Thyroid and Parathyroid Glands PDF

Luke Abela MD3 2019/2020 Thyroid and Parathyroid Glands Clinical Presentations of Thyroid Disease in Surgery Diffuse enlargement of the thyroid gland Goitre refers to any thyroid enlargement. Most goitres in developed countries are colloid goitres (distension due to colloid); idiopathic...

Luke Abela MD3 2019/2020 Thyroid and Parathyroid Glands Clinical Presentations of Thyroid Disease in Surgery Diffuse enlargement of the thyroid gland Goitre refers to any thyroid enlargement. Most goitres in developed countries are colloid goitres (distension due to colloid); idiopathic diffuse or multinodular hyperplasia. Endemic goitres are mostly due to iodine deficiency. They are often asymmetrical and soft, and are composed of hyperplastic nodules. These can be huge, but patients are generally euthyroid. Anaplastic carcinomas cause thyroid swelling predominantly in the elderly. The swelling is very hard and firm, and due to the aggressive and invasive nature of this tumour, patients often present with signs of compression ex dyspnoea, stridor, or hoarseness. Lymphomas of the thyroid may also present with diffuse enlargement. Graves’ disease – smooth thyroid enlargement. Hashimoto’s thyroiditis – moderate enlargement, firm and finely nodular on palpation. Solitary thyroid nodule These may prove to be multinodular on imaging. If small, they may be an incidental finding and tend to be noticed when the patient swallows (the thyroid moves up and down with swallowing). A solitary thyroid nodule can be idiopathic hyperplasia, i.e. a thyroid adenoma. They can also be thyroid cysts. Both fall under the category of a simple colloid goitre. If a thyroid nodule presents in childhood, it is mostly due to malignant disease. In any thyroid nodule, malignancy needs to be excluded by biopsy – FNAc or needle core biopsy. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 A new enlargement of an existing goitre may be due to haemorrhage into a cyst/nodule, growing carcinoma or enlarged hyperplastic nodule. The enlargement may extend retrosternally, compressing the trachea and causing stridor and dyspnoea (trachea may be shifted away from the goitre as well). Painful and tender goitres can be due to thyroid inflammation, as occurs in deQuervain’s thyroiditis and Hashimoto’s thyroiditis. Hyperthyroidism A solitary adenomatous nodule may produce excess T4, autonomously from TSH levels. This nodule is called a toxic or hot adenoma. Hypothyroidism Late result of primary thyroid atrophy, as occurs in conditions such as Hashimoto’s thyroiditis (chronic inflammation leads to fibrosis and atrophy), and also in treatment of hyperthyroidism such as anti- thyroid drugs, radioiodine ablation and total thyroidectomy. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 Approach to Investigating Thyroid Masses Specifically ask for previous neck radiotherapy – greatly increases the risk for thyroid malignancy. General thyroid status Euthyroid/hyperthyroid/hypothyroid. First assessment should be clinical, but confirmation can be obtained by the TSH and T4 levels. In pregnancy and puberty, free T4 and T3 levels should be obtained because the thyroid-binding globulin levels are raised during these phenomena. Hyperthyroidism but normal free T4 – check free T3 levels (may have T3 thyrotoxicosis). Thyroid autoantibodies should be assayed to rule out autoimmune thyroid disease. These include long-acting thyroid stimulating factor, anti-TSH antibodies, anti-TPO antibodies, anti- thyroglobulin antibodies and anti-thyroid microsomal antibodies. Morphology of the gland Ultrasound scanning is used to establish the morphology and also detect and diagnose cysts. CT scanning may reveal retrosternal goitres or metastases of thyroid carcinomas. Tissue diagnosis Usually, the two methods used to obtain a tissue diagnosis are FNAc and needle core biopsy. Biopsy taking may be guided by ultrasound. Needle core biopsies give a larger specimen, therefore carry a greater diagnostic potential. Colloid nodules are generally left in place unless they are causing compressive complications or cosmetic deformities. Malignant nodules are excised. Lymphomas may not be adequately sampled by both FNAc or needle core biopsy. Follicular carcinoma cannot be distinguished from a thyroid adenoma by FNAc; needle core biopsies are needed for both follicular carcinomas and thyroid adenomas. This is because thyroid adenomas arise from follicular cells as well. