IntroductionFluorine-18 fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) is used for non-invasive staging and restaging of solid malignant tumors. PET-CT based criteria have been developed to evaluate the response to targeted therapy. These include the European Organization for Research and Treatment of Cancer (EORTC) and the PET Response Criteria in Solid Tumors (PERCIST). The aim of this study was to determine the agreement between EORTC and PERCIST criteria for treatment response evaluation in patients with solid malignant tumors.Materials and methodsThis was a retrospective study conducted from February 2017 till July 2017. Electronic medical records of patients diagnosed with solid malignant tumors were searched. Experienced radiologists evaluated the PET-CT images based on EORTC and PERCIST criteria. The Kappa (κ) test was used for evaluation of agreement between treatment response according to EORTC and PERCIST criteria.ResultsOut of 54 patients, 41 (75.9%) were male and 13 (24.1%) were female with a mean age of 57.09 ± 10.65 years. According to EORTC criteria, complete metabolic response (CMR) was seen in five (9.3%) of patients, partial metabolic response (PMR) was seen in 36 (66.7%) of patients, progressive metabolic disease (PMD) was seen in nine (16.7%) of patients and stable metabolic disease (SMD) was seen in four (7.4%) of patients. According to PERCIST criteria, CMR was seen in five (9.3%) of patients, PMR was seen in 33 (61.1%) of patients, PMD was seen in nine (16.7%) of patients and SMD was seen in seven (13.0%) of patients. EORTC and PERCIST agreed on 43 (79.6%) of the patients with κ-coefficient of 0.62 indicating good agreement (p-value of <0.001).ConclusionEORTC and PERCIST criteria have a good agreement in evaluating treatment response in solid malignant tumors. Therefore, adoption of EORTC or PERCIST in PET-CT reporting can standardize the evaluation of oncological treatment results.

Although Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) is routinely used in oncological imaging, the F-18 fluorodeoxyglucose (18F-FDG) avidity is not tumor-specific. Numerous benign infective and inflammatory processes may also show increased radiotracer activity. Similarly, abnormal 18F-FDG uptake in an inflamed appendix can pose a diagnostic challenge for the interpreter of oncologic 18F-FDG PET/CT. We present the case of an 18-year-old female with classic Hodgkin's lymphoma who had 18F-FDG PET/CT while undergoing chemoradiotherapy. The scan demonstrated a complete metabolic response to treatment. However, there was increased 18F-FDG uptake in the right iliac region, projecting over the appendix, which, if interpreted as a lymphomatous involvement, would have upscaled the treatment response to progressive disease. The patient was called for additional workup, which included an ultrasound abdomen.The scan revealed classic features of acute appendicitis. However, there was no appendicolith or luminal obstruction. Upon additional questioning, the patient mentioned mild intermittent abdominal pain and anorexia eased by pain relievers for the preceding few days. On deep palpation of her abdomen, there was rebound tenderness in the right iliac region. According to the Alvarado score, it was graded 7 points suggesting probable/likely appendicitis. After collective evaluation of the clinical, laboratory, and imaging findings, the appendicular 18F-FDG uptake was deemed secondary to uncomplicated acute appendicitis rather than a lymphomatous lesion. Our patient refused surgery as she did not have severe abdominal pain. She was hemodynamically stable without signs of luminal obstruction. She was non-operatively managed with broad-spectrum antibiotics for six days. The results of the follow-up complete blood counts and ultrasound examination were negative. Our patient was symptom-free and recovering normally at a twoweek follow-up appointment.We present a follow-up case of classic Hodgkin's lymphoma with incidental uptake in the appendix, which resembled submucosal lymphomatous cell infiltration of the appendix. Careful scrutiny, clinical correlation, physical examination, blood tests, and additional imaging offered helpful insight and led to the correct, benign diagnosis of the 18F-FDG avid appendix.

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