1 · Liver & biliary tree Free

The normal liver has a smooth capsule, sharp inferior edge and a fine, homogeneous mid-level echotexture — slightly brighter than the adjacent renal cortex but similar to or just less bright than the spleen. You navigate the liver by its vessels, and the single most useful skill is telling a portal vein from a hepatic vein.

How to read the vascular landmarks

• Portal veins have bright, echogenic walls (fibrofatty periportal cuff of the portal triad — vein + hepatic artery + bile duct) and run towards the porta hepatis. Flow is normally hepatopetal (into the liver) and appears above the baseline / towards the probe on Doppler.
• Hepatic veins have thin, near-invisible walls and drain towards the IVC and the diaphragm, dividing the liver into segments. They enlarge towards the top of the liver.
• The main lobar fissure — a thin echogenic line running from the gallbladder fossa to the right portal vein — separates right and left lobes and is your pointer to the gallbladder neck.
• The ligamentum teres / falciform ligament (echogenic, in the left lobe) separates medial and lateral segments; the ligamentum venosum separates the caudate lobe.

Portal vein flow — the numbers that matter

Normal portal vein flow is hepatopetal (towards the liver), gently phasic with respiration and a low-velocity, continuous venous waveform. Reversed (hepatofugal) flow, a to-and-fro pattern, or loss of respiratory phasicity points to portal hypertension. Peak/mean velocity typically sits around ~15–40 cm/s, and the main portal vein normally measures ≤ 13 mm in the resting fasting adult.

2 · Gallbladder, pancreas & spleen Free

Gallbladder

Fasting, the normal gallbladder is a thin-walled, anechoic ovoid with clean posterior enhancement (through-transmission) and no internal echoes, shadowing stones or septa. The wall is a single echogenic line measuring < 3 mm; it thickens physiologically after eating (so always scan fasted). It sits at the interlobar fissure — follow that echogenic line from the right portal vein and it points you to the gallbladder neck.

Pancreas

The pancreas lies retroperitoneally, draped over the splenic vein (which runs along its posterior body/tail) and anterior to the SMA and aorta. In young adults it is iso- to slightly hyperechoic relative to normal liver and becomes progressively more echogenic (fatty) with age. The main pancreatic duct is a thin double-line normally measuring ≤ 3 mm in the head, tapering distally.

Spleen

The spleen is a homogeneous, crescentic organ in the left upper quadrant, slightly more echogenic than normal renal cortex and similar to or a touch brighter than liver. Normal maximum (bipolar) length is ≤ 12 cm; > 13 cm is generally splenomegaly. Look for the splenic vein at the hilum and always hunt for a splenule (accessory spleen) near the lower pole.

3 · Kidneys & bladder Free

A normal kidney has three concentric zones on ultrasound: a smooth capsule, a hypoechoic cortex (darker than, or equal to, the liver/spleen), hypoechoic medullary pyramids that can be mistaken for cysts, and a bright central echo complex (renal sinus — fat, vessels and collecting system). The step in brightness between cortex and pyramid is corticomedullary differentiation, and its loss is an early sign of medical renal disease.

What to check

• Length 9–12 cm, with < ~2 cm difference between the two sides. Small, echogenic kidneys suggest chronic disease; a large kidney suggests obstruction, infiltration or acute injury.
• Cortical thickness > ~7 mm and preserved corticomedullary differentiation.
• No hydronephrosis — the central sinus echoes should be a solid bright block with no anechoic branching of a distended pelvicalyceal system.
• The bladder is anechoic with a thin wall (< 3 mm distended, < 5 mm empty) and shows posterior enhancement; look for symmetric ureteric jets on colour Doppler.

4 · Aorta & IVC Free

The abdominal aorta is the left-sided, thick-walled, pulsatile vessel anterior to the vertebral bodies; the IVC is the right-sided, thinner-walled, compressible vessel that varies with respiration. Always measure the aorta outer wall to outer wall, perpendicular to its long axis, in both AP and transverse planes — the single number that defines an aneurysm.

Aorta

• Normal AP diameter is < 2 cm (typically 1.5–2.0 cm), tapering distally to the bifurcation at the umbilicus.
• ≥ 3 cm = abdominal aortic aneurysm (AAA) — the accepted threshold, regardless of shape. Between 2 and 3 cm is “ectatic”. Assess the whole infrarenal course for a hypoechoic mural thrombus that can hide the true lumen.

