18f - fluorodeoxyglucose ( fdg ) positron emission tomography ( pet ) has become an integral part of the management protocol for patients with cancer , where it is used for initial staging , assessment of response to therapy , as well as for detection of recurrent disease . as is seen with other imaging techniques , there are certain pitfalls in the interpretation of pet and pet / computed tomography ( ct ) studies .
it is important that physicians interpreting pet / ct are aware of the potential pitfalls , so that the impact of these pitfalls is minimized and the interpretation is accurate .
awareness of the potential causes that may lead to false positive or negative findings is essential for the interpreter to avoid misreading a scan . here
, we describe one such false positive case on fdg pet / ct , where an inflammatory lung pathology mimicked pulmonary metastases .
a 45-year - old male patient with biopsy - proven adenocarcinoma of the stomach underwent a baseline fdg pet / ct scan for staging workup , which revealed metabolically active disease involving the distal esophagus , gastroesophageal junction ( gej ) , and proximal stomach with metastases to the perigastric , mesenteric , paracaval , and pre - aortic lymph nodes . there were no pulmonary lesions or distant metastases elsewhere detected at this stage .
the patient was planned for definitive therapy with neoadjuvant chemotherapy ( nact ) to be followed by surgery , with a curative intent . on completion of three cycles of nact with cisplatin , epirubicin , and 5-fluorouracil
, the patient was referred for a repeat fdg pet / ct scan for response evaluation and re - assessment of the disease status .
pet / ct scan revealed complete resolution of the nodal lesions and significant reduction in the extent as well as metabolic activity of the primary lesion in the stomach and gej .
in addition , there were multiple , well - defined , fdg avid , 13 cm sized , pulmonary nodules randomly distributed over both the lungs , raising a suspicion of pulmonary metastases [ figure 1 ] .
the lesions revealed moderately high fdg uptake [ maximum standardized uptake value ( suvmax ) of 6.23 . ] on ct images , most of the lesions exhibited a  feeding vessel  sign and some of the lesions showed early cavitation within .
correlation was sought with a hemogram , which revealed normal total as well as differential leucocyte count . at this stage ,
interpretation of the pet / ct findings was progressive disease with development of pulmonary metastases .
( a - d ) standard fdg - pet / ct acquisition in a follow - up case of carcinoma stomach .
pet whole body 3d mip image ( a ) shows multiple fdg avid foci ( black arrows ) in the thoracic region .
axial ct ( b ) and fused pet - ct ( c , d ) images of the thorax reveal multiple , peripherally located , fdg avid , pulmonary parenchymal nodules ( white arrows ) .
the larger lesion in the right lung exhibits a  feeding vessel  sign and shows cavitation within the patient developed fever on the second day following the pet / ct scan and gave history of chills following flushing of the indwelling central venous catheter ( cvc ) .
cvc infection was suspected and the catheter was removed . taking into account the clinical profile and blood culture results ,
the pet / ct findings were reviewed and a provisional diagnosis of septic pulmonary emboli ( spe ) was made .
patient was put on intravenous antibiotics for 4 weeks , following which his fever subsided and blood culture became sterile .
the tip of the removed cvc was sent for bacterial culture , which grew e. cloacae ( the same organism that was found in the blood culture ) , confirming the source of bacteremia .
chest ct done after completion of antimicrobial therapy revealed complete resolution of the lung lesions [ figure 2 ] .
representative axial images ( in lung window ) , reveal complete resolution of the lung lesions that were noted in the earlier scan planned chemotherapy was continued thereafter .
repeat fdg pet / ct done on completion of nact revealed absence of any fdg avid pulmonary lesions , whereas the primary disease in the stomach showed progression [ figure 3 ] .
whole body pet , 3d mip images , before ( a ) and after ( b ) antibiotic therapy .
image ( a ) shows multiple fdg avid foci in the region of thorax ( arrows ) and minimal fdg uptake in the stomach ( arrowhead ) representing metabolically active local disease . image ( b ) reveals absence of any fdg avid focus in the thorax , where - as a large fdg avid lesion is seen in the region of stomach ( arrowhead ) , indicating progression of the primary disease in the stomach to our knowledge , this is the first report of fdg pet / ct imaging findings of spe in a case of known malignancy with an indwelling cvc being the source of infection .
although fdg - pet / ct imaging has achieved great success in the evaluation of malignant disorders , the modality is not specific for the diagnosis of cancer .
uptake of fdg in living cells is determined by the cellular metabolic rate and the number of glucose transporters present in the cells .
apart from tumors , activated inflammatory cells also demonstrate increased expression and upregulation of glucose transport receptors .
a number of studies have reported presence of high fdg uptake in infective and inflammatory lesions , both acute and chronic .
infectious diseases ( mycobacterial , fungal , bacterial ) , sarcoidosis , radiation pneumonitis , and postoperative inflammation have been observed to show intense fdg uptake on pet scan .
often , inflammatory lesions produce fdg uptake patterns that are indistinguishable from those of cancer , leading to false positive results , in patients with a known or suspected malignancy .
