F-18 FDG PET-Positive Cortical Fibrous Defect in a Patient with Peripheral T Cell Lymphoma (PTCL).

Riad, Raef

doi:10.21608/egyjnm.2012.5477

F-18 FDG PET-Positive Cortical Fibrous Defect in a Patient with Peripheral T Cell Lymphoma (PTCL).

Document Type : Review Article

Author

Raef Riad

Lake Imaging Department of Positron Emission Tomography and Nuclear Medicine at St John of God Hospital, Ballarat, Victoria, Australia

10.21608/egyjnm.2012.5477

Abstract

Fibrous cortical defects (FCD) are relatively common skeletal lesions that are often discovered incidentally on radiographs of children and young adults. They are most often located in the metaphysis or diametaphyseal junction of the distal femur or proximal tibia[1–5]. Fibrous cortical defects generally undergo spontaneous regression over time and are rarely seen radiographically after the second decade of life [2, 3]. FCD histological appearance is that of whorled proliferations of spindle cells intermixed with multinucleate giant cells, and "foam" cells. (Fig 1). In some cases the central abnormality may be also surrounded by leucocyte infiltration[13]. Conventional radiographic, CT, and MRI characteristics of fibrous cortical defects have been well described[1–4]. Several studies have also described the appearance of fibrous cortical defects on Tc-99m methylene diphosphonate (Tc-99m MDP) bone scintigraphy [5,6]. On CT a fibrous cortical defect is defined as a radiolucent, cortically based round to ovoid absence of bone measuring less than 2.0 cm in greatest diameter, with sharp sclerotic margins and no associated soft-tissue or bone marrow abnormality. MRI image usually shows cortically based soft tissue replacing bone without involvement of extraosseous soft tissues. On MR, the cortical defect often has a bright centre and a dark peripheral margin on T2- weighted images and shows central enhancement and a dark peripheral margin on contrast-enhanced T1- weighted images[7]. Bone scan shows markedly increased radionuclide accumulation in both early perfusion and delayed bone imaging in typical cortical defects. . However, absence of markedly increased tracer accumulation does not mean this diagnosis should be excluded. The use of F-18 fluorodeoxyglucose positron emission tomography (FDGPET) is established for the staging of malignant disease[8]. However, it is well known that FDG is not a tumor-specific agent and intense FDG uptake can occur in many non-malignant conditions such as infection, active inflammation, healing trauma and benign tumors[9]. As a consequence, increased FDG uptake in a benign lesion can be misinterpreted as a site of metastatic disease in patients with known malignancy. Very few reports have described the appearance of fibrous cortical defects on PET/CT [7].

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