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Abstract
Thyroid cancer is the most common endocrine cancer, it constitutes 1% of all malignancies worldwide and are heterogenous in terms of histology, clinical presentation, treatment and prognosis. It is more common in females than males.
Different imaging modalities are used when evaluating cases of cancer thyroid including:
Ultrasound used mainly to show the presence of nodules, their size and if they are solid or cystic . Radionuclide scanning is the second and most important modality used , radioactive iodine is taken orally or intravenously, this material concentrates in the thyroid gland, pictures are taken to determine cold nodules which may be benign or malignant or hot nodules which are typically benign. Fine needle aspiration is very important to determine the exact nature of the nodule whether benign or malignant. Finally CT and MRI are currently used to detect the size of the tumor and if it has spread to lymph nodes in the neck or distant structures.
Positron emission tomography ( PET) using 18-F-labelled 2 flouro-2 deoxy -D- glucose ( 18 FDG) is a newly established tool used in the diagnosis and follow up of cancer thyroid . The sensitvity of using FDG-PET in the detection of cancer thyroid is very high and more accurate than the other imaging modalities as it is purposed to be capable of differentiating between tumors, scar, fibrosis and necrosis. Moreover can detect recurrent thyroid cancer in cases when radio- active iodine scans have proven to be unreliable or difficult to interpret as differentiated thyroid cancer cells may undergo a process of transformation thus losing some or all of their ability to take up and retain 131-iodine ; Yet still they retain the ability to absorb FDG.