Variation in FDG uptake on PET in patients with radiation-induced pelvic insufficiency fractures: a review of 10 cases

Introduction  The information available on ¹⁸F-fluorodeoxyglucose (FDG) uptake on PET in radiation-induced pelvic insufficiency fracture (PIF) is limited. In this study, we reviewed the findings of FDG-PET in 10 cases with PIF. Materials and methods  We diagnosed 83 cases of PIF in patients who received pelvic radiotherapy between Jan 1995 and Aug 2005. Among these patients, we selected 10 patients who performed FDG-PET and reviewed the FDG uptake. Results  Mild FDG uptake was still present at 6-months after the diagnosis of PIF in two patients. Eight patients had mild and diffuse FDG uptake and two patients had intense and heterogeneous uptake. All patients had vertical uptake parallel to the sacroiliac joints and one patient had the typical ‘H’ sign associated with PIF. The maximum of standardized uptake values was variable and ranged from 2.4 to 7.2. In three patients, follow-up PET images were obtained. All patients had FDG uptake that decreased with time. Conclusion  The FDG-PET demonstrated a variable degree of uptake in patients with a PIF. The pattern of uptake was diffuse and vertical, parallel to the sacroiliac joints. Therefore, clinicians should be careful with the interpretation of FDG uptake around the sacroiliac joints, and keep in mind false-positive lesions such as PIFs.     

18F]Fluorodeoxyglucose as a memory marker of transient myocardial ischaemia

BACKGROUND: Experimental data have shown that glucose utilization increases during acute myocardial ischaemia, and may persist for up to 24 h. Whether fluorodeoxyglucose (FDG) uptake can be imaged as a memory marker of ischaemia in humans is unknown. METHODS: Patients with mild-to-moderate ischaemia on exercise single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) underwent repeat exercise testing within 1-2 weeks. Positron emission tomography (PET) was performed after injection of FDG 60 min post-exercise. SPECT and PET images were assessed visually, aided by circumferential profile-based analysis modified for 'hot-spot' imaging. RESULTS: Twelve men with stress SPECT ischaemia (mean age, 69 years; nine with known coronary artery disease) were studied. The mean rate-pressure products for the first (SPECT) and second (FDG PET) exercise tests were similar (22,841+/-7321 vs. 22,680+/-7393 mmHg x bpm, P=NS). Overall, six of 12 patients studied had evidence of FDG uptake. The extent of ischaemia on SPECT was similar in FDG positive and FDG negative patients (summed difference score 10.6+/-6.9 vs. 8.0+/-1.6, P=NS). All patients with a positive FDG scan had uptake in either an ischaemic SPECT region or in a territory with known CAD by angiography. CONCLUSION: Regional myocardial uptake of FDG is enhanced even when injected 1 h post-exercise stress in a subset of patients with ischaemia on exercise SPECT MPI. The ability to image FDG uptake injected 1 h after an ischaemic episode suggests the potential utility of FDG as a memory marker of transient ischaemia.     

Characteristics of myocardial18F-fluorodeoxyglucose positron emission computed tomography in dilated cardiomyopathy and ischemic cardiomyopathy

Myocardial 18F-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has been used to assess myocardial ischemia and viability, but few studies have conducted on FDG-PET for dilated cardiomyopathy (DCM). We investigated myocardial FDG uptake in patients with DCM in comparison with ischemic cardiomyopathy (ICM). Twenty-four patients with heart failure were included in this study. Fourteen of them were diagnosed as DCM and the other 10 were ICM. All of them underwent myocardial FDG-PET at fasting and after glucose loading the same day. FDG uptake was quantified by the ratio of the counts at the heart to those at the liver (H/L ratio). Left ventricular (LV) function was measured by echocardiography. We classified FDG distribution patterns in the myocardium in the fasting state into 3 types (faint uptake, regional uptake and diffuse uptake). In DCM patients, 5 had faint uptake, 7 had regional uptake, and the other 2 had diffuse uptake. On the other hand, all ICM patient had regional uptake (p < 0.05). In DCM, there were no significant relationships between the patterns and LV functions. On the other hand, there were close correlation between the H/L ratio after glucose loading and the left ventricular ejection fraction (r = 0.680, p < 0.01). The changes in PET images caused by glucose loading were classified into 2 types (non-reversing and reversing patterns). DCM significantly showed a non-reversing pattern (86%, 12 of 14 patients) whereas ICM showed mainly a reversing pattern (70%, 7 of 10 patients; p < 0.05). In conclusion, myocardial FDG uptake after glucose loading may indicate a myocardial viable mass although FDG uptake at fasting was not evidently related to LV function. The change in the pattern of the FDG image from fasting to glucose loading may be useful in differentiating DCM from ICM.     

