the technique of lymphatic mapping and sentinel lymph node biopsy ( slnb ) has emerged in the last two decades as a minimally invasive approach to evaluate regional lymph node basins in patients with intermediate and high - risk primary cutaneous melanoma . in particular , slnb is now recommended as a staging procedure for patients with t2 , t3 or t4 melanomas and clinical uninvolved regional lymph nodes ( clinical stage ib and ii ) and suggested also for patients with t1 melanomas and pathologic features associated with an increased risk of nodal micrometastases ( ulceration , high mitotic rate ,  ) . also positron emission tomography ( pet ) with 18f - fluorodeoxyglucose ( 18f - fdg ) has been extensively investigated in patients with melanoma and plenty of studies have shown its effective role in detecting distant metastases , further increased after the introduction of co - registered computed tomography ( ct ) scan ( 18f - fdg pet / ct ) . in this article , we introduce a case of pt4b thigh melanoma , in which both procedures were performed , together with ultrasonography .
an 82-year - old white male , with a clinically - confirmed cutaneous melanoma of the right thigh , presented to our unit to undergo lymphoscintigraphy , in order to perform slnb at the same time of tumor excision .
lymphoscintigraphy with tc - nanocolloids was performed on a hybrid system philips single - photon emission computed tomography / computed tomography ( spect / ct ) precedence 16 slices ( philips healthcare , eindhoven , the netherlands ) after intradermal injection of the radiopharmaceutical around the primary lesion ( four separate injections , 0.1 ml for each aliquot , total activity 100 mbq ) .
low dose helical ct scan was performed : 120 kv , 100 ma , d - dom control dose , 3 mm slice thickness , 1.5 mm detector collimation , pitch 0.8 , rotation time 0.75 s. spect scan was acquired with the following parameters : 128  128 matrix size , 120 view angle , 10 s time / angle , 5 mm pixel size .
spect / ct images showed uptake of the radiocolloids in a right inguinal lymph node .
on ct co - registered images , anyway , another lymph node with no radiopharmaceutical uptake but with suspicious aspect ( globular morphology , absence of hilum ) was detectable in the crural region , much closer to the primary tumor [ figures 1 and 2 - left panel ] .
axial views of single - photon emission computed tomography / computed tomography ( ct ) lymphoscintigraphy with tc - nanocolloids .
tracer uptake can be seen in the site of injection / primary tumor ( green arrow ) and in a right inguinal node ( yellow arrow ) , while there is no uptake in a crural node with suspicious aspect on ct images ( red arrow ) volume rendering of technetium - labeled radiocolloids single - photon emission computed tomography / computed tomography ( left panel ) and f - fluorodeoxyglucose positron emission tomography / computed tomography ( right panel ) .
the arrows show the sites of primary lesion ( green ) , true  sentinel  crural node ( red ) , false  sentinel
 inguinal node ( yellow ) for this reason , and due to the adverse pathologic features of the removed lesion ( clark 's level iv , breslow 's depth 4.6 mm , ulceration , 89 mitoses / mm , poor inflammatory infiltrate , pt4b ) , the patient was further staged with a f - fdg pet / ct scan after surgery .
pet / ct showed pathologic uptake of the tracer in the suspected right crural lymph node , which was removed : no other nodal or visceral metastases were seen [ figures 2 - right panel and 3 ] .
histology demonstrated signs of chronic inflammation and no neoplastic cells in the inguinal lymph node ( analysis of slices from the whole node with hematoxylin and eosin ( h and e ) stain and confirmation with immunohistochemical staining for s-100 protein in each 
blank  slide ) , while a massive metastasis from melanoma was seen in the crural node ( h and e ) .
no significant uptake can be seen in the site of the removed primary tumor ( green arrow ) and right inguinal node ( yellow arrow ) , while high metabolic activity is demonstrated in the crural node ( red arrow ) neither inguinal lymphadenectomy nor systemic therapy was proposed , due to age and co - morbidity ( hypertensive cardiomyopathy ) and a follow - up based on abdominal , and inguinal ultrasonography was organized .
ten months after surgery the patient developed a metastatic disease , further depicted by a follow - up f - fdg pet / ct scan [ figure 4 ] .
follow - up f - fluorodeoxyglucose positron emission tomography / computed tomography scan ( 1 year after tumor excision ) : multiple secondary lesions can be seen in right inguinal nodes , in the liver and in many skeletal segments
the prognostic factors for cutaneous melanoma have been recently revised in the 7 edition of the american joint committee on cancer ( ajcc ) ( 2009 ) , based on analysis of data for over 50,000 patients of ajcc database .
