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Pitfalls in Oncologic Diagnosis with FDG PET Imaging: Physiologic and Benign Variants¹

¹ Department of Internal Medicine, Division of Nuclear Medicine (P.D.S., R.L.W.)
² Department of Radiology (Y.A.), B1G412 University Hospital, University of Michigan Medical Center, 1500 E Medical Center Dr, Ann Arbor, MI 48109
³ Department of Nuclear Medicine, Veterans Affairs Medical Center, Ann Arbor, Mich (P.D.S.).

	Abstract

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

 
A rapidly emerging clinical application of positron emission tomography (PET) is the detection and staging of cancer with the glucose analogue tracer 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). Proper interpretation of FDG PET images requires knowledge of the normal physiologic distribution of the tracer, frequently encountered physiologic variants, and benign pathologic causes of FDG uptake that can be confused with a malignant neoplasm. One hour after intravenous administration, high FDG activity is present in the brain, the myocardium, and—due to the excretory route—the urinary tract. Elsewhere, tracer activity is typically low, a fact that allows sensitive demonstration of tracer accumulation in many malignant neoplasms. Interpretive pitfalls commonly encountered on FDG PET images of the body obtained 1 hour after tracer administration can be mistaken for cancer. Such pitfalls include variable physiologic FDG uptake in the digestive tract, thyroid gland, skeletal muscle, myocardium, bone marrow, and genitourinary tract and benign pathologic FDG uptake in healing bone, lymph nodes, joints, sites of infection, and cases of regional response to infection and aseptic inflammatory response. In many instances, these physiologic variants and benign pathologic causes of FDG uptake can be specifically recognized and properly categorized; in other instances, such as the lymph node response to inflammation or infection, focal FDG uptake is nonspecific.

Index Terms: Emission CT (ECT), **.12163² • Fluorine • Neoplasms, diagnosis, **.30 • Neoplasms, emission CT (ECT), **.12163, **.30

	INTRODUCTION

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

 
A rapidly emerging clinical application of positron emission tomography (PET) is the detection and staging of cancer with the glucose analogue tracer 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). High target-to-nontarget ratios are obtained with most common neoplasms and allow detection of even anatomically occult neoplasms throughout the body (1). FDG uptake also occurs in nonmalignant tissue, notably the brain and heart, and FDG is excreted in the urinary tract. These sites of physiologic FDG activity are generally readily recognized; however, there are common sites of variable physiologic FDG uptake and benign pathologic FDG uptake that could be confused with malignant neoplasms.

The purpose of this article is to present these interpretive pitfalls so that a radiologist experienced in cross-sectional imaging can avoid false-positive diagnoses and recognize inherently nonspecific findings on FDG PET images obtained for oncologic diagnosis. These pitfalls include variable physiologic FDG uptake in the digestive tract, thyroid gland, skeletal muscle, myocardium, bone marrow, and genitourinary tract and benign pathologic FDG uptake in healing bone, lymph nodes, joints, and sites of infection or inflammation.

	TECHNIQUE

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

 
FDG PET for tumor imaging is typically performed at least 50 minutes after intravenous administration of FDG. This interval allows the increase in tumor tracer activity due to intracellular trapping of FDG (as FDG 6 phosphate) and the concomitant decrease in blood pool and overall background tracer activity to improve tumor-to-background ratios. Although tumor-to-background ratios continue to improve beyond 1 hour after injection (2), the decline in counting statistics due to the physical half-life of F-18 (110 minutes) mandates a compromise between target-to-background ratios and counting statistics; thus, most centers begin emission image acquisitions at approximately 1 hour after injection. The optimal delay between FDG administration and the initiation of the emission image acquisitions has not yet been determined and may be longer than 1 hour for certain tumor imaging applications. The typical dose of FDG in adult patients is 370 MBq (10 mCi), although higher doses approaching 700 MBq are being used. The dose is limited by the dose to the bladder wall because FDG is excreted in the urine (3). Because serum glucose is competitive with FDG, overall image quality and tumor uptake of FDG are diminished by an elevated serum glucose level (4); thus, patients are required to fast for at least 4 hours before the study. Administration of exogenous insulin to reduce the serum glucose level or stimulation of endogenous insulin by means of a meal produces a shift in FDG deposition to insulin-sensitive tissues, including fat and skeletal muscle, with a relative reduction in tumor FDG deposition (5,6).