How to differentiate benign versus malignant cardiac and paracardiac 18F FDG uptake at oncologic PET/CT

Patients undergoing 2-[fluorine 18]fluoro-2-deoxy-d-glucose (FDG) whole-body oncologic positron emission tomography (PET)/computed tomography (CT) are studied while fasting. Cardiac FDG uptake in fasted patients has been widely reported as variable. It is important to understand the normal patterns of cardiac FDG activity that can be seen in oncologic FDG PET/CT studies. These include focal and regional patterns of increased FDG myocardial activity. Focal activity can be observed in papillary muscles, the atria, the base, and the distal anteroapical region of the left ventricle. Regional increased cardiac FDG activity may be diffuse or localized in the posterolateral wall or the base of the left ventricle. Abnormal patterns of cardiac FDG activity not related to malignancy include those associated with lipomatous hypertrophy of the interatrial septum, epicardial and pericardial fat, increased atrial activity associated with atrial fibrillation or a prominent crista terminalis, cardiac sarcoidosis, endocarditis, myocarditis, and pericarditis. Knowledge of these patterns of cardiac FDG activity is important to be able to recognize malignant disease involving the paracardiac spaces, myocardium, and pericardium. With a better understanding of the range of normal and abnormal patterns of cardiac FDG activity, important benign and malignant diseases involving the heart and pericardium can be recognized and diagnosed.     

Comparison of imaging with FDG PET/CT with other imaging modalities in myeloma

Objective To determine the usefulness of FDG PET/CT scanning in the management and staging of myeloma and to assess its strengths and limitations.Design FDG PET/CT scans and all other available imaging studies were reviewed retrospectively from 16 consecutive patients by two experienced musculoskeletal radiologists and two nuclear medicine physicians working in consensus.Patients The 16 patients had undergone a total of 19 FDG PET/CT scans. Radiographs were available in all cases, including 13 skeletal surveys; 25 CT scans (16 chest, three abdominal, four pelvic, one spine, one neck) and 22 MR imaging studies (17 spine, three pelvic, two extremity) also were reviewed. Patients’ records were examined for relevant clinical information. All focal areas of abnormal FDG uptake were correlated with the other imaging studies to determine clinical significance. FDG PET/CT scans also were reviewed to see if small lesions shown on the other imaging studies could be identified in retrospect.Results The 12 men and four women had an average age of 58 years (range 30–69 years). All 16 patients had an established diagnosis of multiple myeloma, with average duration of disease, from time of initial diagnosis to review, of 30 months (range 6 months to 11+ years). The FDG PET/CT scans revealed a total of 104 sites (90 in bone, 14 soft tissue) that were suspicious for neoplastic activity based on a standardized uptake value (SUV) greater than 2.5. Fifty-seven of these sites (55%) were new or previously undetected. The other imaging studies (X-ray, CT, MR) and clinical information confirmed the other 47 areas but also revealed 133 other small skeletal lesions. Six of these 133 additional lesions showed mild FDG uptake on re-review of the PET/CT scans. The FDG PET/CT findings led to management changes in 9/16 patients. MR imaging revealed five cases of diffuse bone involvement (four spine, one scapula) that were not evident by FDG PET/CT.Conclusion FDG PET/CT scans are useful for the management and staging of myeloma. However, if PET/CT were the sole imaging study done, it would miss many additional small lytic skeletal lesions and could miss diffuse spine involvement.     

