RDMS Abdomen cheat sheet

The liver is divided into eight Couinaud segments, each with its own portal venous, hepatic arterial, and biliary branch; hepatic veins run between segments.

The portal triad contains the main portal vein, proper hepatic artery, and common bile duct, all within the hepatoduodenal ligament; the portal vein is the largest.

Normal common bile duct measures up to 6 mm, increasing about 1 mm per decade after age 60, and may reach 10 mm after cholecystectomy.

Adult kidney length is 9-12 cm; the right kidney sits lower than the left because of the liver, and normal renal cortex is hypoechoic to liver and spleen.

Normal spleen measures up to 13 cm in length, 7 cm in width, and 5 cm in thickness, and is slightly more echogenic than the liver.

Pancreas is imaged in the head, neck, body, and tail; the normal pancreatic duct measures 2-3 mm, with the splenic vein and SMA as landmarks.

The bowel wall shows five sonographic layers (gut signature), alternating echogenic and hypoechoic, from mucosa to serosa.

Surface anatomy: the portal splenic confluence lies anterior to the IVC and is formed by the superior mesenteric and splenic veins.

Resistive index: RI = (peak systolic velocity - end-diastolic velocity) / peak systolic velocity; normal renal RI is 0.55-0.70.

Normal hepatic artery shows a low-resistance waveform with continuous forward diastolic flow and RI of approximately 0.55-0.70.

Portal vein flow is continuous, hepatopetal, and gently undulating with respiration and cardiac pulsation; mean velocity is about 15-30 cm/s.

Hepatic veins show a triphasic pulsatile waveform (A, S, D waves) reflecting right heart hemodynamics; loss of pulsatility suggests parenchymal disease.

Doppler angle should be 60 degrees or less; the sample gate is placed mid-vessel with the vessel parallel to the angle corrector.

Fasting SMA shows a high-resistance waveform with early diastolic reversal that converts to low resistance after a meal.

Renal artery acceleration time under 70 ms is normal; a prolonged acceleration time with low amplitude indicates tardus-parvus flow from upstream stenosis.

Renal vein flow is continuous and hepatofugal (toward the IVC); pulsatility may increase with right heart failure.

Simple cyst criteria: anechoic, thin smooth wall, posterior acoustic enhancement, no septations, no internal echoes, and no internal Doppler flow.

Hemangioma typically appears as a homogeneous hyperechoic, well-circumscribed mass with no significant internal Doppler flow.

Hepatocellular carcinoma arises most often in a cirrhotic liver and shows variable echogenicity with arterial hypervascularity on Doppler.

Gallstones are echogenic foci with strong posterior shadowing that move with patient position; sludge is low-level, nonshadowing, and layers dependently.

Wall-echo-shadow (WES) complex indicates a gallbladder packed with stones: two echogenic lines separated by a thin hypoechoic bile layer, with clean shadowing.

Acute pancreatitis: enlarged, hypoechoic pancreas with peripancreatic fluid and indistinct margins; gallstones are a common cause.

Hydronephrosis: mild = anechoic renal pelvis only; moderate = blunted calyces; severe = cortical thinning with bear-paw appearance.

Hepatic steatosis: increased liver echogenicity, increased hepatorenal contrast, and poor penetration of deep structures; may be focal or diffuse.

An infrarenal abdominal aorta is aneurysmal when its outer-to-outer anteroposterior diameter exceeds 3 cm; mural thrombus and residual lumen are measured separately.

Renal artery stenosis: peak systolic velocity above 180-200 cm/s, renal-to-aortic velocity ratio greater than 3.5, and post-stenotic tardus-parvus waveform.

Portal hypertension signs: portal vein diameter over 13 mm, mean velocity below 15 cm/s, and hepatofugal or biphasic flow, often with splenomegaly and varices.

A normal TIPS shows flow velocities of roughly 90-190 cm/s; velocities under 50 cm/s or over 200 cm/s suggest stenosis or dysfunction.

Hepatic artery stenosis after transplant: focal PSV greater than 200 cm/s with tardus-parvus downstream; hepatic artery thrombosis shows no flow.

Superior mesenteric artery stenosis is suggested by a peak systolic velocity greater than 275 cm/s.

