PET scan findings can be false positive

Abstract

Positron emission tomography-computed tomography (PET-CT) scans with [18F]-fluorodeoxyglucose (FDG) and PET-magnetic resonance imaging (MRI) have become standard practice in staging and restaging of colorectal cancer patients by providing important information about the primary cancer as well as metastases. The PET portion of this imaging modality relies on the accumulation of radioactive glucose analog, FDG. In cancer cells, there is an overproduction of glucose transporters and, as a result, increased FDG uptake. However, not all PET-positive lesions are cancer, and in many instances, PET findings can be false positive.A few points need to be considered before understanding FDG. First, not all cancer cells use the same amount of glucose: some use more and some use less. Cancer cells with a faster metabolic rate such as colorectal adenocarcinoma are very FDG avid, whereas others such as mucinous cancers consume less glucose and therefore are less FDG avid. Inflammatory cells also have increased metabolic rates and, as a result, are FDG avid.Many of us have had patients or know of patients who were treated by the medical oncologist for stage IV cancer only to find out what was assumed to be a metastatic lesion was benign on pathology. Other patients have undergone multiple biopsies of supposed metastatic mesenteric lymph nodes that subsequently turned out to be fat necrosis or a granulomatous reaction. FDG-positive lesions often mean cancer, but not always. A variety of lesions have increased FDG radiotracer including infection, inflammation, autoimmune processes, sarcoidosis, and benign tumors. If such conditions are not identified accurately and in a timely manner, misdiagnosis can lead to inadequate therapies.Within the lower gastrointestinal tract, physiological FDG uptake can be highly variable and may range from mild to intense with a focal, diffuse, or segmental distribution. To add to the confusion, swallowed secretions, lymphoid tissue uptake, microbial uptake, infection, and benign tumors show increased FDG uptake. For example, incidental focal FDG uptake in the colon or rectum has only a 47 % probability of showing an underlying adenoma or malignant lesion on colonoscopy [1].It is well documented that surgical staples or suture lines following bowel resection can cause inflammatory or granulomatous changes with scar tissue formation with increased FDG uptake [2]. Often the only way to differentiate between benign and malignant pathology in this setting is by colonoscopy with biopsy. Chemotherapy and surgery itself can produce reactive lymphadenopathy. Radiation therapy can produce an intense inflammatory response that often develops months after treatment with reactive lymphadenopathy, peritoneal changes, and mass development. These changes can appear similar to cancer with increased FDG uptake that can last years after the cessation of therapy.Imaging with a complex technology as with PET-CT or PET-MRI can create a multitude of artifacts confounding diagnosis. PET-CT and PET-MRI use an attenuation-ba...

Survival time prediction in patients with high-grade serous ovarian cancer based on 18F-FDG PET/CT- derived inter-tumor heterogeneity metrics

“…It is difficult to distinguish metastatic malignant lesions from inflammatory sites using 18 F-FDG PET/CT images [ 49 ], especially for inexperienced readers, and relevant patient history and symptoms, knowledge of the typical pattern of metastases for the malignancy under investigation, corresponding CT images, and the help of clinical doctors may guide the interpretation of 18 F-FDG uptake [ 50 ]. Furthermore, this study used a 9-zone abdominal location method to locate metastatic sites, which is relatively simple and user-friendly, particularly for novices.…”

Unexpected coccidioidomycosis presenting as lung nodules with presumptive diagnosis of malignancy

“…An FDG PET scan is commonly used to detect metabolically active malignant lesions and may be used to more accurately stage malignant diseases and to monitor the therapy response of malignant diseases. However, although it is especially helpful in detecting metastatic malignancy, FDG‐positive lesions can also be seen in nonmalignant conditions including infections such as coccidioidomycosis, 4 inflammations, autoimmune disorders, sarcoidosis, and benign tumors 5 . If these conditions are not identified clinically and/or by tissue biopsies, misdiagnosis can lead to inappropriate therapies.…”

“…However, although it is especially helpful in detecting metastatic malignancy, FDG‐positive lesions can also be seen in nonmalignant conditions including infections such as coccidioidomycosis, 4 inflammations, autoimmune disorders, sarcoidosis, and benign tumors. 5 If these conditions are not identified clinically and/or by tissue biopsies, misdiagnosis can lead to inappropriate therapies. Our case describes an FDG‐positive lung nodule in a patient with a history of both diffuse large B‐cell lymphoma and hepatocellular carcinoma.…”

A combination of the geroprotectors trametinib and rapamycin is more effective than either drug alone

“…Brain inflammation increases the requirements for glucose and results in greater 18F-FDG uptake [34] [35]. Microglia are the primary immune cells of the brain and their increased activity has been associated with age-related brain inflammation accompanied by synapse loss and late-onset neurodegeneration [36] [37].…”