Currently, the static distribution of FDG is of interest in oncologic FDG imaging for either local-regional diagnosis or staging in the torso or whole body according to the neoplasm or clinical question. Imaging can be performed as emission only (not attenuation corrected) by means of a sequence of contiguous bed positions, and this method is currently most practical for evaluating the whole body (7). Because most lines of coincidence traverse the entire cross section of the body, attenuation effects and distortion are more pronounced in PET of the body than in single photon emission computed tomography (CT) (8); thus, attenuation correction is often employed to produce images with anatomic fidelity for correlation with anatomic images. Attenuation correction requires performance of a transmission scan before or after the emission image acquisition at each corresponding bed position, a requirement that adds time to the overall image acquisition and—with currently available transmission scan technology—adds noise to the final images (9).

Due to the added imaging time and noise in the images, there is some controversy concerning the overall usefulness of attenuation correction for whole-body or whole-torso FDG PET tumor imaging (10,11). For radiologists familiar with CT, attenuation-corrected FDG PET images do provide a more familiar representation of normal anatomic structures and relationships. Nevertheless, many experienced PET imagers have found emission (non–attenuation-corrected) FDG PET body images adequate, even in challenging locations such as the retroperitoneum, as long as proper attention is given to patient preparation (12). Rapid advances in the technology for attenuation correction and image reconstruction software are reducing the time and noise contributions of attenuation correction; thus, it is likely that FDG PET body images will increasingly be routinely attenuation corrected (9,13).

FDG PET images are generally interpreted qualitatively; focal (nonorgan) FDG uptake above blood pool activity at 1 hour on attenuation-corrected images is considered abnormal except in cases of physiologic variants, such as those described in this article. The degree of FDG uptake is often measured to allow comparison within and between different patients and diseases. The standardized uptake value (SUV) has become a widely used method of measuring static FDG accumulation in tissues. The SUV is computed as follows:

Because the SUV is not a true kinetic rate constant, it is often referred to as a semiquantitative measure (14). If all of the tracer were distributed evenly throughout the body, the SUV in every location would be unity. The SUV serves as a normalized target-to-background measure. The SUV of soft tissue is often less than 1.0 (usually about 0.8). Blood pool activity typically has an SUV of 1.5–2.0 at 1 hour after injection, whereas the SUV of the liver is approximately 2.5 and that of the renal cortex is approximately 3.5. The SUV of malignant neoplasms ranges from slightly greater than 2 to as high as 20. FDG avidity varies between different classes of neoplasms. For example, non–small cell lung cancer has relatively high FDG uptake at 1 hour after injection, with an average SUV of 8.2, whereas breast cancer has an average SUV of 3.2 (15). Increased body fat spuriously elevates the SUV; thus, SUVs are increasingly corrected for lean body mass (16). Because the SUV varies with the time after tracer injection, body weight (if correction for lean body mass is not performed), serum glucose level (when elevated), and use of an average pixel value versus a maximum pixel value for the region of interest, SUVs reported in the literature are not entirely comparable unless all of these parameters are specified (17). When a suitably large patient population is studied, cutoff values for benign versus malignant can be determined for a given diagnostic setting such as indeterminant lung nodules; however, such an approach has not generally proved more accurate than qualitative interpretation by an experienced reader (18,19).

In the cases presented in this article, the FDG PET scans were attenuation corrected (unless otherwise noted) and the emission portion of the scan was performed 50–70 minutes after intravenous administration of 370 MBq of FDG. All of the images were obtained with standard dedicated PET scanners (ECAT 931 [Siemens Medical Systems, Iselin, NJ] or Exact 921 [Siemens]) equipped with full-ring bismuth germinate crystal block detectors. Image reconstruction was performed by means of filtered back projection with a Hanning 0.3 postreconstruction filter. SUVs were measured at 1 hour and corrected for lean body mass and are expressed as the average pixel value over the region of interest. The examples are presented as axial, coronal, or sagittal tomographic images or reprojection images. Interpretation generally involves a review of reprojection images, axial and coronal tomographic images, and to a lesser extent sagittal tomographic images on an interactive computer display. Evaluation of structures—including normal variants and pathologic FDG uptake—is often best performed with axial and coronal tomographic images.

