False Positive F-18 FDG PET/CT of Skeletal Metastasis Due to Solitary Eosinophilic Granuloma

A 31 year old female with a 3 month history of focal right mid posterior thoracic pain, and solitary lytic lesion in the right 7th rib posteriorly on bone scan (SPECT/CT) was referred for PET/CT to identify alternate site for biopsy in suspected malignancy. The patient had no significant past medical history and was afebrile with mildly elevated inflammatory markers. A solitary intensely FDG avid focus was demonstrated localised to a well-defined lytic lesion with partial cortical erosion on the posterior aspect of the right 7th rib. No adjacent soft tissue abnormality was seen. No other site of biopsy was demonstrated. As malignancy (metastatic or primary) was not excluded, CT guided localisation with hookwire and blue dye injection was performed immediately prior to partial resection of the right 7th rib. Histopathology confirmed the diagnosis of eosinophilic granuloma.