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Selection of Patients for Resection of Hepatic Metastases: Improved Detection of Extrahepatic Disease with FDG PET¹

¹ From the Departments of Radiology (I.A.Z., J.R., S.S.) and Nuclear Medicine (S.J.S., G.C., C.N.), McMaster University Medical Centre, 1200 Main St W, Hamilton, Ontario, Canada L8N 3Z5. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received January 31, 2001; revision requested February 26 and received March 28; accepted April 3. Address correspondence to I.A.Z. (e-mail: ianzealley@moose-mail.com).

	Abstract

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

 
A rapidly emerging clinical application of positron emission tomography (PET) is the detection of tumor tissue at whole-body studies performed with the glucose analogue 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). High rates of recurrence after partial hepatic resection in patients with colorectal cancer liver metastases indicate that current presurgical imaging strategies are failing to show extrahepatic tumor deposits. Although FDG PET cannot match the anatomic resolution of conventional imaging techniques in the liver and the lungs, it is particularly useful for identification and characterization of extrahepatic disease. FDG PET can show foci of metastatic disease that may not be apparent at conventional anatomic imaging and can aid in the characterization of indeterminate soft-tissue masses. Several sources of benign and physiologic increased activity at FDG PET emphasize the need for careful correlation with findings of other imaging studies and clinical findings. FDG PET can improve the selection of patients for partial hepatic resection and thereby reduce the morbidity and mortality associated with inappropriate surgery.

Index Terms: Fluorine, radioactive • Liver neoplasms, PET, 761.12163 • Liver neoplasms, metastases, 761.3327

	Introduction

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

 
Functional metabolic imaging with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) is emerging as a useful tool in the management of colorectal cancer (1–6). Findings of a meta-analysis showed that the technique has an overall sensitivity of 97% in the identification of colorectal cancer metastases throughout the whole body and that findings at FDG PET promote changes in management in 29% of cases (7).

Colorectal cancer is the most common metastatic cancer to occur in the liver, and partial hepatic resection is now established as the optimal treatment for surgically resectable disease (8–10). However, improved survival rates are restricted to those patients from whom all metastases can be removed: Foci of disease at extrahepatic sites (not identified preoperatively) are responsible for relapse in approximately 50% of patients who have undergone this major surgical procedure (11,12). It is hoped that the application of FDG PET will lead to improved selection of patients for partial hepatic resection by optimizing the detection of extrahepatic tumor foci throughout the body. One recent series has shown improved survival rates among patients who underwent FDG PET prior to partial hepatic resection (13).

The purpose of this article is to demonstrate the utility of FDG PET in the evaluation of liver metastases from colorectal cancer in patients who are being considered for partial hepatic resection and to emphasize the scope and limitations of the technique for the detection of extrahepatic tumor deposits.

Partial Hepatic Resection for Liver Metastases from Colorectal Cancer
In Western Europe and the United States, the incidence of colorectal cancer is approximately 400,000 new cases per year (10,14,15). In up to 30% of patients, metastases localized to the liver will develop (16). If the liver metastases are left untreated, patients have a dismal prognosis, with 5-year survival estimated at 3% or less, and the results of treatment with systemic chemotherapy or radiation therapy are poor (10).

However, some of these patients will have resectable disease, and surgical treatment with partial hepatic resection offers the potential for cure. Approximately 25% of all colorectal cancer patients in whom liver metastases develop are potential candidates for surgical cure, making "resectable hepatic metastases...an oncologic problem of magnitude comparable to esophageal cancer, brain tumors, or thyroid cancer" (15). Over the past few years, surgical management has become more aggressive, and recent studies have shown 5-year survival rates of 25%–44% among patients who underwent partial hepatic resection (8,9).

Consequently, this treatment has become standard for resectable disease but is a major therapeutic undertaking, with an operative mortality of 2%–7% (12). The basic principle of partial hepatic resection is to remove all anatomically resectable liver lesions, leaving sufficient disease-free liver tissue to allow normal hepatic function. Candidates for partial hepatic resection should have anatomically resectable liver lesions and be free of extrahepatic disease. The role of preoperative imaging in patient selection is to identify this "small, but important, subgroup who may benefit from surgery and...to prevent unnecessary radical surgery...in those likely to gain only a short-term benefit" (16).

