Original Research
Nuclear Medicine
November 2007

Benign Nonphysiologic Lesions with Increased 18F-FDG Uptake on PET/CT: Characterization and Incidence

Abstract

OBJECTIVE. The objective of our study was to characterize benign lesions showing increased 18F-FDG uptake and to determine their incidence on whole-body FDG PET/CT performed in oncologic patients. In addition, the performance of PET alone and PET/CT in characterizing lesions as benign was compared.
MATERIALS AND METHODS. A retrospective review of 1,134 consecutive reports of PET/CT studies performed in patients with proven or suspected malignancy over a 6-month period yielded 289 patients with 313 lesions that showed increased FDG uptake but were suspected to be benign (nonphysiologic) or indeterminate. Lesions were subjectively categorized on the basis of the intensity of FDG uptake (mild, moderate, or marked) as compared with background activity. For each lesion, a decision was made as to whether a benign diagnosis could be obtained by the CT part of the study, the PET pattern, or clinical correlation, or whether histologic sampling was necessary. The performance of PET alone and PET/CT for characterizing lesions as benign was compared. Two hundred twenty-nine of the lesions were assessed further: 210 were benign and 19, malignant. The final diagnosis was determined by pathology (n = 67), PET/CT follow-up (n = 58), correlative imaging (n = 59), clinical correlation (n = 32), or typical benign pattern on PET/CT (n = 13).
RESULTS. The causes for benign uptake of FDG were inflammatory processes (n = 154, 73.3%), benign tumors (n = 23, 11%), hematoma or seroma (n = 17, 8.1%), fracture (n = 7, 3.3%), fat necrosis (n = 3, 1.4%), and others (n = 6, 2.9%). For lesions with moderate or marked uptake of FDG (n = 117, 55.7%), a benign diagnosis could have been suggested on either PET or CT (e.g., a “hot” osteophyte) in 33 lesions (28.2%), on CT alone (e.g., peritoneal fat necrosis) in 38 lesions (32.5%), on PET alone (e.g., sialadenitis) in 10 lesions (8.5%), or by clinical correlation (e.g., dental abscess) in four lesions (3.4%). A benign diagnosis could not be established without histology (e.g., colonic polyp) in 32 lesions (27.4%). The performance of PET/CT was superior to that of PET alone in characterizing lesions as benign (p< 0.001).
CONCLUSION. Benign lesions with increased FDG uptake are found in more than 25% of the PET/CT studies performed in patients with proven or suspected malignancy, with inflammation being the most common cause. Lesion characterization on the CT portion of the PET/CT study increases the specificity of PET/CT reporting, especially for lesions with moderate or marked FDG uptake.

Introduction

There has been an ongoing increase in the routine clinical use of 18F-FDG PET for staging and follow-up of a wide range of oncologic diseases. Although FDG PET is a sensitive imaging technique for the identification of malignant tumors, FDG is not tumor-specific. Variable physiologic sites of uptake may be seen in Waldeyer's tonsillar ring; along the gastrointestinal tract; or in the orbital muscles, brain cortex, myocardium, renal collecting systems, bladder, and gonads [1]. FDG uptake in skeletal muscles and in brown fat located in the neck, supraclavicular regions, axilla, mediastinum, and retroperitoneum has been described as a potential physiologic pitfall in FDG PET interpretation [24]. In addition, the authors of multiple reports have described the uptake of FDG in various nonphysiologic benign lesions, mostly inflammatory processes [5].
The purpose of the current study was to characterize benign lesions showing increased FDG uptake and to determine their incidence on whole-body FDG PET/CT performed in oncologic patients. In addition, the performance of PET alone and PET/CT in characterizing lesions as benign was compared.

