Changes

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 ​and2and2)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/>

An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig1_HTML[[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/>]]

An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig2_HTML[[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. a 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.]]

An external file that holds a picture[[File:Papillary thyroid carcinoma on CT, illustration, etc.Object name is 13244_2016_506_Fig3_HTMLPET CT and ultrasonography.jpg|thumb|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.<ref name=Saeedan2016/>]]

Surgery is the primary mode [[File:Ultrasonography and CT of treatment for DTCsa poorly differentiated invasive thyroid mass. Post total thyroidectomy radioactive iodine (RAI) ablation is an option, especially jpg|thumb|300px|Fig. 5. A poorly differentiated invasive left thyroid mass in patients a 58-year-old female patient. a Sagittal greyscale neck ultrasound shows a large hypoechoic lesion with distant metastasis, tumours larger than 4 cm, or extramacro-calcification and micro-thyroidal disease extensioncalcification. b Sagittal colour Doppler ultrasound shows left internal jugular vein filling defect with detected internal vascularity suggestive of tumour thrombus. c Enhanced axial and coronal CT scans of the neck show heterogeneously enhancing large lesion replacing the left thyroid lobe and extending to the isthmus and the medial aspect of the right thyroid lobe (white arrow). Ultrasound examination is usually adequate in evaluating primary tumours The mass and cervical the conglomerate lymph nodesmeasure 12.5 × 7 × 5. Preoperative cross-sectional imaging with CT or MRI is indicated if there is a concern for local invasion that may alter the patient’s staging as well as surgical approach 8 cm (Figswhite arrows). 4d, ​,55 e Axial enhanced CT scans show enlarged left cervical nodes (white arrow) and ​and 6left internal jugular vein (IJV)6thrombus (black arrows). Note the IJV distention and central enhancing portion in the upper cut (black arrow in e) concerning the tumour thrombus. Some thyroid primaries may be smallf, g Enhanced axial CT scan of the upper chest demonstrate a mass extension into the retrosternal area, diffuseleft tracheoesophageal groove, or multifocal and therefore may be occult on imaging posterior to the trachea (Figwhite arrows in f). 4There are multiple bilateral pulmonary nodules (white arrows in g) .<ref name=Saeedan2016/>]]

An external file that holds a picture, illustration, etc.Object name Surgery is 13244_2016_506_Fig4_HTML.jpgFig. 4A 45-year-old male patient presented with anterior mediastinal metastatic PTC lesions and occult the primary on imagingmode of treatment for DTCs. Histopathology examination of the resected thyroid gland revealed micro-foci of PTC; the largestPost total thyroidectomy radioactive iodine (RAI) ablation is an option, especially in the isthmuspatients with distant metastasis, measured tumours larger than 4 mmcm, or extra-thyroidal disease extension. a Transverse greyscale ultrasound of the thyroid demonstrates homogenous gland with normal echogenicity Ultrasound examination is usually adequate in evaluating primary tumours and sizecervical lymph nodes. No focal lesion or microPreoperative cross-calcifications. b Non-enhanced sectional imaging with CT scan obtained or MRI is indicated if there is a concern for local invasion that may alter the patient’s staging as part of PET/CT examination shows a heterogeneouswell as surgical approach (Figs. 4, large, relatively dense anterior mediastinal mass (white arrow55 and and 6) with peripheral calcification (arrowheads6). Thyroid gland has normal CT appearance with no abnormal FDG uptake Some thyroid primaries may be small, diffuse, or multifocal and therefore may be occult on imaging (not shownFig. 4).<ref name=Saeedan2016/>

