with the development of chemotherapy , control of metastatic colorectal cancer has increased in recent years .
aggressive resection of distant metastases , local recurrence , or peritoneal dissemination has been performed , and good results have been reported [ 1 , 2 ] . particularly , aggressive resection has been recommended for hematogenous metastasis ; however , in pulmonary resection , the presence of mediastinal lymph node recurrence has been reported as a poor prognostic factor .
recommendations for the resection of distant lymph node metastasis are lacking , but it is thought that solitary metastatic lesions should be resected .
the development of various diagnostic imaging such as pet / ct has contributed enormously to performing preoperative staging and detecting postoperative recurrence . here , we present the case of a patient who had a solitary swollen mediastinal lymph node with high accumulation on pet / ct after primary resection of rectal cancer .
however , histopathological results showed no metastasis , and he was diagnosed with reactive lymphadenitis .
we report 1 case study of false - positive diagnosis on pet / ct and compare our findings with previous literature .
a 60-year - old patient presented with positive fecal occult blood and was subsequently diagnosed with rectal cancer ( rs ) .
histopathological examination revealed moderately differentiated adenocarcinoma , and the pathological stage was pt3n1m0 , pstage iiia ( fig .
the oral fluoropyrimidine agent s-1 ( 80 mg / m per day , administered for 4 weeks with a 2-week resting period ) was administered for adjuvant chemotherapy . on postoperative day 239 , a ct scan revealed a solitary swollen mediastinal lymph node ( fig .
2a ) . the patient reported no symptoms of common cold , no palpable lymph nodes , and no murmur in the chest .
laboratory data , including blood count , biochemical findings , and c - reactive protein , were within normal range .
the serum cea level was also normal ( 1.8 ng / ml ; normal value , < 5.0 ng / ml ) ; before primary surgical treatment , it was 5.8 ng / ml . t2-weighted mri showed iso - high intensity , and diffusion - weighted mri showed a high signal at the tracheal bifurcation ( fig .
pet / ct was performed , and abnormal f - fdg uptake appeared in the tracheal bifurcation .
thoracoscopic mediastinal lymph node resection was performed in the prone position on postoperative day 281 .
the surgical procedure was as follows : ( 1 ) a 12-mm port was inserted into the fifth intercostal space on the posterior axillary line with an 8-mm hg pneumothorax ; ( 2 ) a 12-mm camera port was inserted into the ninth intercostal space on the lower scapula line ; ( 3 ) a 5-mm port was inserted into the seventh intercostal space on the posterior axillary line .
on histopathological examination , the resected specimen measuring 33  22 mm in diameter showed enlarged germinal centers without an epithelial component .
immunostaining was performed to detect follicular lymphoma ; bcl-2 was negative , and the patient was diagnosed with reactive lymphadenitis ( fig .
oral capecitabine ( xeloda , 3,600 mg per day , administered for 2 weeks with a 1-week resting period ) was administered for 6 months .
imaging follow - up was performed 2 months after thoracoscopic lymph node resection by ct scan .
we confirmed that the suspicious lymph node was resected and other recurrent lesions did not appear .
the patient is alive at more than 15 months after his second surgery and is being followed up closely .
since the publication of colorectal cancer treatment guidelines in japan , providing appropriate treatment for these patients has become mandatory .
therefore , accurate preoperative diagnosis is important , and postoperative recurrence must be evaluated accurately by various methods of diagnostic imaging . given the advent of fdg- pet and pet / ct in recent years , pet imaging has become essential for improving the detection rate .
studies have reported that pet imaging is more useful than mri or multidetector - row ct ( mdct ) [ 4 , 5 ] . however , in colorectal cancer , the diagnostic capability for lymph node metastasis ( reported as 2951% sensitivity , 85100% specificity , and 6775% diagnostic accuracy ) is insufficient compared to that for the primary tumor [ 6 , 7 , 9 ] . especially for sensitivity , diffusion - weighted mri is more useful than fdg - pet . in our hospital ,
the diagnosis rate of lymph node metastases using preoperative pet / ct for 42 patients with colorectal cancer tended to be lower in specificity ( 77% sensitivity , 71% specificity , and 74% accuracy ) .
