Pancreatic sonographic anatomy

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PANCREATIC SONOGRAPHy anatomy

PANCREATIC SONOGRAPHIC anatomyDr.mohamed solimanGeneral Anatomic Considerations

Pancreas is non-encapsulated, retroperitoneal structure that lies in anterior pararenal space Obliquely in transverse plane spanning between duodenal loop and splenic hilum Level changes on respiratory movemento Craniocaudal shifting of 2-8 cm may occur on respiration Length - 12-15 cm across Pancreas can be identified & localized on ultrasound byo Typical parenchymal architecture, homogeneously isoechoic/hyperechoic echotextureo Surrounding anatomical landmarks: Anterior to splenic vein, SMACritical Anatomic Structures Anatomical division

o Head: Parenchyma to the right of superior mesenteric vesselso Uncinate process: Represents medial extension of head Lies posterior to superior mesenteric vesselso Neck: Narrow portion anterior to superior mesenteric vessels Serves as dividing line between pancreatic head and bodyo Body: Parenchyma to left of superior mesenteric vessels Constitute main bulk of pancreatic parenchymao Tail: Most distal portion of pancreatic parenchyma No clear anatomic landmark separates tail from bodyCritical Anatomic Structures Histological division

o Functionally the pancreas comprised of exocrine and endocrine tissues 80% exocrine tissue; ductal and acinar cells 2% endocrine tissue; islet cell of Langerhans 18% fibrous stroma containing blood vessels,nerves and lymphaticsAnatomic Relationships

Pancreas is closely related to several importantstructures/ organso Gastrointestinal tract & peritoneal spaces Anteriorly: Stomach, transverse colon and root of transverse mesocolon, lesser sac Right: Duodenal loop (esp. second part ofduodenum)Anatomic Relationships - Major vessels

Abdominal aorta: Posterior to body of pancreas Coeliac axis: Related to superior border of pancreas Common hepatic artery: Branch of coeliac axis, related to superior border of pancreatic neck and head Gastroduodenal artery: Branch of coeliac axis, coursing inferiorly anterior to pancreatic head Splenic artery: Branch of coeliac axis, towards the left in tortuous course along superior border of pancreatic body and tail Superior mesenteric artery (SMA): Arises from abdominal aorta just caudal to inferior border of pancreas, descends anterior to uncinate process Inferior vena cava: Posterior to head of pancreas Splenic vein: Coursing transversely from splenic hilum to portal vein confluence posterior to pancreatic tail and body Superior mesenteric vein: Ascends to right of SMA anterior to uncinate process Portal vein: Confluence posterior to pancreatic neck, proximal portion above superior margin of pancreatic headAnatomic Relationships - Common bile duct

Distal portion posterior to or embedded withinpancreatic head Forms common trunk with pancreatic duct in80% to drain into ampulla of VaterImaging technique Transabdominal ultrasound serves as a useful initial imaging modality for suspected pancreatic lesion Advantages of USo Readily available o Relatively inexpensive imaging techniqueo Does not involve ionizing radiation o Supplemented with Doppler US to identify abnormal flow (thrombosis, tumor encasement) or abnormal vascularity (tumor vascularity)o Use as real time imaging guide for interventional procedures Disadvantages of USo Pancreas is retroperitoneal structure and considered "deep" intra abdominal organ for imaging with transabdominal ultrasoundo Limited US beam penetration in obese patient with thick subcutaneous and omental fato Often entire pancreatic parenchyma cannot be completely examined due to overlying bowel gaso Operator-dependent imaging techniqueTechnical consideration in transabdominal USo Examination should begin in transverse plane in midline below xiphisternum, using vascular landmarks to identify pancreas Longitudinal view for further evaluation particularly if lesion is detectedo Pancreatic body can usually be better delineated by transducer pressure to displace overlying bowel gaso If there is abundant bowel gas obscuring pancreatic parenchyma Scanning with patient in various positions including erect, sitting, both obliques and decubitus may help Ask patient to drink plenty of water to distend the stomach which acts as an acoustic windowTechnical consideration in transabdominal USo Using left kidney/spleen as acoustic window,pancreatic tail can be visualized in left coronal viewo Head can be better assessed through rightlateral/decubitus approach in a coronal planeo Place area of interest within the focal zone oftransducero Always examine the rest of the abdomen in detailo Doppler US to aid assessment of patency and flow characteristics of vessels Special US techniques such as endoscopic US (EUS) or intra-operative US (IOU) are useful in detecting small pancreatic tumors (e.g., islet cell tumor) which are not apparent on transabdominal US, CT or MR Cross-sectional imaging techniques including CT and MR are usually required for further characterization of pancreatic lesion detected on US Advantages of CTo Fast scanning in era of multi-detector CT, thus more practical in critically ill patientso Shows calcifications better than other imaging modalitieso Less prQne to technical and interpretative errors Advantages of MRo No ionizing radiation is involvedo Does not require iodinated contrast agento Multiplanar capabilityo Allows easy evaluation of common bile duct and pancreatic duct using MRCP sequencesPATHOLOGY-BASED IMAGING ISSUES

