Pet Positive Benign Pulmonary Nodules: An Unusual Presentation of Lipoid Pneumonia

Abstract

INTRODUCTION: Lipoid Pneumonia (LP) is a parenchymal disease usually related to aspiration or inhalation of fat containing substances that leads to an acute reaction driven by lung macrophages. The etiology can on occasion be endogenous, but overall is a very rare disease that has various radiologic presentations which may even mimic lung carcinoma, making its diagnosis elusive CASE PRESENTATION: A 57 year old woman was referred to us due to the incidental finding on Chest CT of left 1.5 cm hilar adenopathy and 6 mm right middle lobe and 4 mm right upper lobe nodules. Additionally, a 2.2 cm left upper breast density was seen. She was a former smoker (22 PY) who quit 20 years ago, with a history of breast cancer (s/p lumpectomy and XRT 5 years earlier, with benign left axillary dissection) and hyperlipidemia. She was asymptomatic. Denied exposure to coal, silica, and asbestos and worked as a Certified Nurse Assistant.A PET-CT Scan was ordered and this interestingly revealed a left lower lobe (LLL) medial pleural based 12 mm nodule and several peripheral ill defined LLL subpleural densities, all these with FDG uptake of 4.8 to 5.4 respectively. Additionally there was mediastinal uptake (SUV 5.2) in the area of station 7 (though no clear adenopathy was seen on the CT images) and 11L with the scan images showing a 1 cm node. No uptake was seen elsewhere. Subsequently, endobronchial ultrasound (EBUS) guided aspirate biopsies of station 7 and 11L were obtained, demonstrating no malignancy and being consistent with benign lymph node sampling. Therefore a CT guided biopsy of the LLL nodule was performed revealing fragments of alveolated lung parenchyma along with the presence of giant cell reaction to cholesterol clefts. Lipoid pneumonia was diagnosed. A follow-up Chest CT 3 months later showed resolution of the ill defined LLL densities and unchanged LLL nodule and station 7 and 11L adenopathy.DISCUSSION: LP is rare and radiologically may mimic malignancy. It has been reported in all ages and is subcategorized into endogenous and exogenous. Exogenous lipoid pneumonia has been described with acute inhalation (fire eaters) however being more often associated with chronic exposure to animal fat, mineral oil, or vegetable oil inhalation. It is postulated that fatty substances can avoid the trigger of cough reflex and impair the muco-ciliary transport system becoming difficult to expectorate. In the alveoli they are engulfed by macrophages which are unable to metabolize it and when released back into the alveoli, triggers a giant cell reaction. Radiological manifestations are not specific and include reticular and nodular patterns, ground glass opacification, intralobular septal thickening, spiculated mass and fibrosis. These lesions often have increased uptake on FDG PET scan.