Thyroid gland MRI

The role of MRI and CT in thyroid evaluation

Magnetic resonance imaging (MRI) and computed tomography (CT) are used in endocrinology according to strict clinical indications. The primary goal of such examinations is the precise spatial assessment of the pathological process. In particular, tomography is necessary to detect retrosternal extension in multinodular goiter. These imaging methods also reliably determine the presence and degree of tracheal compression.

In confirmed or suspected thyroid malignancies, scanning helps assess the depth of tumor invasion into adjacent anatomical structures. However, it is important to remember the critical absolute contraindication: performing CT with intravenous iodine-containing contrast agent is strictly prohibited when papillary carcinoma is suspected. The use of iodine will make radioiodine treatment (radioiodine treatment) impossible for approximately two months. In such situations, non-contrast techniques or MRI can serve as a safe alternative for surgical planning.

Ultrasound (US) and normal anatomy

Despite the diagnostic power of tomography, ultrasound (US) remains the primary and fundamental imaging method for the neck. When nodes are detected, it is often combined with fine-needle aspiration biopsy (FNAB) or core-needle biopsy.

On panoramic transverse neck ultrasound, normal topographic anatomy is clearly visualized:

• Muscles (from anterior to posterior): sternohyoid (m. sternohyoideus) and sternothyroid (m. sternothyroideus) muscles. Laterally from them runs the large sternocleidomastoid muscle (m. sternocleidomastoideus).
• Vessels: lateral to the gland itself lie the common carotid artery and internal jugular vein.
• Neck organs: the trachea is centrally located, and the cervical esophagus is typically displaced to the left and posteriorly from the airway.

In chronic lymphocytic Hashimoto's thyroiditis at an early stage, ultrasound shows a slightly enlarged lobular gland with a heterogeneous hypoechoic structure. At later stages, the organ decreases in size, and echogenic linear fibrous septa form within it. In Graves' disease, the gland is diffusely enlarged, and color Doppler mapping reveals sharply increased blood flow — the "thyroid inferno" sign (thyroid inferno).

Thyroid malignancies

Diagnostic imaging plays a crucial role in staging tumor processes prior to surgical intervention. There are several main types of carcinomas:

1. Differentiated carcinomas: papillary (most common, 70–80% of all cases) and follicular (10–20%).
2. Medullary carcinoma: accounts for 5–10% of cases. Special attention is paid to it due to its frequent association with multiple endocrine neoplasia syndrome (MEN 2A and 2B).
3. Anaplastic carcinoma: a rare (1–2%) but extremely aggressive, fast-growing tumor. It occurs predominantly in elderly individuals, is characterized by massive invasion into adjacent neck structures, and carries an unfavorable prognosis.
4. Primary lymphoma: most commonly non-Hodgkin lymphoma (NHL). The risk of its occurrence is increased by 70–80 times in patients with long-standing thyroiditis.

Parathyroid gland diagnostics and radionuclide methods

A comprehensive approach is used to detect parathyroid pathologies. Primary hyperparathyroidism is most often caused by a solitary adenoma (80% of cases) or hyperplasia (10–15%). On ultrasound, a typical adenoma appears as a well-defined hypoechoic mass located posterior or inferior to the thyroid gland.

A modern trend in diagnostic imaging is 4D parathyroid CT. This method is gradually replacing traditional 99mTc-sestamibi scintigraphy due to higher spatial resolution and superior anatomical detail. 4D-CT, together with ultrasound, reliably localizes adenomas, significantly facilitating minimally invasive parathyroidectomy.

In general, classical radioisotope diagnostics (using 99mTc-pertechnetate or iodine-123) is used less frequently today as it is being displaced by antibody laboratory tests (anti-TPO, TSH receptor antibodies). Nevertheless, scintigraphy remains relevant for confirming Graves' disease (diffuse increased uptake) or detecting an autonomous "hot" nodule in toxic adenoma against the background of suppressed TSH.

Class and exam questions

What else to study on this topic

• Features of the MRI picture and CT characteristics of the thymus gland (thymomas)
• Topographic anatomy of the neck on transverse slices (CT and US)
• Features of diagnostic imaging of invasive retrosternal goiter
• Specific bone metastases (lung cancer, renal cell carcinoma, melanoma) on MRI

Other topics in the Neuroimaging section

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