Aortic dissection appears as an intimal flap dividing the aorta into a true lumen and a false lumen, each with distinct flow on color Doppler.

Renal vein thrombosis: enlarged hypoechoic kidney with absent venous flow and elevated resistive index above 0.80.

FAST evaluates four windows: perihepatic (Morison's pouch), perisplenic, pelvic (pouch of Douglas), and subxiphoid pericardial.

Free intraperitoneal fluid appears anechoic and conforms to dependent recesses; acute hemorrhage may appear echogenic rather than anechoic.

The spleen is the most commonly injured solid organ in blunt abdominal trauma, followed by the liver.

A subcapsular hematoma is a lenticular or crescentic collection between the capsule and parenchyma that compresses underlying tissue.

A liver laceration appears as an ill-defined heterogeneous or hypoechoic disruption of normal parenchyma, often with associated free fluid.

FAST has limited sensitivity for retroperitoneal injury, hollow viscus rupture, and pelvic fractures, so a negative study does not exclude injury.

Hematoma echogenicity evolves over time: acute collections are echogenic, become complex and hypoechoic, and eventually anechoic.

Spectral and color Doppler are not part of the standard FAST protocol; the exam is grayscale, limited, and repeatable at the bedside.

After cholecystectomy the common bile duct may measure up to 10 mm without obstruction; greater caliber or focal dilatation suggests retained stone or stricture.

Surgical clips in the gallbladder fossa cause bright echogenic reflections with clean posterior shadowing and may mimic stones.

A TIPS stent appears as two parallel echogenic lines connecting the portal vein to a hepatic vein; patency is confirmed with color and spectral Doppler.

A transplanted kidney is usually placed extraperitoneally in the iliac fossa, so the native renal fossa appears empty.

Renal transplant dysfunction is suggested by resistive index above 0.80, absent diastolic flow, or perinephric fluid collections.

Liver transplant requires evaluation of hepatic artery, portal vein, and IVC anastomoses plus perihilar fluid collections and biliary dilatation.

Postoperative collections may be anechoic or complex with septations and debris; ultrasound guides size, location, and drainage planning.

Pancreaticoduodenectomy (Whipple) alters upper abdominal anatomy, so the pancreatic remnant, ducts, and surgical bed must be identified before interpretation.

Higher transducer frequency improves resolution but decreases penetration; abdominal imaging typically uses a curvilinear 2-5 MHz probe.

Axial resolution equals half the spatial pulse length; shorter pulses from higher frequency or fewer cycles per pulse improve it.

Posterior acoustic enhancement occurs behind fluid-filled structures such as cysts and the gallbladder because fluid attenuates sound less than soft tissue.

Acoustic shadowing occurs behind strongly reflecting or attenuating structures such as bone, stones, and gas, producing a dark band deep to them.

Attenuation in soft tissue averages about 0.5 dB/cm/MHz, so deeper structures and higher frequencies return weaker echoes.

Aliasing occurs when velocity exceeds the Nyquist limit (half the pulse repetition frequency); correct by raising the scale, adjusting the baseline, or using continuous wave.

Mirror-image artifact duplicates a structure across a strong reflector such as the diaphragm, creating a false image deep to the reflector.

Edge (refraction) shadowing appears as narrow dark bands at the margins of curved structures such as the gallbladder or fetal head.

ALARA: keep exposure As Low As Reasonably Achievable by using the lowest output power and shortest scanning time that yields diagnostic information.

Mechanical index estimates cavitation risk and is generally kept at or below 1.9 for abdominal scanning; thermal index estimates tissue heating.

Patients fast 6-8 hours before abdominal ultrasound to distend the gallbladder and reduce bowel gas; fasting is also used for renal artery Doppler.

Endocavitary probes contact mucous membranes and are semicritical devices requiring high-level disinfection after each use; surface probes require low-level disinfection.

Documentation includes patient identification, date, transducer orientation, labeled images, and measured values for all reported findings.

Critical or unexpected findings, such as a suspected aneurysm or free fluid after trauma, are communicated directly to the referring clinician.

Ergonomic practice, including neutral wrist posture, arm support, and alternating scanning hands, reduces sonographer musculoskeletal injury.

Standard precautions apply to every patient: hand hygiene, gloves when contacting body fluids, and proper probe and machine cleaning between examinations.