Focal FDG uptake in a pancreatic lipoma mimicking malignancy

Positron emission tomography (PET) using the glucose analog 18-F-fluoro-2-deoxy-D-glucose (FDG) is commonly obtained to stage patients with cancer. Benign lesions can be a source of false-positive PET examinations, leading to incorrect staging and treatment of tumors. Computed tomography can aid in distinguishing between certain benign and malignant lesions. The authors report a case of a pancreatic lipoma producing a false-positive PET examination.     

Pulmonary FDG uptake without a CT counterpart - a pitfall in interpreting PET/CT images

Abnormal pulmonary 18F-FDG foci may occur with benign lesions like pneumonia but seldomly without any pathological CT findings. We report the case of a focal pulmonary 18F-FDG uptake without CT correlate in an initial staging examination of a patient with squamous cell carcinoma of the base of the tongue. A follow-up study did not show any suspicious lesion in this area, but pneumonia with 18F-FDG uptake in another region of the lung. 18F-FDG foci without pathological CT are a rare finding and have been associated with emboli. In the literature two main mechanisms underlying focal 18F-FDG uptake in pulmonary embolism are mentioned: an inflammatory reaction of a pre-existing vascular thrombus and an iatrogenic microembolism caused during injection. In our case the 18F-FDG accumulation was assessed as an iatrogenic pulmonary microembolism.     

Focal F-18 FDG uptake mimicking malignant gastric localizations disappearing after water ingestion on PET/CT images

Diffuse, increased gastric wall F-18 FDG uptake is widely observed during PET/CT examinations, frequently unrelated to malignant findings, but simply caused by inflammatory disease, physiological emptying, or visceral thickening. Hence, elevated F-18 FDG gastric uptake can lead to equivocal misinterpretation, especially in patients with known gastric malignant disease, at posttherapy reevaluation. Gastric wall contraction can increase F-18 FDG uptake, especially for a remnant stomach, increasing the percentage of false-positive results with a direct impact on therapeutic management. One field PET/CT acquisition centered on the hypochondrial regions a few minutes after water ingestion should be performed routinely if standard images are doubtful (increased tracer uptake and visceral thickening) to differentiate benign from malignant uptake.     

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.     

18FDG uptake in brown fat: potential for false positives

CONTEXT: (18)FDG is used widely to enhance PET and PET-CT images. However, this radiotracer tends to be taken up by brown fat, which can lead to false-positive diagnoses. Purpose To determine which patients, areas of the body and circumstances are more likely to be associated with false-positive diagnoses due to (18)FDG uptake in brown fat. METHOD: A review of the literature was conducted on factors that contribute to false-positive diagnoses caused by (18)FDG uptake in brown fat. RESULTS: Brown fat commonly is found in women and children and can be located in the supraclavicular, mediastinal, paravertebral and perirenal areas of the body. Research has shown that these areas can be sources of a false-positive diagnosis because of (18)FDG uptake. Studies also have indicated that cold climate affects the uptake of (18)FDG, contributing to false-positive results on PET-CT examinations. CONCLUSIONS: This literature review should stimulate continued research into and awareness of the potential for false-positive PET findings in women and children during the winter months and in cold climates. This information is especially applicable to young female patients undergoing PET or PET-CT.     

FDG uptake in abdominal mesh implant on FDG PET/CT

A 50-year-old man with peritoneal angiosarcoma underwent total tumor excision along with removal of the total right rectus and medial part of the left rectus muscles 1 year earlier. F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) was performed for suspected recurrence. In the anterior abdominal wall extensive subcutaneous FDG uptake showing linear hypermetabolic zone on PET slices was noted. The patient had a history of a dual mesh implant, which consists of polypropylene and polyvinylidene fluoride for the reinforcement of the abdominal wall during the operation. PET/CT fusion image demonstrated that the finding was due to the dual mesh implant in the anterior abdominal wall most likely representing a foreign body reaction.     

Atypical sarcoid reaction mimicking recurrence on F-18 FDG PET/CT in a patient with breast malignancy

Malignancy may lead to sarcoidosis, which is referred to as sarcoid reaction. This reaction is believed to be a host immune response to the release of soluble antigens from cancer cells. Studies have shown strong 2′-deoxy-2′-[F-18]fluoro-D-glucose (F-18 FDG) uptake in sarcoid reaction and in true sarcoidosis. Therefore, in patients with malignancy, sarcoid reactions can mimic metastasis or recurrence on F-18 FDG positron emission tomography/computed tomography (PET/CT). Herein, we report the case of a 58-year-old woman with a history of left breast cancer whose FDG PET/CT evaluated at 3 months after adjuvant chemotherapy presented hypermetabolic lymphadenopathy in the right supraclavicular and right mediastinal areas. We interpreted these as metastases because the involved lymph nodes were intensely hypermetabolic and appeared newly. Pathologic evaluation of the excised lymph node revealed noncaseating chronic granulomas without malignant cells, indicating a sarcoid reaction. After appropriate steroid therapy, both the size and metabolic activity of the lymphadenopathy substantially decreased. Most sarcoid reactions present as bilateral hilar and peribronchial lymphadenopathies. Our patient presents an atypical example that a sarcoid reaction can also present in a unilateral pattern, making its diagnosis challenging. When interpreting FDG PET/CT images, considering that the sarcoid reaction pattern can vary is crucial.     

