Endoscopic Ultrasound for the Characterization of Subepithelial Lesio

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  • 7/29/2019 Endoscopic Ultrasound for the Characterization of Subepithelial Lesio

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    ultrasound for the characterization of subepithelial lesion... htp://www.uptodate.com/contents/endoscopic-ultrasound-for-the-cha...

    ;;-l ,"$r:li*rs lr.iLi',r,iqi [;4;fof-l*s' Official reprint from UpToDate@ir,,.il ,, illi ,,\ ,/, . l.i fl l l,ti iiil L-ij , t * ilr@2O72 UpToDate@.'ji :l ,i;"' .;;. I :

    S*th*lr'* 1-il;:::,r1 ffir-iit*r #*prL9,y.' ffi#1i*ril,t*ry |** ilt'iit:llty. ** li*r:Sillli A il*r,vr:ll. fu]*, il/:l$#L:, r\r*:: {l -j'r*.ri*, r,\4*, fi$S,:: l ilill[ir]rrf:*tl #in+l:,,*1ir:i, I'J{-t 1;:i--fiAll topics are updated as new evidence becomes available and our ,1 _;. *lli{, . |, ti.,$s is complete.Literature review current through: May 2012. I This topic last updated: Nov 17, 2010.INTRODUCTION - A subepithelial mass or a bulge encountered during an endoscopy can arise from withinany layer of the gastrointestinal tract wall (intramural) or outside of the wall (extramural). They are usuallyfound incidentally during routine imaging with **riilrrcontrast radiography orendoscopy. The differentialdiagnosis includes a number of benign and malignant non-epithelial gastric wall tumors, intramural vessels, andextrinsic compression f rom extramural structures.Endoscopy alone cannot accurately distinguish between intramural and extramural lesions t"il By contrast,endoscopic ultrasonography (EUS) has provided a major breakthrough for characterizing such masses. Thistopic review will provide an overview of the most common subepithelial lesions that can be identifiedendosonographically. Discussions on the individual lesions are also available on the corresponding topicreviews.GENERAL PRINCIPLES FOR IMAGING - EUS provides a number of methods for characterizingsubepithelial lesions:

    . lt provides an understanding of whether the lesion arises from the bowel wall (intramural) or from astructure outside the bowelwall (extramural) compressing the gastrointestinal wall. Extramural lesionsmay be a normal adjacent structure (eg, spleen, aorta, gallbladder) or pathologic structures (eg, splenicartery aneurysm, cyst, tumor). Rarely, the distinction between an intra- and extramural lesion may bedifficult when there is invasion into the gastrointestinalwall.

    . lt can determine the originating layer of intramural lesions, an important clue for achieving a diagnosis(i*iilt J ) Stromal cell tumors, for example, can typically be seen as evolving from the muscularispropria or muscularis mucosa, whereas lipomas typically evolve from the submucosa.o The echogenicity, vascularity, margins, size of the lesion, and absence or presence of adjacent lymphnodes also help to narrow the differential diagnosis.. EUS-guided fine-needle aspiration or trucut biopsy of the lesion may be helpful in some settings. (See

    Ln t :rj,;15rpgli iii rfi_!$l tili{ r;;; :;'.i *ri t rtl r r;,**t,:;.1 )Technical considerations - The following are basic principles that should be understood byendosonographers attempting to visualize subepithelial lesions.

    . The lesions should be localized endoscopically or by cross-sectional imaging (CT, MRl, US) prior todin24 61261201210:09 PM

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    ultrasound for the characterization of subepithelial lesion... http://www.uptodate.com/contents/endoscopic-uhasound-for-the-cha...endosonographic evaluation.The gastrointestinal tract wall echo structure, five layers of alternating bright (hyperechoic) and dark(hypoechoic) lines of approximately 3 to 4 mm thickness should be understood (J_t*i,:.* l).Endoscopic ultrasound imaging should be performed adjacent to the lesion. Water instillation may behelpful to provide adequate acoustic coupling while achieving a focal distance that permits optimalimaging. The focal length for a7.5 MHztransducer is approximately 2.0 centimeters. lmaging can beoptimized by using a minimally inflated, water filled balloon and instilling deaerated water to distend thelumen while providing a medium to transmit the ultrasound waves without reflection.For small (

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    ultrasound for the characterization of subepithelial lesion... http://www.uptodate.com/contents/endoscopic-ultrasound-for-the-cha..Although this technique improved diagnostic yield, it may also increase complications such as bleeding[.:1]. (See --*t'*1,1,'1*;,i',:' ,: ' , . ' " '+ ,ril,lj,'1i]i ili;t$lj-i;lill:*$iliji1tlt+ryr;lsl_.)