generally , local inflammation , abscess formation , inflammatory diseases , and lymphomas may be considered as the causes of false - positive lymph nodes on pet .
although false - positive para - aortic lymph nodes are occasionally identified on pet , to our knowledge , pet false - positive cases associated with colorectal cancer in mediastinal lymph nodes have not been found .
the use of pet / ct for identification of mediastinal lymph nodes has been reported .
physiological accumulation is often observed in hilar lymph nodes and has the following features : ( 1 ) nearly equal accumulation intensity on both sides , and ( 2 ) no swollen lymph nodes in the mediastinum on ct . on the other hand , solitary mediastinal lymph node metastases of cases of colorectal cancer
the present case did not meet the features of physiological accumulation in hilar lymph nodes and showed a solitary enlarged lymph node , high suvs , and high intensity on diffusion - weighted mri .
therefore , we diagnosed the patient with mediastinal lymph node metastasis of colorectal cancer and performed surgical treatment . on the other hand ,
less invasive surgery is desirable for surgical treatment , and advances in video - assisted surgery have been remarkable in recent years .
thoracoscopic esophagectomy has become widespread because it provides a magnified view and an easier approach to the mediastinum .
the biggest advantage of the prone position is a good view of the surgical field without displacing the heart and right lung because of gravity and artificial pneumothorax .
our case maximized the benefits of the prone position , and the patient had a good postoperative course .
even though histopathological findings showed lymphadenitis , the patient had no distinct physical findings and inflammatory response .
the possibility of viral infection can not be ruled out , although it was difficult to diagnose correctly before surgical treatment . in cancer treatment , it is necessary to decide the appropriate strategy on a case - by - case basis with due consideration of the limits of various methods of diagnostic imaging .
moreover , evaluations of pre- and postoperative colorectal cancer recurrence and metastasis using integrated fdg pet / contrast - enhanced ct have been reported .
kitajima et al .   reported 170 postoperative cases , with 93.2% sensitivity , 95.8% specificity , and 94.7% accuracy .
there is no consistent strategy for appropriate treatment of solitary lymph node metastasis in colorectal cancer patients . especially for pet - positive lesions , both sensitivity and specificity may be insufficient .
mediastinoscopy and needle biopsy with bronchoscopy are useful methods ; however , the possibility of disseminated cancer cells remains . in conclusion
, our case report suggests that it is necessary to understand the limits of the diagnostic accuracy of pet / ct in determining the indication for surgical treatment .
additionally , the thoracoscopic approach in the prone position is one of the easy - to - use approaches to the mediastinum .
 18f - fluorodeoxyglucose ( fdg ) positron emission tomography and computed tomography ( integrated fdg pet / ct ) has been used to diagnose recurrence and differentiate postoperative changes from lymph node metastasis in colorectal cancer , although its accuracy is questionable . 
 we report a prone thoracoscopic surgery for a rectal cancer patient in which false - positive mediastinal lymph nodes were found on fdg - pet / ct . 
 a 60-year - old man underwent a laparoscopic high anterior resection and d3 lymph node dissection for rectal cancer . 
 the histopathological diagnosis was moderately differentiated adenocarcinoma of the rectum , stage iiib ( pt3n1m0 ) , necessitating oral fluoropyrimidine agent s-1 . after the primary surgery 
 , a solitary mediastinal lymph node measuring 30 mm in diameter was detected , and abnormal accumulation was confirmed by fdg - pet / ct ( suvmax , 11.7 ) . 
 thoracoscopic resection was performed in the prone position , but histopathological results showed no metastasis . 
 he was subsequently diagnosed with reactive lymphadenitis . 
 the patient was discharged on postoperative day 4 in good condition and is alive without recurrence 12 months after surgery . 
 pet / ct is useful for the detection of colorectal cancer recurrence ; however , it does have a high false - positive rate for mediastinal lymph nodes . 
 there is a limit to its diagnostic accuracy , and one must determine the indication for surgical treatment carefully . 
 surgery in the prone position is a useful and minimally invasive approach to the mediastinum and allows aggressive resection to be performed . 
Introduction
Case Report
Discussion
Conclusions
Disclosure Statement