First and second year — the floor first, then every step
Look at the aortic isthmus on the arterial phase in every trauma CT: an intimal flap, a contour bulge or a pseudoaneurysm there is the injury that kills at the scene or days later.
Orient first
Deceleration injuries tear the aorta where the mobile arch meets the fixed descending aorta — the ISTHMUS, just distal to the left subclavian artery, at the ligamentum arteriosum.
Mediastinal haematoma is a sign, not the diagnosis: it is usually venous. What matters is whether the aortic wall itself is injured, and whether the haematoma touches the aorta.
The ductus diverticulum (a smooth, broad-based bulge at the isthmus with obtuse margins) is the classic mimic of a pseudoaneurysm.
Acquire the study
Arterial phase CT of the chest (the trauma CT), thin slices, with SAGITTAL OBLIQUE (candy-cane) and coronal reformats along the arch.
ECG-gating is not needed for the diagnosis but reduces ascending aortic motion artefact that mimics a flap.
The manoeuvre
Follow the aorta on the sagittal oblique from the root through the arch to the diaphragm; spend time at the isthmus.
Look for an INTIMAL FLAP or intraluminal thrombus projecting into the lumen, and its length in mm.
Look at the external CONTOUR: a focal bulge with acute (sharp) margins is a pseudoaneurysm; a smooth broad-based bulge with obtuse margins is a ductus diverticulum.
Periaortic haematoma: is the fat plane around the aorta preserved, or is there blood directly against the aortic wall?
Measure the aortic diameter at the injury and at the normal aorta proximal and distal, and the distance from the injury to the LEFT SUBCLAVIAN ARTERY origin.
Check the arch branches (innominate, carotids, subclavians) for dissection or pseudoaneurysm, and the ascending aorta just above the valve.
What confirms it
An intimal flap, intraluminal thrombus or contour abnormality of the aortic wall on the arterial phase, confirmed in two planes, with or without periaortic haematoma.
What licenses you to exclude it
A good arterial phase CT with a normal aortic wall and contour excludes significant aortic injury; an isolated anterior mediastinal haematoma with a preserved periaortic fat plane is usually venous — say so explicitly.
The classic misread
Calling a ductus diverticulum a pseudoaneurysm — check the margins and look for a flap.
Calling pulsation artefact of the ascending aorta a dissection flap — it is curvilinear in the left anterior and right posterior positions and does not extend.
Reporting a mediastinal haematoma without commenting on the aortic wall.
Reporting the injury
Classification to use
SVS (Society for Vascular Surgery) grades: I — intimal tear; II — intramural haematoma; III — pseudoaneurysm; IV — rupture. The Starnes (Vancouver) CT classification (intimal tear < 10 mm without contour abnormality / large intimal flap / pseudoaneurysm / rupture) is also used — state which.
Measurements — and how to take them
Aortic diameter at the injury and of the normal aorta proximal and distal (outer wall to outer wall, perpendicular to the centreline).
Length of the intimal flap and of the injured segment, in mm.
Distance from the left subclavian artery origin to the proximal edge of the injury, in mm.
What to report
Location (isthmus, arch, ascending, descending, diaphragmatic hiatus), the lesion type and grade.
Flap length, contour abnormality, pseudoaneurysm size, periaortic haematoma and whether the fat plane is preserved.
Distance from the left subclavian artery origin and the diameters of the proximal and distal normal aorta (the landing zones for TEVAR).
Arch branch involvement; haemothorax; and arch anatomy variants (bovine arch, aberrant right subclavian).
How to report it
CT: "Pseudoaneurysm of the aortic isthmus measuring 22 × 15 mm, beginning 18 mm distal to the left subclavian artery origin, with periaortic haematoma — SVS grade III blunt thoracic aortic injury. Normal aortic diameter 24 mm proximally and 22 mm distally."
What not to report
Do not call mediastinal haematoma "aortic injury" when the aortic wall is normal.
Do not call a ductus diverticulum "possible pseudoaneurysm" without describing the margins that separate them.
Associated injuries to look for
First and second rib, scapular and sternal fractures (high-energy markers), pulmonary contusion, haemothorax, and spinal injury.
What changes management
Grades II–IV usually proceed to endovascular repair; grade I is often managed medically with follow-up CT — the grade is the decision.
Proximity to the left subclavian artery decides whether the stent graft must cover its origin.
Active extravasation or a large left haemothorax — immediate communication.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Thoracic aorta · Ascending and descending thoracic aortic diameter
ascending up to about 40 mm; descending up to about 30 mm
ECG-gated CT or MRI where possible, measured perpendicular to the vessel axis (double-oblique), inner-edge to inner-edge, at named standard levels.
⚠️ THE CONVENTION CHANGES THE NUMBER — inner-to-inner versus outer-to-outer, and gated versus non-gated, differ by several millimetres, which is the whole width of a surveillance decision. Size is body-surface-area and age dependent; indexed thresholds exist. Motion artefact on a non-gated study mimics dissection at the aortic root.
CT · MRI
Thoracic aorta (segmental) · Sinotubular junction, arch and mid-descending diameters — how to report them
each segment is AGE-, SEX- and BSA-INDEXED; report the segment, the convention (inner-to-inner vs outer-to-outer) and the nomogram, not a single remembered millimetre
The root, STJ, mid-ascending, arch and descending aorta do not share one normal number. Surgical thresholds are disease-specific (lower in heritable aortopathy) and are a different table from the normal nomogram. Versioned criterion — verify against the current edition before clinical use.
CT · MRI
Aortic arch (calibre) · Arch diameter at a named level
typically sits between the ascending (~4.0 cm dilated talk) and descending (~3.0 cm) conventional bands; report the double-oblique diameter at a named arch segment rather than inventing a single arch millimetre
Name the level (proximal arch, mid-arch, isthmus). An ungated oblique cut is a different number.
CT · MRI
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.