Role of High-frequency Ultrasound in Diagnosis of Thyroid Pathologies

Abstract

Ultrasound examination of the thyroid gland is widely used in the diagnosis of thyroid disease. This test is easy and rapid to perform, widely available and the results are readily interpreted. Using ultrasound the image of foci of disease within the gland are easily identified, especially using high frequency probes which enable solid nodules up to approx 3 mm to be revealed with 10 MHz probes. In non-nodular thyroid disease the ultrasonic structure guides the diagnosis (thyroiditis, Graves' disease). During the follow-up of thyroidectomised patients ultrasound can easily reveal postoperative anatomic variations and an early diagnosis can be obtained of any signs of local recurrence of the primary disease. Only hemiagenesia and hypoplasia can be accurately evaluated in congenital disease, whereas in the event of the persistence of the thyroglossal duct the latter can only be diagnosed if it presents a cystic evolution. Thyroid ectopia cannot be identified and must be studied using thyroscintigraphy, preferably performed using 131I as the isotope. The acquired pathology is classified into phlogistic processes, diffuse or nodular hyperplasia, benign and malignant neoplasia. This classification is widely accepted by virtually all authors. In thyroiditis, ultrasound may facilitate the diagnosis of De Quervain's non-suppurative sub-acute thyroiditis (TANS) and Hashimoto's chronic thyroiditis, although always in association with clinical and laboratory tests. The most frequent thyroid pathology is without doubt goitre. This disorder may occur in a non-nodular (widespread goitre with an endemic or sporadic pattern) or nodular form which may be single or multiple. The term goitre is used to indicate the increased volume of the thyroid gland independently of the causes which have provoked it. Common goitre is defined as being endemic when in some geographic area 10% of the general population or 20% of the school-aged population suffers from thyroid hyperplasia (areas of goitrogenic endemic disease). Graves' disease may be included in the group of thyroid hyperplasia diseases, although it is distinguished from the simple versions by the marked glandular hyperactivity which creates manifest hyperthyroidism. In this pathology ultrasonography must be supplemented by colour-Doppler wherever possible. Thyroid nodules are subdivided in terms of their echostructure into 5 types: liquid, mixed (prevalently solid or prevalently liquid), hyperechogenic solid, isoechogenic solid and hypoechogenic solid. The characteristics of benign nodules are: hypoechogenic structure, regular edges, complete and uniform hypoechogenic peripheral halo.