Thyroid gland

Simple goiter

The natural history of simple goitre
Stages in goitre formation are:
• Persistent growth stimulation causes diffuse hyperplasia; all lobules are composed of active follicles and iodine uptake is uniform. This is a diffuse persist for a long time but is reversible if stimulation ceases.
• Later, as a result of fluctuating stimulation, a mixed pattern
develops with areas of active lobules and areas of inactive
lobules.
• Active lobules become more vascular and hyperplastic until haemorrhage occurs, causing central necrosis and leaving only a surrounding rind of active follicles.
• Necrotic lobules coalesce to form nodules filled either with iodine-free colloid or a mass of new but inactive follicles
• Continual repetition of this process results in a nodular goitre. Most nodules are inactive, and active follicles are present only in the internodular tissue
Diffuse hyperplastic goitre
Diffuse hyperplasia corresponds to the first stages of the natural history. The goitre appears in childhood in endemic areas but, in sporadic cases, it usually occurs at puberty when metabolic demands are high. If TSH stimulation ceases, the goitre may regress, but tends to recur later at times of stress, such as pregnancy.
The goitre is soft, diffuse and may become large enough to cause discomfort. A colloid goitre is a late stage of diffuse hyperplasia when TSH stimulation has fallen off and when many follicles are inactive and full of colloid

Nodular goitre

Nodules are usually multiple, forming a multinodular goitre. Occasionally, only one macroscopic nodule is found, but microscopic changes will be present throughout the gland; this is one form of a clinically solitary nodule. All types of simple Goitre are more common in the female than in the male owing to the presence of oestrogen receptors in thyroid tissue
Diagnosis
Diagnosis is usually straightforward. The patient is euthyroid, the
nodules are palpable and often visible; they are smooth, usually firm and not hard, and the goitre is painless and moves freely on swallowing
A painful nodule, sudden appearance, or rapid enlargement of a nodule raises suspicion of carcinoma but is usually due to haemorrhage into a simple nodule
Investigations
Thyroid function should be assessed to exclude mild hyperthyroidism,
and the presence of circulating thyroid antibodies tested to differentiate from autoimmune thyroiditis.
Plain radiographs of the chest and thoracic inlet will rapidly demonstrate clinically
significant tracheal deviation or compression.
and CT give more detailed images but rarely influence clinical Ultrasound
management.
FNAC is only required for a dominant swelling in a generalised goitre.
Complications
Tracheal obstruction may be due retrosternal extension of the goitre .
Acute respiratory obstruction may follow haemorrhage into a nodule impacted in the thoracic inlet
Secondary thyrotoxicosis Transient episodes of mild hyperthyroidism are common, occurring in up to 30 per cent of patients
Carcinoma An increased incidence of cancer (usually follicular) has been reported from endemic areas .
Prevention and treatment of simple goitre
In endemic areas, e.g. Switzerland, parts of the USA and
Argentina, the incidence of goitre has been strikingly reduced
by the introduction of iodised salt.
In the early stages, a hyperplastic goitre may regress if thyroxine
is given in a dose of 0.15–0.2 mg daily for a few months.
Although the nodular stage of simple goitre is irreversible,
more than half of benign nodules will regress in size over ten
years. Most patients with multinodular goitre are asymptomatic
and do not require operation. Operation may be indicated
on cosmetic grounds, for pressure symptoms or in response to
patient anxiety. Retrosternal extension with actual or incipient
tracheal compression is also an indication for operation, as
is the presence of a dominant area of enlargement that may be
neoplastic.
There is a choice of surgical treatment in multinodular goitre:
total thyroidectomy with immediate and lifelong replacement
of thyroxine or Subtotal thyroidectomy involves partial
resection of each lobe, removing the bulk of the gland, leaving
up to 8 g of relatively normal tissue in each remnant
Discrete thyroid swellings
A discrete swelling in an otherwise impalpable gland is termed isolated or solitary, whereas the preferred term is dominant for a similar swelling in a gland with clinical evidence of generalised abnormality in the form of a palpable contralateral lobe or generalised mild nodularity .
Investigation
Thyroid function
Serum TSH and thyroid hormone levels should be measured. If hyperthyroidism associated with a discrete swelling is confirmed biochemically, it indicates either a ‘toxic adenoma’ or a manifestation of toxic multinodular goitre. The combination of toxicity and nodularity is important and is an indication for isotope scanning to localise the area(s) of hyperfunction
Autoantibody titres
The autoantibody status may determine whether a swelling is a manifestation of chronic lymphocytic thyroiditis
Isotope scan
Isotope scanning used to be the mainstay of investigation of discrete thyroid swellings to determine the functional activity relative to the surrounding gland according to isotope uptake On scanning, swellings are categorised as ‘hot’ (overactive) ‘warm’ (active) or ‘cold’ (underactive), Routine isotope scanning has been abandoned except when toxicity is associated with nodularity
UltrasonographyThis is widely used as a non-invasive supplement to clinical examination in determining the physical characteristics of thyroid swellings which should be routine in all discrete swellings. There are a number of ultrasonic features in a thyroid swelling associated with thyroid neoplasia
Fine-needle aspiration cytology
Fine-needle aspiration cytology is the investigation of choice in discrete thyroid swellings. FNAC has excellent patient compliance is simple and quick to perform in the outpatient department and is readily repeated,
Thyroid conditions that may be diagnosed by FNAC include colloid nodules thyroiditis, papillary carcinoma medullary carcinoma, anaplastic carcinoma lymphoma. FNAC cannot distinguish between a benign follicular adenoma and follicular carcinoma, as this distinction is dependent not on cytology but on histological criteria, which include capsular and vascular invasion.
Radiology
Chest and thoracic inlet radiographs may confirm tracheal deviation,compression or retrosternal extension and are required when either clinical suspicion or FNAC indicates malignancy.
Other scans
CT and MRI scans give excellent anatomical detail of thyroid swellings but have no role in the first line of investigation
Laryngoscopy is widely used preoperatively to determine the mobility
the vocal cords
Treatment
The main indication for operation is the risk of neoplasia, which includes follicular adenoma as well as malignant swellings ,There are useful clinical criteria to assist in selection for operation according to the risk of neoplasia and malignancy a hard, irregular swelling with any apparent fixity, which is unusual, is highly suspicious. Evidence of recurrent laryngeal nerve paralysis, suggested by hoarseness and a non-occlusive cough and confirmed by laryngoscopy, is almost pathognomonic. Deep cervical lymphadenopathy along the internal jugular vein in association with a clinically suspicious swelling is almost diagnostic of papillary carcinoma
Indications for operation in thyroid swellings.
Neoplasia FNAC positive
Clinical suspicion Age
Male sex, Hard texture, Fixity Recurrent laryngeal nerve palsy, Lymphadenopathy Recurrent cyst
Toxic adenoma
Pressure symptoms
Cosmesis
Patient’s wishes
Thyroid operations
Total thyroidectomy = 2 × total lobectomy + isthmusectomy
Subtotal thyroidectomy = 2 subtotal lobectomy + isthmusectomy
Near-total thyroidectomy = total lobectomy + isthmusectomy +
subtotal lobectomy (Dunhill procedure)
Lobectomy = total lobectomy + isthmusectomy