Although partial hepatic resection is the best available therapeutic option for such patients, the limited improvement in survival with surgery reflects high rates of tumor recurrence. Unidentified sites of extrahepatic disease are an important cause of clinical relapse: Extrahepatic sites are involved in up to 50% of patients who have recurrence after surgery (11,12). Also, a significant proportion of patients is found to have extrahepatic metastases at surgery (17,18); the unnecessary laparotomy in these patients contributes significantly to morbidity and must be considered a failure of diagnostic imaging. Surgeons rely on preoperative imaging for patient selection, but current imaging strategies may fail to show small extrahepatic tumor foci. There is substantial scope for improvement in the preoperative detection of extrahepatic tumor deposits to prevent unnecessary surgery (7).

Principles of FDG PET
FDG PET provides a functional metabolic map of glucose uptake in the whole body. The glucose analogue FDG is labeled with the cyclotron-produced, positron-emitting radioisotope fluorine-18. The resulting radiopharmaceutical F-18 FDG is a substrate for glucose transport proteins in cell membranes and accumulates intracellularly.

Increased metabolic activity in malignant tissue is accompanied by increased glucose uptake relative to that of surrounding normal tissue. This focal increase in glucose uptake can be identified with FDG PET, which allows identification of malignant tumor foci. However, focal increased FDG uptake is nonspecific and may occur in any condition associated with increased tissue metabolism, such as acute or chronic inflammatory processes. By forming images based on functional, rather than anatomic, information, FDG PET has the potential to show tumor foci at an early stage, before any structural abnormality becomes apparent. For instance, normal-sized lymph nodes that are infiltrated by tumor tissue may be identified in this way (19). Similarly, the presence or absence of recurrent tumor tissue in postoperative scar tissue may be inferred by the degree of FDG uptake shown at FDG PET.

Use of FDG PET to Detect Colorectal Cancer Metastases
At most centers, computed tomography (CT) remains the principal imaging modality for the assessment of extrahepatic disease in patients with liver metastases from colorectal cancer who are being considered for partial hepatic resection. FDG PET has the potential to show increased metabolic activity in areas where the presence or absence of tumor tissue cannot be accurately assessed with conventional structural parameters (nonenlarged lymph nodes, low-volume peritoneal disease, postoperative sites). It may also raise suspicion of disease at sites that may have been overlooked or underestimated on the basis of CT findings.

Findings of a meta-analysis quote a "weighted average" sensitivity and specificity of 95% and 77%, respectively, for identification of colorectal cancer tumor deposits with whole-body FDG PET (7). The same meta-analysis showed estimates of sensitivity and specificity of greater than 90% for identification of colorectal cancer liver metastases and of locoregional recurrence at sites of previous colonic resection. However, as the authors point out, published estimates of FDG PET performance in this context should be interpreted with some caution. In the absence of a perfect-criterion standard against which to compare the performance of FDG PET, and without exhaustive follow-up investigation in patients with apparently negative findings at FDG PET, it is impossible to accurately define test characteristics. In particular, the tendency to underestimate the false-negative rates may result in inappropriately high estimates of test sensitivity. Similarly, difficulties with verification of true-negative rates mean that test specificity is difficult to quantify accurately.

A few studies provide carefully verified data for FDG PET performance at specific anatomic sites and indicate that the sensitivity and specificity of FDG PET may be lower than some studies suggest. The sensitivity and specificity for identification of primary colorectal cancer lesions appear to be 95% and 43%, respectively (3), while for identification of pelvic colorectal cancer recurrence, the figures are estimated at 91% and 100%, respectively (20). The specificity of 100% in the latter study (20) should probably be interpreted cautiously in view of several false-positive findings of pelvic recurrence in other studies (2,3). In two studies, FDG PET allowed identification of peritoneal tumor deposits in four of nine patients (sensitivity, 44%) (5,6). Histologic analysis of lymph nodes taken at surgery for primary colorectal cancer lesions suggests that the sensitivity of FDG PET for identification of involved lymph nodes may be only 29% (specificity, 96%) (3). Another factor indicating that sensitivity for identification of involved lymph nodes may be poorer than previously estimated is that modern molecular biology techniques can show tumor tissue in apparently uninvolved lymph nodes. In one study, these lymph node micrometastases were identified in 14 of 26 (54%) lymph node samples that were negative for colorectal cancer involvement at conventional histologic examination, and their presence was shown to be associated with reduced survival (21).