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 Functional activity of glandular tissue This is assessed by radioiodine; this is taken up avidly by functioning thyroid tissue. The thyroid gland is imaged after radioiodine administration, and one of the following four patterns may be observed: Diffuse homogenous uptake – found in normal thyroid glands or diffuse hyperactive thyroid glands. Generalised, patchy uptake – found in multinodular goitres, where hyperplastic nodules are less active than the surrounding normal tissue (the patches correlate with the hyperplastic nodules). Cold nodules – mostly these indicate tumours, as the majority of thyroid tumours are non-secretory therefore do not take up iodine. Hot nodules – these indicate toxic adenomas, and represent an autonomous focus of T4 secretion with suppression of the rest of the thyroid gland secretory activity. Radioiodine scanning may identify ectopic thyroid tissue (in the tongue, or along the thyroglossal duct), retrosternal goitres and metastatic thyroid carcinoma. Radioiodine is given orally and is mostly used for middle-aged and elderly patients. It is contraindicated in pregnancy as it can cause foetal thyroid damage and genetic anomalies. The radioiodine emits β-radiation, therefore destroys most active thyroid tissue within a few months, which is the time period that elapses when the effects of radioiodine therapy kick in. Until this happens, anti-thyroid drugs are continued. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 The radioiodine is then excreted via the kidneys, faeces, breath, sweat and saliva. Gamma rays may also be emitted; patients should maintain a certain distance for a period depending on who they are around. Females planning pregnancy should avoid doing so until 6 months after therapy has ended. Higher doses have a better chance of eliminating hyperthyroidism, but also have a higher risk of inducing hypothyroidism. Radioiodine may make thyroid ophthalmopathy worse. Surgical management This is indicated when: A quick and effective cure is needed, ex in Graves’. Patients are unresponsive to antithyroid drugs. Toxic multinodular goitre – reveals the cosmetic deformities. Hot nodules – avoiding suppression of the surrounding normal thyroid tissue. Pre-op assessment involves laryngoscopy to assess the patency of the vocal cords. This helps in determining whether ex a long-standing change in voice was there pre-op or post-op (due to a lesion to the RLN/ELN). Thyroid function should be normalised pre-op; thyrotoxicosis may precipitate cardiac arrhythmias as it carries anaesthetic risks. Manipulation of the gland during surgery may result in massive release of thyroid hormones and may cause a fatal thyroid storm. To avoid this, anti-thyroid drugs are given for several weeks prior to the operation, and Lugol’s iodine is given c. 10 days prior to surgery so that vascularity to the enlarging portion is reduced and hence making excision easier. Surgery aims to remove enough thyroid tissue to render the patient euthyroid, but also leaves enough tissue not to render the patient hypothyroid. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 Thyroid Malignancies Nearly all thyroid malignancies originate from thyroid follicular cells, except for the medullary carcinomas. Papillary and follicular carcinoma are well-differentiated, whilst anaplastic carcinomas are poorly differentiated and highly aggressive. Medullary carcinomas arise from parafollicular cells (which secrete calcitonin). Lymphomas usually arise in pre-existing Hashimoto’s thyroiditis due to lymphocytic infiltration of the latter. Exposure to radiation in childhood greatly predisposes to thyroid cancer. Papillary carcinoma Commonest thyroid malignancy by far, and females are affected c. 3 times more than males. Incidence is in ages 30-45 years. The tumour forms a branching papillary structure with a fibrovascular stroma, and it often contains calcified psammoma bodies. These tumours grow slowly and are multicentric. MMSA – SCOME Notes Database Luke Abela MD3 2019/2020 Metastasis occurs late, and into central and lateral cervical lymph nodes. Distant metastases are rare (occur in lung and bone). Papillary carcinomas carry the best prognosis, with even better prognosis for minimal papillary carcinomas (single tumour