直肠癌：MRI与临床课件

直肠癌：MRI与临床2022/12/18直肠癌：MRI与临床2022/12/141直肠为大肠的末段，长约15-16cm，位于小骨盆内。上端平第3骶椎处接续乙状结肠，沿骶骨和尾骨的前面下行，穿过盆膈，下端以肛门而终。直肠肛门直肠为大肠的末段，长约15-16cm，位于小骨盆内。上端平第2外科学上，将由盆筋膜脏层包绕的直肠周围脂肪结缔组织、血管、神经和淋巴组织统称之为直肠系膜（mesorectum）。直肠癌环周切缘（circumferentialresectionMargin，CRM）是一个外科学概念，是指围绕直肠系膜的盆腔脏层筋膜，即直肠系膜筋膜（mesoretalfascia，MRF）。相关基本概念全直肠系膜切除术（totalmesorectalexcisionTME）解剖学基础：腹膜返折以上的直肠有腹膜覆盖，返折以下的直肠无腹膜，而由盆筋膜所覆盖。盆筋膜分脏层和壁层，其脏层是由腹膜下筋膜向下位于腹膜返折以下，其浅叶包绕盆腔的内脏，如膀胱、子宫、直肠等而形成。盆筋膜壁层与脏层相对应，是由腹膜下筋膜的深叶进入盆腔后覆盖盆壁四周而形成的。临床意义：直肠系膜筋膜（MRF）是直肠与周围邻近器官间的重要屏障，可有效防止直肠炎症或肿瘤等向其它腹膜外间隙扩散，对阻止肿瘤局部浸润和远处转移有重要意义。外科学上，将由盆筋膜脏层包绕的直肠周围脂肪结缔组织、血管、神3来源：中国临床解剖学杂志2005年第23卷第4期明确直肠系膜的解剖学结构是应用全直肠系膜切除术(totalmesorectalexcision,TME)

治疗直肠癌的基础。但至今，有关直肠系膜的报道也仅限于零星的外科解剖资料[1,2]，对直肠系膜形态结构的解剖学研究存在较大的分歧[3]。该文章进行了专题解剖学研究，以期为临床TME广泛开展提供应用基础理论。研究显示：1直肠系膜筋膜（即盆脏筋膜）在直肠和直肠系膜周围是一个连续、完

整的结构，下端止于直肠肛管连接处；2直肠系膜是由环绕在直肠周围的血管、淋巴管、神经及脂肪等疏松

的结缔组织构成。本结果与Bisset等[4]的研究相类似。直肠系膜的定义应该是包绕在袖套样直肠系膜筋膜（即盆脏筋膜，并包括该筋膜在内）之内的直肠周围所有的血管、淋巴管和淋巴结、神经及脂肪组织等。作者通过仔细地解剖盆脏筋膜，认为直肠和“直肠系膜”一起被完整地包裹在含胶原纤维的袖套样盆脏筋膜中，因此，沿直肠盆脏筋膜外解剖，可以将直肠系膜完整地切除，并且切除后腹下神经和盆丛仍完整地保留在盆腔侧壁上，未受损害。本研究用MRI检测直肠系膜的结果也证实了这一点。解剖学研究与MRI影像来源：中国临床解剖学杂志2005年第23卷第4期明确直肠系膜4图2盆腔标本解剖前的MRI(T1WI)箭头示直肠系膜筋膜为均匀的低信号线；三角示直肠系膜则为均匀高信号。图3盆腔标本解剖后的MRI(T1WI)箭头示直肠系膜筋膜所产生的低信号线所在的位置；三角示直肠系膜。

图1盆腔矢状剖面新鲜标本（虚线之间为直肠系膜）。来源：中国临床解剖学杂志2005年第23卷第4期图2盆腔标本解剖前的MRI(T1WI)图3盆腔标本解剖5RectalCancer-MRstaging2.0

RhiannonvanLoenhout,FrankZijta,MaxLahaye,ReginaBeets-TanandRobinSmithuis

RadiologyDepartementoftheMedicalCentreHaaglandenintheHague,TheNetherlandsCancerInstituteinAmsterdamandtheAlrijneHospitalinLeiderdorp,theNetherlands直肠癌：MR分期RectalCancer-MRstaging2.06Introduction

Totalmesorectalexcision

TNM-stage

MRprotocolDWI

Locationofthetumor

Lowrectalcancer

T-stage

T1andT2

T3T3withMRFinvolvement

T4a-Invasionperitonealreflection

T4b-Invasionsurroundingorgans

Extramuralvascularinvasion(EMVI)

N-stage

Extramesorectallymphnodes

RegionalLymphnodes

Surgery

LowAnteriorResection(LAR)

Abdomino-Perineal-Resection(APR)

IntersphinctericAPRandELAPE

Chemo-andRadiotherapy

StructuredMRreport

PublicationdateDecember17,2015Thisisanupdatedversionofthe2010article.Thetwomajoradvancementsinthetreatmentofrectalcanceraretotalmesorectalexcision(TME),andneoadjuvantradiotherapyandchemotherapy(1,2,3).

Bothhavedramaticallychangedthelocalrecurrenceandsurvivalrates.MRIisthemostaccuratetoolforthelocalstagingofrectalcancerandisapowerfultooltoselecttheappropriatetreatment(4,5,6).