An external file that holds a picture, illustrationIn patients with known thyroid malignancies, etc.Object name is 13244_2016_506_Fig5_HTML.jpgFig. 5A poorly differentiated invasive left thyroid mass in a 58non-year-old female patient. a Sagittal greyscale neck ultrasound shows a large hypoechoic lesion with macro-calcification and micro-calcification. b Sagittal colour Doppler ultrasound shows left internal jugular vein filling defect with detected internal vascularity suggestive of tumour thrombus. c Enhanced axial and coronal CT scans of the neck show heterogeneously enhancing large lesion replacing the left thyroid lobe and extending enhanced exam is preferred due to the isthmus and the medial aspect possible undesired interference of the right free iodide contrast medium with thyroid lobe (white arrow). The mass and the conglomerate lymph nodes measure 12.5 × 7 × 5.8 cm (white arrows). d, e Axial enhanced CT scans show enlarged left cervical nodes (white arrow) and left internal jugular vein (IJV) thrombus (black arrows)iodide I-131 uptake for 6–8 weeks or more. Note the IJV distention and central enhancing portion in This would adversely affect the upper cut (black arrow in e) concerning the tumour thrombus. f, g Enhanced axial CT scan management of the upper chest demonstrate a mass extension into the retrosternal area, left tracheoesophageal groove, these patients by delaying diagnostic thyroid scintigraphy and posterior to the trachea (white arrows radioiodine ablation in f). There are multiple bilateral pulmonary nodules (white arrows in g)patients with DTCs for 2–6 months.<ref name=Saeedan2016/>

An external file that holds a pictureThe radiologist must evaluate the central structures draping the thyroid gland including the trachea, illustrationoesophagus, etclarynx, and pharynx, as well as the recurrent laryngeal nerve.Object name Invasion is 13244_2016_506_Fig6_HTML.jpgFig. 6A 61-year-old female patient with locally aggressive PTC. a Enhanced axial CT scan of suspected if the neck demonstrates a heterogeneous infiltrative thyroid massabuts the airway or oesophagus for more than 180 degrees. This mass diffusely involves the entire gland Luminal deformity, mucosal thickening, and circumferentially encases mucosal focal irregularity are more specific indicators of invasion. Obliteration of the trachea with involvement fat planes of bilateral the tracheoesophageal grooves (white arrows). b, c Additional groove in three axial cranial images show right cricoid cartilage destruction (black arrows in b), right thyroid cartilage destruction (black arrow in c), right and signs of vocal cord paralysis (white arrows in b), and bilateral cervical lymphadenopathy (arrowheads)are indicative of recurrent laryngeal nerve invasion.<ref name=Saeedan2016/> In patients with known thyroid malignancies, a non-enhanced exam is preferred due to Invasion of these central structures meets the possible undesired interference of free iodide contrast medium with thyroid iodide I-131 uptake criteria for 6–8 weeks or moreT4a disease (Figs. This would adversely affect the management of these patients by delaying diagnostic thyroid scintigraphy 5 and radioiodine ablation in patients with DTCs for 2–6 monthsand6)6).<ref name=Saeedan2016/>

The radiologist must evaluate the central structures draping the thyroid gland including the tracheaArterial invasion constitutes T4b disease, oesophaguswhich may preclude curative surgery. More than 180 degrees of arterial encasement is suggestive of invasion, larynxhowever, and pharynxarterial deformity or narrowing is much more suspicious for invasion. The carotid artery is the most commonly involved artery; however, as well as the recurrent laryngeal nervemediastinal vessels should also be examined. Invasion is suspected if the thyroid mass abuts Encasement of the airway carotid artery or oesophagus mediastinal vessels for more than 180 270 degreesis unlikely to be resectable. Luminal deformityOn the other hand, mucosal thickening, and mucosal focal irregularity are more specific indicators occlusion or effacement of the internal jugular vein can occur without invasionand does not influence surgical resectability or staging. Obliteration Asymmetry of the fat planes of strap muscle and the tracheoesophageal groove in three axial images and tumour abutting its external surface are signs of vocal cord paralysis are indicative of recurrent laryngeal nerve invasion. Invasion However, invasion of these central structures meets the criteria for T4a disease pre-vertebral musculature is more challenging, as a large lesion can compress the muscle without invasion (Figs. 5 and ​and6and6)6).<ref name=Saeedan2016/>

