Imaging Methods
Computed tomography (CT) and magnetic resonance imaging (MRI) are used to assess retrosternal extension of multinodular goiter, the degree of tracheal compression, and tumor invasion into surrounding structures.
Important rule: CT with intravenous iodine-containing contrast is strictly contraindicated if papillary carcinoma is suspected. The administration of exogenous iodine makes radioactive iodine therapy impossible for about two months.
4D-CT is increasingly used to search for parathyroid adenomas. This method surpasses traditional 99mTc-sestamibi scintigraphy in spatial resolution and anatomical detail accuracy. 4D-CT combined with ultrasound allows planning minimally invasive gland removal, especially if intraoperative parathyroid hormone monitoring is available.
Diagnostics of thyroiditis
On ultrasound, the appearance of inflammatory thyroid diseases depends on their type and stage:
- Chronic lymphocytic thyroiditis (Hashimoto's): In the early stages, the gland is enlarged, has a lobulated contour, and its parenchyma is hypoechoic and heterogeneous. In the late stage, the organ decreases in size, and bright hyperechoic fibrous strands (septa) appear against the background of inhomogeneous tissue.
- Graves' disease (diffuse toxic goiter): Ultrasound shows a diffusely enlarged, hypoechoic, and heterogeneous gland. Color Doppler mapping (CDM) reveals a specific sign: totally increased blood flow, the so-called "thyroid inferno". Scintigraphy with 99mTc-pertechnetate demonstrates a diffuse and uniform increase in radiopharmaceutical uptake.
Malignant neoplasms
Malignant thyroid tumors are divided into several morphological types, which differ in incidence and prognosis:
- Differentiated carcinomas: Papillary (the most frequent, 70–80% of cases, frequently metastasizes to lymph nodes) and follicular (10–20%).
- Medullary carcinoma: Accounts for 5–10% of cases, frequently developing as part of multiple endocrine neoplasia (MEN 2A and 2B) syndromes.
- Anaplastic carcinoma: Rare (1–2%), predominantly seen in elderly patients. On contrast-enhanced CT, it appears as an aggressive tumor with indistinct margins, invading the prethyroid muscles and esophagus. The prognosis is extremely poor.
- Primary lymphoma (NHL): The risk of its occurrence increases 70–80 fold in patients with long-standing thyroiditis.
Parathyroid pathology
The most common problem requiring imaging is primary hyperparathyroidism. Its main cause in 80% of cases is a solitary adenoma. Hyperplasia of all glands (10–15%), multiple adenomas (2–3%), or carcinoma (about 1%) are less common.
On the sonogram, a typical adenoma appears as a well-defined hypoechoic nodule lying posterior or inferior to the thyroid gland. If the mass in the neck is not found, CT or MRI is used to search for ectopic adenomas, which may hide in the superior mediastinum, retro-pharyngeally, or along the thyrothymic ligament.
Lymph node assessment
Ultrasound is the method of choice for the initial assessment of neck lymphadenopathy. Accurate identification of affected nodes (staging) is critical: for example, in squamous cell carcinoma, involvement of any node (ipsilateral or contralateral) or extracapsular extension reduces survival by 50%.
| Sign | Healthy normal | Pathological changes |
|---|---|---|
| Size (short axis) | Less than 1 cm | Enlarged |
| Shape (longitudinal/transverse) | Elongated (ratio > 2) | Rounded (ratio < 2) |
| Echogenicity | Normal | Hypoechoic, cystic areas possible |
| Blood flow (CDM) | Normal (in the hilum of the node) | Abnormal or absent |
Briefly: answers to topical questions
What tumors, besides medullary thyroid carcinoma, are part of multiple endocrine neoplasia (MEN) syndromes 2A and 2B?
In addition to medullary thyroid carcinoma, multiple endocrine neoplasia (MEN) syndromes 2A and 2B include the following tumors and associated lesions:
- Pheochromocytoma — occurs in both types of syndrome (MEN 2A and 2B); early manifestation is possible in MEN 2B.
- Hyperparathyroidism — is a component of MEN 2A syndrome.
- Multiple neuromas — are located on the lips, tongue, and conjunctiva in MEN 2B.
- Ganglioneuromatosis / multiple ganglioneuromas — affect the gastrointestinal tract and urinary system; conjunctival, tongue mucosal, oral, esophageal, and intestinal ganglioneuromas have also been described in MEN 2B.
What radiopharmaceuticals are used for thyroid and parathyroid scintigraphy?
The following radiopharmaceuticals are used for thyroid and parathyroid scintigraphy:
- 99mTc-pertechnetate — used to study the thyroid gland, allowing differentiation of diffuse toxic goiter (diffuse uptake) from toxic adenoma (focal uptake).
- 99mTc-sestamibi (99mTc-sestamibi) — used to diagnose parathyroid pathologies, helping to identify and localize hyperactive adenomas in primary and secondary hyperparathyroidism.
What ultrasound criteria (TIRADS system) indicate a high risk of malignancy in a thyroid nodule?
A high risk of malignancy in a thyroid nodule (EU-TIRADS 5 category) is indicated by the presence of at least one suspicious ultrasound feature. These criteria include:
- Hypoechoic nodule.
- Irregular shape.
- Blurred / lobulated margins.
- Microcalcifications.
The risk of malignancy for EU-TIRADS 5 is 26–87%.
A normal lymph node on ultrasound looks like a rugby ball (elongated), whereas a metastatic one looks like a soccer ball (rounded and "bloated").
Class and exam questions
Why is CT contrast contraindicated in suspected papillary carcinoma?
Intravenous contrast contains iodine, which saturates the tissues. This will make effective radioactive iodine therapy impossible for at least two months after the scan.
How to differentiate Graves' disease from toxic adenoma on scintigraphy?
In Graves' disease, the radiopharmaceutical (e.g., 99mTc-pertechnetate) accumulates diffusely and uniformly in the gland. In toxic adenoma, a single "hot" nodule is visible that actively takes up the radiopharmaceutical, while the rest of the glandular tissue is suppressed and does not accumulate the drug.
Where are ectopic parathyroid adenomas most commonly located?
They can be located in the superior mediastinum, along the thyrothymic ligament, as well as in the retroesophageal or retropharyngeal spaces.
What else to study on this topic
- Topographic anatomy and the 7 levels of neck lymph nodes
- Ultrasound differentiation of cystic neck masses (laryngocele, thyroglossal duct cyst)
- Multiphasic 4D-CT in localization of ectopic parathyroid glands
- Ultrasound-guided fine-needle aspiration biopsy (FNAB)
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Other topics in the Neuroimaging section
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