Materials and Methods

Patient Population

A retrospective review of 1,134 consecutive reports of PET/CT studies performed in patients with proven or suspected malignancy over a 6-month period (between January and June 2003) yielded 289 patients with 313 lesions that showed increased FDG uptake but were suspected to be benign (nonphysiologic) or indeterminate. The patients included 152 females and 137 males who ranged in age from 1 to 85 years (mean, 58 years; median, 59 years). Table 1 summarizes the indications for PET/CT in these patients. Two hundred fifty-three of the patients had a known malignancy and were referred for staging or follow-up. The remaining 36 patients had no previously diagnosed malignancy and were referred for evaluation of a lung mass (n = 26), lymphadenopathy (n = 6), adrenal mass (n = 2), or nonspecific bone lesion (n = 2) on conventional imaging.
TABLE 1: Indications for Performing PET
Indication for PETNo. of Patients (n = 289)
Lymphoma104
Colorectal cancer46
Lung cancer45
Melanoma19
Cervical cancer12
Breast cancer11
Pancreatic cancer3
Esophageal cancer2
Sarcoma2
Thyroid cancer2
Unknown primary tumora2
Immature teratoma1
Ovarian cancer1
Renal cell carcinoma1
Squamous cell carcinomab1
Carcinoma of vulva1
No known malignancy
36
a
Metastatic.
b
Neck.
Two hundred twenty-nine of the 313 lesions were assessed further. The remaining patients were lost to follow-up, or the referring physician chose not to request further assessment of the reported indeterminate or presumed benign lesion, and a final diagnosis was not available. Of the lesions that were assessed further, 19 (in 18 patients) were malignant and 210 (in 194 patients) were benign and represent the study cohort. The final diagnosis was determined by pathology (n = 67), PET/CT follow-up (n = 58), correlative imaging (n = 59), clinical correlation (n = 32), or typical benign pattern on PET/CT (n = 13).
Malignant lesions were diagnosed histologically (n = 17) or by clear progression of disease at the same site on follow-up PET/CT (n = 2) (Table 2). Clinical correlation enabled identification of multiple benign entities, including dental abscesses, an infected sebaceous cyst, postoperative changes in the chest or abdominal wall in patients examined within 1 month after surgery, subcutaneous granulomas at a port insertion site or at injection sites, a hematoma or seroma, a skin infection, and infectious mononucleosis with positive serology for Epstein-Barr virus. Typical patterns on PET/CT included FDG uptake around a hip replacement prosthesis, with a differential diagnosis of loosening of the prosthesis or infection, as well as costochondritis, bursitis, and tenosynovitis. These patterns have been previously described in the literature [6, 7].
TABLE 2: Intensity of 18F-FDG Uptake in Malignant Lesions on PET/CT
Total (n = 19)Intensity of FDG Uptake Compared with Background Activity
StructureMildModerateMarked
Pharynx1 1 
Thyroid4 22
Lung5221
Bronchial stump11  
Lymph node3111
Abdominal wall scar1 1 
Peritoneum11  
Colon1  1
Bone
2

2

Note—Data are number of lesions.

PET/CT Scanning

Patients were asked to fast for at least 4 hours before undergoing the examination. All patients had glucose levels below 150 mg/dL. Patients received an IV injection of 370–666 MBq (10–18 mCi) of FDG. Data acquisitions were performed 60–120 minutes after injection using an integrated in-line PET/CT system (Discovery LS, GE Healthcare). Iodinated oral contrast material was administered for bowel opacification. Data acquisition was as follows: CT was performed first from the head to the pelvic floor with 140 kV, 80 mA, a tube rotation time of 0.5 second, a pitch of 6, and a 5-mm section thickness, which was matched to the PET section thickness. Immediately after CT, a PET emission scan was obtained that covered the identical transverse field of view. The acquisition time was 5 minutes for each table position. PET image data sets were reconstructed iteratively using CT data for attenuation correction, and coregistered images were displayed on a workstation (Xeleris, GE Healthcare).

Lesion Analysis and Statistics

Studies were then analyzed by a panel of two experienced reviewers in consensus. Lesions were subjectively categorized as showing mild, moderate, or marked uptake on the basis of the intensity of FDG uptake compared with background activity (Fig. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J). For each lesion, a decision was made as to whether a benign diagnosis could be obtained by the CT part of the study, the PET pattern, or clinical correlation, or whether histologic sampling was necessary.
Lesions with moderate or marked FDG uptake are a subgroup of lesions for which a benign diagnosis may be challenging and PET assessment alone may be falsely positive for malignancy. For these lesions, the specificity of FDG PET and fused PET/CT for correctly identifying lesions as benign was assessed and compared using the McNemar test. A p value of < 0.05 was considered statistically significant.