apart from the features of the primary lesion ( thickness , mitotic rate , ulceration ) , the histologic status of regional nodes has been confirmed as the most powerful independent predictor of survival in clinically node - negative patients .
the technique of slnb , first proposed in the 1980s , made inroads once it was clear that the treatment of regional node disease while still microscopic afforded a survival benefit compared to waiting for clinically evident disease .
this strategy , minimally invasive , allows the use of more aggressive surgical approaches and systemic therapies only in higher - risk patients , with occult stage iii disease .
it has shown high sensitivity ( especially when performed with spect / ct - aided lymphatic mapping and multiple peri - tumour injections ) with very low false - negative rate , mainly related to technical problems associated with identification of the true sentinel node ( sn ) by nuclear medicine physicians and surgeons and errors in tissue sampling and interpretation by pathologists .
thus , even if new and more sensitive molecular techniques have already shown promising results , slnb with pathological assessment is now the recommended staging procedure for all stage i and ii patients with primary melanomas > 1.0 mm in thickness .
nonetheless , with the introduction and the development of noninvasive metabolic imaging techniques ( such as f - fdg pet / ct ) also in patients affected by melanoma , the hypothesis that even slnb could be avoided and replaced by the analysis of tumor metabolism in the lymphatic basin has emerged . in the last 15 years , almost 20 papers concerning the diagnostic performance of f - fdg pet / ct in comparison to slnb ( and ultrasonography ) can be found in literature , all pointing out , with few exceptions , a very low sensitivity of f - fdg pet / ct in discovering small lymph node metastases if compared with slnb . in this scenario ,
our report looks somewhat interesting , suggesting the possible utility of pet / ct even in the evaluation of regional disease in selected patients .
the key point seems to be the missed identification of sentinel lymph node by lymphoscintigraphy , probably due to the obstruction of lymphatic flow to the true sn and the consequent deviation of the flow to another node .
this situation has already been described in some papers about sns in melanoma and also in breast cancer . in 2009 , for example , lam et al .
described three cases in which preoperative lymphoscintigraphy failed to show sns containing metastatic melanoma ( all with significant tumor involvement ) , that were discovered by ultrasound and then confirmed by fine - needle aspiration biopsy and histopathology .
the same circumstance was previously described by estourgie in 2003 in two breast cancer patients : in that report , both lymphoscintigraphy with tc - nanocolloid and patent blue dye administration failed to identify the true sn , completely invaded by tumor and discovered by intra - operative palpation of the biopsy wound . what seems new here
is that not only lymphoscintigraphy , but even preoperative ultrasonography failed to identify the metastatic crural node . in this setting , in our opinion , a double lesson can be learnt .
first , this report confirms that a small risk of missing sentinel lymph node by lymphoscintigraphy exists ( especially in thick melanoma ) and highlights the added value of a hybrid tomographic study ( spect / ct ) , that allows a morphologic evaluation of the interested region too .
second , it shows that f - fdg pet / ct , usually performed for 
n staging  ( for the well - known lack of sensitivity in the study of the lymphatic basin ) , could give important information also about regional disease in selected patients .
the selection of the staging procedures to perform should always be individualized , considering general and local features of the disease , and evaluating together with the patient the risks and benefits of each technique .
 the american society of clinical oncology guidelines recommend sentinel lymph node biopsy ( slnb ) for all patients with melanoma tumors of intermediate thickness ( between 1 and 4 mm ) . in case of patients with thick melanoma tumors ( > 4 mm ) , slnb may be recommended as well , for staging purposes and to facilitate regional disease control . 
 we report a case of an 82-year - old man , undergone excision of a cutaneous melanoma of the right thigh , which shows some limitation of slnb in thick melanoma . 
 lymphoscintigraphy , performed as single - photon emission computed tomography / computed tomography ( spect / ct ) , failed to identify the real sentinel lymph node , as tracer uptake was seen in a right inguinal node . due to the presence on ct co - registered images of another suspicious node ( with no radiopharmaceutical uptake ) in the crural region , and considering the  high - risk  pathologic features of the removed primary lesion , a 18f - fluorodeoxyglucose positron emission tomography / ct ( 18f - fdg pet / ct ) staging scan 
 was planned . 
 pet / ct showed high metabolic activity in the suspected crural lymphadenopathy . 
 histopathology demonstrated massive invasion of the crural (  sentinel  ) node and no metastatic cells in the inguinal node . 
 this report highlights both the higher accuracy of lymphoscintigraphy , when performed as spect / ct and the potential utility of 18f - fdg pet / ct in regional staging . 
INTRODUCTION
CASE REPORT
DISCUSSION