Brown fat in breast cancer patients: analysis of serial 18F-FDG PET/CT scans

Purpose It has recently been suggested that FDG accumulation in the brown adipose tissue varies as a function of age, sex and outdoor temperature. The aim of this study was to assess changes in FDG uptake in brown fat in patients based on serial PET/CT scans and to compare our results with previous findings. Methods Early response to neoadjuvant chemotherapy in 33 female breast cancer patients was assessed by FDG PET. Five PET/CT scans were performed for each patient. PET/CT images were analysed retrospectively. PET scans were considered positive when diffuse, symmetrical, abnormal “USA” (uptake in supraclavicular area) fat was detected. Results A total of 163 PET images were analysed. Seventy-four PET scans (45%) revealed abnormal FDG uptake in the supraclavicular area. These foci were present on uncorrected and attenuation-corrected images. FDG uptake was identical on all five scans in only five patients. No significant relationship was found between abnormal FDG uptake and outdoor temperature, age or time interval between chemotherapy and PET. Abnormal FDG uptake in the neck seemed to predominantly occur in patients with a low body mass index (p<0.05). Most significant changes in the PET/CT scan results were observed during chemotherapy with docetaxel (p<0.05). When observed, bilateral uptake in the neck was more intense than background uptake (p<0.00001). Conclusion This study shows that FDG uptake in the neck varies as a function of time, that it is unrelated to age or outdoor temperature, and that bilateral uptake is generally intense.     

Relation of myocardial perfusion at rest and during pharmacologic stress to the PET patterns of tissue viability in patients with severe left ventricular dysfunction

Background. Stress perfusion imaging can assess effectively the amount of jeopardized myocardium, but its use for identifying underperfused but viable myocardium has yielded variable results. We evaluated the relation between measurements of myocardial perfusion at rest and during pharmacologic stress and the patterns of tissue viability as determined by positron emission tomographic (PET) imaging.Methods and Results. We studied 33 patients with coronary artery disease and left ventricular (LV) dysfunction (LV ejection fraction, 30% ± 8%). PET imaging was used to evaluate regional myocardial perfusion at rest and during pharmacologic stress with [¹³N]-ammonia as a flow tracer, and to delineate patterns of tissue viability (ie, perfusion-metabolism mismatch or match) using [¹⁸F]-deoxyglucose (FDG). We analyzed 429 myocardial regions, of which 229 were dysfunctional at rest. Of these, 30 had normal perfusion and 199 were hypoperfused. A severe resting defect (deficit>40% below normal) predicted lack of significant tissue viability; 31 of 35 regions (89%) had a PET match pattern denoting transmural fibrosis. Although regions with mild or moderate resting defects (deficit <40% below normal) showed evidence of metabolic activity, perfusion measurements alone failed to identify regions with PET mismatch (reflecting hibernating myocardium). Reversible stress defects were observed with slightly higher frequency in regions with a PET mismatch (10 of 37) than in those with a PET match (36 of 162) pattern of viability. A reversible stress defect was a specific (78%) marker, but was a relatively insensitive marker (27%) of viable myocardium as defined by the PET mismatch pattern.Conclusions. In patients with LV dysfunction, the severity of regional contractile abnormalities correlates with the severity of flow deficit at rest. Severe reductions in resting blood flow in these dysfunctional regions identify predominantly nonviable myocardium that is unlikely to have improved function after revascularization. Although dysfunctional myocardium with mild to moderate flow reductions contains variable amounts of viable tissue (as assessed by FDG uptake), flow measurements alone do not distinguish between regions with PET mismatch (potentially reversible dysfunction) and PET match (irreversible dysfunction). The presence of an irreversible defect on stress imaging is a relatively specific (78%) marker of PET match, whereas a reversible stress defect is a rather insensitive (27%) marker of viability, as defined by the PET mismatch pattern.     

Diffuse FDG shoulder uptake on PET is associated with clinical findings of osteoarthritis