	GENERAL DISTRIBUTION OF FDG IN THE BODY

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

 
FDG accumulation is most intense in the brain, which is dependent on glycolytic metabolism, and in the myocardium, which also relies on glycolytic metabolism in the nonfasting state. Because FDG is excreted in the urine, intense FDG activity is encountered in the intrarenal collecting systems, ureters, and bladder. Less intense tracer activity is present in the liver, spleen, bone marrow, and renal cortex (Fig 1). At 1 hour after tracer injection, blood pool tracer activity results in moderate background tracer activity in the mediastinum, whereas lung activity is low (Fig 2). Although a recent meal (within 4 hours) often causes intense myocardial FDG uptake, fasting by patients for the usual 4–18 hours before FDG administration does not invariably suppress myocardial FDG uptake.

View larger version (77K): [in this window] [in a new window] [Download PPT slide]   Figure 1.  Normal distribution of FDG. Anterior reprojection emission FDG PET image shows the normal distribution of FDG 1 hour after intravenous administration. Intense activity is present in the brain (straight solid arrows) and the bladder (curved arrow). Lower-level activity is present in the liver (open arrow) and kidneys (arrowheads). i = site of FDG injection.

View larger version (81K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Normal distribution of FDG. Anterior reprojection attenuation-corrected FDG PET images of the chest and upper abdomen in patients who had fasted show minimal (a) and intense (b) myocardial FDG uptake. With attenuation correction, lung tracer activity is nearly absent and low-level tracer activity is present in the mediastinum and heart cavity due to the blood pool. Low-level hepatic and renal activity is also present. Arrowheads indicate abnormal FDG uptake in small bronchogenic carcinomas.

View larger version (79K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Normal distribution of FDG. Anterior reprojection attenuation-corrected FDG PET images of the chest and upper abdomen in patients who had fasted show minimal (a) and intense (b) myocardial FDG uptake. With attenuation correction, lung tracer activity is nearly absent and low-level tracer activity is present in the mediastinum and heart cavity due to the blood pool. Low-level hepatic and renal activity is also present. Arrowheads indicate abnormal FDG uptake in small bronchogenic carcinomas.

	SITES OF VARIABLE PHYSIOLOGIC FDG UPTAKE

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

View larger version (41K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (92K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (71K): [in this window] [in a new window] [Download PPT slide]   Figure 3d.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (68K): [in this window] [in a new window] [Download PPT slide]   Figure 3e.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 3f.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (78K): [in this window] [in a new window] [Download PPT slide]   Figure 3g.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (75K): [in this window] [in a new window] [Download PPT slide]   Figure 3h.  FDG uptake in the stomach. (a, b) Axial (a) and coronal (b) FDG PET images show that FDG uptake in the stomach wall (arrows in b) is readily identified in the presence of gaseous distention. (c) Axial FDG PET image shows that FDG uptake in the stomach wall is readily identified in the presence of a contracted stomach that maintains a gastric configuration. (d, e) Axial FDG PET images show that a laterally situated (d) or medially situated (e) contracted stomach (arrow) can appear as a discrete focal abnormality. In both d and e, there is no other region of FDG uptake to suggest a gastric configuration. i in e = injection site, r = normal renal tracer activity. (f) Axial FDG PET image shows that inhomogeneous FDG uptake in the stomach wall (arrow) can simulate an FDG-avid mass. The faint outline of the stomach is discernible (arrowhead), but the stomach is laterally displaced by hepatomegaly. (g) Axial FDG PET image shows that primary gastric carcinoma (arrow) can also produce inhomogeneous FDG uptake, as can gastric lymphoma. (h) Axial FDG PET image shows that focal, inhomogeneous stomach wall uptake can be simulated by a metastatic lesion of the adjacent left adrenal gland (arrow).