ThedecisionwhetherapatientwithrectalcancerisacandidateforTMEonlyorneoadjuvanttherapyfollowedbyTME,ismadeonthefindingsonMRI(7).2015年12月17日的更新版：直肠癌治疗的2个重要进展，一是全直肠系膜切除术(TME)，二是新辅助放疗和化疗。这两方面的措施明显改善了直肠癌局部的复发率和生存率。MRI是直肠癌局部分期最精确的评价方法，并作为非常有用的工具用于选择适宜的治疗。这里讨论的问题是：直肠癌病人，是只能选择TME？还是采用新辅助治疗而随后再行TME？通过MRI的表现作出决定。IntroductionSurgeryPublicati7Themesorectalfascia(MRF)playsacrucialroleinthetreatmentplannnig.InTMEthemesorectalfasciaistheresectionplaneandithastobetumor-free.

Adistanceofthetumortothemesorectalfasciaof⩽1mmisregardedasnotsuitableforTMEandiscalledaninvolvedMRF.ThismeansthatthetumorhastobedownstagedbeforeTMEispossible.OnMRIthemesorectalfathashighsignalintensityonbothT1-andT2-weightedimages.

Themesorectalfatissurroundedbythemesorectalfascia,whichisseenasafinelineoflowsignalintensity(arrows).

HighresolutionT2-imagesareneededtoclearlyidentifytheMRF(7).Rectumissurroundedbymesorectalfatwithinthemesorectalfascia(arrows).TotalmesorectalexcisionIn1979surgeonRichardJohnHealdintroducedthetotalmesorectalexcision(TME).InTMEtheentiremesorectalcompartmentincludingtherectum,surroundingmesorectalfat,perirectallymphnodesanditsenvelope,themesorectalfascia(MRF),iscompletelyremovedbyprecisedissectionalonganatomicalplanes(figure).TMEisthebestsurgicaltreatmentforrectalcancerprovidedthattheresectionmarginisfreeoftumor.Itisnowastandardtechniqueandpartofproceduressuchaslowanteriorresection(LAR),inwhichtherectumandsigmoidcolonareresectedorabdominoperinealresections(APR),inwhichtherectumandanalcanalareresected.1979年外科医生RichardJohnHeald开展了全直肠系膜切除术（totalmesorectalexcision，TME）.TME中的全直肠系膜包括直肠、周围系膜脂肪、淋巴结及其包膜，即直肠系膜筋膜（mesoretalfascia，MRF）完全切除（图）。全直肠系膜切除术(TME)已被证明是直肠癌根治的最佳外科手术方法。直肠由直肠系膜筋膜（箭）内直肠系膜的脂肪包绕直肠系膜筋膜全直肠系膜切除*MRF在直肠癌治疗计划中扮演关键角色。*在TME中，做直肠系膜筋膜切除计划必须要求该系膜筋膜无肿瘤侵犯。*癌灶至直肠系膜筋膜的距离⩽1mm时，被认为不适合TME，这称为直肠系膜筋膜受侵。*这意味着直肠癌在做TME之前必须处于早期。*在MRI上，直肠系膜脂肪在T1WI和T2WI表现为高信号。*直肠系膜脂肪由直肠系膜筋膜（盆腔脏层筋膜）环绕，表现为线样低信号影（箭）。*为清晰地证实MRF结构，高分辨T2WI是必须的。Themesorectalfascia(MRF)pl8TheMRFisonlycircumferentialinthelow-rectumbelowtheanteriorperitonealreflection(seenextillustration).TheMRFdoesnotapplytotheanteriorperitonealizedsurfaceoftheanteriormid-andhighrectum.直肠系膜筋膜（MRF）仅仅是在前腹膜返折处下面的直肠下段呈圆周环绕；而直肠系膜筋膜（MRF）不适用于前表面由腹膜被覆的中、上段直肠。直肠系膜（mesorectum）TheMRFisonlycircumferentia9ThetreatmentofapatientwithrectalcancerdependsontheTNM-stageandwhethertheMRFisinvolved.T-staging

T1andT2tumorsarelimitedtothebowelwall.

T3tumorsgrowthroughthebowelwallandinfiltratethemesorectalfat.

Theyarefurtherdifferentiatedin:T3a

<1mmextensionbeyondmuscularispropriaT3b

1-5mmextensionbeyondmuscularispropriaT3c

5-15mmextensionbeyondmuscularispropriaT3d:>15mmT3MRF+tumorwithin1mmofMRFMRF-notumorwithin1mmofMRFTheN-stageisbasedonthenumberofsuspiciouslymphnodes:N0nosuspiciousnodesN11-3suspiciousnodesN2⩾4suspiciousnodesRef:ColonandRectumCancerStaging-quickreference(AJCC)直肠癌病人的治疗依赖于TNM分期以及是否存在MRF受侵。T（肿瘤）分期T1和T2肿瘤限于肠壁；T3肿瘤穿过肠壁和侵犯直肠系膜的脂肪，亚型：T3a:超出肠壁固有肌层小于1mmT3b:超出肠壁固有肌层1-5mmT3c:超出肠壁固有肌层5-15mmT3d:大于15mmT3MRF+：肿瘤在MRF的1mm之内MRF-：MRF的1mm之内没有肿瘤T4a:侵犯腹膜T4b：侵犯邻近脏器N（区域淋巴结）分期是根据可疑淋巴结的数目N0没有可疑淋巴结N1发现1-3个可疑淋巴结N2发现4个或以上的可疑淋巴结直肠癌的TNM分期（肿瘤分期、区域淋巴结分期）Thetreatmentofapatientwit10ThisfigureillustratestheT-stageandmesorectalfasciainvolvementintheaxialplane,whichisusuallythebestimagingplanefortheT-staging.左图：直肠癌的T分期与直肠系膜筋膜受侵在轴位上的表现。器官轴位扫描是肿瘤T分期最好的成像方位。直肠环周切缘（CRM,即MRF）示意图：