The sensitivity of FDG PET for identification of mucinous-type colorectal cancer metastases is lower than that for the more common nonmucinous-type tumor (22). As one might expect, the nondetectability of mucinous-type tumors has been shown to be associated with relative abundance of mucin and with tumor hypocellularity (23).

Overall, compared with conventional anatomic imaging techniques, FDG PET has been shown to help in the identification of unexpected foci of tumor tissue in 46 of 229 patients (20%) in four studies (1,2,4,6). In candidates for partial hepatic resection (1,4,6), findings at FDG PET are reported to have influenced management in 30 of 111 patients (27%).

In this article, we briefly describe our technique for FDG PET and show its use in patients who are potential candidates for partial hepatic resection. While findings at FDG PET of the liver are illustrated, most emphasis is placed on the evaluation of extrahepatic disease sites, which is where the real strength of FDG PET has been shown to lie. Cases of abdominal, pelvic, pulmonary, and mediastinal metastatic disease are presented alongside examples of physiologic and benign increased FDG uptake at sites that may mimic malignant disease. The importance of correlating FDG uptake with clinical findings and results of conventional, anatomic imaging studies is highlighted.

	FDG PET Technique

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

 
Image Acquisition
Our technique for FDG PET has been previously described in this journal (24), and we present an abbreviated summary here. Most patients are requested to fast for at least 6 hours prior to scanning. Patients with diabetes mellitus are allowed a normal therapeutic and dietary regimen at breakfast and then undergo fasting for 4 hours prior to injection of FDG. An intravenous dose of 5 mCi (185 MBq) of FDG is administered, and scanning is performed after a 45-minute delay for FDG uptake. Immediately before image acquisition, patients are encouraged to empty their bladders to reduce artifact from urinary FDG activity.

Images are acquired with an ECAT ART tomograph (Siemens/CTI, Knoxville, Tenn). This machine is a partial-ring bismuth germanate-crystal scanner that we use in three-dimensional mode (no septa) during whole-body imaging. Although the sensitivity (in terms of counts per minute per millicurie) is equivalent to that of more modern full-ring scanners, our images may appear noisier because of scatter. For these whole-body studies (pelvis to base of skull), emission data are acquired at four to six overlapping bed positions (8 minutes per position, 15-cm field of view, 6-cm overlap). We do not use attenuation correction for these examinations. The application of attenuation correction to whole-body PET is controversial (25). In one lung cancer phantom study, attenuation correction was found to have no influence on lesion detectability (26), while another study showed that attenuation correction may impair lesion detectability in patients with metastatic breast cancer (27). Image reconstruction is performed with filtered back projection. In some instances, we apply an iterative reconstruction algorithm (ordered subset expectation maximization [OSEM], two iterations, eight subsets) to reduce the influence of artifacts that arise from filtered back projection (eg, when excessive artifact arises from intense bladder activity).

Image Interpretation
The data are viewed at a computer workstation (Sun Microsystems, Mountain View, Calif) that presents simultaneous reprojection images in three orthogonal planes (axial, coronal, and sagittal) and allows the reader to adjust image window and level settings to suit the particular study. The viewer may scroll through these displays and can also review a maximum pixel–weighted volumetric representation of the whole-body acquisition from all angles. We believe that this interactive approach is superior to reading from film. FDG PET images are interpreted alongside all other relevant imaging studies available at the time of referral; they include CT images of the chest, abdomen, and pelvis. In this article, we present many of the FDG PET images together with relevant CT findings.