Arterial invasion constitutes T4b disease<gallery mode=packed heights=180px>File:US of visually normal thyroid, which may preclude curative surgerybut CT of mediastinal metastatic papillary thyroid carcinoma.jpg|Fig. More than 180 degrees 4. A 45-year-old male patient presented with anterior mediastinal metastatic PTC lesions and occult primary on imaging. Histopathology examination of arterial encasement is suggestive the resected thyroid gland revealed micro-foci of invasionPTC; the largest, howeverin the isthmus, arterial deformity measured 4 mm. a Transverse greyscale ultrasound of the thyroid demonstrates homogenous gland with normal echogenicity and size. No focal lesion or narrowing is much more suspicious for invasionmicro-calcifications. The carotid artery is the most commonly involved artery; howeverb Non-enhanced CT scan obtained as part of PET/CT examination shows a heterogeneous, large, the relatively dense anterior mediastinal vessels should also be examinedmass (white arrow) with peripheral calcification (arrowheads). Encasement Thyroid gland has normal CT appearance with no abnormal FDG uptake (not shown).<ref name=Saeedan2016/>File:CT of the carotid artery or mediastinal vessels for more than 270 degrees is unlikely to be resectablelocally progressive papillary thyroid carcinoma.jpg|Fig. 6. A 61-year-old female patient with locally aggressive PTC. On the other hand, occlusion or effacement a Enhanced axial CT scan of the internal jugular vein can occur without invasion and does not influence surgical resectability or stagingneck demonstrates a heterogeneous infiltrative thyroid mass. Asymmetry of This mass diffusely involves the strap muscle entire gland and circumferentially encases the tumour abutting its external surface are signs trachea with involvement of invasionbilateral tracheoesophageal grooves (white arrows). Howeverb, c Additional axial cranial images show right cricoid cartilage destruction (black arrows in b), invasion of the pre-vertebral musculature is more challengingright thyroid cartilage destruction (black arrow in c), as a large lesion can compress the muscle without invasion right vocal cord paralysis (Figs. 5 white arrows in b), and ​and6)6bilateral cervical lymphadenopathy (arrowheads).<ref name=Saeedan2016/></gallery>

Finally, the possibility of metastatic disease should be excluded. PTCs and medullary thyroid carcinomas tend to metastasize to regional lymph nodes. According to the AJCC/UICC TNM staging system, the nodal stage is classified by site: N1a indicates level VI nodal involvement, including paratracheal nodes; N1b indicates unilateral or bilateral lateral cervical nodal disease or superior mediastinal nodal disease (Figs. 4, ​,55 and ​and6and6)6).<ref name=Saeedan2016/>

The likelihood of positive anatomic imaging is greater when serum Tg is >10 ng/mL. A diagnostic CT scan adds additional value to neck US in detecting central compartment macro-metastases in the mediastinum and retro-tracheal area. According to the recent American Thyroid Association guidelines, an upper chest and neck CT scan with IV contrast should be obtained when: 1) neck US is inadequate in visualizing possible local nodal disease (high Tg, negative neck US, and RAI imaging); 2) US is not able to delineate the disease completely, as in the case of bulky recurrent nodal disease; or 3) evaluation of possible recurrent invasive disease is needed (Figs. 7, ​,88 and ​and9and9).9). CT scans are also the most sensitive diagnostic tool for the detection of pulmonary micro-metastases. Many of the neck US features that are considered as suggestive signs of disease recurrence are also applicable to CT examination. These signs might include sizable rounded nodules in the thyroid bed, fine calcifications, or cystic change.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig7_HTML.jpgFig. 7A 51-year-old female patient post total thyroidectomy for PTC with elevated thyroglobulin measurement. a Axial non-enhanced CT scan of the neck at the level of the thyroid bed demonstrates a well-defined, rounded, homogenously dense soft tissue situated between the trachea and left internal jugular vein (white arrow). b Transverse ultrasound image of the neck demonstrates a well-defined, homogenous, hypoechoic soft tissue nodule measuring 6 mm (white arrow) with no detected micro-calcifications. Biopsy showed a predominantly residual normal thyroid tissue with micro-foci of PTC.<ref name=Saeedan2016/>