spe is an uncommon disorder in which infection originating at an extrapulmonary site is transported to the lungs via the bloodstream .
microorganisms embedded in thrombin get mobilized from the nidus of infection and lodge in pulmonary arteries leading to infarction and metastatic abscess formation .
the most common sources of infection include infected heart valves , thrombophlebitis , and infected indwelling venous catheters or pacemaker wires .
clinical symptoms of spe are usually nonspecific and commonly include one or more out of fever , cough , hemoptysis , shortness of breath . and chest pain . occasionally , an active extrapulmonary focus of infection may be obvious at the time of presentation .
this coupled with frequent occurrence of immunosupression and neutropenia in such patients predisposes them to spe .
high fdg uptake is generally accepted to be associated with malignant lesions . in a patient with known malignancy undergoing fdg pet scan , finding of multiple fdg avid , discrete , pulmonary nodules with  feeding vessels 
stage , nearly ruling out the probability of a complete cure for the patient . as is evident from the findings in our case
, spe can closely mimic metastases , with the pulmonary lesions showing high metabolic activity on fdg pet and exhibiting a morphology akin to metastatic deposits on ct .
presence of high fdg uptake in spe has been documented by a number of authors and is attributed to the high glycolytic rate of activated macrophages and polymorphs that are abundantly present in most inflammatory lesions . in a patient with known malignancy undergoing fdg pet scan ,
if multiple fdg avid pulmonary nodules are detected as a new finding , high index of suspicion must be maintained to rule out the possibility of septic emboli and to avoid a catastrophic mistake of labeling these lesions as metastases .
clinical inputs ( history of fever , chills , respiratory symptoms , an obvious site of extrapulmonary infection ) and hemogram results when integrated with the imaging findings can aid in providing vital clues that point towards the diagnosis of spe .
clinical indicators that favor spe are history of concurrent febrile illness , neutropenia , and a positive blood culture confirming the presence of bacteremia .
studied the clinical course and imaging features in 14 patients of spe and concluded that spe presented with variable , often nonspecific clinical and radiographic features and the diagnosis was usually suggested by the presence of a predisposing factor , febrile illness , and ct findings of multiple , peripheral , nodular lung infiltrates , with or without cavitation .
reviewed ct scans of 18 patients with documented spe and concluded that , in an appropriate clinical setting , characteristic ct features of septic emboli can suggest the correct diagnosis .
rossi et al . have opined that , on ct , the most characteristic features of spe include discrete pulmonary parenchymal nodules with cavitation , which often exhibit lower lobe predominance and presence of nodule - feeding vessels .
in addition , subpleural heterogeneous wedge - shaped opacities may also be identified in a majority of patients with spe .
although the phenomenon of  mixed  response to chemotherapy ( where some of the cancerous lesions show regression while other lesions show progression ) is well known , a patient with known cancer on chemotherapy developing new fdg avid lesions at a distant site while the pre - existing disease shows regression should alert the interpreting physician to the possibility of an unrelated pathology ( e.g. , infection or inflammation ) as the cause of new lesions .
spe is a rare condition that may mimic pulmonary metastases on fdg pet / ct imaging , especially in a patient with a known malignancy .
indwelling cvc is a predisposing factor and can act as a source of infected emboli in such cases . in cancer patients with indwelling cvc ,
if fdg avid pulmonary nodules are detected , high index of suspicion should be maintained to rule out spe .
analysis of ct morphology of the lesions is critical for arriving at the correct diagnosis .
ct features most characteristic of spe include discrete , peripheral , pulmonary nodules of varying sizes , with cavitation and presence of additional subpleural wedge - shaped opacities .
a positive blood culture confirms presence of bacteremia and resolution of lung lesions following antimicrobial therapy , clinches the diagnosis of spe .
 inflammatory lesions may sometimes show intense tracer uptake and mimic neoplastic lesions on ( 18 ) f - fluoro - deoxyglucose ( fdg ) positron emission tomography / computed tomography ( pet / ct ) . 
 we report one such false positive case on fdg pet / ct , where septic pulmonary emboli ( spe ) mimicked pulmonary metastases . a 45-year - old man with stomach cancer had an indwelling central venous catheter ( cvc ) in situ while on neoadjuvant chemotherapy . 
 he underwent fdg pet / ct scan for response assessment and the images revealed multiple , intensely fdg avid , peripheral , lung nodules with feeding vessels , which were suspicious for pulmonary metastases . a day later , the patient developed fever with chills and his blood culture showed bacterial growth ( enterobacter cloacae ) . a provisional diagnosis of spe from an infected cvc was made . 
 chemotherapy was withheld , cvc removed , and the catheter tip was sent for bacterial culture . following a 4-week course of antibiotic treatment , the patient became afebrile . 
 culture from the cvc tip grew the same organism , as was seen earlier in the patient 's blood culture , thus pin - pointing the source of infection in our case . 
 diagnosis of spe was clinched when follow - up ct chest done after completion of antibiotic course showed complete resolution of the lung lesions . 
Introduction
Case Report
Discussion
Conclusion
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