	Results of Hepatic and Extrahepatic FDG PET Studies

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

 
Liver
The normal liver, like the spleen, renal cortex, and bone marrow, is a site of diffuse, moderate FDG activity (28). Metastases usually manifest as discrete foci of increased activity in the liver (Fig 1), but larger lesions, some of which have necrotic centers, may appear as rings of increased activity (Fig 2). Large metastases are generally readily identified, but some small lesions are not identifiable at FDG PET (Fig 3); occasionally even large metastases are not associated with focal increased FDG uptake (Fig 4). In a lesion-by-lesion analysis of resected liver specimens, FDG PET demonstrated only 70% of liver metastases, and the sensitivity of FDG PET in the detection of metastases was confirmed to be related to lesion size (6).

View larger version (62K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.   Increased FDG uptake in liver metastases in a 66-year-old woman. (a) FDG PET images show intense FDG uptake at multiple sites in the liver, especially in segments 2 and 3. (b) Corresponding axial image acquired during CT with arterial portography shows that the large perfusion defect in segments 2 and 3 is due to extensive tumor involvement. Another, discrete metastatic deposit is evident in segment 4a (arrowhead).

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.   Increased FDG uptake in liver metastases in a 66-year-old woman. (a) FDG PET images show intense FDG uptake at multiple sites in the liver, especially in segments 2 and 3. (b) Corresponding axial image acquired during CT with arterial portography shows that the large perfusion defect in segments 2 and 3 is due to extensive tumor involvement. Another, discrete metastatic deposit is evident in segment 4a (arrowhead).

View larger version (70K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.   FDG uptake in liver metastasis and lymph nodes involved by tumor tissue in a 65-year-old man. (a) In the coronal FDG PET image, a ring-shaped area (large arrowhead) of FDG uptake in the right lobe of the liver corresponds to a large, solitary liver metastasis. Lymph node involvement in the mediastinum, periaortic region, and pelvis is also evident (small arrowheads). Myocardial FDG uptake is prominent in the coronal and sagittal images; this physiologic finding is variable and is not seen in Figure 1a. (b) Corresponding axial CT image shows periaortic lymphadenopathy (arrowheads).

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.   FDG uptake in liver metastasis and lymph nodes involved by tumor tissue in a 65-year-old man. (a) In the coronal FDG PET image, a ring-shaped area (large arrowhead) of FDG uptake in the right lobe of the liver corresponds to a large, solitary liver metastasis. Lymph node involvement in the mediastinum, periaortic region, and pelvis is also evident (small arrowheads). Myocardial FDG uptake is prominent in the coronal and sagittal images; this physiologic finding is variable and is not seen in Figure 1a. (b) Corresponding axial CT image shows periaortic lymphadenopathy (arrowheads).

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.   Small liver metastasis without increased FDG uptake in a 77-year-old woman. (a) Axial image acquired during CT with arterial portography shows a small metastasis in segment 7 (arrowhead). (b) FDG PET images obtained in the same patient show no corresponding focal increased FDG uptake on the axial image (large arrowhead). A separate metastasis in the left lobe of the liver (small arrowheads) was also evident at CT with arterial portography.

View larger version (71K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.   Small liver metastasis without increased FDG uptake in a 77-year-old woman. (a) Axial image acquired during CT with arterial portography shows a small metastasis in segment 7 (arrowhead). (b) FDG PET images obtained in the same patient show no corresponding focal increased FDG uptake on the axial image (large arrowhead). A separate metastasis in the left lobe of the liver (small arrowheads) was also evident at CT with arterial portography.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.   Large liver metastasis without increased FDG uptake in a 68-year-old man. (a) Axial image acquired during CT with arterial portography shows a large perfusion defect in segment 6 (arrowhead). This lesion is a metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increased FDG uptake in this region (arrowheads).

View larger version (71K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.   Large liver metastasis without increased FDG uptake in a 68-year-old man. (a) Axial image acquired during CT with arterial portography shows a large perfusion defect in segment 6 (arrowhead). This lesion is a metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increased FDG uptake in this region (arrowheads).

