Endoscopic Ultrasound
EUS: radial versus linear
Endoscopic ultrasound answers questions that cross-sectional imaging cannot: pancreatic masses and cysts, subepithelial lesions, biliary strictures, and locoregional staging of esophageal, gastric, and rectal cancer. Radial echoendoscopes provide 360-degree images and are best for staging and anatomical survey. Linear echoendoscopes allow needle passage and are used for FNA/FNB and for EUS-guided drainage.
Preparation resembles standard endoscopy; sedation is often moderate to deep. For pancreaticobiliary lesions, identify the mass, assess vascular involvement, and sample with FNB (preferred over FNA for solid lesions because of better yield and histology). For pancreatic cysts, characterize size, septations, mural nodules, main duct dilation, and solid components; do not sample every cyst, and avoid needling when the diagnosis will not change management.
Subepithelial lesions are described by layer of origin, size, echotexture, and margins. A fourth-layer hypoechoic lesion is likely a GIST or leiomyoma; EUS-FNB provides tissue for risk stratification. EUS also diagnoses chronic pancreatitis (ductal and parenchymal criteria) and can guide celiac plexus neurolysis or pseudocyst drainage.
Traps: using a radial scope when FNA is planned, failing to stage before surgery, and needling a cystic lesion unnecessarily. Needle-tract seeding is rare but discussed in malignant cases.
Rule of thumb: radial for staging, linear for tissue.
Worked example: a 68-year-old with painless jaundice and a 2.5 cm pancreatic head mass with double duct sign undergoes linear EUS-FNB; the result confirms adenocarcinoma and guides neoadjuvant therapy.