An external file that holds <gallery mode=packed heights=200px>File:CT and ultrasonography of residual normal thyroid tissue after thyroidectomy.jpg|Fig. 7. A 51-year-old female patient post total thyroidectomy for PTC with elevated thyroglobulin measurement. a Axial non-enhanced CT scan of the neck at the level of the thyroid bed demonstrates a well-defined, rounded, homogenously dense soft tissue situated between the trachea and left internal jugular vein (white arrow). b Transverse ultrasound image of the neck demonstrates a picturewell-defined, illustrationhomogenous, etchypoechoic soft tissue nodule measuring 6 mm (white arrow) with no detected micro-calcifications.Biopsy showed a predominantly residual normal thyroid tissue with micro-foci of PTC.<ref name=Saeedan2016/>Object name is 13244_2016_506_Fig8_HTMLFile:Recurrence of papillary thyroid carcinoma.jpg|Fig. 8. A 48-year-old male patient post total thyroidectomy with PTC recurrence. a Transverse greyscale ultrasound of the neck demonstrates a left thyroid bed heterogeneous, predominantly hypoechoic irregular lesion with calcifications (white arrow). b A spot image of iodine 123 total body scan of the neck demonstrate a focus of abnormal radiotracer uptake at the left thyroid bed (Black arrows) between the annotated markers. c Enhanced axial CT scan of the neck demonstrates an enhancing large left thyroid bed mass (white arrow) with no calcifications. The lesion exerts a mass effect on the oesophagus (black arrow) and is inseparable from the trachea.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig9_HTMLFile:Ultrasonography and CT of persistent papillary thyroid carcinoma with nodal metastasis.jpg|Fig. 9. A 58-year-old male patient with persistence PTC at thyroid bed with hypervascular nodal metastasis. a–c Transverse greyscale and colour Doppler neck ultrasound demonstrate hypoehoic soft tissue in the left thyroid bed (white arrow in a). There are a heterogeneous enlarged lymph nodes at level 2 and 3 with markedly increased vascularity (white arrow in b and c). d–f Enhanced axial CT images of the neck demonstrate a 2.7 × 1.4 cm hypodense soft tissue lesion anterior to the left carotid sheath (white arrow). There are left-sided enhancing abnormal and enlarged lymph nodes at cervical level 2 and 3 (black arrows).<ref name=Saeedan2016/></gallery>

An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig10_HTML[[File:Thyroid CT with metastatic squamous cell carcinoma.jpg|thumb|Fig. 10. Metastatic squamous cell carcinoma of unknown origin in a 42-year-old female patient. a, b Axial and coronal enhanced neck CT scan demonstrates infiltrative hypodense left thyroid lobe lesions (white arrows). There are multiple necrotic cervical nodal metastases (white block arrows).<ref name=Saeedan2016/>]]

Thyroid lymphoma represents about 5 % of thyroid malignancies. Non-Hodgkin’s lymphoma is the most common type and can be secondary to generalized lymphoma or a primary tumour. Primary thyroid lymphoma usually pre-exists with Hashimoto’s thyroiditis. On CT scans with and without contrast, lymphomas tend to have low attenuation values. Thyroid lymphomas have variable appearance and mostly manifest as a solitary mass (80 %). They may also manifest as multiple nodules (15 % to 20 %) or as a bulky mass replacing the entire gland with extra-thyroid extension (Figs. 11 and ​and12and12).12). The presence of cervical lymphadenopathy supports such a diagnosis. Although it is uncommon, tumour necrosis has been reported.<ref name=Saeedan2016/>

An external file that holds a picture, illustration, etc.<gallery mode=packed heights=200px>Object name is 13244_2016_506_Fig11_HTMLFile:Thyroid CT with non-Hodgkin’s large B-cell lymphoma.jpg|Fig. 11. Thyroid non-Hodgkin’s large B-cell lymphoma in a 66-year-old female patient. a Axial enhanced neck CT scan demonstrates left thyroid lobe and isthmus homogeneously hypodense and minimally enhancing mass (white arrows). This lesion invades the prevertebral muscles (black arrows). Note the multiple enlarged level V lymph nodes (white arrowheads). b Post-treatment image shows significant reduction in size and mass effect of the left thyroid infiltrative mass, with almost complete resolution of the left cervical lymphadenopathy.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig12_HTMLFile:Thyroid CT with diffuse thyroid large B-cell lymphoma.jpg|Fig. 12. Diffuse thyroid large B-cell lymphoma in 79-year-old female patient. a Axial enhanced neck CT scan demonstrates a homogeneously hypodense and minimally enhancing large right thyroid solid mass (long white arrow) extending into the thyroid isthmus. It is encasing the right carotid artery (short white arrow) and displacing of the trachea and oesophagus to the left side.<ref name=Saeedan2016/></gallery>

