Nodular goitre

Multinodular goitre

Multinodular goitre is exceedingly common world-wide, occurring in about 4% of the world's population. The aetiology is unknown. The natural history is a progressive enlargement of the goitre with an increase in the size and number of the nodules, with a tendency to hyperthyroidism in later life. Multinodular goitre is associated with a low incidence of malignancy. Since this malignancy may not affect the largest nodules in the goitre, FNA cannot be relied on for the definitive exclusion of malignancy.

Multinodular goitre alone is not an indication for treatment. Medial therapy by suppression of TSH using thyrox-ine, has failed to have any impact on the progression of the disease and seems inappropriate in view of the tendency of the gland to become hyperthyroid. Radioiodine has also been tried without marked success. Treatment is therefore by surgery which will also afford the opportunity to examine the gland histologically.

Surgical treatment of multinodular goitre should be by total lobectomy or total thyroidectomy. Sub-total resection results in a reported 15% recurrence rate requiring further surgery. Re-resection of a lobe which has previously had a sub-total resection is associated with a 2-4% incidence of permanent recurrent laryngeal nerve damage. The indications for surgery are:

• large dominant nodule;

• increasing gland size;

• increasing size of one nodule;

• retrosternal extension;

• hyperthyroidism;

• symptomatic airway or oesophageal compression. Massive cervical enlargement may not be associated with any compression symptoms. Any patient presenting with dysphagia, dyspnoea, or venous compression should be suspected of having a retrosternal goitre, malignancy or thyroiditis.

In those patients not treated surgically, long-term follow-up is recommended by serial ultrasound scanning and thyroid function tests.

Solitary thyroid nodule

Solitary thyroid nodules may be either:

Cysts. The aetiology is unknown. Histology consists of a thin-walled cyst with a fibrous capsule. In an uncomplicated cyst the fluid is clear. Clinically the patient may present with sudden appearance of a painful swelling indicating haemorrhage into the cyst and, although this may be frightening to the patient, it is rarely associated with any significant compression problems. Where ultrasound scan confirms a thin-walled cyst, treatment is by simple aspiration. However, if any of the following are present:

• scan suggests a thick-walled cyst;

• scan suggests a solid component to the cyst;

• scan suggests any irregularity in the line of the cyst wall;

• fluid aspirate is blood stained;

• swelling does not disappear completely on aspiration;

• swelling recurs rapidly after aspiration then treatment should be by surgical removal. The incidence of malignancy in apparently simple thyroid cysts referred to a surgical clinic has been reported to be as high as 10% and is usually associated with a small papillary carcinoma in the wall of the cyst. The cytology of the fluid is unreliable in excluding malignancy.

Solitary thyroid adenoma. The aetiology is unknown. The histology is of a follicular lesion with a thin capsule and no cell infiltrate into or through the capsule. The natural history of follicular adenoma is of progressive enlargement. It is unclear whether follicular adenoma progresses to microinvasion into the capsule and ultimately to frank carcinoma in a step wise fashion. Investigation is by:

• thyroid function tests to exclude a toxic hot nodule;

• ultrasound scan to exclude a cyst;

Since the cytology of follicular adenoma and carcinoma is identical, it is impossible to exclude malignancy by FNAC of a follicular lesion. The treatment of a solitary thyroid nodule which shows follicular cells on FNAC is by thyroid lobectomy. If the lesion is an adenoma, lobectomy is curative since these lesions are not multifocal. Frozen section histology to try to confirm the diagnosis of malignancy or adenoma can be technically very difficult and is not always accurate, even in the most expert hands.

In a patient who is biochemically thyrotoxic with a solitary nodule, an isotope scan is useful to confirm whether the nodule is a 'hot' hyperfunctioning adenoma with a surrounding suppressed gland or whether the patient has primary thyrotoxicosis and has a cold nodule present. This differentiation is vital if surgery is contemplated.

Malignancy. Despite its vascularity, the thyroid is rarely the site of secondary malignancy. Patients with spread from bronchogenic and breast carcinoma have been described but are very rare and kidney tumour (hypernephroma) is responsible for most cases. Since the thyroid is an ectodermal tissue, the commonest primary malignancy is an adenocarcinoma. In the elderly patient however, a primary non-Hodgkin's lymphoma may develop and this is particularly common in patients with known Hashimoto's thyroiditis.

1. Thyroid lymphoma is a non-Hodgkin B cell lymphoma. Diagnosis by FNAC may be difficult, particularly in the presence of thyroiditis, and therefore open biopsy may be necessary. Surgery is usually not possible and therefore most patients are treated by external radiotherapy. The tumour tends to occur in the elderly and the 5 year survival figure is very low.