OBJECTIVE: Our objective was to examine the degree and pattern of (18)F-FDG uptake within the shoulder as a potential marker of joint inflammation or injury. SUBJECTS AND METHODS: Twenty-four patients undergoing (18)F-FDG PET for clinical oncologic assessment completed questionnaires regarding history of shoulder disease, trauma, pain, and/or functional impairment. Thorough physical examination of the shoulder was performed. A clinical diagnosis of specific shoulder derangement or normal was established for each patient. PET scans were evaluated blindly by a nuclear medicine physician and a musculoskeletal radiologist qualitatively for location, distribution, and intensity of shoulder uptake. Standardized uptake values (SUV) were measured. RESULTS: Twenty-one patients had shoulder PET findings. Fourteen had clinical findings consistent with a specific diagnosis in the PET-positive shoulder. The remaining seven PET-positive patients were clinically normal. Three recognizable patterns of uptake were appreciable. Eight of 10 patients with diffuse uptake had findings of osteoarthritis (n = 7) or bursitis (n = 1). Two of four patients with focal greater tuberosity uptake had findings of rotator cuff injury. Two of four patients with focal glenoid uptake had findings of frozen shoulder. SUV showed a positive correlation with subject age (p < 0.01), but no association with clinical findings was identified. CONCLUSION: The pattern of FDG uptake within the shoulder may point to specific clinical entities. While focal uptake is less reliably related to clinical findings, diffuse uptake is associated with signs and symptoms of osteoarthritis or bursitis.     

Value and limitation of myocardial fluorodeoxyglucose single photon emission computed tomography using ultra-high energy collimators for assessing myocardial viability

Single photon emission computed tomography (SPECT) using ultra-high energy collimators permits wide clinical application of (18)F-fluorodeoxyglucose (FDG) imaging without the use of expensive positron emission tomography (PET) cameras. This study was designed to evaluate the value of FDG SPECT using ultra-high energy collimators in assessing myocardial viability compared with FDG PET on a regional basis. We prospectively studied 33 patients with ischaemic heart disease. The patients were injected with 555 MBq of FDG under a hyperinsulinaemic glucose clamp, and FDG PET was performed 40 min later. FDG SPECT using ultra-high energy collimators was performed immediately after FDG PET. The images of the left ventricular myocardium were divided into nine segments and the regional defect score was assessed visually using a four-point scale (0=normal to 3=defect). Regional FDG uptake (%uptake) was quantitatively analysed using polar maps. In 297 segments of all the 33 patients, agreement between the defect scores based on FDG SPECT images and those based on FDG PET images was 70%, and agreement within one rank was 96% (kappa value=0.52). The %uptake based on FDG SPECT images significantly correlated with that based on FDG PET images (r=0.77, P<0.01). However, the defect scores in the inferior wall based on FDG SPECT images were higher (1.41+/-1.14) than those based on FDG PET images (1.06+/-1.12, P<0.01). When the viable region is defined as %uptake > or =50% in FDG PET studies, the optimal cut-off level of %uptake based on FDG SPECT images was 60% in the anterior wall, apex, septum and lateral wall (accuracies, 97%, 93%, 96% and 99%, respectively), and 45% in the inferior wall (accuracy, 99%). It is concluded that FDG SPECT using ultra-high energy collimators can be used for the assessment of myocardial viability as accurately as FDG PET. However, a slight difference was observed in the defect scores mainly due to attenuation in the inferior wall. Therefore, a slightly different cut-off level for assessing myocardial viability should be applied to the inferior wall when using FDG SPECT.     

Diagnostics of “non-acute” vascular prosthesis infection using <Superscript>18</Superscript>F-FDG PET/CT: our experience with 96 prostheses

Introduction  Vascular prosthesis infection (VPI) is a life-threatening complication that occurs in 0.5–5% of prostheses. Low-grade infections in non-acute patients are a diagnostic challenge requiring a new method with good diagnostic accuracy. The aim of this work was to define the accuracy of ¹⁸F-FDG PET/CT in these settings and to identify essential parameters of the evaluation. Material and methods  PET/CT was performed prospectively in 76 consecutive patients with a total of 96 vascular prosthetic grafts in which infection was suspected. PET/CT scans were analysed in terms of the presence and intensity of focal and diffuse FDG uptake, the presence of an anastomotic pseudoaneurysm, the presence of an irregular boundary of infiltration, a combination of these, and the uptake ratio between the graft and blood background. The gold standard was based on operative/histopathological finding or a clinical follow up of >6 months. Results  Among the various assessed parameters only focal FDG uptake and an irregular graft boundary were significant predictors of VPI. Focal intense FDG uptake together with an irregular boundary of the lesion on CT scan predicted VPI with 97% probability, while smooth lesion boundaries and no focal FDG uptake predicted a probability of VPI of less than 5%. Even in lesions with nondiagnostic inhomogeneous focal FDG uptake (18/96) an irregular boundary effectively helped in decision-making with a probability of 28% (smooth) or 77% (irregular) for VPI. Conclusion  PET/CT gave reliable results with an accuracy >95% in 75% of prostheses. PET/CT can identify those prostheses (25% of prosthesis) for which its diagnostic accuracy is diminished to 70–75%. In our series PET/CT was an excellent diagnostic modality for suspected VPI.     