A goiter is an abnormal thyroid gland proliferation that manifests as multi-nodular, uni-nodular, or non-nodular diffuse glandular enlargement. A goiter is formed of solid matrix, colloid cysts, blood products, calcification, and fibrosis, and this heterogeneity may lead to variable appearances on a CT scan (Figs. 13, ​,1414 and ​and15and15)15). US is more sensitive in evaluating thyroid nodules within a goiter; however, a symptomatic goiter may require surgical treatment with total thyroidectomy, and in this case CT plays an additional role in preoperative evaluation. Specific aspects for examination on a CT scan during the preoperative evaluation for goiter include extension, mass effect, and suspicious features of malignancy.<ref name=Saeedan2016/>

An external file that holds a picture, illustration, etc.<gallery mode=packed heights=200px>Object name is 13244_2016_506_Fig13_HTMLFile:CT of goiter.jpg|Fig. 13. A 27-year-old female patient known to have goiter. a, b Axial and sagittal enhanced CT scan images of the neck demonstrate a heterogeneously enhancing, enlarged thyroid gland with scattered calcifications (white arrow), cystic changes, and substantial retro-sternal extension (black asterisks). No lymphadenopathy or substantial airway narrowing.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig14_HTMLFile:Ultrasound and CT of Hashimoto’s thyroiditis.jpg|Fig. 14. A 19-year-old male patient known to have multi-nodular goiter and FNA, showing underlying Hashimoto’s thyroiditis. a, b Sagittal and transverse greyscale and colour Doppler ultrasound of the neck demonstrate a hypoechoic enlarged right thyroid lobe with small hyperechoic regenerative nodules and marked hypervascularity (white arrows). c, d Enhanced axial CT scan images of the neck demonstrate a heterogeneously enhancing and enlarged thyroid gland, left more than right lobe, and the trachea is markedly narrowed.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig15_HTMLFile:CT and ultrasonography of Hashimoto’s thyroiditis.jpg|Fig. 15. A 33-year-old female patient who presented with neck swelling and pain and was later diagnosed with Hashimoto’s thyroiditis. a Axial enhanced CT scan of the neck demonstrates minimal diffuse enlargement of the thyroid gland, especially the isthmus (white arrow). b Transverse greyscale ultrasound of the neck demonstrates heterogeneously enlarged thyroid and thickened isthmus, measuring 8.6 mm.<ref name=Saeedan2016/></gallery>

Inflammatory thyroid disorders include acute infectious thyroiditis, Hashimoto’s thyroiditis, Riedel’s thyroiditis, and granulomatous thyroiditis (de Quervain’s). Hashimoto’s thyroiditis is associated with an increased risk of lymphoma and papillary thyroid carcinoma. The CT scan findings of thyroiditis are nonspecific and variable (Figs. 14, ​,1515 and ​and16and16)16). The thyroid gland has a very high iodine concentration, resulting in high CT attenuation (80–100 Hounsfield Units). The presence of thyroiditis can be suggested by a diffusely enlarged and hypo-attenuating (around 45 Hounsfield Units) thyroid gland. This is probably due to follicular cell destruction and reduced thyroid iodine concentration. Marked homogenous enhancement is typically expected. Therefore, moderate thyroid enhancement in a case of thyroiditis suggests a diffuse inflammatory process. It is essential to clinically correlate this with a thyroid function test and serum autoantibody levels.<ref name=Saeedan2016/>

An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig16_HTML[[File:Ultrasonography and CT of midline ectomic thyroid with Hashimoto’s thyroiditis.jpg|thumb|Fig. 16. Midline ectopic thyroid with Hashimoto’s thyroiditis in a 49-year-old female patient. a Transverse greyscale ultrasound shows a 1.6 × 0.8 cm solid, well-defined, heterogeneous area (white arrow) in the midline, superior to the thyroid gland. It is iso-echogenic to the thyroid gland with no definite connection to the thyroid gland. b Transverse colour Doppler ultrasound shows significant increase in vascularity. c Axial enhanced neck CT scan at the level of thyroid cartilage demonstrates midline infrahyoid hyperdense soft tissue mass (white arrow) embedded within the strap muscle.<ref name=Saeedan2016/>]]

