positron emission tomography - computed tomography is useful for diagnosing primary and metastatic lesions of esophageal cancer . the sensitivity and specificity of a pet / ct are also relatively preferable to other diagnostic imaging tools . although the number of cases is few , false positives exist in which an inflammatory tumor mass and a nonspecific tumor mass are difficult to differentiate between , even when combined with other image findings . in cases of esophageal cancer , the types of treatment and their prognosis are greatly affected if there is a metastasis or recurrence . positron emission tomography - computed tomographic false positives can not simply be ignored even if they appear to be due to inflammation or some other factors . this case report discusses the reasons to conduct a pet / ct test and its limitations in diagnosing esophageal cancer . the subjects of this investigation had suspected metastasis from a pet / ct which occurred before surgery of the 129 resected cases of esophageal cancer at our department from june 2010 to march 2015 . however , after surgery , biopsy and/or follow - up observation , only the cases that were confirmed as metastasis negative were considered to be pet / ct false positives for this assessment . there were 3 cases of preoperative pet / ct false positives ( table 1 ) . two cases in which bone metastasis was suspected revealed almost normal range of squamous cell carcinoma ( scc)associated antigen , alkaline phosphatase , and serum calcium levels . abbreviations : ln , lymph node ; m , metastasis ; mt , middle thoracic lesion of esophagus ; n , node ; t , tumor ; ut , upper thoracic lesion of esophagus . in case 1 , a 59-year - old man , without particular medical history , had a diagnosis of esophageal carcinoma by endoscopy . multiple bone metastases were suspected by a pet / ct in the spine , sternum , ribs , and pelvic bone ( figure 1 ) . after conducting a ct - guided biopsy of the right iliac bone , the patient is alive with no recurrence 4  years and 10  months after surgery , although the false - positive lesions in pelvic bone are still detected by pet / ct . in the case 1 , multiple bone metastases were suspected by a positron emission tomography - computed tomography in the pelvic bone ( suvmax  =  2.94 ) . in case 2 , a 71  year - old man , without particular medical history , abnormal accumulations of fluorodeoxyglucose ( fdg ) in the manubrium sterni , vertebra th5 , and the pedicle of vertebral arch were found by pet / ct . therefore , after the sufficient informed consent , the patient underwent a laryngopharyngeal esophagectomy , a transhiatal esophagectomy without thoracotomy , and reconstruction with the gastric tube through the posterior mediastinal route . pathological finding showed poorly differentiated scc of esophagus and moderately differentiated scc of hypopharynx with a cervical lymph node metastasis . the patient is alive with no recurrence 3  years and 11  months after the surgery . in case 3 , a 76-year - old man , without particular medical history , had a diagnosis of a superficial esophageal cancer by endoscopy . he was suspected of lymph node metastasis of right recurrent nerve lymph node ( figure 2 ) by preoperative pet / ct . . scattered silicotic nodules and inflammatory lymphadenopathy might be caused by pneumoconiosis ( figure 3 ) . case 3 was suspected of right recurrent nerve lymph node metastasis by preoperative positron emission tomography - computed tomography ( suvmax  =  3.00 ) . pathological finding of case 3 revealed scattered silicotic nodules in resected lymph nodes with infiltration of histiocytosis to sinusoid . in esophageal cancer treatment , fdg - pet / ct is also used to diagnose metastases and to judge the effectiveness of treatment . especially , pretherapeutic there are cases when the surgery may not apply to a patient if remote metastasis or high - grade lymph node metastasis is found . many cases have already been reported claiming that fdg - pet is a useful modality for a pretherapeutic staging . esophageal cancer causes 30% to 40% of lymph node metastases among cancers that spread to the submucosa , and the prognosis of esophageal cancer is known to be defined by the presence of lymph node metastasis , how many metastases are present , and how much the metastasis spreads . therefore , evaluating lymph node metastasis is a very important factor in deciding the course of treatment . the diagnosability of lymph node metastasis using a fdg - pet for esophageal cancer is generally reported to have a sensitivity of 32% to 51.9% , a specificity of 94.2% to 100% , and an accuracy of 48% to 93% . in addition , fdg - pet / ct , which is a combination of a fdg - pet and a ct , improves the diagnosability even more . yuan et al have reported that they evaluated the diagnosability of lymph node metastasis using fdg - pet / ct for esophageal squamous cancer and found a sensitivity of 94% , a specificity of 92% , and an accuracy of 92% . however , the size of a lymph node that can be detected by pet / ct is said to be only 6 to 8  mm , thus it is difficult to detect micrometastasis . also , detecting metastasis to neighboring lymph nodes could be difficult in cases with a lot of fdg accumulation in the primary lesion , or accumulation in the intestinal tract such as in the stomach , or in the heart . the fdg accumulates in inflamed lymph nodes as well , so false positives often appear in hilar lymph nodes or in patients who have chronic lung disease . lymph node metastasis was suspected after a preoperative pet / ct for the case 3 , as described above , but it was actually an inflammatory lymphadenopathy caused by pneumoconiosis . dual - time - point fdg - pet has been reported to be useful in reducing this kind of false positive . it uses the time differences of peak fdg accumulation for inflammation versus for tumors . after injecting the fdg , pet has revealed occult distant metastases at nodal and non - nodal sites in 5% to 40% of patients . distant metastases of esophageal squamous cancer are mainly found in the lungs , liver , and bones . kato et al reported the diagnosability of fdg - pet for esophageal cancer as having a sensitivity of 92% , a specificity of 94% , and an accuracy of 93% . when comparing those numbers to bone scintigraphy , whose diagnosabilities are 77% , 84% , and 82% , respectively , the diagnosability of fdg - pet is superior , especially for osteolytic lesions . but 2 false positives out of 44 cases came from pet , showing that fdg - pet is not perfect . the suvmax of metastic tumor might be helpful to increase the accuracy of pet / ct . our previous study demonstrated that the suvmax of the primary tumor was positively correlated with tumor size and vessel invasion and was positively related to the suvmax of metastic tumor . in the report , the diagnostic accuracy of pet / ct ( 87.3% ) was higher than that of conventional ct scans . when diagnosing metastatic bone tumors , the positive predictive value of bone metastasis is known to be quite high if the findings for both pet and ct match . therefore , even when bone metastasis is suspected due to abnormal fdg accumulation after a fdg - pet , yet no bone destruction image is found in the same site by ct , then interventional radiology or a surgical biopsy should be conducted to obtain a pathological diagnosis . this case report was on 3 patients with suspected metastasis due to a false - positive pet / ct who were later confirmed to not have metastasis . the metastases were originally suspected after conducting a pet / ct before surgery to treat esophageal cancer or during the postoperative course . conducting a pet / ct is useful when diagnosing esophageal cancer metastasis , but there should be an awareness of the possibility of false positives . therapeutic decisions should be made based on appropriate and accurate diagnoses , and a pathological diagnosis should be actively introduced if necessary .
of 129 esophagectomies at our institute from june 2010 to march 2015 , we experienced three preoperative positron emission tomography - computed tomographic ( pet / ct ) false positives . 
 bone metastasis was originally suspected in 2 cases , but they were later found to be bone metastasis negative after a preoperative bone biopsy and clinical course observation . 
 the other cases suspected of mediastinal lymph node metastasis were diagnosed as inflammatory lymphadenopathy by a pathological examination of the removed lymph nodes . 
 conducting a pet / ct is useful when diagnosing esophageal cancer metastasis , but we need to be aware of the possibility of false positives . 
 therapeutic decisions should be made based on appropriate and accurate diagnoses , with pathological diagnosis actively introduced if necessary .