Results

Tables 3, 4, 5 summarize the body regions and intensity of uptake of the 210 benign lesions. The causes for benign uptake of FDG were inflammatory processes (n = 154, 73.3%), benign tumors (n = 23, 11%), hematoma or seroma (n = 17, 8.1%), fracture (n = 7, 3.3%), fat necrosis (n = 3, 1.4%), and others (n = 6, 2.9%).
TABLE 3: Benign Uptake of 18F-FDG in the Chest on PET/CT
Intensity of FDG Uptake Compared with Background Activity
Structure and DiagnosisMildModerateMarked
Lung   
    Inflammationa961
    Stitch granuloma  1
    Anthracosis 1 
    Granuloma 11
    Lipoid pneumonia  1
    Radiation pneumonitis61 
    Pulmonary hemorrhage1  
    Acute lung infarct1  
    Intralobar sequestration1  
    Lung abscess11 
    Pneumonia11 
    Bronchiolitis obliterans with organizing pneumonia  1
    Langerhans cell histiocytosis  1
Bronchus   
    Ulcerated intrabronchial inflammatory polyp  1
Pleura   
    Inflammatory plaque12 
Pericardium   
    Postpericardiotomy changes2  
Breast   
    Papilloma1  
    Benign lesiona
1


Note—Data are number of lesions.
a
Not otherwise specified.
TABLE 4: Benign Uptake of 18F-FDG in the Abdomen and Pelvis on PET/CT
Intensity of FDG Uptake Compared with Background Activity
Structure and DiagnosisMildModerateMarked
Peritoneum and mesentery   
    Mesenteric panniculitis1  
    Granulomaa1  
    Postradiation ascites1  
    Postoperative infiltration of peritoneum21 
    Hemoperitoneum1  
    Fat necrosis  1
    Epiploic appendagitis 1 
    Abdominal abscess  2
Gastrointestinal tract   
    Esophagitis 2 
    Diverticulitis 33
    Crohn's diseaseb  1
    Terminal ileitisc  1
    Colon adenoma 24
    Perianal fistula  1
Adrenal   
    Adrenal adenoma11 
Genitourinary   
    Calyceal diverticulum  1
    Urethral diverticulum  1
    Cervixd1  
    Hydrometra and endometritis
2


Note—Data are number of lesions.
a
Surgical clip.
b
Esophagus, ileum, rectum.
c
Mycobacterium avium-intracellulare.
d
Postradiation.
TABLE 5: Benign Uptake of 18F-FDG in Body Regions Other Than Chest, Abdomen, or Pelvis on PET/CT
Intensity of FDG Uptake Compared with Background Activity
Structure and DiagnosisMildModerateMarked
Head and neck   
    Sinusitis121 
    Dental abscess 22
    Thyroid adenoma 44
    Sialadenitis 2 
    Mastoiditis 1 
Lymph node   
    Reactive221 
    Mycobacterium avium-intracellulare  1
Skeletal   
    Osteoarthritisa11 
    Bone spur 1 
    Hip replacement  4
    Fracture511
    Post—bone biopsy changes 2 
    Enthesopathy 1 
    Bursitis1  
    Synovitis2  
    Tendinitis2  
    Costochondritis1  
    Enchondroma11 
    Exostosis 1 
    Nonossifying fibroma1  
    Gaucher's disease1  
Muscle   
    Abscessb  1
    Postradiation myositis 2 
Skin or subcutaneous   
    Postoperative scar96 
    Postoperative seroma4  
    Postoperative hematoma72 
    Abscess or infection 3 
    Granulomac74 
    Fat necrosis 1 
    Vasculitis 1 
Other   
    Atherosclerosis11 
    Neurofibroma
1