Ectopic thyroid tissue may be detected in the tongue near the foramen cecum (90 %) and along the midline between the thyroid isthmus and posterior tongue, lateral neck, mediastinum, and oral cavity. The most frequent location is the base of the tongue (Figs. 16, ​,1717 and ​and18and18).18). In 70 % of cases, the ectopic thyroid is the only functional thyroid tissue present in the body (Fig. 18).<ref name=Saeedan2016/>

An external file that holds a picture, illustration, etc.<gallery mode=packed heights=200px>Object name is 13244_2016_506_Fig17_HTMLFile:CT and scintigraphy of ectopic thyroid on the parotid gland.jpg|Fig. 17. Ectopic thyroid on the left parotid gland with a palpable left parotid mass in a 69-year-old male patient. a, b Axial and coronal enhanced neck CT scan demonstrates well-defined homogeneous enhancing mass (white arrows) within the left parotid gland with preserved surrounding fat planes. It also shows a normal thyroid in normal position in the lower neck. c Image taken 20 minutes after 5 mCi injected Tc99m-Pertechnetate shows normal thyroid uptake of tracer and physiological uptake in the salivary glands (short black arrow). There is a distinct focus of abnormal tracer accumulation in the left parotid/submandibular region. Patient was given lemon juice with evident normal washout from the salivary glands and relative retention by this abnormal focus (long black arrow).<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig18_HTMLFile:CT and scintigraphy of lingular ectopic thyroid.jpg|Fig. 18. Lingular thyroid in a 33-year-old male who presented with oropharyngeal bleeding. a Axial enhanced neck CT scan at the level of mandible demonstrates a 3 × 3 × 3.4 cm round, partly well-delineated, heterogeneously enhancing lesion (white arrow). It is predominantly on the left side of the oropharynx and to some extent at the mid part of the base of the tongue. Thyroid gland was normal (not shown). b Image of the anterior face and neck taken 20 minutes after Tc99m-Pertechnetate injection shows absent thyroid radiotracer uptake in normal thyroid anatomical location (black short arrows). There is an area of increased uptake (long black arrows) corresponding to posterior tongue mass identified on CT scan.<ref name=Saeedan2016/></gallery>

A thyroglossal duct cyst (TDC) is a duct remnant between the foramen cecum and thyroid isthmus. Most TDCs are located below the hyoid bone and in the midline. The more caudal the cyst, the more likely it will be off midline within 2 cm (Fig. 19 and ​and20and20).20). On a CT scan, a TDC appears as a well-circumscribed area of fluid attenuation with thin walls. The cyst wall can become thick with an enhancing rim indicative of current or previous infection. These cysts maybe complicated by haemorrhage, infection, or malignancy. Therefore, their US and CT scan appearance may vary based on their content. Nodular enhancement within a TDC should initiate further workup to exclude malignancy (Fig. 21). US-guided FNA of these suspicious nodular areas is considered an appropriate next diagnostic step, taking into consideration the high rate of false negative results.<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig19_HTML.jpgFig. 19Long-standing infected thyroglossal duct cyst in a 29-year-old male patient. a Transverse greyscale ultrasound at midline, just above the level of the thyroid gland, shows an oval cystic lesion with internal echoes (white arrows) and posterior enhancement (arrowheads). b Transverse colour Doppler ultrasound shows surrounding peripheral flow (white arrow). c Axial enhanced neck CT scan at the level of the thyroid cartilage demonstrates a slightly off-midline, well-defined, homogeneous cystic lesion embedded in the left strap muscle with peripheral enhancement (white arrow). It shows no calcification or internal enhancement. Thyroid gland was normal (not shown).<ref name=Saeedan2016/> An external file that holds a picture, illustration, etc.Object name is 13244_2016_506_Fig20_HTML.jpgFig. 20Recurrent/residual thyroglossal duct cyst in a 39-year-old male patient. The first resection of thyroglossal duct cyst showed histopathology evidence of Hurthle cell type thyroid cancer. However, the second resection showed signs of chronic inflammation, with no malignant cells. a, b Enhanced axial and sagittal neck CT scans demonstrate a unilocular cystic lesion arising from the tongue base and extending through the partially resected hyoid bone. This cystic lesion has peripheral enhancing wall, which becomes more thick over its inferior aspect associated with surrounding fat stranding at the surgical site (white arrow). There are no internal septations, nodules or masses, or calcifications. c Transverse view of power Doppler ultrasound at the submental area demonstrates cystic lesion and internal debris with no detected internal vascularity.<ref name=Saeedan2016/>