IVC and collapsibility

The IVC diameter and its respiratory collapsibility estimate right-atrial pressure / volume status. In a spontaneously breathing patient a normal IVC is ≤ 2.1 cm with > 50% collapse on a sniff — suggesting a normal/low RA pressure. A plethoric IVC (> 2.1 cm) that collapses < 50% suggests elevated RA pressure / volume overload.

5 · Thyroid & neck Free

The normal thyroid is a homogeneous, hyperechoic gland (brighter than the strap muscles) with a fine texture, straddling the trachea as two lobes joined by a thin midline isthmus. Key relations: the common carotid artery and internal jugular vein lie posterolateral, the hypoechoic longus colli muscle sits behind, the trachea (bright anterior arc, dirty shadow) is medial, and the oesophagus peeps out behind the left lobe.

What to check

• Lobe size: each lobe ~4–6 cm cranio-caudal, ~1.3–1.8 cm in AP and transverse. The isthmus is < 3 mm AP.
• Vascularity: normal on colour Doppler is sparse, scattered flow (“no thyroid inferno”). Diffusely increased flow suggests Graves / thyroiditis.
• Parathyroids are normally not seen; when enlarged they appear as hypoechoic ovals posterior to the gland. Normal cervical lymph nodes are elongated, hypoechoic with a preserved echogenic fatty hilum and hilar (central) vascularity.

6 · Obstetric & gynae Free

Uterus — zonal anatomy & the endometrial stripe

The normal uterus shows three zones on ultrasound: an outer myometrium (mid-level echoes), an inner hypoechoic junctional zone, and the central endometrium — the “endometrial stripe” — whose thickness and pattern change through the cycle:

• Menstrual/early proliferative: thin, echogenic, ~2–4 mm.
• Late proliferative (peri-ovulatory): a trilaminar “three-line” sign, ~6–10 mm.
• Secretory (luteal): thick, uniformly echogenic, ~7–14 mm (up to ~16 mm).
• Post-menopausal (no bleeding): thin, < 5 mm (< 4 mm if bleeding is being investigated).

Ovaries

Almond-shaped, with peripheral follicles around a more echogenic stroma. Normal reproductive-age ovarian volume ≈ 5–10 mL (V = L × W × H × 0.52); a dominant follicle up to ~2.5 cm before ovulation is normal. Post-menopausal ovaries are small (< ~8 mL) and often hard to see.

Early pregnancy — the milestone sequence (SRU discriminatory values)

7 · Scrotum & testis Free

The normal testis is an ovoid organ with a smooth, homogeneous, mid-level (granular) echotexture, surrounded by the bright echogenic tunica albuginea. An echogenic band running through it — the mediastinum testis — is the hilum where vessels and tubules converge and is a reliable landmark. A trace of anechoic fluid in the tunica vaginalis is normal (physiologic hydrocele).

Epididymis and Doppler

• The epididymis caps the testis: the head (globus major) at the superior pole is iso/slightly hyperechoic to testis; the body and tail run along the posterolateral aspect and are usually isoechoic or slightly less echogenic.
• Normal Doppler: symmetric, low-resistance intratesticular arterial flow with continuous forward diastolic flow. Always compare both sides on the same settings — the key question in acute pain is present and symmetric flow (torsion shows absent/reduced flow).

8 · Vascular — carotid Free

The carotid system is where grey-scale, colour and spectral Doppler come together. The common carotid artery (CCA) runs up the neck and divides at the bulb into the internal (ICA) and external (ECA) carotid arteries. Knowing which is which is the whole examination, and the spectral waveform tells you as reliably as the anatomy.

Telling ICA from ECA

• ICA — usually larger, posterolateral, no branches, and a low-resistance waveform: broad systolic peak with high continuous forward diastolic flow (it feeds the low-resistance brain).
• ECA — usually smaller, anteromedial, has branches (the superior thyroid is first), and a high-resistance waveform: sharp systolic peak with low or absent diastolic flow. The temporal tap (percussing the preauricular temporal artery) sends oscillations down the ECA to confirm it.
• CCA — intermediate waveform, reflecting the blended ICA + ECA outflow.

Intima-media thickness (IMT)

Measured on the far wall of the distal CCA, the normal IMT is < 0.9 mm; values ≥ 0.9–1.0 mm denote increased cardiovascular risk and ≥ 1.5 mm (focal) defines a plaque. Measure in a plaque-free segment, perpendicular to the wall, in end-diastole.