Two main categories to differentiate on imaginginclude neoplasm (most commonly ductal pancreaticcarcinoma) and pancreatitiso Ductal pancreatic carcinomas typically cause narrowing or obstruction of vessels and ducts, and extend dorsally to coeliac axis and SMA originso Acute pancreatitis causes fluid exudation and fatinfiltration, extends ventrally and laterally to mesentery and anterior pararenal space, less common cause for ductal obstructionDifferential diagnoses of cystic pancreatic mass

o Common Pseudocyst Mucinous cystic tumor Serous cystadenoma Necrotic pancreatic ductal carcinoma Intraductal papillary mucinous tumor (IPMT)o Uncommon Simple/congenital cyst (e.g., Von Hippel Lindau syndrome, adult polycystic kidney disease) Solid and papillary neoplasm of pancreas Lymphangioma Cystic metastases/lymphomaConditions to consider if dilated pancreatic duct is seen

o Chronic pancreatitis: Parenchymal or intraductalcalcification, atrophic pancreaso Pancreatic ductal carcinoma: Common bile andpancreatic ductal dilatation for most commonlesions in pancreatic heado Periampullary tumoro IPMTo Obstructing distal common bile duct (CBD) stoneEmbryologic Events

Embryologically, pancreas is developed from dorsal and ventral pancreatic budso Body-tail segment developed from dorsal pancreatic budo Head-uncinate segment developed from ventral pancreatic bud During normal development, ventral bud migrates dorsally around fetal duodenum to merge with dorsal bud to form pancreatic substance and branching pancreatic and bile ductsPractical Implications Failure or anomalies of rotation or fusion may result in congenital lesions such as annular pancreas, pancreas divisum, agenesis of dorsal pancreas Ventral (head-uncinate) and dorsal (body-tail) segments may have different echotexture that may be misinterpreted as pathology Pancreatic ductal obstruction of either dorsal or ventral buds may lead to dilatation of involved portion with sparing of uninvolved segmentsClinical Importance

Ductal pancreatic carcinoma: Usually presents late with poor overall prognosis, surgically not operable in most cases Serous cystadenoma: No malignant potential, microcystic/macrocystic in appearances Mucinous cystic pancreatic tumor: Regarded as pre-malignant lesion, predominantly cystic with septations +/- solid component Islet cell tumor: Hypervascular primary tumor and liver metastases, most commono Insulinoma, functional tumors small at presentationo Non-functional tumors large at diagnosis Solid and papillary neoplasm, metastases, lymphoma; rare lesionsPancreas measurement

liveraortaHASAIVCpancreassvPV

liverpancreasPV confluenceaortaSMAIVCFalciform ligament

pancreasPVSMAaortaIVCRenal vTransverse transabdominal ultrasound showsanatomical relationship of the pancreas to thesplenic vein SMA portal vein confluence abdominal aorta and IVC

pancreasSVSMAPV confluenceaortaIVCTransverse transabdominal ultrasound shows thenormal anatomical relationship of the uncinate process which is medial extension of pancreatic headbehind the SMV SMA pancreatic neck.

uncinate processpancreatic headSMVSMApancreatic neckTransverse transabdominal ultrasound shows normal pancreatic tail with homogeneous echotexture.

pancreatic tailSVSMAIVCAortaTransverse transabdominal ultrasound performed with a high-frequency transducer in a thin patient shows a non-dilated pancreatic duct within the pancreaticbody.

pancreatic ductTransversetransabdominal ultrasoundshows the homogeneousechotexture of the pancreas in a healthy patient. Notethe lack of pancreatic ductaldilatation and parenchymalmasslcalcification.

pancreasTransverse transabdominalultrasound shows anill-defined hypoechoiccarcinoma in the pancreatichead causing obstructionand dilatation of thepancreatic duct .

Pancreatic headpancreatic ductTransversetransabdominal ultrasoundshows global swelling with adiffusely hypoechoic echopattern of the pancreas = suggestive of acutepancreatitis. Note presenceof small peri-pancreatic fluid

pancreasperi-pancreatic fluidperi-pancreatic fluidTransversetransabdominal ultrasoundshows calcifications within the pancreaticparenchyma in patient withchronic pancreatitis relatedto alcohol abuse.

calcificationsTransversetransabdominal ultrasound shows thewell-circumscribed,unilocular, cystic lesion in the pancreatic tail. Therest of the pancreas