Stress perfusion/metabolism imaging: A pilot study for a potential new approach to the diagnosis of coronary disease in women

BACKGROUND: The diagnosis of coronary artery disease (CAD) in women continues to be a challenge. F-18 deoxyglucose (FDG) positron emission tomography (PET) has been used for detection of myocardial ischemia at rest. Little has been reported about FDG stress imaging. The aim of this pilot study was to assess stress FDG PET imaging for defining CAD in a group of women referred for chest pain. METHODS: Stress FDG imaging was performed in 19 women (mean age 59 +/- 10 years). All had abnormal stress testing before entering the study. FDG and 2-methoxy-2-methylpropyl isonitrile were injected at peak stress (treadmill n = 8, dipyridamole n = 11) followed by PET and single photon emission computed tomography image acquisitions. Myocardial ischemia was defined by regions that demonstrated both a defect on perfusion imaging and increased FDG uptake relative to uptake in normal perfusion zones. Defect/normal zone FDG ratios were also determined. Coronary angiography was performed on all patients. RESULTS: Average, or mean, body mass index was high at 29.2 +/- 5 kg/m2. Nine of 19 patients had significant CAD. Eight of 9 with CAD had FDG-defined ischemia. Nine of the 10 without CAD had negative FDG images (sensitivity 89%, specificity 90%). The average defect/normal zone FDG ratio was greater in patients with CAD than in those without (2.4 +/- 1.9 vs 0.9 +/- 0.4, P < .05). CONCLUSIONS: Regional FDG uptake in areas of perfusion defects with stress increased in this group with CAD. These pilot data suggest that stress FDG PET may be diagnostically helpful in obese female patients. This novel approach may complement current methods of CAD detection in women and warrants further study.     

Baastrup’s disease (kissing spine) demonstrated by FDG PET/CT

18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) is a widely used imaging modality in cancer patients. However, there are many potential non-neoplastic causes of FDG uptake. We report a case of FDG uptake between the spinous processes, secondary to Baastrup’s disease. Knowledge of this pattern of uptake is helpful in diagnosing Baastrup’s disease and avoiding false-positive diagnoses.     

Scalene muscle uptake: a potential pitfall in head and neck PET/CT

Purpose To describe increased 2-deoxy-2-[¹⁸F] fluoro-D-glucose (FDG) uptake in the scalene muscles in a large population of patients referred for evaluation with FDG positron emission tomography/computed tomography (PET/CT) imaging. Methods The study met criteria for institutional review board exemption. FDG PET/CT images from 410 patients (179 males; mean age 56.8 years, range 6-88) were retrospectively reviewed for the presence or absence of FDG uptake in the neck that corresponded to the scalene muscles on the concurrent CT scan. Medical records were reviewed and data including age, sex, smoking history, reason for referral, and history of obstructive airways disease, thoracotomy, and thoracic radiation were recorded and evaluated. Results One hundred and forty-seven of the 410 scans (36%) demonstrated increased FDG uptake on PET that corresponded to the scalene muscles on the CT scan. The uptake was most often bilateral, symmetrical, and linear (n = 117). Other patterns of scalene muscle uptake included unilateral and linear uptake (n = 27) and unilateral and focal uptake (n = 3). Scalene muscle uptake was more common in patients referred for evaluation of lung carcinomas compared to other types of tumors (52% vs. 32%, p = 0.05). Conclusion Linear FDG uptake in scalene muscles is a commonly seen pattern on PET/CT. This finding should be recognized as a distinct entity and not misinterpreted on transverse images as metastatic disease.     