    o Endoscopic submucosal dissection - An alternative to EMR is the use of the needle-knife to incise theoverlying mucosa. This approach, known as endoscopic submucosal dissection, was first described in2003 in a patient with a metastasis from colon cancer presenting as a submucosal gastric tumor [:i].Endoscopic submucosal dissection has been used primarily for the treatment of mucosal gastric andesophageal cancers in Japan and Germany [fr,iij More recently, ESD has been described for theresection of subepithelial tumors [,:,*].Carefuldissection using a modified needle-knife such as the lnsulated Tip (lT) knife enables en blocresection of a submucosal tumor. ESD requires an exceptional level of operator skill, is time consuming,and is associated with significant complication rates, especially bleeding and perforation. As a result,ESD should be reserved for centers specialized in this advanced procedure. (See "{ii;;q1:11;1t;;;;;; 1:!^aar..a..5 .---l r- *, i.'/;ii ,i r, :lr ^r...;- -. \'..:.... '. '' " ' t '" IFine needle aspiration (EUS-FNA) - Standard 19,22, or 25 gauge needles may be used for fineneedle aspiration to provide an adequate tissue sample for cytological diagnosis. This is often used inconjunction with immunohistochemical staining, such as for c-kit (CD 117). A larger guillotine biopsyneedle has been used [t]1, but larger needles increase the risk of bleeding and it is unclear if these'::...Y.F. v " ; :..- ." *. "" /

    Trucut biopsy - EUS-FNA typically yields a small tissue sample that is insufficient for histologicalexamination. Large caliber cutting needles were designed to acquire larger tissue specimens withpreserved tissue architecture that can provide a histologic diagnosis. (See "il:*d*s-c+ilf ril|irltr::tii:.rj

    ACCURACY - Multiple studies have evaluated the accuracy of EUS in characterizing subepithelial lesions.Studies focusing on specific lesions are presented below. As a general rule, the ability of EUS alone todistinguish among subepithelial lesions is variable. As a result, histology is still considered to be the "goldstandard."Some representative studies have shown the following:

    A prospective study evaluating the accuracy of EUS in characterizing 100 consecutive patients withsubepithelial lesions found that EUS findings alone correctly predicted the specific lesion type in only 48percent of cases where biopsy confirmation had been obtained [j]. Most misclassifications occurred inhypoechoic lesions in the third and fourth layers, which include carcinoids, GlSTs, aberrant pancreas,and granular cell tumors.ln a second study, the results of endoscopic resection or biopsies after unroofing in 54 submucosallesionswerecomparedwiththeEUSfindings[11] Theoverallaccuracyof EUSindeterminingthelayerof origin and location of lesion was 80 percent; six lesions were located deeper in the Gl wall thanestimated by EUS and five were more superficial. EUS and pathology findings coincided in 74 percentof lesions.

    o ln a third study, 22 patients underwent EUS prior to endoscopic resection of gastric subepithelial lesionsIif i]. EUS alone correctly diagnosed 10 (46 percent) of the lesions. The lesions that were incorrectlydiagnosed included pancreatic rests (n = 5) and gastritis cystica profunda (n = 2)

    EXTRAMURAL LESIONS - Normal anatomic structures and extraluminat benign and malignant tumors can61261201210:09 PM

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    ultrasorutd for the characterizationof subepithelial lesion... http://www.uptodate.com,/contents/endoscopic-ultrasound-for-the-cha.compress the gastrointestinaltract and mimic an intramuraltumor. lncidental lesions are being detected morecommonly with the increasing use of total body scans in healthy patients. EUS can assist in furthercharacterizing such findings.Endoscopic appearance - Extramural lesions are commonly seen as a bulge located in the gastrointestinal(Gl) tract with normal overlying mucosa, usually with a smooth border and no significant irregularity (lt$.r*,--).Endosonographic findings - A normal appearing five-layer gastrointestinal wall structure is seen interposedbetween the lesion and the bowel lumen. Specific echo features vary depending upon the type of structureidentified. As an example, the splenic vessels appear as an anechoic structure that can be followedlongitudinally' The spleen may appear to have a homogeneous echogenicity. A pancreatic pseudocystoriginates from a region of the pancreas, and is commonly hypoechoic or anechoic.Diagnosis - Knowledge of normal endoscopic ultrasound anatomy is required to determine if a structure isnormal or abnormal. Common normal extrinsic structures include the splenic artery, spleen, gallbladder, leftlobe of the liver, and the pancreas [1li]. Abnormalstructures include pancreatic pseudocysts, enlarged lymphnodes, aneurysms, omental metastasis, and hepatic and pancreatic tumors. one group reported 100 percentaccuracy in distinguishing extramural from intramural structures [1L].GASTRoINTESTINAL STRoMAL TUMoRS - The nomenclature of gastrointestinal mesenchymal tumors isevolving with an increased understanding of molecular, histologic, and clinical features that distinguish differenttypes of tumors [i4:i1]. One of the most common mesenchymaltumors i