Thyroid tumours

Benign thyroid tumours

Most are follicular adenomas
Papillary adenomas are rare
All papillary tumours should be considered malignant

Follicular adenoma

Of all follicular lesions - 80% benign and 20% malignant
They are smooth and discrete lesions with glandular or acinar pattern
They are encapsulated usually 2-4 cm in diameter
Adenomas can not be differentiated from carcinoma on FNA cytology
Requires histological assessment of capsular invasion
Various histological types are described:
- Embryonal - rudimentary acini. No Colloid
- Foetal
- Simple
- Colloid - Well formed acini. Much colloid
- Macrofollicular
- Microfollicular

Toxic adenoma

Account for 5% of cases of thyrotoxicosis
Female : Male ratio is 9:1
Presentation - 54% with a nodule and 37% with thyrotoxicosis
95% of toxic adenomas are benign
Thyrotoxicosis not usually associated with eye signs
Hot nodule on scintigraphy
Treatment is by thyroid lobectomy
Require post operative thyroxine until suppressed gland returns to normal

Malignant thyroid tumours

Differentiated thyroid cancer accounts for 80% of thyroid neoplasms
Female : Male ratio is 4:1
Usually presents as solitary thyroid nodule in young / middle age adult
Nodule more likely to be malignant in man or child
Papillary and follicular tumours are biologically very different

Picture provided by Dr M Schutgens, University of Malawi, Malawi

Comparison of papillary and follicular tumours

Papillary tumours Follicular tumours

Multifocal Solitary

Unencapsulated Encapsulated

Lymphatic spread Haematogenous spread

Metastasize to regional nodes Metastasize to lung, bone and brain

Papillary and mixed tumours

50% tumours are less than 2 cm diameter at presentation
Tumours less than 1 cm diameter regarded as minimal or micropapillary lesions
Psammoma bodies and 'orphan Annie' nuclei are characteristic histological features
30 - 50% are multicentric with simultaneous tumour in contralateral lobe
Early spread occurs to regional lymph nodes
'Lateral aberrant thyroid' almost always metastatic papillary carcinoma
Thyroid lobectomy adequate for minimal lesions
Total thyroidectomy is otherwise surgery of choice
Many tumours are TSH dependent
TSH suppression with post-operative thyroxine appropriate
Thyroxine reduces recurrence and improves survival
80% nodes have microscopic involvement
Role of prophylactic lymph node dissection at time of initial surgery unclear
Lymph node dissection does not improve survival
Alternative is to sample the lymph nodes
If negative - no further surgery
If positive - modified neck dissection

Follicular tumours

Can not differentiate follicular adenoma and carcinoma on FNA cytology
Treatment of all follicular neoplasms is thyroid lobectomy with frozen section
If frozen section confirms carcinoma - total thyroidectomy
If frozen section confirms adenoma - No further surgery required
Total thyroidectomy allows detection of metastases using ¹²³I Scanning during follow up
All patients require suppressive thyroxine therapy
Follow up of thyroid carcinoma
Annual ¹²³I scanning to detect asymptomatic recurrence
Treatment of such recurrence can still be curative
Need to be off T₄for at least one month with conversion to T₃
Serum Thyroglobulin - increasing levels often first sign of recurrence
May allow detection of recurrence without inconvenience of scintigraphy

Total thyroidectomy vs.. thyroid lobectomy for differentiated tumours

Arguments for total thyroidectomy

Multifocal disease occurs in opposite lobe in 50% cases
Total thyroidectomy reduces risk of local recurrence
Ablation with radioiodine is facilitated
Serum thyroglobulin can be used as a tumour marker for progression or recurrence
In experienced hands, morbidity of total thyroidectomy is low

Arguments for thyroid lobectomy

Many patients do not require radioiodine
Progression to undifferentiated carcinoma is rare
Significance of micro-foci in contralateral lobe is uncertain
No evidence that more extensive procedure is associated with better prognosis
Higher incidence of hypoparathyroidism after total thyroidectomy

Anaplastic carcinoma

Accounts for less than 5% thyroid malignancies
Occurs in elderly and is usually an aggressive tumour
Local infiltration causes dyspnoea, hoarseness and dysphagia
Thyroidectomy seldom feasible
Incision biopsy should be avoided as it often causes uncontrollable local spread
Radiotherapy and chemotherapy important modes of treatment
Death usually occurs within 6 months

Thyroid lymphoma

Accounts for 2% of thyroid malignancies
Often arises with Hashimoto's thyroiditis or non-Hodgkin's B-cell lymphoma
Presents as a goitre in association with generalised lymphoma
Diagnosis can often be made by FNA cytology
Radiotherapy is treatment of choice
Prognosis is good - often more than 85% 5 year survival

Medullary carcinoma of the thyroid

Accounts for 8% of thyroid neoplasms
Arises from para-follicular C-cells
20% of cases are familial
Autosomal dominant inheritance with almost complete penetrance
Can occur as part of MEN IIa and MEN IIb syndromes
Genetically determined cases are often bilateral and multifocal
At risk patients can be identified by looking for missense mutation in RET proto-oncogene
These patients can be offered prophylactic thyroidectomy
80% of cases are sporadic
Sporadic cases usually unilateral
50% have lymph nodes at presentation
Tumours metastasize to nodes and via blood to bone, liver and lung
They produce calcitonin, calcitonin gene related peptide and CEA
Total thyroidectomy is treatment of choice
Calcitonin can be used in follow up for the presence of metastatic disease

Bibliography

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