T2肿瘤限于肠壁

T3肿瘤

：T3CRM（环周切缘）-；T3CRM+（红箭）

T4肿瘤浸润精囊和前列腺

当距筋膜1毫米内出现淋巴结时则需要报告，尤其是大的淋巴结（蓝箭）。ThisfigureillustratestheT-11Nstaging

Lymphnodeinvolvementisanimportantfactorforthetreatmentandtheprognosisofthepatient.

MRhasproventohavealowdiagnosticaccuracyfordistinguishingpositiveornegativelymphnodeswhencharacterizationisbasedonsizecriteriaalone.AtthemomentintheNetherlandsweuseacombinationofbothsizeandmorphologiccriteriaaslistedinthetable.Nodeslargerthan9mmarealwaysregardedassuspicious.

Smallerlymphnodesneedadditionalmalignantcharacteristicstobeconsideredsuspicious.Sincestagingandtreatmentofrectalcancerisconstantlyevolving,youmayhavetocheckyourlocaloncologyteamforthelatestdevelopments.N（区域淋巴结）分期区域淋巴结受侵是直肠癌治疗和预后的一个重要因素。对形态上属于正常大小的淋巴结，究竟是属于阳性还是阴性的淋巴结，MR对此诊断正确率很低。N分期：可疑淋巴结恶性特征边界模糊不均匀圆形短轴cN期N0:无可疑淋巴结N1:1-3可疑淋巴结N2:4或4个以上的淋巴结小于5mm:需要3个恶性特征5-9mm:需要2个恶性特征大于9mm:常为提示恶性左边的图表是依据淋巴结大小与具有的恶性特征两方面定义可疑恶性淋巴结：大于9mm的淋巴结应列为可疑恶性。较小的淋巴结需要有恶性特征，方可考虑可疑恶性。（注：这里没有提到MRI的DWI表现）区域淋巴结分期：可疑淋巴结的影像学判定Nstaging

Lymphnodeinvolvem12Treatment

ThetreatmentisbasedontheclinicalorcTNM.

ThecTNMisbasedontheresultsofendoscopyandimaging.Lowrisktumors

T1,T2andborderlineT3withoutsuspiciousnodescandirectlyundergosurgery.Intermediaterisktumors

T3with>5mminvasionortumorswith1-3suspiciousnodes-willbetreatedwithshorttermradiotherapypreoperatively.Highrisktumors

T3withinvolvedMRForT4tumorsortumorswith4ormoresuspiciousnodeswillreceiveneoadjuvantchemotherapyandlongtermradiationtherapyandwillberestagedtodeterminewhetherTMEispossibleAftertheoperationthesurgicalspecimenisanalyzedbythepathologist.直肠癌治疗直肠癌的治疗依据临床或cTNMcTNM是依据内窥镜和影像学一、低风险肿瘤T1，T2和T3边缘线没有可疑淋巴结能够直接接受外科手术。二、中间级风险肿瘤侵犯范围大于5mm或伴1-3个可疑淋巴结的T3，需要做短期的术前放疗。三、高风险肿瘤MRF侵犯的T3，或T4肿瘤或肿瘤伴4个或更多可疑淋巴结，需要接受新辅助化疗和长时间的放疗再重新评价实施TME的可能性。手术后，切除标本由病理学家分析。新辅助化疗、长时间放疗TME短时间放疗

N0无可疑淋巴结N11-3个可疑淋巴结

N24个以上可疑淋巴结

T1T2T3≤5mm侵润T3>5mm侵润T3≤1mm距离MRFT4器官侵犯TMETreatment直肠癌治疗直肠癌的治疗依据临床或cTNM13MRprotocolT2-weightedFSE

Highresolution2DT2WIFSEinthesagittal,axialandcoronalplanearerequiredforstate-of-the-artstagingofrectalcancer.

Theslicethicknessshouldbe3mm.Gadolinium-enhancedMRdoesnotimprovediagnosticaccuracyandisnotincludedintheprotocol.Startwiththesagittalseries.

Thesecanbeusedtoplantheaxialimages,perpendiculartotherectalwallatthelevelofthetumortoavoidvolumeaveraging(yellowbox).Coronalimagesareplannedparalleltotheanalcanal(greenbox),especiallyinlow-rectaltumorsinordertoaccuratelyevaluatethedepthoftumorinvasionintotheanalsphincter.ThecranialborderoftheFOVisvertebralbodyL5,thecaudalborderisbelowtheanalcanal.Angulation

Properangulationisofvitalimportanceincorrectlyidentifyingtumorborders.

