ALL THAT PET POSITIVE IS NOT CANCER

Abstract

TOPIC: Procedures TYPE: Fellow Case Reports INTRODUCTION: PET (Positron emission tomography)/CT (Computed tomography) is a common modality used to diagnose and stage various malignancies. Radiotracer FDG (Fluoro18-deoxyglucose) is not cancer-specific and false-positive results may be observed in a wide variety of non-malignant conditions. Here we describe a patient with FDG avid left lower lobe endobronchial mass. CASE PRESENTATION: 75 years old female with a medical history significant for type 2 diabetes mellitus, seizure disorder was referred to pulmonology clinic with shortness of breath, intermittent wheezing, and non-productive cough for 2 months. She denied chest pain, orthopnea, fever, chills, weight or appetite changes, night sweats. The patient is a former smoker with less than 20 pack-year, quit two decades ago. On physical exam, the patient was saturating 92% in room air. BMI was 44.99 kg/m2. Lung examination showed reduced breath sounds at the left lung base. The rest of the exam was unremarkable. The pulmonary function test was normal. Outpatient evaluations were unremarkable. Chest X-ray showed left lower lobe infiltrates. CT chest showed left lower lobe consolidation vs atelectasis of left lung base followed with PET/CT which revealed increased FDG uptake in left lower lobe intraluminal density with SUV 6.5 concerning for malignancy with endobronchial involvement vs inflammatory process. Diagnostic bronchoscopy showed left lower lobe bronchus with significant mucosal hyperemia and edema with yellowish-white foreign body (FB) which was successfully retrieved with endobronchial biopsy forceps and noted to a piece of corn. The patient's symptoms resolved. DISCUSSION: The reported false positive rate of PET/CT was 13% and attributed to FDG uptake by inflammatory cells at the sites of inflammation or infection. Most common FDG avid non-infectious inflammatory etiologies include sarcoidosis, atherosclerosis, pneumoconiosis, and focal foreign body-related inflammation. FB aspiration in the tracheobronchial tree is rare in adults and usually presents with subtle respiratory symptoms with paucity in imaging. Risk factors include loss of consciousness from trauma, drug, seizure disorder or alcohol intoxication, dysphagia related to age-related slowing, stroke, dementia, or Parkinson's disease. In our case, false positives artifacts were related to a focal foreign body (FB) related inflammation with an elevated risk of aspiration related to a seizure disorder, and advanced age. Removal of FB from the tracheobronchial tree may be achieved with flexible bronchoscopy with biopsy forceps or retrieval basket. Rigid bronchoscopy may be needed if flexible bronchoscopy was unsuccessful. CONCLUSIONS: It is essential to understand false positive results while interpreting PET/CT results. FB aspiration in adults is rare and high clinical suspicion is necessary for the diagnosis. Removal of FB can usually be accomplished with bronchoscopy. REFERENCE #1: Common causes of False-positive F18 FDG PET/CT scans in oncology- Kevin R Carter, Eduard Kotlyarov; Vol,50, special number: pp.29-35, September 2007 Brazilian Archives of Biology and Technology- an International Journal. REFERENCE #2: Non-asphyxiating tracheobronchial foreign bodies in adults- Lan RS, Eur Respir J. 1994;7(3): 510 REFERENCE #3: Tracheobronchial foreign bodies in adults- Limper AH, Prakash UB, Ann Intern Med. 1990; 112(8):604 DISCLOSURES: No relevant relationships by Mansur Assaad, source=Web Response No relevant relationships by Rajamurugan Meenakshisundaram, source=Web Response No relevant relationships by FARAZ Siddiqui, source=Web Response