Note—Data are number of lesions.
a
Not otherwise specified.
b
Mycobacterium avium-intracellulare.
c
Injection, port, stitch.
For the benign lesions with moderate or marked uptake of FDG (n = 117/210, 55.7%), a benign diagnosis could have been suggested on either PET or CT (Fig. 2A, 2B, 2C) in 33 lesions (28.2%), on CT alone (Fig. 3A, 3B, 3C, 3D, 3E, 3F) in 38 lesions (32.5%), on PET alone (Fig. 4) in 10 lesions (8.5%), or by clinical correlation (e.g., dental abscess) in four lesions (3.4%). A benign diagnosis could not be established without histology (Fig. 5A, 5B, 5C) in 32 lesions (27.4%).
Fig. 1A Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of FDG (arrows) (maximum standardized uptake value = 8.1) in 57-year-old woman with histologically proven bronchiolitis obliterans with organizing pneumonia.
Fig. 1B Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of FDG (arrows) (maximum standardized uptake value = 8.1) in 57-year-old woman with histologically proven bronchiolitis obliterans with organizing pneumonia.
Fig. 1C Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of FDG (arrows) (maximum standardized uptake value = 8.1) in 57-year-old woman with histologically proven bronchiolitis obliterans with organizing pneumonia.
Fig. 1D Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show moderate uptake of FDG (arrows) in 50-year-old man with left adrenal adenoma that was stable for more than 2 years.
Fig. 1E Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show moderate uptake of FDG (arrows) in 50-year-old man with left adrenal adenoma that was stable for more than 2 years.
Fig. 1F Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (A), PET (B), and fused PET/CT (C) images show moderate uptake of FDG (arrows) in 50-year-old man with left adrenal adenoma that was stable for more than 2 years.
Fig. 1G Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (G), PET (H), fused PET/CT (I), and correlative fat-suppressed T2-weighted MR (J) images show mild uptake of FDG (arrows, H–J) in 56-year-old woman with neurofibroma involving C6–C7 nerve root.
Fig. 1H Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (G), PET (H), fused PET/CT (I), and correlative fat-suppressed T2-weighted MR (J) images show mild uptake of FDG (arrows, H–J) in 56-year-old woman with neurofibroma involving C6–C7 nerve root.
Fig. 1I Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (G), PET (H), fused PET/CT (I), and correlative fat-suppressed T2-weighted MR (J) images show mild uptake of FDG (arrows, H–J) in 56-year-old woman with neurofibroma involving C6–C7 nerve root.
Fig. 1J Composite figure of three patients showing mild, moderate, or marked uptake of 18F-FDG in benign lesions as compared with background activity. CT (G), PET (H), fused PET/CT (I), and correlative fat-suppressed T2-weighted MR (J) images show mild uptake of FDG (arrows, H–J) in 56-year-old woman with neurofibroma involving C6–C7 nerve root.

Performance of PET Alone and PET/CT

For the 117 lesions with moderate or marked uptake of FDG, for which a benign diagnosis on PET alone may be challenging, PET alone correctly identified 43 lesions as benign with a specificity of 37%, whereas PET/CT correctly identified 81 lesions as benign with a specificity of 69% (p < 0.001). When taking into account clinical correlation as an adjunct to characterizing lesions as benign, the specificities of PET and PET/CT improve to 40% and 73%, respectively (p < 0.001).