View larger version (32K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (82K): [in this window] [in a new window] [Download PPT slide]   Figure 4bxy.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (57K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (49K): [in this window] [in a new window] [Download PPT slide]   Figure 4d.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (45K): [in this window] [in a new window] [Download PPT slide]   Figure 4e.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 4f.  FDG uptake in the large intestine. (a, b) Axial (a) and coronal (b) FDG PET images show extensive uptake in the transverse colon (left image in a, right image in b) and cecum (right image in a, left image in b). The inhomogeneity of the FDG accumulation in the transverse colon results in discrete focal abnormalities on the reconstructed images. When isolated, intense focal FDG uptake in the cecum, as in other segments of the colon, can be misinterpreted as an abnormal FDG-avid mass in the abdomen. (c) Axial FDG PET image shows that when the colon is filled with gas, a region of FDG uptake can resemble peritoneal or mesenteric carcinomatosis. (d) Axial FDG PET image of the chest obtained at the lower extent of the field of view shows how a limited field of view can complicate identification of physiologic FDG uptake in the intestine. There is FDG uptake in the hepatic flexure with colonic interposition (arrow), which could be misdiagnosed as a neoplasm in the hepatic dome or costophrenic sulcus. (e, f) Coronal FDG PET image (e) and correlative CT scan (f) clearly show the colon (arrows). This example emphasizes the importance of anatomic correlation with PET results.

View larger version (39K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  FDG uptake in the small intestine. (a) Axial FDG PET images (left image obtained at a higher level than right image) show typical segmental FDG uptake in the ileum. FDG uptake is not present elsewhere in the intestine. (b) Axial FDG PET image shows FDG uptake in the terminal ileum and cecum (arrow) with additional isolated foci of uptake in segments of the small intestine (arrowheads); these foci could be mistaken for mesenteric lymph node metastases.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  FDG uptake in the small intestine. (a) Axial FDG PET images (left image obtained at a higher level than right image) show typical segmental FDG uptake in the ileum. FDG uptake is not present elsewhere in the intestine. (b) Axial FDG PET image shows FDG uptake in the terminal ileum and cecum (arrow) with additional isolated foci of uptake in segments of the small intestine (arrowheads); these foci could be mistaken for mesenteric lymph node metastases.

View larger version (19K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  FDG uptake in the thyroid gland in a nongoitrous, euthyroid patient. Sequential axial FDG PET images (shown from superior [left] to inferior [right]) (a), coronal FDG PET image (left image in b), and sagittal FDG PET image (right image in b) show relatively intense FDG uptake in the thyroid gland.

View larger version (17K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  FDG uptake in the thyroid gland in a nongoitrous, euthyroid patient. Sequential axial FDG PET images (shown from superior [left] to inferior [right]) (a), coronal FDG PET image (left image in b), and sagittal FDG PET image (right image in b) show relatively intense FDG uptake in the thyroid gland.

View larger version (66K): [in this window] [in a new window] [Download PPT slide]   Figure 7.  FDG uptake in skeletal muscle due to muscle contraction during the FDG uptake phase. Posterior reprojection FDG PET image of a patient who was allowed a short walk after FDG administration shows intense FDG accumulation in the gluteal musculature (arrows).

View larger version (11K): [in this window] [in a new window] [Download PPT slide]   Figure 8.  FDG uptake in skeletal muscle. Coronal FDG PET images of the neck (shown from anterior [left] to posterior [right]) show intense and relatively symmetric FDG activity in portions of the sternocleidomastoid and trapezius muscles (arrowheads).

View larger version (85K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.  Asymmetric or isolated FDG uptake in skeletal muscle. (a) Coronal FDG PET image of a patient who used his left arm before FDG injection reveals FDG uptake in only a small portion of the left trapezius muscle (arrow). (b) Axial FDG PET image of the same patient shows FDG uptake (arrowhead) with an appearance suggestive of a large metastatic or primary neoplasm of the chest wall. (c) Axial FDG PET image shows FDG uptake in the left pterygoid muscle (arrow) in a patient who underwent contralateral neck surgery. Although the patient did not speak during the FDG uptake phase, muscle imbalance due to loss of the contralateral musculature resulted in the FDG uptake, which could be misinterpreted as a neoplasm of the skull base. c = normal cerebellar tracer uptake.

