Contents
Introduction
Description
Block Taking
Introduction
Specimens of the thyroid gland are the commonest endocrine specimen received by histopathology departments (assuming that gonadal excisions are excluded). Removal of the thyroid gland is usually performed for neoplasia or non-neoplastic goitres, or sometimes to treat hyperthyroidism.
Three types of thyroid specimens are likely to be received.
- Lobectomy - usually reserved for follicular adenoma or carcinoma
- Subtotal thyroidectomy - usually performed only for Grave's disease; a small portion of the isthmus is preserved
- Total thyroidectomy - the whole gland is removed
In practice it may not be possible to distinguish a subtotal and total thyroidectomy macroscopically.
Description
The description of a thyroid gland specimen should state whether one or both lobes are received. For a total or subtotal thyroidectomy the natural shape of the gland should permit it to be anatomically orientated, provided that the gland is not too distorted; this orientation may not be possible for a single lobe unless orientation markers have been applied by the surgeon.
The
weight of the specimen is probably the single most useful dimension.
Each lobe should be measured in three perpendicular linear dimensions, as should the isthmus. The measurements of the components can be supplemented by those for the gland as a whole (in three dimensions).
It should be stated if the gland appears symmetrical or not. Graves' disease tends to produce symmetrical hyperplasia of the gland. A goitre may or may not be symmetrical whereas a neoplasm will usually cause asymmetrical enlargement.
Inking the gland before slicing it is prudent. Whether or not a tumour reaches the surface of the gland is an important parameter of the pathological report. In addition, the surface of the gland in effect constitutes a margin. The use of different colours to denote anterior from posterior is helpful due to the different anatomical relations of the thyroid in these directions. Similarly, distinguishing the medial and lateral aspects of the lobes preserves maximal information.
Once the specimen has been inked the usual method for cutting is to slice the specimen in the transverse plane from superior to inferior. The shape of the gland may make it difficult to slice the two lobes in an identical fashion; if the lobes are asymmetrical this can be impossible and it is acceptable to have a different number of slices for each lobe, provided that this is documented if any further references to the position of a lesion by its slice is employed.
The description of the slices focuses on whether or not a tumour is present. In Graves' disease, the slices will generally have a similar appearance and there will be no focal lesion.
Thryoid tumours are usually solitary from the macroscopic perspective, although papillary carcinoma is renowned for its ability to be multifocal, so it is important to be alert to the possibility of more than one tumour existing in the same specimen.
The description of a thyroid tumour follows general principles. The tumour should be measured in three dimensions and its appearance noted. The relationship to the margins should be noted. Strictly speaking, six margins can be described for a thyroid tumour: anterior and posterior; superior and inferior; medial and lateral.
Multinodular goitres probably pose the greatest challenge during cut up. Their cut surface is often heterogenous and features cystic regions (due to accumulation of colloid) and possibly fibrosis. However, these typically lack the qualities of a tumour, which tends to stand out from the adjacent thyroid and is a focal lesion. By contrast, although a multinodular goitre possesses a heterogenous cut surface, this heterogeneity is recapitulated throughout the gland and lacks the uniqueness of a tumour. The description of a multinodular goitre should reflect this. It should also be remembered that a multinodular goitre may nevertheless contain a tumour that was not suspected clinically.
Block Taking
For Graves' disease and other non-neoplastic goitres representative samples of the thyroid should be obtained from both lobes and isthmus. The basic principles of one block per centimetre or one per ten grams of tissue may help to guide the number of blocks that are taken. If a multiodular goitre has any unique, focal lesions or unusual features, these should be sampled specifically, with a note as to the closest margin and inclusion of that margin in at least one block of the region.
Thyroidectomies performed for a neoplasm follow the usual methods for the block taking of the tumour of a solid organ. The blocks should allow the tumour to be characterised. Four of the six margins should usually be demonstrable within one slice, albeit that several blocks may be necessary to include all of them. An en face block of each of the superior and inferior pole of the affected lobe will complete the last two margins. A couple of blocks of the thyroid away from the tumour should also be taken and the unaffected lobe should not be forgotten in these blocks; opinion is divided as to whether it is necessary to block the entire thyroid gland in the case of papillary carcinoma: these tumours can be multifocal and the additional foci only visible microscopically.
The important variation in the block taking of a thyroid tumour is that if a tumour has been diagnosed as a follicular lesion on FNA, then the entire tumour must be embedded. Differentiating a follicular adenoma from a follicular carcinoma is impossible in an FNA and requires transcapsular or vascular invasion to be demonstrated in the histopathological specimen. Both these types of invasion can be focal and missed if the tumour is only sampled.
Lymph nodes or parathyroid tissue may be included on the surface of a thyroid specimen and attempts should be made to check for these and embed them if they are present.