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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.<ref name=Saeedan2016/>
[[File:CT of thyroid colloid nodule with calcification.jpg|thumb|Fig. 1. An incidentally discovered colloid nodule with calcification, shown on CT scan of a 58-year-old female patient. a Non-enhanced axial CT scan of the neck demonstrates a coarse calcification at the left thyroid inferior pole. b Sagittal grey scale ultrasound of the thyroid demonstrates a heterogeneous nodule with predominant cystic component. Calcification was not seen in the ultrasound, probably due to its lower location in the superior mediastinum.<ref name=Saeedan2016/>]]
Organized
==Normal anatomy==
The thyroid normally has homogeneous high attenuation values on a CT scan, as compared to adjacent muscles, due to its high iodine concentration. It shows avid iodine contrast enhancement due to its hypervascularity.<ref name=Saeedan2016/>
==Evaluation==
===Calcifications===
[[File:CT of thyroid colloid nodule with calcification.jpg|thumb|Fig. 1. An incidentally discovered colloid nodule with calcification, shown on CT scan of a 58-year-old female patient. a Non-enhanced axial CT scan of the neck demonstrates a coarse calcification at the left thyroid inferior pole. b Sagittal grey scale ultrasound of the thyroid demonstrates a heterogeneous nodule with predominant cystic component. Calcification was not seen in the ultrasound, probably due to its lower location in the superior mediastinum.<ref name=Saeedan2016/>]]
The most notable features of calcifications are:
*Calcified nodules (higher risk of thyroid cancer and lymph node metastases)
:*Multiple punctate calcifications (highest risk of cancer)<ref group="notes" name="calcifications">The study contained preoperative CT findings, not including incidentally discovered abnormalities, and other studies have not seen a significant correlation between calcifications and malignancy.<br>-{{cite journal|last1=Bin Saeedan|first1=Mnahi|last2=Aljohani|first2=Ibtisam Musallam|last3=Khushaim|first3=Ayman Omar|last4=Bukhari|first4=Salwa Qasim|last5=Elnaas|first5=Salahudin Tayeb|title=Thyroid computed tomography imaging: pictorial review of variable pathologies|journal=Insights into Imaging|volume=7|issue=4|year=2016|pages=601–617|issn=1869-4101|doi=10.1007/s13244-016-0506-5}}</ref>
:*Single punctate calcification (high risk of cancer)<ref group="notes" name="calcifications"/>
:*Coarse calcification (lower risk of cancer)<ref group="notes" name="calcifications"/>
:*Peripheral calcification (lower risk of cancer)<ref group="notes" name="calcifications"/>
Ultrasonography is generally the initial choice of further imaging, and 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 2).<ref name=Saeedan2016/>
==Incidental thyroid findings on CT scan==
The thyroid gland can have variable CT scan findings, such as calcifications, single or multiple nodules, cysts, or diffuse enlargement.<ref name=Saeedan2016/>
[[File:CT and ultrasound of thyroid colloid nodule.jpg|thumb|Fig. 2. A 51-year-old female patient post left hemi-thyroidectomy, with incidentally discovered right thyroid colloid nodule on CT scan. an Enhanced axial CT scan of the neck demonstrates a well-defined, hypodense right thyroid nodule (white arrow) with no internal calcifications or cervical lymphadenopathy. b Transverse greyscale thyroid ultrasound demonstrates a well-defined, hypoechoic right thyroid lobe nodule with a central echogenicity including comet tail (ring down) artefacts (white arrow). No vascularity (not shown) or calcifications were detected.]]
