SonographyAcademy

Curriculum · Clinical Ultrasound: Multisystem Diagnostic & Point-of-Care Sonography

Abdominal & Aortic Sonography: Aorta/AAA, Renal & FAST

The abdominal aorta and AAA (measuring outer-to-outer AP diameter, thresholds, screening), renal survey and hydronephrosis grading, and the FAST exam windows for free fluid.

~40 min · level: advanced · POCUSAbdomen draft — pending clinical review

Learning objectives

  • Scan the abdominal aorta and measure the maximal outer-to-outer AP diameter; define and triage AAA.
  • State the AAA screening recommendation and the surgical-size thresholds.
  • Recognize and grade hydronephrosis on a renal sonogram.
  • List the FAST windows and the most dependent space each interrogates.

Abdominal POCUS answers focused questions — Is the aorta aneurysmal? Is there hydronephrosis? Is there free fluid? — and is the highest-yield, most time-critical of these is the aorta, because a ruptured AAA kills within minutes.

Loading model…
Real anatomy mesh · Human-Organ3D · MIT · drag to rotate, scroll to zoom
Live 3D kidney — rotate to relate the longitudinal sonographic plane (cortex → medulla → central sinus → hilum) to the organ.

Scan the aorta in transverse from the xiphoid to the bifurcation, measuring the maximal anteroposterior diameter, outer wall to outer wall, perpendicular to the vessel. The aorta lies anterior and slightly left of the vertebral body (which casts a posterior shadow); the IVC is to the patient's right and is compressible/respirophasic.

2D B-mode (curvilinear)Abdominal aorta — POCUS (patient with abdominal pain after AAA repair)
Reveal findings
  • Measure outer-wall to outer-wall AP, perpendicular to the vessel, at the widest point — include mural thrombus in the diameter.
  • Normal infrarenal aorta < 2 cm; aneurysm = ≥ 3 cm (focal dilation ≥ 1.5× the normal segment also qualifies).
  • The vertebral body's posterior acoustic shadow and aortic pulsatility orient you; don't mistake an oblique cut (over-estimates) for a true AP.

You measure the maximal outer-to-outer anteroposterior diameter of the abdominal aorta as 3.6 cm. This is:

Real clinical clip · Ben Smith (Ultrasound of the Week) · CC BY-SA 4.0 · UOTW #20 — Ultrasound of the Week, via Wikimedia Commons · caliper calibrated from the on-screen depth scale (approximate)
Abdominal aorta POCUS in a patient with abdominal pain after AAA repair. Freeze on the widest point and measure the outer-to-outer AP diameter with the caliper (calibrated from the depth scale, approximate).
ItemValue

Normal infrarenal aorta

< 2 cm (≈ < 3 cm at all ages)

Aneurysm (AAA)

≥ 3 cm AP, outer-to-outer

Elective repair threshold

≈ 5.5 cm (men) / 5.0 cm (women), or growth > 0.5 cm/6 mo or symptoms

USPSTF screening

One-time scan in men 65–75 who ever smoked

POCUS performance for AAA

Sensitivity ~ 99% for detecting the aneurysm (not rupture)

Abdominal aorta — sizes, thresholds, and screening.

Renal survey. Identify the kidney's echogenic central sinus, the hypoechoic medullary pyramids, and the cortex; compare cortical echogenicity to the adjacent liver/spleen. Hydronephrosis is dilation of the collecting system — anechoic, branching, connecting centrally.

GradeAppearance

Mild

Splaying/anechoic fluid in the central sinus (calyces); 'pelvic' fullness

Moderate

Dilated calyces ballooning, interconnected; cortex preserved

Severe

Massively dilated calyces/pelvis with cortical thinning

Qualitative hydronephrosis grading (POCUS).

The right upper quadrant also holds the gallbladder — scan it fasting, in the left-lateral-decubitus position, for stones (echogenic, mobile, shadowing), wall thickening (> 3 mm), and pericholecystic fluid.

2D B-modeGallbladder — longitudinal (left lateral decubitus)

Which combination is the classic sonographic triad of acute calculous cholecystitis?

