page_title: Computed tomography of the thyroid
section_title: Incidental thyroid findings on CT scan
hierarchical_section_title: Computed tomography of the thyroid / Incidental thyroid findings on CT scan
caption_attribution_description: English: For context, see Computed tomography of the thyroid.
context_page_description: In CT scan of the thyroid, focal and diffuse thyroid abnormalities are commonly encountered. These findings can often lead to a diagnostic dilemma, as the CT reflects the nonspecific appearances. Ultrasound examination has a superior spatial resolution and is considered the modality of choice for thyroid evaluation. Nevertheless, CT detects incidental thyroid nodules and plays an important role in the evaluation of thyroid cancer.
  In this pictorial review covers a wide spectrum of common and uncommon, incidental and non-incidental thyroid findings from CT scans. It will also include the most common incidental thyroid findings. In addition, the role of imaging in the assessment of thyroid carcinoma and preoperative thyroid goiter is explored, as well as localization of ectopic and congenital thyroid tissue.
  Thyroid ultrasonography is the modality of choice for thyroid evaluation. Yet, focal and diffuse thyroid abnormalities are commonly encountered during the interpretation of computed tomography exams performed for various clinical purposes. For example, CT often detects incidental thyroid nodules. It plays an important role in the evaluation of thyroid cancer.
context_section_description: The thyroid gland can have variable CT scan findings, such as calcifications, single or multiple nodules, cysts, or diffuse enlargement.
  Thyroid calcifications on a CT scan can be seen in both benign and malignant thyroid lesions. Sonographic examination of the thyroid can differentiate between micro-calcifications, which are highly associated with papillary thyroid carcinoma, and eggshell calcifications, which favour a benign process such as colloid cysts (Figs. 1 and and2)2). In a retrospective review of preoperative CT scan, 35 % (135 of 383) of the patients had detectable intra-thyroidal calcifications. Among them, 48 % had a histopathologically proven thyroid cancer. Calcified nodules had a significantly higher incidence of thyroid cancer and lymph node metastases. The incidence of thyroid cancer among nodules with different calcifications patterns were 79 % of nodules with multiple punctate calcifications, 58 % of nodules with a single punctate calcification, 21 % of nodules with coarse calcification, and 22 % of nodules with peripheral calcification. Most of the single calcified nodules were malignant. However, this did not include patients with ITNs and the sample is skewed towards malignancy. Another study evaluated the presence of ITNs on CT scans and found that 12 % of thyroid nodules were calcified, with no significant correlation between malignant or potentially malignant histology and punctate calcifications. As a result, some researchers believe that calcification per se is not a suspicious CT sign, and have suggested that calcified thyroid nodules on CT scans should be treated the same as non-calcified nodules.
  Thyroid cystic changes are variable, ranging from simple cysts with a thin wall to complex cysts with septations and solid components. An adenoma may undergo cystic degeneration. It is important to note that papillary carcinoma may mimic a benign-looking cyst. Simple serous cysts appear with fluid density on a CT scan, whereas a cyst with haemorrhage or high thyroglobulin content is iso-dense to muscle.
  Thyroid nodules that are detected by an imaging study but have not been previously detected or suspected clinically are considered to be ITNs. ITNs are one of the most common incidental findings on neck imaging. ITNs are reported in up to 25 % of chest CT scans, and in 16–18 % of cervical region cross-sectional imaging, including CT and MRI scans. The rate of malignancy in the detected ITNs on CT and MRI scans varies from 0 % to 11 %. Incidentally detected thyroid carcinomas are more likely to be papillary thyroid carcinomas (PTCs) (Fig. 3). Incidentally detected cancers tend to be smaller in size and less likely to have distant metastasis, as compared to clinically suspected thyroid cancers.
  On CT scans, a malignant lesion is suspected when the margins are ill-defined and there is extra-thyroid extension, lymph node involvement, or invasion of the surrounding structures. The absence of these features does not exclude malignant tumours, especially papillary, follicular, and medullary thyroid carcinomas (Fig. 3). Therefore, ultrasound is the modality of choice for thyroid lesion evaluation, due to its superior spatial resolution compared to CT examinations. Sonographic features of malignancy are micro-calcifications, acoustic shadowing, anti-parallel orientation, marked hypoechogenicity, irregular or microlobulated margins, and increased vascularity. CT scans lack the ability to detect these reliable sonographic signs of malignancy. Therefore, further management of ITNs, if required, usually begins with thyroid ultrasound and FNA should be considered according to the ultrasound findings.
  The American College of Radiology (ACR) flowchart and recommendations for ITNs detected by CT or MRI offer general guidance and are not applicable to all patients. The recommendations are primarily based on the presence or absence of suspicious features, nodule size, patient's age, patient's life expectancy, and patient's comorbidities. Suspicious features that can be detected on CT scans include signs of local invas
caption: Fig. 3. An incidental PTC in a 62-year-old male patient with lymphoma. a, b Enhanced axial CT scan and fused PET/CT scan of the neck demonstrate a well-defined, hypodense right thyroid nodule (white arrow) with high FDG uptake. The FDG-avid uptake in the left side (circle) is related to patient's known lymphoma, which resolved after treatment. c, d Transverse greyscale and sagittal colour Doppler ultrasound of the neck demonstrate a right thyroid irregular hypoechoic lesion with some micro-calcifications (white arrows) and increased vascularity.[1]
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