Inthisexampletheaxialimageswereoriginallynotproperlyangulated(redlinesnotperpendiculartothetumor).

ThisresultedinthefalseimpressionthattheMRFwasinvolvedontheanteriorside(redcircle).

AfterproperangulationitwasclearthattheMRFwasnotinvolved(yellowcircle).MR检查方案T2WIFSE序列高分辨2D快速自旋回波T2WI的矢状、轴位及冠状是直肠癌检查的基本序列，层厚取3mm。Gd-DTPA不改善诊断的准确性，故检查方案中不予包括。扫描从矢状序列入手。轴位成像时注意要使扫描线垂直于肿瘤部的肠壁，从而避免形态的失真（黄框）。冠状成像，扫描线平行于肛管（绿框），尤其是低位直肠癌用于准确评价肿瘤侵犯肛门括约肌的深度。扫描范围：FOV的头侧包括腰5椎体，尾侧缘包括肛管下缘。扫描线的倾斜角适当的扫描线倾斜角对识别肿瘤的边界至关重要。左图的举例：红线未与肿瘤垂直，造成MRF前缘受侵之假象（红圈）。在给予适当的倾斜角后，清楚显示MRF未受侵（黄圈）。MRprotocolT2-weightedFSEAn14DWIDiffusionweightedimagingcanbeusefulfor。ThefigureshowsasemicircularT3tumorwithperirectalinvasionextendingfrom3-9o'clockofthecircumference.CorrespondingdiffusionrestrictionontheADCmapandcalculatedDWI(b=1000s/mm2)。DWIinrestaging

DWIisveryusefulindeterminingtheresponsetochemoradiation.InthiscasethereispersistenthighsignalonimageswithhighB-values.whichindicatesincompleteresponse.DWI在原发癌的分期中，DWI有助于肿瘤及淋巴结的检测。左上图显示半环形T3肿瘤并周围3-9点钟范围的环周侵犯。对应的DWI扩散受限（b值=1000）。肿瘤再分期：DWIDWI在肿瘤化疗、放疗效果判断中，是非常有用的。右上图病例在新辅助放疗后，在高B值图上存在持久性的高信号，它表明疗效反应的不均衡性。ADCADCDWIB=1000放化疗后，不能只对比大小，也不可能又做活检吧？DWIDWIinrestagingDWI肿瘤再分期：D15插入：转移性肿瘤治疗效果影像学的评估：DWI

（附2个病例展示）加深印象插入：转移性肿瘤治疗效果影像学的评估：DWI加深印象16T2WIT1WIDWIADC8月9月11月本院3.0T病例胆囊癌腹膜后转移癌灶治疗前后三个月的变化（同样的B值）。看DWI对癌灶活性检测敏感性评价。T2WIT1WIDWIADC8月9月11月本院3.0T病例胆172015年5月、6月、9月、12月CT平扫。期间化疗射频治疗后呢？如何评价疗效？结肠癌肺转移灶2015年5月、6月、9月、12月CT平扫。期间化疗射频治疗182016年3月CT平扫（右下肺肿块增大，另注意左肺新出现了结节灶）。4月下旬行右肺肿块的射频消融治疗5.5mm2016年3月CT平扫（右下肺肿块增大，另注意左肺新出现了结195月11日CT平扫轴位：右肺肿块CT增强后期轴位：右肺肿块射频消融治疗后，右肺的肿块疗效如何？5月11日CT平扫轴位：右肺肿块CT增强后期轴位：右肺肿块射20冠状图：右下叶肿块平扫加增强那么射频治疗后的CT平扫加增强能判断右下灶的治疗效果吗？很难判断！冠状图：右下叶肿块平扫加增强那么射频治疗后的CT平扫加增强能21平扫增强CT值无大的差别8.0mm2016年5月11日CT，再看看左侧结节也只是较前稍增大，打药前后密度上没啥特征平扫增强CT值无大的差别8.0mm2016年5月11日CT，22再看看：右肺病变2016年5月20日MRIT1WIT2WI轴位压脂肪T2WI再看看：右肺病变2016年5月20日MRIT1WIT2WI轴23左肺结节的T2WI压脂肪图：与右肺病灶的信号明显不同左肺结节的T2WI压脂肪图：与右肺病灶的信号明显不同24注：ADC图中央区的低值，不要误认为扩散受限！为什么？左肺的结节扩散受限右侧肺肿块及左肺结节的DWI（b=800）注：ADC图中央区的低值，不要误认为扩散受限！为什么？左肺的25左右肺部病灶的中b值（b=150）图左右肺部病灶的中b值（b=150）图26MRI多期增强检查：右侧肺肿物无明显强化MRI多期增强检查：右侧肺肿物无明显强化27左肺小结节MR动态增强：可见强化预扫早期中期后期左肺小结节MR动态增强：可见强化预扫早期中期后期28左肺的结节灶可见强化（冠状）左肺的结节灶可见强化（冠状）292016-8-15即3个月后再复查MRI9.79cm2016-8-159.79cm30直肠癌：MRI与临床课件31从这个肺部病例，也看出MRI技术综合使用的优势，尤其DWI技术在评价肿瘤活性的重要应用价值。从这个肺部病例，也看出MRI技术综合使用的优势，尤其DWI技32LocationofthetumorTherectumextendsfromtheanorectaljunctiontothesigmoid.