Real clinical clip · AhmedAlElg · CC BY-SA 4.0 · Gallbladder Ultrasound — Wikimedia Commons
Real gallbladder scan (left lateral decubitus). Trace the anechoic lumen and the wall; in the live loop, rolling the patient tests whether an echogenic focus is mobile (a stone) rather than a fixed polyp.
WindowProbe locationMost dependent space checked

RUQ (Morison's)

Right flank, mid-axillary

Hepatorenal recess (+ caudal liver tip, R pleural space)

LUQ

Left posterior axillary, higher/more posterior

Splenorenal recess + subphrenic space (+ L pleural)

Pelvis

Suprapubic, sagittal & transverse

Rectovesical / rectouterine (Douglas) pouch

Subxiphoid (cardiac)

Sub-xiphoid

Pericardial sac (effusion/tamponade)

FAST windows.
Worked example — which space fills first?

In a supine adult with intraperitoneal hemorrhage from a liver laceration, which single FAST view is most likely to be positive first, and why?

Solution.

The RUQ / Morison's (hepatorenal) recess is the most dependent intraperitoneal space in the supine adult, so free blood tracks there preferentially — making the RUQ view the highest-yield single window. Sensitivity rises with the caudal liver tip and serial/repeat scanning.

Key takeaways

  • Measure the abdominal aorta in transverse as the maximal outer-wall-to-outer-wall AP diameter, perpendicular to the vessel and including mural thrombus; oblique cuts overestimate size.
  • An AAA is defined by an AP diameter of at least 3 cm (or focal dilation 1.5x the adjacent normal segment), with elective repair around 5.5 cm in men / 5.0 cm in women, growth over 0.5 cm per 6 months, or symptoms.
  • USPSTF recommends a one-time screening scan in men 65-75 who ever smoked, and POCUS is about 99% sensitive for detecting the aneurysm but not the rupture, so a hypotensive patient with a known AAA should be treated as rupture without waiting for sonographic blood.
  • Hydronephrosis is graded mild (sinus splaying), moderate (interconnected calyceal dilation with preserved cortex), and severe (massive calyceal/pelvic dilation with cortical thinning); mimics include renal vessels (fill on color Doppler), peripelvic cysts, and an extrarenal pelvis.
  • The four FAST windows are RUQ/Morison's hepatorenal recess, LUQ splenorenal/subphrenic, suprapubic rectovesical/rectouterine pouch, and subxiphoid pericardial sac, with Morison's pouch the most dependent intraperitoneal space supine and therefore the highest-yield single view.

Check your understanding

Registry-style items with worked rationales.

1An abdominal aortic aneurysm is defined by a maximal aortic diameter (outer-to-outer) of at least:recall

2When measuring the abdominal aorta, the correct technique is:application

3Severe hydronephrosis is distinguished from moderate primarily by:analysis

4In a supine trauma patient, the single most dependent intraperitoneal space — and thus highest-yield FAST view — is:application

Go deeper — trusted free resources

Hand-picked, verified links to authoritative open resources. Opens in a new tab.

Radiopaedia
Abdominal Aortic Aneurysm

Comprehensive reference covering AAA definition, the >3 cm threshold, sonographic appearance, surveillance, and rupture imaging findings.

Open →
The POCUS Atlas
Aorta POCUS Scanning Guide

Hands-on point-of-care technique for transverse and longitudinal aortic views with normal and aneurysmal image examples.

Open →
ACEP SonoGuide
FAST Exam in Trauma

Step-by-step emergency ultrasound guide to the four FAST windows for detecting free fluid in the peritoneal, pericardial, and pleural spaces.

Open →
Radiopaedia
Hydronephrosis

Renal reference detailing collecting-system dilatation, sonographic grading, and pitfalls relevant to bedside renal ultrasound.

Open →

References

  1. American College of Emergency Physicians. Ultrasound Guidelines: Emergency, Point-of-care, and Clinical Ultrasound Guidelines in Medicine. 2016/2023.
  2. US Preventive Services Task Force. Screening for Abdominal Aortic Aneurysm: Recommendation Statement. JAMA. 2019;322(22):2211-2218.
  3. Moore CL, Copel JA. Point-of-care ultrasonography. N Engl J Med. 2011;364(8):749-757.
  4. Kremkau FW. Sonography Principles and Instruments. 9th ed. Elsevier; 2016.