Discussion

A systematic review of consecutive PET/CT studies performed over a 6-month period showed that benign nonphysiologic uptake of FDG was encountered in more than 25% of the studies. Almost three quarters of these lesions were inflammatory. In more than half of the benign nonphysiologic sites of increased FDG uptake, the intensity of uptake may be moderate or marked compared with background activity, making a benign diagnosis with PET alone challenging, with a potentially high incidence of false-positive interpretations. The complexity of image interpretation is confounded by potential physiologic uptake of FDG along the gastrointestinal tract and the overlap in the degree of FDG uptake in benign and malignant tumors involving certain organs, such as the thyroid, adrenal glands, or colon. In addition, after surgery, the degree of FDG uptake in inflammatory processes, postsurgical change, and recurrent tumor may also overlap.
Several studies have shown that fusion of PET data with CT improves not only the sensitivity of PET but also its specificity [8, 9]. The advantage of PET/CT over PET alone can be attributed to the low anatomic resolution of PET and the difficulty in lesion localization on PET. Morphologic data from CT may assist in improving the diagnostic accuracy of nonspecific lesions with increased FDG uptake [911].
Although an argument could be made that PET scans are often interpreted side-by-side with correlative imaging, several studies have shown that interpreting fused PET/CT images has an advantage over the former review method. Pelosi et al. [10] reported that for lesion localization alone, PET/CT had ambiguous findings for only 3.4% of lesions compared with 15.3% with PET and correlative imaging (p < 0.0001). In an additional study, investigators assessing 168 lesions in oncology patients found localization was incorrect in almost 10% of lesions despite side-by-side correlation with CT. Furthermore, fused imaging has been found to be superior for the assessment of small lesions; lesions adjacent to chest or abdominal wall; and lesions adjacent to mobile organs such as the diaphragm, the mesentry, or loops of bowel [8].
In the current study, although PET alone or PET and clinical correlation could suggest a benign diagnosis for some of the benign lesions with moderate or marked uptake of FDG (39% and 40%, respectively), CT localization and characterization on fused PET/CT images helped to correctly classify an additional one third of lesions as benign. In certain instances, such as pulmonary Langerhans cell histiocytosis, lipoid pneumonia, epiploic appendagitis, or abdominal fat necrosis (secondary to surgery, trauma, or pancreatitis), CT findings are pathognomonic or are at least highly suggestive [1214] (Figs. 3A, 3B, 3C, 3D, 3E, 3F and 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I). Because FDG uptake in these lesions may be high, they may simulate tumor on PET: Lipoid pneumonia may appear as a malignant lung tumor, the multiple nodules in Langerhans cell histiocytosis may appear as lung metastases, and fat necrosis may falsely be interpreted as a metastatic peritoneal deposit or as local tumor recurrence.
Some of the benign lesions encountered in our patient population were benign tumors (11%). CT and correlative radiography may confirm a benign lesion, as was the case with one adrenal adenoma (with attenuation values of < 10 H on unenhanced CT) and one enchondroma of the femur. However, in more than 27% of benign tumors with moderate or marked uptake of FDG, biopsy was necessary for final diagnosis. Biopsy was needed in cases of focal FDG uptake in the thyroid, the colon, or an intrabronchial polyp because the degree of FDG uptake and the morphologic appearance of the lesions could not be used to reliably confirm or exclude malignancy. Similarly, lymph nodes with significant uptake of FDG due to inflammatory or infectious conditions may also require histologic sampling. The only exception may be for symmetric uptake of FDG in hilar and mediastinal lymph nodes due to lymphoid follicular hyperplasia secondary to smoking or chronic pulmonary disease. On CT, these nodes may contain calcifications or may show higher attenuation values than the surrounding great vessels. A previous study examining the performance of FDG PET/CT in staging non–small cell lung cancer showed that histologically nodes with this appearance on CT were reactive with follicular hyperplasia in the cortex and showed anthracotic pigmentation with macrophage infiltration in the medulla [15].
Fig. 2A Benign pattern suggested on both CT and PET in 41-year-old man with Crohn's disease. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of 18F-FDG in long segment of concentrically thickened distal ileum (arrows) with submucosal deposition of fat, which is suggestive of inflammatory bowel disease. Crohn's disease was confirmed on histology.