Therectosigmoidjunctionisarbitrarilydefinedas15cmabovetheanorectalangle.

Atumormorethan15cmabovetheanorectalangleisregardedandtreatedasasigmoidtumor.Rectalcancercanbedividedinto:Lowrectalcancer:

Distalborderis0-5cmfromtheanorectalangleMidrectalcancer:

Distalborderis5-10cmfromtheanorectalangleHighrectalcancer:

Distalborderis10-15cmfromtheanorectalangle肿瘤的定位直肠是由肛门上延伸并与乙状结肠相接的部分。*直肠-乙状结肠结合部长度不恒定，一般指位于直肠肛管角上15cm处。*超过直肠肛管角15cm以上的肿瘤，是作为乙状结肠肿瘤定义并治疗。直肠癌的划分：*低位直肠癌直肠肛管角上0-5cm的直肠末端*中位直肠癌直肠肛管角上5-10cm的直肠末端*高位直肠癌直肠肛管角上10-15cm的直肠末端LocationofthetumorTherectu33LowrectalcancerLowrectalcancerhasahigherlocalrecurrencerate.

Thedistaltaperingofthemesorectalfatimpliesthatlowrectalcancermoreeasilyinvadesthemesorectalfascia,pelvicwallandsurroundingorgans.

Itwillbemoredifficultforthesurgeontogetatumorfreeresection(seefigure).Thereportshoulddescribetherelationshipofthetumortotheanalsphinctercomplexincaseoflowrectalcancer.Theinternalsphincteristhedistalcontinuationofrectalcircularfibers.

Consequently,ifatumorextendscaudallyintotheinternalsphincter,itisconsideredaT3tumor.Involvementoftheintersphinctericplane,externalsphincterandlevatormusculatureshouldbeassessed,asthismayinfluencetreatmentplanning(seesectionsurgery).

Involvementoftheintersphinctericplaneisbestobservedoncoronalplanes(figure)(7).Lowrectalcancerwithextensionofthetumorintheinternalsphincterandintersphinctericspace.Thelongitudinalmusclelayerwithintherightintersphincterisspace,canstillbedepicted(arrow)低位直肠癌

低位直肠癌局部复发率较高。直肠系膜远端的脂肪逐渐变细意味着低位直肠癌更容易侵入MRF及盆壁与周围的结构，外科手术根治肿瘤将会更难。低位直肠癌，肿瘤侵犯内括约肌及内括约肌间隙。右侧内括约肌间隙内的纵行的肌层得以显示（箭）。*低位结肠癌病例，诊断报告应叙述肿瘤与直肠括

约肌复合体的关系。*肛门内括约肌是直肠环形纤维在末端的延续，因此，如果肿瘤延伸至尾侧而进入内括约肌，则

被认定为T3肿瘤。*肿瘤对内括约肌平面的侵犯时，由于会影响到治疗计划，因而要对外括约肌、肛提肌进行评估。*MR上采用冠状位（注意扫描角度，见前述），最适于观察内括约肌平面的侵犯。LowrectalcancerThereportsh34T-stageSemicircularT2tumorinthedistalrectum,withsharplydemarcationoftheexternalmuscularlayer.T1andT2T1andT2tumorsarelimitedtothebowelwallandhaveagoodprognosis.MRimagingisunabletodistinguishbetweentumorextensionintothemucosa,submucosaandmuscularispropriaandthereforecannotdifferentiatebetweenTis(insitu),T1andT2tumors.AlthoughT1tumorscouldbetreatedwithlocalexcision,thetreatmentofchoiceinbothT1andT2tumorsisTME.Onlyifthereisapreferenceforlocalexcisionthroughtransanalendoscopicmicrosurgery(TEM-procedure),endorectalUScanbehelpful,becauseitsometimescandifferentiatebetweenT1andT2tumors.KeyfindinginT1andT2rectaltumorsisanintactexternalmuscularislayer,whichisidentifiedasahypointensethinlinesurroundingtherectum(figure).肿瘤分期肿瘤分期T1或T2肿瘤限于肠壁；T3a:超出肠壁固有肌层小于1mmT3b:超出肠壁固有肌层1-5mmT3c:超出肠壁固有肌层5-15mmT3d:大于15mmT3MRF+：肿瘤在MRF的1mm之内MRF-：MRF的1mm之内没有肿瘤T4a:侵犯腹膜T4b：侵犯邻近脏器（见前介绍）肿瘤1期和肿瘤2期1期和2期的肿瘤限于肠壁，预后好。MR成像不能区分二者：侵犯粘膜层或粘膜下层，还是侵及固有肌层。因此，不能鉴别1期即原位癌和2期的肿瘤。虽然1期的肿瘤应该是局部切除，但在实际治疗的选择上，对1、2期还是采用TME.如果适合经内窥镜下微创做肿瘤局部切除，直肠超声会有帮助，因有时可区分T1与T2期的肿瘤。T1与T2期的直肠肿瘤关键的表现是外肌层完整，它表现为直肠环周的线状低信号（图，此时若结合DWI更有意义）。直肠远侧半圆形T2期肿瘤，外肌层边缘锐利。T-stageSemicircularT2tumori35T3T3-tumorsgrowthroughtheexternalmuscularisintothesurroundingmesorectum.Astherectumdoesnotcontainaserosallayer,tumorinvadesdirectlyintothemesorectalfatandcanspreadtolymphnodesandbeyond.Spreadintothemesorectumcanbedepictedasspiculesoflowsignalintensityinthehyperintensemesorectalfatordistortionofthehypointensemuscularispropria.T3-tumorsarefurtherdifferentiatedin:T3a:tumourextends<1mmbeyondmuscularispropriaT3b:tumourextends1-5mmbeyondmuscularispropriaT3c:tumourextends5-15mmbeyondmuscularispropriaT3d:tumourextends>15mmbeyondmuscularispropriaMRF-notumorwithin1mmofMRFMRF+tumorwithin1mmofMRFT3MRF-rectalcancer.Semicircularmidrectumtumorwithtumorinvasionintothemesorectum,extendingfromapp.1-4o’clockofthecircumference.直肠癌T3期伴直肠系膜筋膜阴性（MRF-）。半圆形的中位直肠癌伴肿瘤侵犯直肠系膜，侵及圆周范围1-4点钟位。*T3（肿瘤3期）肿瘤生长透过外肌层而侵犯周围的直肠系膜。*因为直肠没有浆膜层，肿瘤直接侵犯直肠系膜脂肪并可扩散至淋巴结甚至其以外。*肿瘤扩散至直肠系膜，表现为位于直肠系膜脂肪内针状的低信号或者为低信号的粘膜固有层变形。T3期肿瘤进一步划分：T3a:肿瘤超出肠壁固有肌层小于1mmT3b:肿瘤超出肠壁固有肌层1-5mmT3c:肿瘤超出肠壁固有肌层5-15mmT3d:肿瘤超出肠壁固有肌层大于15mmMRF-：MRF的1mm之内没有肿瘤MRF+：肿瘤在MRF的1mm之内T3T3MRF-rectalcancer.Semi36Perirectalstranding