Abdomen and Pelvis
Although a false-positive finding of focal FDG uptake is unusual in patients with liver metastases from colorectal cancer (6), several physiologic and benign causes of focally increased activity must be distinguished from metastatic disease. Increased activity can be seen in all segments of normal bowel tissue; the mechanism underlying this phenomenon is unclear (28). This normal finding can usually be identified by its pattern, which is often a linear "string of beads" appearance (Figs 5, 6). More limited bowel uptake, which forms discrete foci of increased activity, can be impossible to distinguish from tumor deposits, and correlation with findings of other imaging modalities is required. Such focal FDG up-take is often seen in the stomach (Fig 7) and at ileostomy and colostomy sites (Fig 8). Since stomas may be sites of tumor recurrence, correlation with clinical findings, as well as findings of other imaging studies, should be sought.

View larger version (65K): [in this window] [in a new window] [Download PPT slide]   Figure 5.   FDG uptake in normal bowel tissue in a 68-year-old man. FDG PET images show the linear string of beads appearance in the right flank that is characteristic of FDG activity in the right part of the colon (small arrowheads). Physiologic increased FDG uptake is also seen in the stomach (large arrowhead).

View larger version (62K): [in this window] [in a new window] [Download PPT slide]   Figure 6.   FDG uptake in normal bowel tissue in a 73-year-old man. FDG PET images show the linear string of beads appearance in the left flank that is characteristic of FDG activity in the left part of the colon (arrowheads).

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.   FDG uptake in a normal stomach in a 63-year-old man. (a) FDG PET images show intense physiologic uptake of FDG in the stomach (large arrowhead) below the myocardium. FDG uptake in the wall of the gas-distended left part of the colon is also evident (small arrowheads). (b) Corresponding axial CT image shows the normal, distensible stomach filled with air and oral contrast material.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.   FDG uptake in a normal stomach in a 63-year-old man. (a) FDG PET images show intense physiologic uptake of FDG in the stomach (large arrowhead) below the myocardium. FDG uptake in the wall of the gas-distended left part of the colon is also evident (small arrowheads). (b) Corresponding axial CT image shows the normal, distensible stomach filled with air and oral contrast material.

View larger version (81K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.   Increased FDG uptake at a normal colostomy site in a 56-year-old man. (a) FDG PET images show that the focus of increased FDG uptake in the abdominal wall (arrowheads) is related to a colostomy site. (b) Corresponding axial CT image shows a normal colostomy site. There was no evidence of colorectal cancer recurrence at CT, clinical examination, or follow-up.

View larger version (132K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.   Increased FDG uptake at a normal colostomy site in a 56-year-old man. (a) FDG PET images show that the focus of increased FDG uptake in the abdominal wall (arrowheads) is related to a colostomy site. (b) Corresponding axial CT image shows a normal colostomy site. There was no evidence of colorectal cancer recurrence at CT, clinical examination, or follow-up.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.   Benign increased uptake of FDG related to a laparotomy scar. (a) FDG PET images show increased FDG uptake in the abdominal wall in the midline (arrowheads). This finding is related to healing in a recent laparotomy scar. (b) Corresponding axial CT image shows metal surgical clips (arrows) and inflammatory changes in adjacent subcutaneous fat. The patient had undergone laparotomy a few days before. There was no evidence of tumor deposit in the laparotomy scar at follow-up CT and clinical examination.

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.   Benign increased uptake of FDG related to a laparotomy scar. (a) FDG PET images show increased FDG uptake in the abdominal wall in the midline (arrowheads). This finding is related to healing in a recent laparotomy scar. (b) Corresponding axial CT image shows metal surgical clips (arrows) and inflammatory changes in adjacent subcutaneous fat. The patient had undergone laparotomy a few days before. There was no evidence of tumor deposit in the laparotomy scar at follow-up CT and clinical examination.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.   Benign postsurgical scarring without increased uptake of FDG in a 69-year-old man. (a) Axial CT image shows a presacral soft-tissue mass associated with streaking of adjacent fat. The appearance is suspicious for recurrent tumor at the site of previous resection of rectal cancer. (b) Corresponding FDG PET images show no focal increase in FDG uptake in the presacral region (arrows). Residual FDG activity is seen in the bladder (arrowheads). No tumor recurrence was evident at clinical examination or at 1-year follow-up CT.