Incidental colonic fluorodeoxyglucose uptake: correlation with colonoscopic and histopathologic findings

PURPOSE: To evaluate the pattern and degree of incidental colonic fluorodeoxyglucose (FDG) uptake in patients without colorectal carcinoma who underwent whole-body FDG positron emission tomography (PET) for other purposes and compare them with colonoscopic and/or histopathologic findings. MATERIALS AND METHODS: Cases of 27 patients without known history of colorectal carcinoma who were referred for evaluation with whole-body FDG PET and displayed incidental colonic uptake were reviewed retrospectively. Colonoscopy was performed in 10 patients; histopathologic analysis, in two; and both, in 15. The colonic FDG uptake patterns were nodular-focal, nodular-multifocal, segmental, and diffuse. The FDG uptake level was scored with a four-point scale in relation to hepatic uptake. Binomial distribution was used to calculate 95% CIs for the probability of finding an abnormality at histologic examination, as predicted by findings at FDG PET. RESULTS: Colonoscopic findings in eight patients with a diffuse uptake pattern were normal. Thirteen patients with nodular high FDG uptake had pathologic findings. Six (22%) of the 27 patients were not suspected of having a malignancy, and seven had benign neoplasms. With a 95% CI, nodular high FDG uptake implies at least a 79% chance that histopathologic findings may be abnormal. Colitis was seen in five of six patients with a segmental pattern of high FDG uptake. CONCLUSION: Colonoscopy is a reasonable next step for further diagnostic examination of patients who display nodular high FDG uptake in the colon. Diffuse FDG uptake often is associated with normal findings at colonoscopy, while segmental high uptake may imply inflammation.     

Diffuse and diffuse-plus-focal uptake in the thyroid gland identified by using FDG-PET: prevalence of thyroid cancer and Hashimoto's thyroiditis

Objective To investigate and evaluate the prevalence of incidental thyroid diffuse and diffuse-plus-focal fluorine-18 fluorodeoxyglucose (FDG) uptake in healthy subjects who underwent cancer screening on positron emission tomography (PET) scan, and also to evaluate the prevalence of thyroid cancer and Hashimoto's thyroiditis. Methods We carried out a retrospective review of 1626 subjects who underwent PET scanning at our institution. Diffuse uptake was defined as FDG uptake in the whole thyroid gland, whereas diffuse-plus-focal uptake was defined as a thyroid lesion with both diffuse uptake and focal FDG uptake. The maximum standardized uptake value of the thyroid lesions was recorded and reviewed. In each selected subject with positive thyroid FDG uptake, serum thyroid-stimulating hormone, thyroid hormone, and thyroid antibodies were measured. Fine needle aspiration cytology was performed on patients with a definite nodule using ultrasonography. Results Twenty-nine subjects (1.78%) were identified as having either diffuse FDG uptake (n = 25, 1.53%) or diffuse-plus-focal FDG uptake (n = 4, 0.24%). All subjects with diffuse FDG uptake were diagnosed as having Hashimoto's thyroiditis. In 1 of the 25 subjects with diffuse FDG uptake and two of the four with diffuse-plus-focal FDG uptake, histopathologic diagnosis showed papillary thyroid carcinoma associated with Hashimoto's thyroiditis. However, PET scan did not detect papillary carcinoma associated with Hashimoto's thyroiditis in one of the three subjects. Conclusions Our results suggest that although diffuse FDG uptake usually indicates Hashimoto's thyroiditis, the risk of thyroid cancer must be recognized in both diffuse FDG uptake and diffuse-plus-focal FDG uptake on PET scan.     

Significance of incidental fluorodeoxyglucose uptake in the parotid glands and its impact on patient management

