18F-FDG uptake in the normal appendix in adults: PET/CT evaluation

Assessing the utility of FDG PET/CT study in diagnosis of early acute appendicitis

Acute appendicitis is a common surgical emergency that can be challenging to diagnose due to its varied clinical presentations. Standard imaging methods include ultrasonography, computed tomography (CT), and Magnetic resonance imaging (MRI), but fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18 F-FDG PET/CT), typically used for oncology, can incidentally detect appendicitis through increased radiotracer uptake associated with inflammation. The paper discusses two cases where acute appendicitis was identified during PET/CT scans conducted for cancer evaluations. In cancer patients, diagnosing appendicitis is difficult due to overlapping symptoms from chemotherapy, metastasis, or radiation effects. Clinicians and radiologists must remain vigilant for incidental appendicitis findings in PET/CT scans, as early diagnosis can prevent complications despite its rarity in oncology imaging.

Rare Presentation of Late Complications After Undiagnosed Perforated Appendicitis Mimicking Recurrent Endometrial Carcinoma on 18F-FDG PET/CT

ABSTRACT

Acute appendicitis is one of the most common causes of acute abdominal pain. Undiagnosed or untreated appendicitis can lead to serious complications. The most frequent complication of acute appendicitis is perforation with subsequent formation of a localized periappendiceal abscess or diffuse bacterial peritonitis. Late occurring complications following undiagnosed appendix perforation can pose a diagnostic challenge due to uncharacteristic clinical and imaging presentation. Herein, we describe late findings of undiagnosed perforated appendicitis that on 18F-FDG PET/CT mimicked recurrent endometrial carcinoma disease in a 67-year-old woman.

Incidental [18F]PSMA-1007 Appendiceal Uptake Mimicking Nodal Disease

ABSTRACT

When interpreting an [18F]prostate specific membrane antigen (PSMA)-1007 PET/CT, it is important to understand the normal biodistribution of the tracer. A 73-year-old man with prostate cancer underwent [18F]PSMA-1007 PET/CT for biochemical recurrence. There was no abnormal uptake in the prostatectomy bed, but PSMA-avid pelvic nodal disease was found. Incidental intense focal uptake was also noted corresponding to the tip of the appendix, which was concluded to be physiological. This is an example of an uncommon site of physiological uptake of [18F]PSMA-1007 in the appendix.

Variants and Pitfalls in PET/CT Imaging of Gastrointestinal Cancers

In the past two decades, PET/CT has become an essential modality in oncology increasingly used in the management of gastrointestinal (GI) cancers. Most PET/CT tracers used in clinical practice show some degree of GI uptake. This uptake is quite variable and knowledge of common patterns of biodistribution of various radiotracers is helpful in clinical practice. 18F-Fluoro-Deoxy-Glucose (FDG) is the most commonly used radiotracer and has quite a variable uptake within the bowel. 68Ga-Prostate specific membrane antigen (PSMA) shows intense uptake within the proximal small bowel loops. 11C-methyl-L-methionine (MET) shows high accumulation within the bowels, which makes it difficult to assess bowel or pelvic diseases. One must also be aware of technical artifacts causing difficulties in interpretations, such as high attenuation oral contrast material within the bowel lumen or misregistration artifact due to patient movements. It is imperative to know the common variants and benign diseases that can mimic malignant pathologies. Intense FDG uptake within the esophagus and stomach may be a normal variant or may be associated with benign conditions such as esophagitis, reflux disease, or gastritis. Metformin can cause diffuse intense uptake throughout the bowel loops. Intense physiologic uptake can also be seen within the anal canal. Segmental bowel uptake can be seen in inflammatory bowel disease, radiation, or medication induced enteritis/colitis or infection. Diagnosis of appendicitis or diverticular disease requires CT correlation, as normal appendix or diverticulum can show intense uptake. Certain malignant pathologies are known to have only low FDG uptake, such as early-stage esophageal adenocarcinoma, mucinous tumors, indolent lymphomas, and multicystic mesotheliomas. Response assessment, particularly in the neoadjuvant setting, can be limited by post-treatment inflammatory changes. Post-operative complications such as abscess or fistula formation can also show intense uptake and may obscure underlying malignant pathology. In the absence of clinical suspicion or rising tumor marker, the role of FDG PET/CT in routine surveillance of patients with GI malignancy is not clear.