View larger version (89K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.   Benign postsurgical scarring without increased uptake of FDG in a 69-year-old man. (a) Axial CT image shows a presacral soft-tissue mass associated with streaking of adjacent fat. The appearance is suspicious for recurrent tumor at the site of previous resection of rectal cancer. (b) Corresponding FDG PET images show no focal increase in FDG uptake in the presacral region (arrows). Residual FDG activity is seen in the bladder (arrowheads). No tumor recurrence was evident at clinical examination or at 1-year follow-up CT.

View larger version (79K): [in this window] [in a new window] [Download PPT slide]   Figure 11.   FDG activity in the normal urinary collecting system in a 74-year-old man. FDG PET images show FDG activity in urine, revealing the right pelvicaliceal system, ureter (arrowheads), and bladder.

View larger version (79K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.   Increased FDG uptake in a nonenlarged celiac lymph node involved by tumor tissue in a 75-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the celiac region (arrowheads). Foci of increased FDG uptake in the liver correspond to liver metastases in segments 4a (long arrow) and 4b (short arrow). (b) Corresponding axial CT image shows a nonenlarged lymph node at this site (arrowhead). This lymph node was not apparent at a previous CT study and was found to be enlarged at a subsequent CT study. Although no biopsy was performed (the patient had metastatic disease at other sites), these imaging changes strongly suggest that the lymph node is involved by tumor tissue.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.   Increased FDG uptake in a nonenlarged celiac lymph node involved by tumor tissue in a 75-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the celiac region (arrowheads). Foci of increased FDG uptake in the liver correspond to liver metastases in segments 4a (long arrow) and 4b (short arrow). (b) Corresponding axial CT image shows a nonenlarged lymph node at this site (arrowhead). This lymph node was not apparent at a previous CT study and was found to be enlarged at a subsequent CT study. Although no biopsy was performed (the patient had metastatic disease at other sites), these imaging changes strongly suggest that the lymph node is involved by tumor tissue.

View larger version (89K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.   Increased FDG uptake in an enlarged iliac lymph node involved by tumor tissue in a 78-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the left iliac region (arrowheads). A large liver metastasis in segments 2 and 3 is also evident (long arrows), as is physiologic uptake of FDG in the stomach (short arrow). (b) Corresponding axial CT image shows a CT-guided biopsy needle tip within an enlarged left iliac lymph node. The location of this lymph node corresponds to the area of increased FDG uptake on the FDG PET images. Findings of the biopsy were positive for tumor tissue.

View larger version (170K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.   Increased FDG uptake in an enlarged iliac lymph node involved by tumor tissue in a 78-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the left iliac region (arrowheads). A large liver metastasis in segments 2 and 3 is also evident (long arrows), as is physiologic uptake of FDG in the stomach (short arrow). (b) Corresponding axial CT image shows a CT-guided biopsy needle tip within an enlarged left iliac lymph node. The location of this lymph node corresponds to the area of increased FDG uptake on the FDG PET images. Findings of the biopsy were positive for tumor tissue.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 14a.   Benign enlarged celiac lymph node without increased FDG uptake in a 67-year-old man. (a) Axial CT image shows an enlarged lymph node (arrowhead) anterior to the common hepatic artery. This appearance is suspicious for tumor involvement. (b) Corresponding FDG PET images show no focal increase in FDG uptake in the celiac region. An ultrasonography-guided biopsy was performed, and findings in the sample were negative for tumor tissue. A metastasis is evident in the tip of the right lobe of the liver (large arrowhead). The apparent ventral abdominal wall hernia on the sagittal image (small arrowheads) is an artifact caused by the patient’s hands folded together across the abdomen during scanning.

View larger version (70K): [in this window] [in a new window] [Download PPT slide]   Figure 14b.   Benign enlarged celiac lymph node without increased FDG uptake in a 67-year-old man. (a) Axial CT image shows an enlarged lymph node (arrowhead) anterior to the common hepatic artery. This appearance is suspicious for tumor involvement. (b) Corresponding FDG PET images show no focal increase in FDG uptake in the celiac region. An ultrasonography-guided biopsy was performed, and findings in the sample were negative for tumor tissue. A metastasis is evident in the tip of the right lobe of the liver (large arrowhead). The apparent ventral abdominal wall hernia on the sagittal image (small arrowheads) is an artifact caused by the patient’s hands folded together across the abdomen during scanning.