Difficultyindistinguisingtruemesorectaltumorinvasionfromdesmoplasticreaction,isthemaincauseofoverstaging.However,topreventunderstaging,itisrecommendedtostageatumorasT3whenstrandingispresent.HereweseetwotumorswithasimilarMR-appearance.

InAtherewasperirectaltumorinvasion.

InBthetumorwaslimitedtothebowelwall,i.e.aT2-tumor.

Theperirectalstrandinginthelattercasewastheresultofadesmoplasticreaction.直肠周“绳索征”直肠系膜肿瘤侵犯还是促结缔组织增生反应，二者的鉴别困难，而且是造成高估的主要原因。然而，为了防止低估，如若存在绳索征，则被推荐用于T3期肿瘤的分期。这里的两例肿瘤具有相似的MRI表现。图A有肿瘤周围侵犯图B肿瘤被限制在肠壁，即T2期肿瘤。其周围的绳索征是一种促结缔组织增生性反应。Perirectalstranding直肠周“绳索征”直37T3withMRFinvolvementInthedescriptionofT3-tumors,thereportshouldincludetheshortestdistancebetweenthetumormarginandtheMRF.

InvolvementoftheMRFresultsinanincreasedriskforlocalrecurrence.TheMRFisconsideredinvolvedwhenthedistancebetweenthetumormarginandMRFislessthan1mm.

Althoughapositivemarginduetoasuspiciouslymphnodeshouldbeassessedandreported,thisisnotregardedasadeterminationfactorindefiningMRFinvolvement.Theimageshowsatumorthatinfiltratesthemesorectalfatwithinvolvementoftheresectionmarginontheposteriorside(arrow).

ThistumorisclassifiedasT3MRF+.

Thispatientwillbetreatedwithchemotherapyandalongcourseofradiotherapy.Ifthetreatmentissuccessful,asdemonstratedbyarestagingMRI,aTMEwillbeperformed.Lowrectaltumorwithinvolvedmesorectalfascia.低位直肠癌侵犯直肠系膜筋膜T3期肿瘤伴直肠系膜筋膜（MRF）侵犯*在T3肿瘤的描述中，需要报告的内容应包括：肿瘤边缘至MRF的最短距离。*MRF侵犯可增加肿瘤局部复发的危险。*MRF受侵的定义：肿瘤缘与MRF间的距离小于1mm。*尽管由于可疑淋巴结导致MRF缘阳性的评估及诊断报告，但这并不能当做确定MRF受侵的决定性因素。*左图的影像显示有直肠系膜脂肪侵润的直肠肿瘤侵犯后侧的切缘。该例肿瘤分期为T3MRF+。*该病人采取的治疗：化疗加长时间的放疗。*若治疗效果是成功的，则由MRI对其再分期并决定实施TME。T3withMRFinvolvementLowrec38T4a-InvasionperitonealreflectionThelowrectumistotallycoveredbythemesorectalfascia.

Inthemid-rectumitiscoveredbythemesorectalfasciaontheposteriorandlateralside,butontheanteriorsideitiscoveredbythevisceralperitoneum.

Growthintothevisceralperitoneummeansspreadtotheperitonealcavity.Onasagittalimagetheanteriorperitonealreflectionisthetransitionbetweenthenon-peritonealizedandperitonealizedportionoftherectum.

