The Pathophysiologic Basis of Nuclear Medicine

surgery. Detailed histopathological examination (- value of 95%, where in only one case was metastasis cluding multilevel sectioning, immunohistochemistry found in a non-SLN [94]. staining, monoclonal antibody staining, and reverse All the efforts in SLN identification so far discussed transcriptasepolymerase chain reaction assay) can re- werebasedoninjectionofadyeintothesubserosall- vealmicrometastasesandleadstoultrastaging,butap- er(intraoperatively)orinthesubmucosallayer(pre- plication of the technique to all lymph nodes in a re- eratively usinga colonoscope orproctoscope). The use sectedspecimenisnotpracticallyfeasible.Thesentinel ofaradiotracertodelineatethelymphaticchannelswas lymph node concept is therefore a method capable of highlighted in a very small number of publications. A pointingoutthefirstnodetoreceivedrainagefromthe group of 56 colorectal cancer patients had sentinel tumorandtorepresentthefirsttoharbormicrometas- lymph node mapping intraoperatively using gamma tasisifany.Theutilizationoftheconceptinthecontext probeguidanceastheonlymethodforSLNidentifi- ofcolorectalcancerisdifferentthanthatinbreastcan- tion.SLNsweredetectedin91%ofpatients.Metastasis cerasanexample.Inthelatter,SLNidentification wasseenin22%ofSLNsasopposedto3%ofnon-SLNs. aims to avoid unnecessary surgical exploration and InfourcasesSLNswerefalselynegativelyinthepr- resection of axillary nodes in the basin if the SLN is enceofmetastasisinothernon-SLNs,andanadvanced negative for tumor. In colorectal cancer, however, the case of colorectal cancer was a common finding (a T3 regional lymph nodes are already removed en block primary tumor) [95]. Whether tumor burden causes andthereisnochangeinsurgicalextentoutofthein- blockingordiversionoflymphaticchannelsremainsto formation derived from SLN status. Alternatively, the be investigated. aim is to identify (either intraoperatively or during Trochaetal.[96]studied48colorectalpatientsusing pathologicalexamination)asmallergroupofnodesin a combination of radiotracer and blue dye. thespecimenandtofocusallhistopathologicalefforts Inallidentifiednodesthereweresignificantlyfewer on such nodes in order to dramatically increase the nodes positive by both methods “blue and hot” than yield.Inaddition,anappealingfeatureisthatcolorec- “blueonly”.Inaddition,nodalmetastasiswasmore tal cancer exhibits a very predictable pattern for lym- commoninthoseblueandhotthanblueonlynodes. phaticdrainagechannels.Despitealloftheseobserva- This signifies that dual-agent examination more ac- tions and expectations, the application of the sentinel ratelyidentifiesSLNandaccordinglyfurtherdecreases lymphnodeconceptincolorectalcancer(asinallgas- thenumberofnodestobeexaminedbythepathologist.