LAUSR

An osteoid osteoma (OO) is a rare osteoblastic benign bone tumor representing approximately 14% of all bone tumors. It usually arises from cortico-diaphyseal and metaphyseal regions of long bones, mostly in the lower limbs, and affects prevalently children and young male adults [1]. Clinical presentation depends on the site of the tumor. However, most patients experience continuous night-time pain, which is relieved by salicylates or non-steroidal anti-inflammatory drugs. OO is characterized by a well-vascularized Bnidus^ centrally, surrounded by a zone of thickened cortex and bone sclerosis. Bone scintigraphy and computed tomography (CT) are the main and complementary imagingmodalities for the diagnosis of OO [2], athough magnetic resonance imaging (MRI) and X-rays can also be used. Recently, new hybrid imaging as single-photon emission computed tomography-computed tomography (SPECT-CT), F–FDG PET/CT, and F–Fluoride PET/CT might improve the accuracy in the diagnosis of the benign lesion [3, 4]. Ga-PSMA PET/CT is increasingly used in prostate cancer for staging and restaging, but increased PSMA activity has been reported in other different non-prostate malignancies and in normal organs (e.g., kidney, duodenum, parotid and submandibular salivary glands, spleen, lacrimal glands, and liver) [5]. To our knowledge, this is the first case detecting high PSMA uptake in OO, suggesting a possible PSMA expression related to osteoblast activity.