Itisimportanttonoticeiftumorspreadontheanteriorsideisbeloworabovetheperitonealreflection.OnsagittalT2-weightedimagestheperitonealreflectioncanbedepictedasahypointensethinlineconnectingthebladderwiththeanterosuperioraspectoftherectum.T4a期肿瘤：腹膜反折部的侵犯*低位直肠全部由直肠系膜筋膜覆盖。*中位直肠由后部、侧部的直肠系膜覆盖，而前部则由腹膜脏层覆盖。*当病变累及脏层腹膜则意味着肿瘤向腹膜腔扩散。*左侧矢状图上，腹膜前反折部是直肠非腹膜化与腹膜化的过度部分。*如果肿瘤扩散点是在前侧，应将腹膜反折的上或下区作为重要的关注点。*T2WI矢状图上，腹膜的反折被描述为连接膀胱与直肠前上方向的细线状低信号影。T4a-Invasionperitonealrefl39OnthisaxialT2-weightedimagethereistumoringrowthalongthevisceralperitoneum(arrow).Theperitonealreflectionismarkedbythearrow-youmayhavetoenlargetheimage.Theperitonealreflectioncanbedifficulttorecognize.

Itistheborderbetweentheintraperitonealmesocolicfatandthemesorectalfat.Onthissagittalimageofthesamepatientperitonealmetastasesareseen(arrow).Noticethattherearealsosuspiciouslymphnodesinthemesorectum.同一病人的矢状T2WI图显示腹膜转移灶（箭）注意到，直肠系膜也有数个可疑淋巴结。腹膜转移可疑淋巴结轴位T2WI，肿瘤沿脏层腹膜生长（黄箭）。腹膜反折由白箭标记。可放大看。腹膜反折不容易显示出来。腹膜反折是腹腔内结肠系膜脂肪与直肠系膜脂肪的界限。腹膜反折OnthisaxialT2-weightedimag40AT4b-tumorinvadesthesurroundingstructuressuchaspelvicwall,vagina,prostate,bladderorseminalvesicles.TumorinvasionisdefinedaslossoftheinterveningfatplaneandcorrespondingT2signalabnormalitywithintheinvolvedsurroundingstructure.OnthesagittalT2W-imagethereislossoffatplanebetweentherectumandtheposteriorwallofthevagina.

Onaxialimagestherelativelylowsignalintensityofthetumorisseentoextendintotheposteriorwallofthevagina(arrow).T4b-InvasionsurroundingorgansT4b肿瘤：邻近器官侵犯T4b肿瘤邻近结构侵犯，比如盆壁、阴道、前列腺、膀胱、或精囊腺。临近结构侵犯：受侵的结构周围脂肪层消失并相应的T2WI信号异常。T2WI矢状位像，阴道后壁与直肠间的脂肪层消失。T2WI轴位像，可见相对低信号的肿瘤侵及阴道后壁（箭）。AT4b-tumorinvadesthesurrou41Scrollthroughtheaxialimagesandseehowthelowsignalintensityofthetumorisseentoextendintotheposteriorwallofthevagina(arrows).Theseimagesdemonstrateatumorextendingintotheposteriorwalloftheuterus.这些图像证实肿瘤侵及子宫后壁连续的轴位图显示直肠较低信号的肿瘤侵及阴道后壁的程度（箭）Scrollthroughtheaxialimage42Extramuralvascularinvasion(EMVI)VascularinvasionisariskfactorforrecurrentdiseaseandistobeincludedinstandardizedMRreporting.

EMVIisassociatedwithT3-andT4tumors(10,11).EMVIissuspectedifavascularstructureincloseproximitytothetumorisexpanded,irregularorinfiltratedbytumorsignalintensity(seefigure).壁外的血管侵犯（EMVI）肿瘤壁外血管侵犯是病变复发的危险因素，需体现在标准的MR诊断报告中。若血管结构密切贴近邻近的肿瘤，表现为扩展性、不规则或侵润性并接近肿瘤信号特点时，应该怀疑EMVIExtramuralvascularinvasion(43N-stageTheN-stageisanimportantriskfactorforlocalrecurrence.MRhasalowaccuracyfordistinguishingpositiveornegativelymphnodesifcharacterizationisbasedonsizealone.

Predictionofnodalinvolvementisimprovedbyusingthebordercontourandsignalintensitycharacteristicsoflymphnodes(Table)(12).Lymphnodes<5mmareconsideredsuspiciousifthreemalignantcharacteristicsarepresent(seetable).Lymphnodes5-9mmareconsideredmalignantiftwooutofthreemalignantcharacteristicsarepresent.Lymphnodeswithashortaxis⩾9mmarealwaysincludedinthenumberofsuspiciousnodes.Whenindoubt,aborderlinesuspiciouslymphnodeshouldnotbeconsideredassuspicious.

