False positive 18FDG PET-CT results due to exogenous lipoid pneumonia secondary to oily drug inhalation

Abstract

Rationale:Exogenous lipoid pneumonia is a rare condition due to abnormal presence of oily substances in the lungs. It is a rarely known cause for false positive 18FDG PET-CT results and can sometimes lead to invasive investigations. Searching and finding the source of the oily substance is one of the keys to the diagnosis. Inhalation of oily drugs during snorting has rarely been described.Patient concerns:A patient with well controlled HIV infection was referred for an 18FDG PET-CT to assess extension of Kaposi's disease, recently removed from his right foot. The patient had no particular symptoms.Diagnoses:Abnormal uptake of 18FDG was found in a suspicious lung nodule. An experienced radiologist thought the nodule was due to lipoid pneumonia.Interventions:Bronchoalveolar lavage fluid did not contain lipid-laden macrophages but bronchoscopy showed violet lesions resembling Kaposi's disease lesions. Lobectomy was performed after a multidisciplinary discussion.Outcomes:Anatomopathological analysis revealed the nodule was due to lipoid pneumonia. The patient's quality of life did not diminish after the operation and he is still in good health. The source of the oily substance causing lipoid pneumonia was found after the surgery: the patient used to snort oily drugs.Lessons:The presence of a suspicious lung nodule possibly due to lipoid pneumonia in a patient with known Kaposi's disease was difficult to untangle and lead to invasive surgery. It is possible that if a source of exogenous lipoid pneumonia had been found beforehand, surgery could have been prevented.

Exogenous lipoid pneumonia mimicking multifocal subpleural tumors

“…ELP is the most common type of lipoid pneumonia and has been reported as a result of aspiration or inhalation of oil substances (animal, vegetal, or mineral origin) [4,5,6,8]. In our case, no exogenous source was found initially.…”

“…Two spicular changes (25 mm and 9 mm, respectively) in the upper right lobe showed fat density (-30-150 HU) on the CT scan, but the value of SUV 5 without local and distal expansion induced suspicion for a malignant tumor; therefore, lobectomy was multidisciplinary suggested and performed. Pathohistological examination confirmed ELP [8]. A differential diagnosis of ELP includes the following: nonspecific interstitial pneumonia, collagen vascular diseases, chronic eosinophilic pneumonia, idiopathic pulmonary fibrosis, hypersensitive pneumonitis, sarcoidosis, lung tumors (benign and malignant), bacterial pneumonia (acute and chronic), and pulmonary alveolar proteinosis [5,17].…”

Pattern of FDG-PET uptake in lipoid pneumonia simulating lung cancer

“…Recently, FDG-PET plays a crucial role on diagnosing lung cancers; however, pseudo-positive FDG uptake has been reported in lipoid pneumonia, resulting in the simulation of lung cancers [ [3] , [4] , [5] , [6] ]. We comprehensively searched English literature and summarized 9 cases of lipoid pneumonia conducting FDG-PET as presented in Table 1 [ [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] ].…”

“…CT-fat density was evaluated in 5 cases, in which 4 cases manifested spotty distribution. On FDG-PET, SUVs ranged between 3.2 and 11.6 [ [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] ] with an exception of negative uptake in one case [ 11 ]. In all cases, SUVs exceeded a threshold of 2.5 that was previously proposed for the best discrimination between benign and malignant solitary lung nodules [ 12 ], illustrating a limitation of SUV alone for discriminating from lung cancers.…”

A case report of exogenous lipoid pneumonia associated with avocado/soybean unsaponifiables

“…We currently do not know the value of PET scans in ELP evaluation. Nonetheless, several papers have reported cases of ELP mimicking neoplastic nodules on PET-CT, with moderate uptake of up to 4.4 of SUVmax [18–20].…”