Additional: axillary, internal thoracic chain, cardiophrenic nodes.

Lung Lobes and Fissures

• Right lung: oblique and horizontal fissures; upper, middle, lower lobes.
• Left lung: oblique fissure only; upper and lower lobes; lingula is inferior part of upper lobe.
• Pleura: double layer; pleural space for effusion (dependent fluid) or pneumothorax (gas).

Lung Segmental Anatomy (Summary Table)

• Segments follow bronchial branches; right has 10, left has 8.

Chest Wall and Adjacent Structures

• Bones: ribs 1–12; spine; manubrium and sternum; clavicles; acromioclavicular joints; scapulae; proximal humeri.
• Muscles visible: pectoralis major/minor; rotator cuff; paraspinal muscles.
• Thyroid gland in lower neck often visible; typically bright with contrast.
• Upper abdomen often included: liver, gallbladder, pancreas, spleen, adrenals, kidneys; check adrenals in lung cancer.

Systematic Approach to Reading a Chest CT

• Review scout image first for broader coverage and incidental findings.
• Soft tissue window: identify devices (pacemakers, lines, tubes).
• Chest wall and lower neck: include thyroid; scan spinal canal for incidental issues.
• Heart and pericardium: chamber enlargement; thrombus or tumor; pericardial space pathology.
• Coronaries: look for calcifications or stents on non-gated scans.
• Mediastinal vessels: measure pulmonary trunk; >3.0 cm suggests pulmonary hypertension.
• Pulmonary arteries: follow for incidental emboli even on routine contrast scans.
• Aorta: measure ascending aorta if large; >4.0 cm is aneurysmal; follow arch and descending aorta.
• Esophagus and mediastinal masses: assess by compartments.
• Lymph nodes: survey supraclavicular, prevascular, AP window, paratracheal, subcarinal, paraesophageal, hilar, internal thoracic, cardiophrenic, axillary.
• Pleura: on soft tissue for effusion/thickening/calcification; on lung window for pneumothorax in non-dependent areas.
• Airways: assess trachea and bronchi; note right-sided aspiration tendency.
• Lung parenchyma: quick overview by quadrants, then detailed search for nodules.
• MIP images: use to detect nodules as dots amid linear vessels; confirm on standard axial images.
• Bones: survey ribs posterior and anterior, clavicles, sternum, spine, scapulae, humeral heads; include sagittal review for spine and sternum.
• Upper abdomen: quick review of solid organs and bowel segments seen; look for adrenal nodules.

Key Terms & Definitions

• CTPA: CT pulmonary angiogram targeting pulmonary arteries for emboli.
• CTA chest: arterial phase CT highlighting aorta and arterial tree.
• Carina: tracheal bifurcation into main bronchi.
• AP window: mediastinal space between aortic arch and pulmonary artery.
• MIP: maximum intensity projection; thick-slab technique enhancing linear high-density structures.
• Moderator band: muscular band in right ventricle; septomarginal trabecula.
• Crista terminalis: normal ridge in right atrium; can mimic pathology if unfamiliar.

Action Items / Next Steps

• Practice scrolling through full chest CT cases using interactive cases.
• Review “A Practical Introduction to CT” before continuing this series.
• Prepare for the next video: CTPA technique, detailed segmental anatomy, and diagnosing acute and chronic pulmonary emboli.