Thyroid computed tomography imaging: pictorial review of variable pathologies

Abstract

Focal and diffuse thyroid abnormalities are commonly encountered during the interpretation of computed tomography (CT) exams performed for various clinical purposes. These findings can often lead to a diagnostic dilemma, as the CT reflects the nonspecific appearances. Ultrasound (US) examination has a superior spatial resolution and is considered the modality of choice for thyroid evaluation. Nevertheless, CT detects incidental thyroid nodules (ITNs) and plays an important role in the evaluation of thyroid cancer. In this pictorial review, we cover a wide spectrum of common and uncommon, incidental and non-incidental thyroid findings from CT scans. We also discuss the most common incidental thyroid findings, best practices for their evaluation, and recommendations for their management. In addition, we explore the role of imaging in the assessment of thyroid carcinoma (before and after treatment) and preoperative thyroid goiter, as well as localization of ectopic and congenital thyroid tissue.

Teaching points: • Thyroid disorders tend to have non-specific CT appearances. • ITNs are common on neck CT. • ITN management depends on nodule size, age, health status, lymphadenopathy, and invasion. • CT is used in assessment of cancer extension, mass effect, invasion, and recurrence. • CT plays a role in preoperative planning in patients with symptomatic goiter.

Keywords: Computed tomography; Ectopic thyroid; Goiter; Incidental thyroid nodule; Thyroid cancer.

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

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

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

Fig. 4

A 45-year-old male patient presented with anterior mediastinal metastatic PTC lesions and occult primary on imaging. Histopathology examination of the resected thyroid gland revealed micro-foci of PTC; the largest, in the isthmus, measured 4 mm. a Transverse greyscale ultrasound of the thyroid demonstrates homogenous gland with normal echogenicity and size. No focal lesion or micro-calcifications. b Non-enhanced CT scan obtained as part of PET/CT examination shows a heterogeneous, large, relatively dense anterior mediastinal mass (white arrow) with peripheral calcification (arrowheads). Thyroid gland has normal CT appearance with no abnormal FDG uptake (not shown)

Fig. 5

A poorly differentiated invasive left thyroid mass in a 58-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 to the isthmus and the medial aspect of the right 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). Note the IJV distention and central enhancing portion in the upper cut (black arrow in e) concerning the tumour thrombus. f, g Enhanced axial CT scan of the upper chest demonstrate a mass extension into the retrosternal area, left tracheoesophageal groove, and posterior to the trachea (white arrows in f). There are multiple bilateral pulmonary nodules (white arrows in g)

Fig. 6

A 61-year-old female patient with locally aggressive PTC. a Enhanced axial CT scan of the neck demonstrates a heterogeneous infiltrative thyroid mass. This mass diffusely involves the entire gland and circumferentially encases the trachea with involvement of bilateral tracheoesophageal grooves (white arrows). b, c Additional axial cranial images show right cricoid cartilage destruction (black arrows in b), right thyroid cartilage destruction (black arrow in c), right vocal cord paralysis (white arrows in b), and bilateral cervical lymphadenopathy (arrowheads)

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 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

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

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)

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)

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

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

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

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

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

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

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)

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

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 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)

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

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)

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