View larger version (63K): [in this window] [in a new window] [Download PPT slide]   Figure 15a.   Increased FDG uptake in a small abdominal tumor deposit in a 50-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the left flank (arrowheads). Focal increased uptake in the anterior abdominal wall (arrow) is related to healing in a recent laparotomy scar. (b) Corresponding axial CT image shows a small soft-tissue mass in the mesenteric fat (arrow). Serial CT studies showed this nodule to be enlarging. Although no biopsy was performed, these imaging changes strongly suggest that the nodule is a tumor deposit.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.   Increased FDG uptake in a small abdominal tumor deposit in a 50-year-old man. (a) FDG PET images show a discrete focus of increased FDG uptake in the left flank (arrowheads). Focal increased uptake in the anterior abdominal wall (arrow) is related to healing in a recent laparotomy scar. (b) Corresponding axial CT image shows a small soft-tissue mass in the mesenteric fat (arrow). Serial CT studies showed this nodule to be enlarging. Although no biopsy was performed, these imaging changes strongly suggest that the nodule is a tumor deposit.

View larger version (80K): [in this window] [in a new window] [Download PPT slide]   Figure 16a.   Increased FDG uptake associated with low-volume peritoneal tumor deposits in a 70-year-old man. (a) FDG PET images show a patchy, diffuse region of increased FDG uptake in the central part of the abdomen (arrowheads). After examination of the images at the workstation, it was believed that the pattern of increased FDG uptake was not typical for normal bowel activity. (b) Axial CT image obtained in the same patient does not demonstrate any corresponding soft-tissue abnormality, and the patchy increased FDG uptake was attributed to activity in the bowel. The patient underwent laparotomy in preparation for partial hepatic resection, but multiple, small (<1-cm-diameter), biopsy-proved peritoneal tumor deposits were found. In retrospect, it appears that the unusual distribution of FDG uptake at the FDG PET study was due to these peritoneal tumor deposits. Increasing experience with FDG PET may allow us to select patients with this suspicious appearance for laparoscopy prior to partial hepatic resection.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 16b.   Increased FDG uptake associated with low-volume peritoneal tumor deposits in a 70-year-old man. (a) FDG PET images show a patchy, diffuse region of increased FDG uptake in the central part of the abdomen (arrowheads). After examination of the images at the workstation, it was believed that the pattern of increased FDG uptake was not typical for normal bowel activity. (b) Axial CT image obtained in the same patient does not demonstrate any corresponding soft-tissue abnormality, and the patchy increased FDG uptake was attributed to activity in the bowel. The patient underwent laparotomy in preparation for partial hepatic resection, but multiple, small (<1-cm-diameter), biopsy-proved peritoneal tumor deposits were found. In retrospect, it appears that the unusual distribution of FDG uptake at the FDG PET study was due to these peritoneal tumor deposits. Increasing experience with FDG PET may allow us to select patients with this suspicious appearance for laparoscopy prior to partial hepatic resection.

View larger version (64K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.   Increased FDG uptake in a lung metastasis in a 66-year-old man. (a) FDG PET images show focal increased FDG uptake anteriorly in the right lung base (large arrowheads). A large ring-shaped liver metastasis is also evident (small arrowheads). (b) Corresponding axial CT image shows an apparently solitary, biopsy-proved lung metastasis at the site of increased FDG uptake in the base of the right lung (arrowhead).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.   Increased FDG uptake in a lung metastasis in a 66-year-old man. (a) FDG PET images show focal increased FDG uptake anteriorly in the right lung base (large arrowheads). A large ring-shaped liver metastasis is also evident (small arrowheads). (b) Corresponding axial CT image shows an apparently solitary, biopsy-proved lung metastasis at the site of increased FDG uptake in the base of the right lung (arrowhead).

View larger version (105K): [in this window] [in a new window] [Download PPT slide]   Figure 18a.   Lung metastasis without increased FDG uptake in a 72-year-old woman. (a) Axial CT image shows a small lung metastasis in the left lung base (arrowhead). The nature of this lesion was determined with surgical excision biopsy, which helped to confirm metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increase in FDG uptake in the left lung base.