Fig. 2B Benign pattern suggested on both CT and PET in 41-year-old man with Crohn's disease. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of 18F-FDG in long segment of concentrically thickened distal ileum (arrows) with submucosal deposition of fat, which is suggestive of inflammatory bowel disease. Crohn's disease was confirmed on histology.
Fig. 2C Benign pattern suggested on both CT and PET in 41-year-old man with Crohn's disease. CT (A), PET (B), and fused PET/CT (C) images show marked uptake of 18F-FDG in long segment of concentrically thickened distal ileum (arrows) with submucosal deposition of fat, which is suggestive of inflammatory bowel disease. Crohn's disease was confirmed on histology.
Fig. 3A CT pattern suggestive of benign diagnosis. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in enlarged distal external iliac node (arrows) on right in 52-year-old man with lymphoma. Focal abnormal uptake of FDG in left groin (arrowheads) is localized on CT to iliopsoas tendon, which is consistent with tendinosis.
Fig. 3B CT pattern suggestive of benign diagnosis. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in enlarged distal external iliac node (arrows) on right in 52-year-old man with lymphoma. Focal abnormal uptake of FDG in left groin (arrowheads) is localized on CT to iliopsoas tendon, which is consistent with tendinosis.
Fig. 3C CT pattern suggestive of benign diagnosis. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in enlarged distal external iliac node (arrows) on right in 52-year-old man with lymphoma. Focal abnormal uptake of FDG in left groin (arrowheads) is localized on CT to iliopsoas tendon, which is consistent with tendinosis.
Fig. 3D CT pattern suggestive of benign diagnosis. CT (D), PET (E), and fused PET/CT (F) images show focal uptake of FDG in left flank (arrows) in 70-year-old man. Fused PET/CT image (F) shows uptake to be in small soft-tissue-attenuation mass with fat-attenuation center suggestive of fat necrosis, which was proven histologically.
Fig. 3E CT pattern suggestive of benign diagnosis. CT (D), PET (E), and fused PET/CT (F) images show focal uptake of FDG in left flank (arrows) in 70-year-old man. Fused PET/CT image (F) shows uptake to be in small soft-tissue-attenuation mass with fat-attenuation center suggestive of fat necrosis, which was proven histologically.
Fig. 3F CT pattern suggestive of benign diagnosis. CT (D), PET (E), and fused PET/CT (F) images show focal uptake of FDG in left flank (arrows) in 70-year-old man. Fused PET/CT image (F) shows uptake to be in small soft-tissue-attenuation mass with fat-attenuation center suggestive of fat necrosis, which was proven histologically.
The common denominator for the majority (> 73%) of benign lesions showing abnormal uptake of FDG in this study was active inflammation, whether infectious, such as mycobacterial infection, or noninfectious, such as postsurgical granulomas or osteoarthritis. Increased uptake of FDG in inflammation may be explained by the recruitment of activated WBCs (granulocytes, lymphocytes, and macrophages). These cells have been found to have enhanced levels of glucose transporters (GLUTs), especially GLUT 3 and, to a lesser extent, GLUT 1 [16], and to have an increased affinity to deoxyglucose through various cytokines and growth factors. For example, tumor necrosis factor α is a cytokine produced primarily by monocytes and has been shown to activate macrophages in experimental models of inflammation as well as clinically in rheumatoid arthritis or as a response to bacterial endotoxins [17, 18]. Activated monocytes directly activate reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which imposes an acute metabolic demand met by an increased use of both internal energy stores and exogenous metabolites such as glucose [19, 20]. Recently, in vitro studies have shown that activation of monocytes without further activation of NADPH oxidase is sufficient to increase glucose metabolism [19]. These pathophysiologic processes may explain the increased uptake of FDG encountered in active inflammatory processes.
Fig. 4 PET pattern suggestive of benign diagnosis in 57-year-old woman. PET image shows diffuse uptake of 18F-FDG in left shoulder that is suggestive of synovitis.
Fig. 5A Histologic diagnosis necessary to define benign lesion in 59-year-old man. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in polypoid lesion (arrows) along right wall of rectum. Resected specimen (not shown) revealed tubulovillous adenoma with no evidence of malignancy.
Fig. 5B Histologic diagnosis necessary to define benign lesion in 59-year-old man. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in polypoid lesion (arrows) along right wall of rectum. Resected specimen (not shown) revealed tubulovillous adenoma with no evidence of malignancy.