BACKGROUND AND OBJECTIVES: Minimal-to-low grade fluorodeoxyglucose (FDG) uptake in the parotid glands is regarded as a normal variant in a whole-body survey with FDG-PET. Not frequently, however, a relatively intense or asymmetric FDG uptake is encountered in the parotid glands. The aim of this study was to determine the causes and characteristics of this 'FDG accumulation of uncertain significance' in the parotid glands in patients without any known or suspected pathologies at the time of whole-body FDG-PET. In addition, we also examined patients in whom there was no documented evidence of parotid pathology before FDG-PET scan and a suspicion of disease involvement was first raised in the reports in view of focal uptake in the FDG-PET images. MATERIALS AND METHODS: A total of 25 patients with 49 PET examinations [46 PET and three PET/computed tomography (CT) scans] were identified from the retrospective examination of PET reports and were analyzed in this study. Only those cases with no earlier history of disease involvement of parotid gland or known parotid pathology before FDG-PET were selected for this analysis. These patients were selected from a population of patients with a known malignancy elsewhere who underwent conventional whole-body FDG-PET or PET/CT for staging, disease viability assessment, or treatment monitoring purposes and had demonstrated varying patterns of FDG uptake (unilateral, bilateral, symmetric, or asymmetric) in the parotid glands. FDG uptake in the parotid glands was reported to be of uncertain significance in the majority of these patients and further correlation was suggested in the PET reports. In five patients with asymmetric and focally enhanced FDG uptake, a suspicion of disease involvement was raised in the reports. The results of appropriate correlative investigations with MRI, low-dose nonenhanced attenuation CT images (based on PET/CT scans), and histopathology (in cases in which focal lesions were revealed by the anatomic imaging modalities and biopsy was performed) carried out subsequent to the FDG-PET scans were reviewed for a definitive conclusion with regard to the significance of the FDG uptake in the parotid glands in these patients. In the absence of any focal pathology, clinical and follow-up FDG-PET data were reviewed for a logical conclusion, which were available in a majority of these patients. Standardized uptake values (maximum) were calculated by generating a manual region of interest over FDG activity. The pattern and the intensity of the FDG uptake were correlated with the final diagnosis. RESULTS: In six of the 25 patients with diffuse and symmetrical FDG uptake no clearcut pathology was demonstrated by clinical or radiological examinations. Five patients of this subgroup also demonstrated associated enhanced FDG activity in the submandibular salivary glands. Nineteen patients (76%) demonstrated asymmetric FDG uptake. Among these, focally enhanced uptake was observed in seven patients (28% of the total number of patients and 36.8% of the patients who demonstrated asymmetric FDG uptake in the parotids). Twelve patients (48% of total patients and 63.2% of the patients who demonstrated asymmetric FDG uptake) demonstrated asymmetric and diffuse FDG uptake pattern. No revelation of disease either by the MRI or follow-up clinical and FDG-PET examinations was observed in patients with asymmetric diffuse uptake. Five of the seven patients, who had asymmetric focal uptake in one of the parotids, were found to have focal lesions in either correlative MRI or low-dose nonenhanced CT. The final diagnosis based upon histopathology revealed primary parotid tumors (e.g., Warthin's tumor and pleomorphic adenoma, which presented as FDG-avid parotid incidentaloma) or metastatic disease involvement. CONCLUSION: Both the pattern and intensity of FDG uptake have important implications for differential diagnosis in the salivary glands in whole-body FDG-PET. A bilaterally symmetrical increased uptake is usually physiological. An asymmetrical uptake, especially when focal, would warrant further radiological and histopathological correlation to rule out disease involvement. At times, this can lead to the detection of an asymptomatic hitherto unknown etiology, which would have been otherwise interpreted as a metastatic disease in the background of an existing malignancy in these patients; this is noteworthy as it may have a bearing on the subsequent management of these patients.     

Assessment of the spatial pattern of colorectal tumour perfusion estimated at perfusion CT using two-dimensional fractal analysis

The aim was to evaluate the feasibility of fractal analysis for assessing the spatial pattern of colorectal tumour perfusion at dynamic contrast-enhanced CT (perfusion CT). Twenty patients with colorectal adenocarcinoma underwent a 65-s perfusion CT study from which a perfusion parametric map was generated using validated commercial software. The tumour was identified by an experienced radiologist, segmented via thresholding and fractal analysis applied using in-house software: fractal dimension, abundance and lacunarity were assessed for the entire outlined tumour and for selected representative areas within the tumour of low and high perfusion. Comparison was made with ten patients with normal colons, processed in a similar manner, using two-way mixed analysis of variance with statistical significance at the 5% level. Fractal values were higher in cancer than normal colon (p ≤ 0.001): mean (SD) 1.71 (0.07) versus 1.61 (0.07) for fractal dimension and 7.82 (0.62) and 6.89 (0.47) for fractal abundance. Fractal values were lower in ‘high’ than ‘low’ perfusion areas. Lacunarity curves were shifted to the right for cancer compared with normal colon. In conclusion, colorectal cancer mapped by perfusion CT demonstrates fractal properties. Fractal analysis is feasible, potentially providing a quantitative measure of the spatial pattern of tumour perfusion.     