View larger version (68K): [in this window] [in a new window] [Download PPT slide]   Figure 18b.   Lung metastasis without increased FDG uptake in a 72-year-old woman. (a) Axial CT image shows a small lung metastasis in the left lung base (arrowhead). The nature of this lesion was determined with surgical excision biopsy, which helped to confirm metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increase in FDG uptake in the left lung base.

View larger version (75K): [in this window] [in a new window] [Download PPT slide]   Figure 19a.   Incidental finding of a primary lung cancer associated with increased FDG uptake in a 75-year-old woman. (a) FDG PET images show a focal increase in FDG uptake in the upper lobe of the right lung (arrowheads). (b) Corresponding axial CT image shows a biopsy-proved bronchoalveolar carcinoma. The site corresponds to the area of focal increased uptake of FDG.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 19b.   Incidental finding of a primary lung cancer associated with increased FDG uptake in a 75-year-old woman. (a) FDG PET images show a focal increase in FDG uptake in the upper lobe of the right lung (arrowheads). (b) Corresponding axial CT image shows a biopsy-proved bronchoalveolar carcinoma. The site corresponds to the area of focal increased uptake of FDG.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.   Mediastinal lymph node involved by tumor tissue but not associated with increased FDG uptake in a 66-year-old man. (a) Axial CT image shows the tip of a biopsy needle immediately anterior to an enlarged lymph node. Findings of the biopsy sample were positive for metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increase in FDG uptake in the anterior mediastinum.

View larger version (62K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.   Mediastinal lymph node involved by tumor tissue but not associated with increased FDG uptake in a 66-year-old man. (a) Axial CT image shows the tip of a biopsy needle immediately anterior to an enlarged lymph node. Findings of the biopsy sample were positive for metastasis from a nonmucinous-type primary colorectal cancer. (b) FDG PET images obtained in the same patient show no corresponding focal increase in FDG uptake in the anterior mediastinum.

View larger version (84K): [in this window] [in a new window] [Download PPT slide]   Figure 21a.   Increased FDG uptake in benign pulmonary hilar lymph nodes in a 69-year-old man. (a) FDG PET images show several discrete foci of increased FDG uptake in the hilar regions of both lungs (arrowheads). (b) Corresponding axial CT image shows calcification in a nonenlarged left hilar lymph node (arrow). Several smaller hilar lymph nodes were similarly calcified. Although no definitive diagnosis was made, the increased FDG activity was most likely due to chronic low-grade inflammation, as no lymph node enlargement was evident on serial follow-up radiographs.

View larger version (102K): [in this window] [in a new window] [Download PPT slide]   Figure 21b.   Increased FDG uptake in benign pulmonary hilar lymph nodes in a 69-year-old man. (a) FDG PET images show several discrete foci of increased FDG uptake in the hilar regions of both lungs (arrowheads). (b) Corresponding axial CT image shows calcification in a nonenlarged left hilar lymph node (arrow). Several smaller hilar lymph nodes were similarly calcified. Although no definitive diagnosis was made, the increased FDG activity was most likely due to chronic low-grade inflammation, as no lymph node enlargement was evident on serial follow-up radiographs.

View larger version (87K): [in this window] [in a new window] [Download PPT slide]   Figure 22.   Benign increased FDG uptake in muscle tissue in a 75-year-old man. FDG PET images show increased FDG uptake in the right pectoral muscle group (arrowheads). This finding is attributable to inflammation. The patient reported that he had strained these muscles during vigorous snow shoveling on the evening prior to scanning. Similar increased FDG uptake is sometimes seen in the gluteal muscles of patients who have been ambulant during the period between FDG injection and PET.

	Summary

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

	Acknowledgments

 
We thank Margo Thompson for her invaluable assistance in the preparation of the PET images for this article.

	Footnotes

 
Abbreviations: FDG = 2-[fluorine-18]fluoro-2-deoxy-D-glucose, PET = positron emission tomography

	References

Top Abstract Introduction FDG PET Technique Results of Hepatic and... Summary References

 

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