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.  Asymmetric or isolated FDG uptake in skeletal muscle. (a) Coronal FDG PET image of a patient who used his left arm before FDG injection reveals FDG uptake in only a small portion of the left trapezius muscle (arrow). (b) Axial FDG PET image of the same patient shows FDG uptake (arrowhead) with an appearance suggestive of a large metastatic or primary neoplasm of the chest wall. (c) Axial FDG PET image shows FDG uptake in the left pterygoid muscle (arrow) in a patient who underwent contralateral neck surgery. Although the patient did not speak during the FDG uptake phase, muscle imbalance due to loss of the contralateral musculature resulted in the FDG uptake, which could be misinterpreted as a neoplasm of the skull base. c = normal cerebellar tracer uptake.

View larger version (46K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.  Asymmetric or isolated FDG uptake in skeletal muscle. (a) Coronal FDG PET image of a patient who used his left arm before FDG injection reveals FDG uptake in only a small portion of the left trapezius muscle (arrow). (b) Axial FDG PET image of the same patient shows FDG uptake (arrowhead) with an appearance suggestive of a large metastatic or primary neoplasm of the chest wall. (c) Axial FDG PET image shows FDG uptake in the left pterygoid muscle (arrow) in a patient who underwent contralateral neck surgery. Although the patient did not speak during the FDG uptake phase, muscle imbalance due to loss of the contralateral musculature resulted in the FDG uptake, which could be misinterpreted as a neoplasm of the skull base. c = normal cerebellar tracer uptake.

View larger version (44K): [in this window] [in a new window] [Download PPT slide]   Figure 10xy.  Irregular myocardial FDG uptake in a patient who had fasted for 12 hours before FDG injection. Axial FDG PET images of the chest (shown from superior [top left] to inferior [bottom right]) show the outlines of the left and right ventricles. There are discrete foci of intense FDG activity (arrows), which could be mistaken for mediastinal lymph nodes at the base of the heart.

View larger version (44K): [in this window] [in a new window] [Download PPT slide]   Figure 11axy.  FDG uptake in bone marrow. (a) Axial FDG PET images (shown from superior [top left] to inferior [bottom center]) show normal FDG activity in the marrow of the vertebral bodies (arrows). Sagittal FDG PET image (bottom right) clearly shows the modest FDG uptake at each vertebral body. (b) Axial FDG PET images (shown from superior [top left] to inferior [bottom center]) of a patient with lung cancer show metastases to the marrow spaces of the vertebral bodies (arrowheads) and left pedicle (arrow). Sagittal FDG PET image (bottom right) shows the irregular intensity and nonuniform distribution of the FDG uptake in the metastases. Metastases are also present in the left rib and sternum.

View larger version (41K): [in this window] [in a new window] [Download PPT slide]   Figure 11bxy.  FDG uptake in bone marrow. (a) Axial FDG PET images (shown from superior [top left] to inferior [bottom center]) show normal FDG activity in the marrow of the vertebral bodies (arrows). Sagittal FDG PET image (bottom right) clearly shows the modest FDG uptake at each vertebral body. (b) Axial FDG PET images (shown from superior [top left] to inferior [bottom center]) of a patient with lung cancer show metastases to the marrow spaces of the vertebral bodies (arrowheads) and left pedicle (arrow). Sagittal FDG PET image (bottom right) shows the irregular intensity and nonuniform distribution of the FDG uptake in the metastases. Metastases are also present in the left rib and sternum.