Pulmonary drug toxicity: FDG-PET findings in patients with lymphoma

Objective The objective of this study was to evaluate the prevalence and positron emission tomography (PET) imaging features of pulmonary drug toxicity in patients with lymphoma during or just following chemotherapy. Methods A total of 677 PET scans on 460 patients with lymphoma (351 non-Hodgkin’s lymphoma, 92 Hodgkin’s disease, and 17 both Hodgkin’s and non-Hodgkin’s lymphoma) were performed for the evaluation of chemotherapy response. In 51 patients, abnormal accumulation on both sides of the chest was reported. A review of medical records, ¹⁸fluorodeoxyglucose (¹⁸FDG)-PET scans, and chest computed tomography (CT) was performed, and cases with probable drug toxicity were identified. Inclusion criteria of probable drug toxicity were abnormal but symmetrical FDG accumulation in both lungs seen during or just following the completion of chemotherapy, the abnormal accumulation or corresponding abnormal CT findings resolved on sub sequent studies, exclusion of clinical diagnosis of pneumonia, radiation pneumonitis, or lymphoma involvement. Results In 10 patients (six men and four women, average age 47.3), 2.2% of cases, probable drug toxicity was identified. In all 10 cases, diffuse and subpleural-dominant FDG accumulation was seen on FDG-PET scans, and scattered or diffuse ground-glass opacities were observed on chest CT. Four patients reported symptoms, and six patients did not report any symptoms. Conclusions Diffuse and peripheral-dominant FDG accumulation in the lung, which may represent pulmonary drug toxicity, was not uncommon in patients with lymphoma who underwent chemotherapy. FDG-PET scan might be able to detect pulmonary drug toxicity in asymptomatic patients.     

Non-Specific Disease Mimicking Malignancy: Two Cases of FDG Uptake in the Extremities

FDG PET is an imaging technique used to assess regional differences in glucose metabolism. A variety of diseases, including malignancy, can show abnormal FDG uptake in bone marrow. PET/CT demonstrated non-specific uptake in the extremities of two patients with fever of unknown origin (FUO). Both patients showed focal and symmetric FDG uptake in the bone marrow of the arms and legs. Although the results of these cases were not diagnostic, the unique uptake pattern of PET/CT should be considered a non-specific reactive change as well as malignancy or other possibilities in the initial differential diagnosis.     

Clinical utility of FDG PET/CT in acute complicated pyelonephritis—results from an observational study

Background

Acute complicated pyelonephritis (ACP) is an upper urinary tract infection associated with coexisting urinary tract abnormalities or medical conditions that could predispose to serious outcomes or treatment failures. Although CT and magnetic resonance imaging (MRI) are frequently used in patients with ACP, the clinical value of ¹⁸F–fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) has not been systematically investigated. This single-center retrospective study was designed to evaluate the potential usefulness of FDG PET/CT in patients with ACP.

Methods

Thirty-one adult patients with ACP who underwent FDG PET/CT were examined. FDG PET/CT imaging characteristics, including tracer uptake patterns, kidney volumes, and extrarenal imaging findings, were reviewed in combination with clinical data and conventional imaging results.

Results

Of the 31 patients, 19 (61%) showed focal FDG uptake. The remaining 12 study participants showed a diffuse FDG uptake pattern. After volumetric approximation, the affected kidneys were found to be significantly enlarged. Patients who showed a focal uptake pattern had a higher frequency of abscess formation requiring drainage. ACP patients showing diffuse tracer uptake patterns had a more benign clinical course. Seven patients had suspected extrarenal coinfections, and FDG PET/CT successfully confirmed the clinical suspicion in five cases. FDG PET/CT was as sensitive as CT in identifying the six patients (19%) who developed abscesses. Notably, FDG PET/CT findings caused a modification to the initial antibiotic regimen in nine patients (29%).

Conclusions

FDG PET/CT may be clinically useful in the assessment of patients with ACP who have a progressive disease course.