Fig. 5C Histologic diagnosis necessary to define benign lesion in 59-year-old man. CT (A), PET (B), and fused PET/CT (C) images show abnormal uptake of 18F-FDG in polypoid lesion (arrows) along right wall of rectum. Resected specimen (not shown) revealed tubulovillous adenoma with no evidence of malignancy.
Fig. 6A Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT image obtained using lung window setting (A), PET image (B), and zoomed CT image obtained using soft-tissue window setting (C) show marked uptake of FDG (arrows) in subpleural mass in left lower lobe of lung in 77-year-old woman. Zoomed CT image shows fat attenuation in center of mass, which is suggestive of lipoid pneumonia.
Fig. 6B Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT image obtained using lung window setting (A), PET image (B), and zoomed CT image obtained using soft-tissue window setting (C) show marked uptake of FDG (arrows) in subpleural mass in left lower lobe of lung in 77-year-old woman. Zoomed CT image shows fat attenuation in center of mass, which is suggestive of lipoid pneumonia.
Fig. 6C Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT image obtained using lung window setting (A), PET image (B), and zoomed CT image obtained using soft-tissue window setting (C) show marked uptake of FDG (arrows) in subpleural mass in left lower lobe of lung in 77-year-old woman. Zoomed CT image shows fat attenuation in center of mass, which is suggestive of lipoid pneumonia.
Fig. 6D Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (D), PET (E), and fused PET/CT (F) images. CT image shows multiple cysts (thin arrow, D) and nodules (thick arrow, D) in both lung fields in 61-year-old man. PET and fused PET/CT images show abnormal uptake of FDG in nodule (arrows, E and F). Findings are suggestive of Langerhans cell histiocytosis, which was confirmed on biopsy.
Fig. 6E Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (D), PET (E), and fused PET/CT (F) images. CT image shows multiple cysts (thin arrow, D) and nodules (thick arrow, D) in both lung fields in 61-year-old man. PET and fused PET/CT images show abnormal uptake of FDG in nodule (arrows, E and F). Findings are suggestive of Langerhans cell histiocytosis, which was confirmed on biopsy.
Fig. 6F Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (D), PET (E), and fused PET/CT (F) images. CT image shows multiple cysts (thin arrow, D) and nodules (thick arrow, D) in both lung fields in 61-year-old man. PET and fused PET/CT images show abnormal uptake of FDG in nodule (arrows, E and F). Findings are suggestive of Langerhans cell histiocytosis, which was confirmed on biopsy.
In conclusion, benign lesions with increased FDG uptake are common, found in more than one quarter of PET/CT studies performed, with inflammation being the most common cause. Precise lesion localization and characterization on the CT portion of the PET/CT study improve the specificity of PET/CT reporting, especially for lesions with moderate or marked FDG uptake that may easily be mistaken for tumor.
Fig. 6G Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (G), PET (H), and fused PET/CT (I) images show marked masslike abnormal uptake of FDG (arrows) on PET image in 53-year-old man. CT shows lung infiltrate thought to represent pneumonia. Infiltrate resolved on CT performed after antibiotic therapy (not shown).
Fig. 6H Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (G), PET (H), and fused PET/CT (I) images show marked masslike abnormal uptake of FDG (arrows) on PET image in 53-year-old man. CT shows lung infiltrate thought to represent pneumonia. Infiltrate resolved on CT performed after antibiotic therapy (not shown).
Fig. 6I Composite figure of three patients with benign lung lesions on 18F-FDG PET/CT. CT (G), PET (H), and fused PET/CT (I) images show marked masslike abnormal uptake of FDG (arrows) on PET image in 53-year-old man. CT shows lung infiltrate thought to represent pneumonia. Infiltrate resolved on CT performed after antibiotic therapy (not shown).

Footnote

Address correspondence to U. Metser ([email protected]).

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 1203 - 1210
PubMed: 17954662

History

Submitted: February 18, 2007
Accepted: June 5, 2007

Keywords

  1. benign lesions
  2. FDG PET
  3. oncologic imaging
  4. PET/CT
  5. whole-body imaging

Authors

Affiliations

Ur Metser
Department of Nuclear Medicine, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, 6 Weizman St., Tel-Aviv 64239, Israel.
Department of Radiology, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel-Aviv, Israel.
Elka Miller
Department of Radiology, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel-Aviv, Israel.
Hedva Lerman
Department of Nuclear Medicine, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, 6 Weizman St., Tel-Aviv 64239, Israel.
Einat Even-Sapir
Department of Nuclear Medicine, Tel-Aviv Sourasky Medical Center, Sackler Faculty of Medicine, 6 Weizman St., Tel-Aviv 64239, Israel.

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