View larger version (31K): [in this window] [in a new window] [Download PPT slide]   Figure 12xy.  FDG uptake in bone marrow in a patient treated with granulocyte colony-stimulating factor. Axial FDG PET images (shown from superior [top left] to inferior [bottom center]) and a sagittal FDG PET image (bottom right) show intense FDG uptake in the vertebral bodies and sternum. The intense uptake resulted from expansion of the bone marrow due to the granulocyte colony-stimulating factor. Marrow activity in the ribs, scapula, and proximal humeri is also evident.

View larger version (41K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

View larger version (46K): [in this window] [in a new window] [Download PPT slide]   Figure 13bxy.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 13c.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

View larger version (65K): [in this window] [in a new window] [Download PPT slide]   Figure 13dwxyz.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 13e.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 13f.  Urinary excretion of FDG. (a) Axial FDG PET images (left image obtained at a higher level than right image) show the common finding of focal urinary FDG activity in the upper-pole calix of the left kidney (arrowhead). (b) Consecutive axial FDG PET images (shown from superior [top left] to inferior [bottom right]) of a patient with lung cancer show focal urinary FDG activity in the upper-pole calix of the left kidney (arrows) and a metastasis to the left adrenal gland (arrowheads). (c) CT scan of the same patient as in b clearly shows the relationship between the left adrenal mass and the left upper-pole calix. (d, e) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (d) and a coronal FDG PET image (e) show isolated urinary FDG activity in a small extrarenal pelvis (arrows). This finding could be misinterpreted as FDG-avid paraaortic or renal hilar lymph nodes if the relationship to the kidney is not clearly demonstrated. (f) Correlative CT scan shows intrapelvic fat with a small, medially displaced ureter (arrow).

The endometrium can also demonstrate elevated FDG uptake, which should not be confused with a uterine or presacral neoplasm (20). Moderately intense FDG uptake occurs in the testes (Fig 14). This is a normal finding, especially in younger patients, and tends to decline with advancing age (32). Such uptake should not be confused with a primary testicular neoplasm.

View larger version (30K): [in this window] [in a new window] [Download PPT slide]   Figure 14.  FDG uptake in the testes. Axial FDG PET image shows physiologic FDG uptake in the testes.

	SITES OF BENIGN PATHOLOGIC FDG UPTAKE

Top Abstract INTRODUCTION TECHNIQUE GENERAL DISTRIBUTION OF FDG... SITES OF VARIABLE PHYSIOLOGIC... SITES OF BENIGN PATHOLOGIC... SUMMARY References

View larger version (73K): [in this window] [in a new window] [Download PPT slide]   Figure 15awxyz.  FDG uptake in healing bone. (a, b) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (a) and a sagittal FDG PET image (b) obtained 6 weeks after cardiac surgery show FDG uptake (SUV = 3.3) in a healing sternum. (c) Axial FDG PET images (left image obtained at a higher level than right image) of a patient who experienced lateral fractures of two right ribs 3 weeks before imaging show FDG uptake (SUV = 2.3) in the healing fractures (arrows). Six weeks later, FDG uptake in the fractures had diminished slightly (SUV = 2.1).

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 15b.  FDG uptake in healing bone. (a, b) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (a) and a sagittal FDG PET image (b) obtained 6 weeks after cardiac surgery show FDG uptake (SUV = 3.3) in a healing sternum. (c) Axial FDG PET images (left image obtained at a higher level than right image) of a patient who experienced lateral fractures of two right ribs 3 weeks before imaging show FDG uptake (SUV = 2.3) in the healing fractures (arrows). Six weeks later, FDG uptake in the fractures had diminished slightly (SUV = 2.1).

View larger version (51K): [in this window] [in a new window] [Download PPT slide]   Figure 15c.  FDG uptake in healing bone. (a, b) Axial FDG PET images (shown from superior [top left] to inferior [bottom right]) (a) and a sagittal FDG PET image (b) obtained 6 weeks after cardiac surgery show FDG uptake (SUV = 3.3) in a healing sternum. (c) Axial FDG PET images (left image obtained at a higher level than right image) of a patient who experienced lateral fractures of two right ribs 3 weeks before imaging show FDG uptake (SUV = 2.3) in the healing fractures (arrows). Six weeks later, FDG uptake in the fractures had diminished slightly (SUV = 2.1).