thyroid lecture.pdf

Prepared by Thyroid ultrasound Dr.Mahabad Naqishbandi ABHS(Radiology) Normal anatomy Ultrasound can demonstrate the following normal structures in the neck: Carotid arteries. Jugular veins. Thyroid gland. Trachea. Surrounding muscles. Important structure to scan Vessels. The vascular bundle (the car...

Prepared by Thyroid ultrasound Dr.Mahabad Naqishbandi ABHS(Radiology) Normal anatomy Ultrasound can demonstrate the following normal structures in the neck: Carotid arteries. Jugular veins. Thyroid gland. Trachea. Surrounding muscles. Important structure to scan Vessels. The vascular bundle (the carotid artery and the jugular vein) is behind and between the sternocleidomastoid muscle and lateral to the thyroid gland. These vessels are very accessible for ultrasonography. The carotid artery, bifurcating into the internal and external branches, will be seen as a tubular structure with hyperechogenic walls and an echo-free centre: the walls are smooth and difficult to compress with the transducer. The jugular vein is lateral to the carotid artery and the walls are more easily compressed. The veins vary in diameter during the different phases of respiration and the Valsalva maneuver. Thyroid look The thyroid consists of two lobes, one on either side of the trachea joined in the midline by an isthmus. The thyroid gland and the isthmus have the same homogeneous echo texture, and the lobes should be equal in size. On transverse scans, the section is usually triangular; on longitudinal scans, it is oval. The outline should be smooth and regular The thyroid gland is normally 15-20 mm thick, 20-25 m m in width, and 30-50 mm in length. Muscles. The sternocleidomastoid muscle is the only muscle of particular importance in pediatric patients. The muscles are band-like structures which are less echogenic than the thyroid. On transverse scans, the outlines are well defined but varies from circular to ovoid in section. Lymph nodes. Normal lymph nodes can sometimes be seen as hypoechogenic structures less than 1cm in diameter. Transverse scan: the common carotid artery, jugular vein, thyroid gland and sternocleidomastoid muscle. Transverse scan: the common carotid artery, jugular vein, and sternocleidomastoid muscle. Transverse scan: the normal thyroid gland, including the isthmus Abnormal thyroid Thyroid abnormalities may be local or diffuse, single or multiple. Focal masses Solid. About 70% of focal lesions are thyroid nodules and over 90% of these will be adenomas, which are very seldom malignant. The ultrasound appearance of an adenoma is variable and it may be impossible to differentiate between a benign thyroid adenoma and a malignant tumour: the ultrasound characteristics are similar, and size is not important. Both benign and malignant tumours can be hypo- or hyperechogenic; both may contain cystic components. However if the mass is well circumscribed, with a surrounding thin, hypochogenic halo, there is a 95% probability that it is a benign adenoma. When there is central necrosis, the possibility of malignancy should be considered. Cystic. True cysts of the thyroid are rare. Characteristically, they are well circumscribed, with smooth walls, and are echo-free, unless there has been haemorrhage into the cyst. Haemorrhage or an abscess may occur in the thyroid, appearing as a cystic or complex pattern with ill-defined edges. Focal abnormality Thyroid enlargement The thyroid may be enlarged, sometimes extending retrosternally. Enlargement may affect only part of a lobe, a whole lobe, the isthmus or both lobes. Enlargement is usually hyperplastic and is ultrasonically homogeneous. Causes: endemic goiter, lack of iodine, puberty, hyperthyroidism or hyperplasia following partial thyroidectomy. If the ultrasound density of the thyroid is heterogeneous, there are usually multiple nodules (a multinodular goitre); the nodules may be solid or complex on ultrasound. Heterogeneous enlargement In autoimmune thyroiditis, the thyroid becomes heterogeneous and may resemble a multinodular goitre. Small thyroid Asmall, homogeneous, hypochogenic thyroid may indicate acute thyroiditis. Abscess The size and shape of a cervical abscess are very variable, and the outline is often very irregular and unclear. On ultrasound, there are usually internal echoes. In children, abscesses are most commonly in the retropharyngeal region. Adenopathy On ultrasound, lymph nodes will appear as hypoechogenic masses with regular outlines, solitary or multiple, nodular, oval or round, and variable in size from 1 cm upwards. Ultrasound cannot determine the cause of the lymph node enlargement. Cystic hygromas (lymphangiomas) These are of variable size, are usually situated laterally in the neck, and may extend to the thorax or axilla. On ultrasound they are fluid-filled, often with septa. Less common abnormalities Hematoma echogenic masses in the cervical muscles, a cystic or complex mass may be a thyroglossal cyst (in the midline), a branchial cleft cyst (in the lateral neck) or a dermoid. Vascular abnormalities It is possible with ultrasound to demonstrate atheromatous plaques and show stenosis in the carotid artery, but it is not possible to evaluate blood flow without Doppler ultrasound and, in many cases, angiography. Thank you