2. Adenocarcinoma can be sub-classified according to the cell of origin into tumours arising from follicular cells or from the parafollicular or C-cells (produce calcitonin).

• Medullary carcinomas arise from C-cells and can be subdivided into two types:

The sporadic tumour with no family history presents as a solitary nodule and is treated by total thyroidectomy, node dissection and thyroxine replacement. There is no indication to suppress TSH with this tumour as it is not TSH dependent. Patients should be followed by regular calcitonin assays to detect early recurrence. The 5 year survival figure is 50%.

The familial form is usually multifocal in origin and is associated with MEN (MEN) II syndrome (see below). The treatment is as for sporadic medullary carcinoma but it has a less favourable prognosis, especially in the MEN IIB subtype. In patients who are known to belong to MEN II families, it may be possible to detect and treat those members of the family who will develop medullary carcinoma before they actually develop the disease (see below).

• Adenocarcinoma arising from follicular cells can be subdivided into differentiated and undifferentiated forms. The former are papillary and follicular carcinomas and it is likely that the undifferentiated form, which occurs in elderly patients, may represent a progression from one of the differentiated forms.

Papillary carcinoma is the commonest thyroid malignancy, accounting for over 60% of cases. It tends to occur under the age of 40, is particularly common in teenagers, but can arise at any age. The younger the patient, the more pure is the histological form and the better the life expectancy, with teenagers having a normal life expectancy in almost all cases. In older patients, variant forms of papillary carcinoma are encountered, such as 'follicular variant' and 'tall columnar cell variant', and these have a poorer prognosis.

The patient usually presents with a solitary thyroid nodule and is euthyroid. Metastases are present on approximately 50% of cases to ipsilateral cervical nodes. Distant metastases are exceedingly rare. Diagnosis is made by FNAC confirming papillary cells with optically clear nuclei and nuclear clefts. Since the tumour is usually multifocal in site in the thyroid, total thyroidec-tomy is recommended. Where enlarged nodes are present, these should be removed. Block neck dissection affords no clear benefit over simple node excision. Patients with micro-papillary carcinoma (<1cm) with no nodal involvement should receive thyroxine at a dose to suppress TSH. For all other cases, radioiodine should also be administered about 6 weeks post-surgery.

It is important that these patients are followed up to ensure that their TSH remains suppressed. Thyroglobulin should also be assayed regularly and may give an indication of early tumour recurrence.

Follicular carcinoma can also occur at any age but is most common in the middle-aged female. It is not associated with the good prognosis of papillary carcinoma, 5 year survival rates being about 50%. Histologically the tumour exists in two forms: micro-invasive follicular carcinoma and frankly invasive follicular carcinoma.

The micro-invasive form has a thick capsule with tumour cells penetrating into the capsule but not through into the thyroid substance. There is no vascular or lymphatic invasion. This tumour presents as a solitary nodule and is not multifocal in the thyroid. Treatment is therefore by thyroid lobectomy and thyroxine at a dose to suppress TSH. This results in a good long-term remission.

Invasive follicular carcinoma tends to spread by the vascular as well as the lymphatic route. The patient's presentation may therefore be by metastatic disease, especially if spread is to bone. The majority of patients present with a solitary thyroid nodule and the tumour is diagnosed histologically by tumour capsule penetration into the surrounding thyroid and/or by lymphatic and vascular invasion. Since the cell structure of follicular adenomas, micro-invasive carcinomas, and invasive carcinomas is identical, FNAC is unable to differentiate between these, and formal excision by lobectomy is necessary for accurate diagnosis.

Treatment of invasive carcinoma is by total thyroidectomy, central neck node clearance to the carotid sheaths laterally, radioiodine ablation at 6 weeks and thyroxine to suppress TSH. Bone metastases may require local therapy with external radiotherapy and tend to be radiosensitive.

Figure 16.4. MRI of undifferentiated carcinoma of the thyroid gland showing invasion of the tracheal wall and common carotid artery.

Undifferentiated carcinoma is a highly aggressive and unpleasant tumour. It is difficult to diagnose by FNAC, is not amenable to surgical resection, and progresses rapidly in the neck producing obstructive problems (Fig. 16.4). It responds poorly to radiotherapy and patients rarely survive beyond 1 year. Tracheostomy for respiratory obstruction is not recommended. This usually has a very short-term effect with the patient progressing to further respiratory obstruction due to tumour fungating at the tracheostomy opening.

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