The final episode turns EUS from a guide for therapy into a diagnostician and a palliator, and it runs on one habit: reason from substrate to answer. The five alternating wall layers plus echotexture place a subepithelial lesion and narrow the differential before a needle moves, so a hypoechoic layer-four mass is a GIST until tissue proves otherwise. The needle choice then turns on a single distinction, cells versus architecture, because lymphoma, GIST, and autoimmune pancreatitis all live in structure a core preserves and cytology destroys. Finally the same probe that finds the tumor treats its pain: alcohol neurolysis for cancer, a reversible steroid block for benign disease, with complications that read straight off the interrupted sympathetic outflow. Topics covered The five EUS gut-wall layers Layer-four GIST versus leiomyoma Size threshold for sampling muscularis lesions Other layers by echotexture Fine needle aspiration versus biopsy Rapid on-site evaluation and cyst fluid Celiac plexus neurolysis for cancer pain Neurolysis versus reversible block in benign disease Complications from interrupted sympathetic outflow Key decisions Place a subepithelial lesion by its wall layer and echotexture: a hypoechoic homogeneous mass arising from layer four, the muscularis propria, is a GIST until proven otherwise. Do not call a layer-four hypoechoic mass a leiomyoma on imaging, because GIST (CD117 and DOG1 positive) and leiomyoma (desmin and smooth muscle actin positive) are indistinguishable sonographically and separate only on immunohistochemistry. Obtain tissue for any muscularis-propria lesion two centimeters or larger, since within layer four increasing size correlates with malignant behavior. Choose the needle by whether the diagnosis lives in cells or architecture: cytology suffices for pancreatic adenocarcinoma, but lymphoma, GIST, and autoimmune pancreatitis need a fine needle biopsy core, which also largely obviates rapid on-site evaluation. Read pancreatic cyst fluid against the epithelium: CEA above one hundred ninety-two or glucose below fifty favors a mucinous cyst, while high amylase points to ductal communication. Perform celiac plexus neurolysis with absolute alcohol plus bupivacaine for unresectable pancreatic cancer pain, targeting visible ganglia directly when you can see them for better analgesia. For benign chronic pancreatitis pain use a reversible celiac plexus block with bupivacaine and a corticosteroid, not alcohol neurolysis, because the nerve regenerates and irreversible destruction risks lasting deafferentation. For the full chapter with MCQs, tables, and primary-guideline references, visit www.boardpearls.com. Questions or feedback: [email protected].

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“What did the council decide on item 42?” — answered with the speaker and the moment.

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