Focal tracer uptake: a potential artifact in contrast-enhanced dual-modality PET/CT scans.

This study was performed to evaluate a possible artifact related to the administration of intravascular contrast agent in dual-modality PET/CT imaging. METHODS: Thirty oncology patients underwent whole-body PET/CT. CT images, which were collected in the presence of intravenous and oral iodinated contrast agent, were used for PET attenuation correction. PET images were assessed for the artifact, defined as a region of high count rate on attenuation-corrected images in accurate coregistration with a contrast-enhanced blood vessel. Intravascular enhancement of thoracic veins was quantified by application of regions of interest, and quantities in patients with the artifact (group 1) and without the artifact (group 2) were correlated. Body surface area was calculated for all patients. RESULTS: The contrast-induced PET artifact was present in 4 (13%) of 30 patients. Mean density differences in intravascular enhancement were highly significant (P < 0.001) in a comparison of group 1 (2,262 +/- 304 Hounsfield units [HU]) and group 2 (1,058 +/- 209 HU). Body surface area was significantly lower (P = 0.035) in the patients of group 1 (1.67 +/- 0.11 m(2)) than in the patients of group 2 (2.01 +/- 0.18 m(2)). CONCLUSION: Contrast-enhanced dual-modality PET/CT examinations may result in a PET artifact that is due to the transient bolus passage of undiluted intravenous contrast agent.     

Tracer uptake in mediastinal and paraaortal thoracic lymph nodes as a potential pitfall in image interpretation of PSMA ligand PET/CT

Purpose

Since the introduction of ⁶⁸Ga-PSMA-11 PET/CT for imaging prostate cancer (PC) we have frequently observed mediastinal lymph nodes (LN) showing tracer uptake despite being classified as benign. The aim of this evaluation was to further analyze such LN.

Methods

Two patient groups with biphasic ⁶⁸Ga-PSMA-11 PET/CT at 1 h and 3 h p.i. were included in this retrospective evaluation. Group A (n?=?38) included patients without LN metastases, and group B (n?=?43) patients with LN metastases of PC. SUV of mediastinal/paraaortal LN of group A (n?=?100) were compared to SUV of LN metastases of group B (n?=?91). Additionally, 22 randomly selected mediastinal and paraaortal LN of patients without PC were immunohistochemically (IHC) analyzed for PSMA expression.

Results

In group A, 7/38 patients (18.4%) presented with at least one PSMA-positive mediastinal LN at 1 h p.i. and 3/38 (7.9%) positive LN at 3 h p.i. with a SUVmax of 2.3?±?0.7 at 1 h p.i. (2.0?±?0.7 at 3 h p.i.). A total of 11 PSMA-positive mediastinal/paraaortal LN were detected in nine patients considering both imaging timing points. SUVmax of LN-metastases was 12.5?±?13.2 at 1 h p.i. (15.8?±?17.0 at 3 h p.i.). SUVmax increased clearly (> 10%) between 1 h and 3 h p.i. in 76.9% of the LN metastases, and decreased significantly in 72.7% of the mediastinal/paraaortal LN. By IHC, PSMA-expression was observed in intranodal vascular endothelia of all investigated LN groups and to differing degrees within germinal centers of 15/22 of them (68.1%). Expression was stronger in mediastinal nodes (p?=?0.038) and when follicular hyperplasia was present (p?=?0.050).

Conclusion

PSMA-positive mediastinal/paraaortal benign LN were visible in a notable proportion of patients. PSMA-positivity on the histopathological level was associated with the activation state of the LN. However, in contrast to LN metastases of PC, they presented with significantly lower uptake, which, in addition, usually decreased over time.

     

False-positive lesions mimicking breast cancer on FDG PET and PET/CT

OBJECTIVE: Incidental (18)F-FDG-avid breast lesions are commonly encountered in patients with cancer who undergo staging PET/CT. This pictorial essay discusses breast lesions that show increased FDG activity, mimicking breast cancer, with biopsy-confirmed benign diagnosis. CONCLUSION: Acute and chronic inflammation, physiologic lactation, and benign breast masses, including silicone granuloma, fat necrosis, fibroadenoma, and postsurgical changes, may show increased FDG uptake on PET/CT. These conditions can often be differentiated from malignancy by correlative imaging, including mammography, sonography, or MRI.