An external file that holds <gallery mode=packed heights=200px>File:Ultrasonography and CT of a thyroglossal duct cyst.jpg|Fig. 19. Long-standing infected thyroglossal duct cyst in a 29-year-old male patient. a Transverse greyscale ultrasound at midline, just above the level of the thyroid gland, shows an oval cystic lesion with internal echoes (white arrows) and posterior enhancement (arrowheads). b Transverse colour Doppler ultrasound shows surrounding peripheral flow (white arrow). c Axial enhanced neck CT scan at the level of the thyroid cartilage demonstrates a pictureslightly off-midline, illustrationwell-defined, etchomogeneous cystic lesion embedded in the left strap muscle with peripheral enhancement (white arrow).It shows no calcification or internal enhancement. Thyroid gland was normal (not shown).<ref name=Saeedan2016/>Object File:CT and ultrasonography of recurrent or residual thyroglossal duct cyst.jpg|Fig. 20. Recurrent/residual thyroglossal duct cyst in a 39-year-old male patient. The first resection of thyroglossal duct cyst showed histopathology evidence of Hurthle cell type thyroid cancer. However, the second resection showed signs of chronic inflammation, with no malignant cells. a, b Enhanced axial and sagittal neck CT scans demonstrate a unilocular cystic lesion arising from the tongue base and extending through the partially resected hyoid bone. This cystic lesion has peripheral enhancing wall, which becomes more thick over its inferior aspect associated with surrounding fat stranding at the surgical site (white arrow). There are no internal septations, nodules or masses, or calcifications. c Transverse view of power Doppler ultrasound at the submental area demonstrates cystic lesion and internal debris with no detected internal vascularity.<ref name is 13244_2016_506_Fig21_HTML=Saeedan2016/>File:CT and MRI of papillary thyroid carcinoma arising from a thyroglossal duct cyst.jpg|Fig. 21. Papillary thyroid carcinoma arising from a thyroglossal duct cyst in a 28-year-old male. a Axial enhanced CT scan shows a large complex cystic lesion (white arrows) adherent to the anterior aspect of the hyoid bone. It has an enhancing mural solid nodules and calcifications (black arrows). There is no cervical lymphadenopathy. b Axial short tau inversion recovery (STIR) MRI image near the same level shows complex lesion of high signal intensity (long white arrows) with solid mural nodules (short white arrow). c Axial fat saturated T1 MRI image post contrast administration shows the complex cystic lesion with thick enhancing wall (long white arrows) and enhancing mural nodules (short white arrows).<ref name=Saeedan2016/></gallery>

An external file that holds a picture[[File:CT, illustrationultrasonography, etc.Object name is 13244_2016_506_Fig22_HTMLSPECT and scintigraphy of intra-thyroid parathyroid adenoma.jpg|thumb|Fig. 22. A 26-year-old male patient with elevated serum parathyroid hormones and calcium secondary to intra-thyroid parathyroid adenoma. a, b Enhanced axial and coronal CT scan of the neck demonstrate a well-defined hypodense right thyroid nodule (white arrows). c Bone window coronal CT scan shows lytic expansile lesions at the right mandible and left frontal bone (white arrows). d Transverse colour Doppler ultrasound of the neck demonstrates a well-defined, heterogonous, predominantly hypoechoic right thyroid nodule measuring 2.7 cm, with mild increased vascularity and no internal micro-calcifications (white arrow). e, f Delayed anterior planar and fused SPECT/CT parathyroid Sestamibi scan at 2 hours demonstrate persistent focal activity in the right thyroid lobe (white arrows). Note the scattered mandibular/maxillary uptakes in planar image representing the known brown tumours.<ref name=Saeedan2016/>]]