Consequently,alesserN-stageshouldbeassigned.区域性淋巴结分期N（区域淋巴结）分期区域淋巴结分期是直肠癌局部复发的重要危险因素。若仅以大小特征评价，MR依此很难区分阳性还是阴性的淋巴结，诊断正确率很低。对淋巴结的信号特征及边缘轮廓的评价可改善受侵淋巴结的预测（见表）。*<5mm的淋巴结，如果具备左边的图表中3个恶性特征则被考虑可疑淋巴结。*5-9mm的淋巴结，如果具备左边的图表中2个恶性特征则被考虑可疑淋巴结。*淋巴结最短经⩾9mm的淋巴结，多被考虑可疑淋巴结。N分期：可疑淋巴结恶性特征边界模糊不均匀圆形短轴cN期N0:无可疑淋巴结N1:1-3可疑淋巴结N2:4或4个以上的淋巴结小于5mm:需要3个恶性特征5-9mm:需要2个恶性特征大于9mm:常为提示恶性当淋巴结不确定或处于可疑淋巴结临界线时，按非可疑淋巴结看待。N-stageTheN-stageisanimpor44Diffusionweightedimagescanbehelpfulindetectinglymphnodes(figure).Howeverdiffusionimagesarenotsuitableforcharacterization.

HighresolutionT2W-imagesareusedtodeterminesizeandmorphologiccharacteristics.Noticethatthediffusionimageisinverted.BettervisualisationoflymphnodesoninvertedDWIcomparedtocorrespondingT2WI.OnthissagittalT2W-imagealowrectalcancerwithmultiplenodesinthemesorectalfatontheposteriorside.Someofthenodesonthisimageareheterogenousandhaveirregularborders.

Thereweremorethan4suspiciousnodesinthispatient(N2-stage).ThispatientwillreceiveneoadjuvantchemoradiationandaTMEdependingonthefindingsofthefollow-upMRI.受侵淋巴结极佳的视觉：DWI图与对应的T2WI图*DWI有助于淋巴结检测（图）。*然而，DWI图像不适宜描述病变的特征。*高分辨T2WI用于淋巴结大小及其形态特征的描述。*注：DWI图是反转图。*T2WI矢状图显示低位直肠癌伴后部直肠系膜的脂肪内多发结节。*该图上，一些结节信号不均匀并边缘不规则。*该病人有4个以上的可疑淋巴结（分期：N2）。*需要接受新辅助化疗，TME手术取决于MRI随访的表现而定。Diffusionweightedimagescan45ExtramesorectallymphnodesItisimportanttolookbeyondthemesorectumforlymphnodes(arrow).

Theseextramesorectalnodesareimportant,becausetheycanbeacauseoflocalrecurrence,becauseinastandardTMEproceduretheseextramesorectallymphnodeswillnotberesected.Suspiciousextramesorectallymphnodeshavetobeincludedinthestandardreporting,sotheradiationandsurgicalplanningcanbeadapted.TheimageshowsacircularT3tumorwithextramuralvascularinvasion(EMVI),bridgingtotherightextramesorectalspace(yellowarrow).Inadditionthereisasuspiciousextramesorectallymphnode(greencircle).直肠系膜外淋巴结*直肠系膜远处看到的淋巴结非常重要。*这些直肠系膜外的淋巴结之所以重要，是因为它是导致局部复发的原因；

还因为在TME手术标准中，这些直肠系

膜外淋巴结并不被切除。*直肠系膜外可疑淋巴结必须要包括在标准的诊断报告中，以便放疗或手术

计划参考。*左图：显示直肠环形T3期肿瘤伴壁

外血管侵犯（EMVI），该血管桥接至右

侧直肠系膜外间隙（黄箭）。*此外，直肠系膜外有一可疑淋巴结（绿圈）。Extramesorectallymphnodes直肠系46ThisaxialT2W-imageisofapatientwithextramesorectalnodalrecurrenceafterTME(arrow).

InastandardTMEproceduretheseextramesorectallymphnodesarenotresected.

ThismeansthatafterTMEsurgerynotalltumordepositswillhavebeenremoved.

Thefindingofmalignantextramesorectallymphnodesentailsthatatleastamoreextensivesurgicalapproachisnecessarytoremoveallthecancerdepositsoraboostofradiotherapytotheareasofrisk.LocalrecurrenceofrectalcancerafterTMEduetopositiveextramesorectallymphnodes由于直肠系膜外的淋巴结阳性，直肠癌TME术后局部复发。轴位T2WI图，TME术后直肠系膜外淋巴结复发灶（箭）。在标准的TME手术中，这些直肠系膜外淋巴结是不切除的。直肠系膜外恶性淋巴结表现至少得需要广泛性的外科手术，用于切除所有的癌转移灶或对可疑区域实施放疗协助。ThisaxialT2W-imageisofap47RegionalLymphnodesRegionallymphnodesarelocatedalongtheprovidingvesselsoftherectum.

Notethatlymphnodesarepotentiallysuspiciousatthelevel-orproximallyoftheprimarytumor,followingthenormallymphdrainage(figure).TheAJCCconfineslocoregionallymphnodeinvolvementtotheperirectal,sigmoidmesenteric,inferiormesenteric,lateralsacral,presacral,internaliliac,sacralpromontory(Gerota's),internaliliac,superiorrectal(hemorrhoidal),middlerectal(hemorrhoidal),andinferiorrectal(hemorrhoidal)lymphnodes.Lymphnodesoutsideoftheseareasareconsideredmetastaticdisease(M1).

Forexamplesuspiciousinguinallymphnodesifthedistalanalsphinctercomplexisinvolved.Regionallymphnodedrainage.Thelymphnodesinredaremetastaticnodes.区域淋巴结（N）引流。红色的淋巴