ULTRASOUND AND FINE-NEEDLE ASPIRATION BIOPSY IN DIAGNOSIS OF THYROID NODULES
Bence-Žigman Zdenka
Klinički zavod za nuklearnu medicinu I zaštitu od zračenja, KBC Zagreb
Population studies suggest that 4-8 % of asymptomatic adults have thyroid nodules. As increasing numbers of patients undergo ultrasound examination for medical evaluations, more and more thyroid nodules are being detected, in 20-40% of examined patients.
Ultrasound can detect nonpalpable nodules. Sometimes nonpalpable nodules can be large but situated in posterior part of the lobe or in inferior parts of the neck in upper mediastinum, but sometimes it can be very small nodules.
Nodular thyroid disease is a heterogeneous disorder with regard to clinical, functional or histological aspects: nodules can be single or multiple, hyper or hypo functional, nodular goitre, benign or malignant tumours. It can be associated with autoimmune thyroid diseases. Therefore, controversy remains as to the optimal management of patients with thyroid nodules.
Malignant nodules account for approximately 3-5 % of all nodules.
Ultrasonically guided fine-needle biopsy is method of choice for determining the risk of malignancy. Ultrasound guidance enables biopsies of the lesions 2-3 mm in diameter.
Nodules can be cystic, solid, and solid with cystic degenerations, with calcifications, with regular contour or with irregular contour. The precise description of echostructure of the nodules and localisation in thyroid make easier the choice of the nodules for biopsies.
Understanding of histological presentation of nodules helps in understanding of echographic presentation, making the echographic critera of malignancy.
Isoechogenic nodule, with echostructure similar as normal thyroid, is typical finding for benign lesions as macro-follicular adenoma or macro-follicular nodular goitre. Such the isoechogenic nodules are surrounded by hipoechogenic rim - “halo” sign. The sound is reflected on boundaries solid tissue – colloid. Therefore such tissue is rich of echoes. Cystic degenerations of such nodules are frequently being observed. The finding of isoehogenic nodule is of low probability of malignancy although 14% of thyroid cancers present such echo pattern. In these cases histological analyses revealed mostly preserved follicular structure.
Hypoechogenic nodules correspond to microfolllicular nodular goitres, microfollicular adenomas or carcinomas. If it has regular contours and homogenous echopattern we are not able to distinguish adenoma from carcinoma, as you can see on this slide. Such nodules are poor with echoes because of cellular dominancy – there are no many boundaries to reflect the sound. If the contour of hypoechogenic nodule is irregular or blurred, or microcallcifications or grouped callcifications are presented the probability of carcinoma is very high with specificity of 97 %.
Echographical criteria of malignancy make easier the choice of the nodules for biopsies. In our study of about 1000 carcinomas, in 50% of analysed cases thyroid carcinoma is recognized by ultrasound due its typical presentation like a hypoehogenic nodule of irregular shape or with calcifications. Specificity for these findings is high 97 %, but sensitivity is 50 %, because 33 % of thyroid carcinomas are presented as hypoehogenic nodules of regular contour, as micro-follicular adenomas and micro-follicular nodular goitres. Isoechogenic nodule, with echostructure similar as normal thyroid, surrounded with “halo”, is of low probability of malignancy although 14% of thyroid cancers show such echopattern. 2% of carcinomas are presented in a form of a cyst with solid tissue inside. Cystic thyroid nodules can be cystic nodular goitre, cystic alteration of adenoma or carcinoma. Because of that ultrasonically guided fine needle aspiration of solid tissue inside the cyst is recommended to get cellular material for analysis.
Colour Doppler is additional tool for understanding vascularity of nodules. Nodular goitre usually shows weak nodular vascularity. Hyperfunctional nodules usually show different types of increased vascularity. Adenomas show peripheral vascularity in capsule. Pathological vascularisation of carcinomas have not be always presented, but very suspect sign of malignancy is if scintigraphicaly cold nodule shows increased intranodal vascularity by colour Doppler .
Ultrasonically guided cytology is a highly specific method, 97%, and quite sensitive, about 90%, in the diagnosis of papillary and medullary carcinoma, but the most difficult is diagnosis of follicular and Hurthle cell carcinoma. Such well-differentiated carcinomas may have the identical cells like adenoma, but the principal distinction from adenoma is in the interface of the capsule and the normal parenchyma. Carcinoma is diagnosed when the tumour extends into or through the capsule and invades small veins. The diagnosis of follicular carcinoma is possible only on the basis of pathological findings, preferably of the multiple slices of the whole nodule. Therefore, the cytological finding can be given as “follicular tumour” only, and cannot strictly specify whether we are dealing with adenoma or carcinoma. If we include cytological finding follicular tumour as positive finding for thyroid carcinoma sensitivity rises to 95%.
Another problem with ultrasound and cytological diagnostics are autoimmune thyroid diseases. Functional and histological changes in autoimmune disease have not be uniform in whole thyroid, some parts have normal follicular structure, and some parts have small follicles without colloid with more or less lymphocitic infiltration, sometimes Hurthle cells are dominant. Because of that ehostructre can be more or less hypoechogenic. Such changes sometimes look like nodules, but sometimes-real nodules are present, carcinomas and adenomas. Fine-needle aspiration of all changes that look like nodules is recommended. Analysis of cytological samples in autoimmune thyroid diseases require experienced cytologist. Different cytological findings can be found from different parts of thyroid and different cytological findings can be found in different phases of disease.
Some nodules can be afunctional and some hyperfunctional. Comparison of ultrasound and cytological findings with scintigraphy is very helpful in recognizing hyper and hypo-functional nodules and helps in making diagnosis and in decision on surgery treatment.
Repeat fine needle aspiration is recommended if insufficient cellular material or atypical cells of undetermined significance is present or if echographic criteria of malignancy are present but cytological finding is benign. Repeat fine needle aspiration of cytological benign nodules is not necessary except if the nodules grow up or change their echostructure. 38.
If the nodules are in both lobes and we decided to send the patient to surgery the best treatment is total thyroidectomy although the nodules are benign.
Small non-palpable neck lymph nodes can easily be detected by ultrasound. They are presented as hypoechogenic nodules sometimes with central echogenic hilum. Experienced examiner can recognise metastatic lymph node due to its round shape, or more ehogenic, irregular or cystic appearance or abnormal peripheral vascularity but metastatic lymph node can look like benign hyper-plastic lymph node as well. Therefore, some of the most suspicious but also some of unsuspicious lymph nodes on the both sides of the neck have to be chosen for the fine needle biopsy. Lymph node metasteses usually are situated on the same side as primary tumour, but in 15% of cases with lymph node metastases bilateral metastases were found. If lymph node metastases are diagnosed lymph node dissection is performed at the same time with total thyroidectomy. The precise description of localisation of metastatic lymph node and relation with blood vessels are very useful for the surgeon. If paratracheal lymph nodes are visualised paratracheal dissection should be always done. There is no need to perform fine-needle biopsy of paratracheal lymph nodes, because some nodules can be malignant, and some can be benign, especially if autoimmune disease is associated with carcinoma.
Conclusion: Thyroid nodules are common and heterogeneous disorder; therefore the suggestion for optimal management of patients with thyroid nodules is good education and experience in all fields of diagnostics and therapy of thyroid diseases.