ThyrotoxicosisThe term thyrotoxicosis is retained because hyperthyroidism, i.e. symptoms due to a raised level of circulating thyroid hormones is not responsible for all manifestations of the disease.
Clinical, types are:
• diffuse toxic goitre (Graves’ disease);
• toxic nodular goitre;
• toxic nodule;
Diffuse toxic goitre
Graves’ disease, a diffuse vascular goitre appearing at the same time as the hyperthyroidism, usually occurs in younger women and is frequently associated with eye signs The syndrome is that of primary thyrotoxicosis and the hypertrophy and hyperplasia are due to abnormal thyroidstimulating antibodies
Toxic nodular goitre
A simple nodular goitre is present for a long time before the hyperthyroidism, usually in the middle-aged or elderly, and very infrequently is associated with eye signs. The syndrome is that of secondary thyrotoxicosis.
Toxic nodule
A toxic nodule is a solitary overactive nodule, which may be part of a generalised nodularity or a true toxic adenoma and the normal thyroid tissue surrounding the nodule is itself suppressed and inactive
Clinical features
The symptoms are:
• tiredness• emotional lability• heat intolerance• weight loss• excessive appetite• palpitations
The signs of thyrotoxicosis are:
• tachycardia• hot, moist palms• exophthalmos• eyelid lag/retraction• agitation• thyroid goitre and bruit
Symptomatology
Thyrotoxicosis is eight times more common in women than in men. It may occur at any age. The most significant symptoms are loss of weight despite a good appetite, a recent preference for cold, and palpitations. The most significant signs are the excitability of the patient, the presence of a goitre, exophthalmos and The goitre in primary thyrotoxicosis is diffuse and vascular;. The onset is abrupt
Hyperthyroidism is usually more severe than in secondary thyrotoxicosis but cardiac failure is rare.
In secondary thyrotoxicosis, the goitre is nodular. The onset is insidious and may present with cardiac failure or atrial fibrillation. It is characteristic that the hyperthyroidism is not severe. Eye signs other than lid lag and lid spasm (due to hyperthyroidism) are very rare
Diagnosis of thyrotoxicosis
Most cases are readily diagnosed clinically. Difficulty is most likely to arise in the differentiation of mild hyperthyroidism from an anxiety state when a goitre is present. In these cases, the thyroid status is determined by the diagnostic tests described earlier.
Thyrotoxicosis should always be considered in:
• children with a growth spurt, behaviour problems or myopathy;
• tachycardia or arrhythmia in the elderly;
• unexplained diarrhoea;
• loss of weight.
Principles of treatment of thyrotoxicosisNon-specific measures are rest and sedation and in established thyrotoxicosis should be used only in conjunction with specific measures, i.e. the use of antithyroid drugs, surgery and radioiodine.
Antithyroid drugs Those in common use are carbimazole and propylthiouracil. to block the cardiovascular effects of the elevated T4. Antithyroid drugs are used to restore the patient to a euthyroid state and to maintain this for a prolonged period in the hope that a permanent remission will occur . Antithyroid drugs cannot cure a toxic nodule.
• Advantages. No surgery and no use of radioactive materials.
• Disadvantages. Treatment is prolonged and the failure rate is at least 50 per cent. The duration of treatment may be tailored to the severity of the toxicity with milder cases being treated for only six months and severe for two years before stopping therapy.,
Initially, 10 mg of carbimazole is given three or four times a day, with a latent interval of 7–14 days before clinical improvement is apparent When the patient becomes biochemically euthyroid, a maintenance dose of 5 mg two or three times a day is given for 6–24 months
Surgery
• Advantages. The goitre is removed, the cure is rapid, .
• Disadvantages. Recurrence of thyrotoxicosis occurs in approximately 5 per cent of cases when subtotal thyroidectomy is carried out. There is a risk of permanent hypoparathyroidism and nerve injury. Young women tend to have a poorer cosmetic result from the scar.
Radioiodine
Radioiodine destroys thyroid cells and, as in thyroidectomy reduces the mass of functioning thyroid tissue to below a critical level.
• Advantages. No surgery and no prolonged drug therapy.• Disadvantages. Isotope facilities must be available. The patient must be quarantined while radiation levels are high and avoid pregnancy and close physical contact, particularly with children. Eye signs may be aggravated.