Histological Typing of Thyroid Tumours - libdoc.who.int - World ...

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76 3 Malignant Lymphomas (Figs.75, 76) Malignant lymphomas can involve the thyroid as the only manifestation of the disease or as part of systemic spread. The majority of primary thyroid lymphomas arise on a background of chronic thyroiditis. Cases of thyroid lymphoma have often been misdiagnosed in the past as small cell carcinoma of diffuse type, mainly because of entrapment of follicles and 'packing' of their lumina by tumour cells. Staining for leucocyte common antigen or similar antigens is usually positive in malignant lymphoma, and is therefore of use in the differential diagnosis. Tumour extension outside the thyroid capsule is associated with an unfavourable prognosis. If dissemination occurs, involvement of the gastrointestinal tract is often a feature. The large majority of thyroid lymphomas are of non-Hodgkin's type and should be classified using the same terminology as is applied to lymphoid tissues. Most are of the diffuse, large, non-cleaved (centroblastic) type, a B-cell malignancy of follicular centre cell derivation. The second most common form is the immunoblastic type, sometimes exhibiting prominent plasmacytoid features. Cases of primary plasmacytomas of the thyroid have also been reported. 4 Miscellaneous Tumours Parathyroid tissue can occasionally be found within the thyroid gland. Normal parathyroid tissue is usually easily distinguished from thyroid tissue but intrathyroid parathyroid lesions, especially adenomas with follicular structures or oncocytic changes, may pose diagnostic problems. Paragangliomas identical to those occuring in the carotid body can exceptionally be found within the thyroid, sometimes in association with paragangliomas at other sites (Figs.77,78). They can resemble medullary carcinomas with a nesting configuration of the tumour cells. A very rare and unusual thyroid tumour of young individuals composed of an admixture of spindle-shaped (keratin-positive) epithelial cells and well-differentiated mucin-producing glandular structures has been described as 'spindle cell tumour with mucous cysts'. This is a low-grade malignancy of obscure histogenesis which should be distinguished from undifferentiated carcinoma and malignant teratoma.
77 Exceptionally, teratomas can be seen in or adjacent to the thyroid. Most of them occur in the newborn and are usually benign. Tumours with features of carcinosarcoma are classifred as undifferentiated carcinoma (see discussion under'Undifferentiated Carcinoma'). 5 Secondary Tlmours (Figs.79-82) Microscopic metastases to the thyroid are common findings in carefully studied autopsies of patients with malignant tumours, particularly malignant melanomas and carcinomas of lung and breast. They are however rarely a cause of clinical thyroid enlargement. While any carcinoma may present in this way, renal cell carcinoma shows a particular predilection for large clinically solitary thyroid metastases. These may simulate a primary thyroid neoplasm both clinically and pathologically, often showing one or several sharply limited tumours that may have a central hyalinized scar and histologically resemble clear cell follicular carcinoma or adenoma. Staining for thyroglobulin can help distinguish these tumours from primary clear cell tumours of the thyroid. The majority of thyroid tumours composed solely of clear cells appear to be metastases. The thyroid may be involved by direct extension from head-and-neck tumours including pharyngeal, laryngeal and oesophageal squamous cell carcinomas. 6 Unclassified Tirmours Benign or malignant tumours that cannot be placed in any of the categories described above. 7 Tirmour-like Lesions Hyperplastic goitres (Figs.83-88), both diffuse and nodular [e.g. Graves' disease (Basedow's disease), endemic goitre and dyshormonogenetic goitresl, often exhibit areas of follicular proliferation with infoldings which may simulate neoplastic papillae. The macropapillary structures of nodular hyperplasia may also be confused with papillary carcinoma. Hyperplastic nodular goitres often contain encapsulated adenoma-like lesions with atypical cellularity and irregularity of outline at the capsular margin suggesting the diagnosis of follicular
Page 1 and 2: Histological Typing of Thyroid Tumo
Page 3 and 4: General Preface to the Series Among
Page 5 and 6: Preface to Histological Typing of T
Page 7 and 8: Table of Contents Introduction Hist
Page 9 and 10: XII Sobin. L.H.. Dn Department of G
Page 11 and 12: aspiration as a pre-operative diagn
Page 13 and 14: Definitions and Explanatory Notes 1
Page 15 and 16: 1.2 Malignant 1.2.1 Follicular Carc
Page 17 and 18: 9 1.2.2 Papillary Carcinoma (Figs.
Page 19 and 20: with metastasis from those that are
Page 21 and 22: 73 pleomorphism than normal C cells
Page 23: 75 guished from direct extension fr
Page 27: Subject Index Page Figures Adenolip
Page 31 and 32: L) G' * ry x340 Fig.6. Follicular a
Page 33 and 34: Fig.9, Atypical adenoma. Considerab
Page 35: )1 "i, tt hig. 13. llralinizing tru
Page 39: 31 x 135 Fig.2l. Follicular carcino
Page 42 and 43: 1A J+ Fig.21. Follicular carcinoma,
Page 44 and 45: x 135 Fig,31. Follicular carcinoma,
Page 46 and 47: Fig.35. Papillary carcinoma. Psammo
Page 49: Fig. 41. Papillary carcinoma, folli
Page 52 and 53: Fig.47. Medullary carcinoma. Same c
Page 54 and 55: 46 x 340 Fig.57. Medullary carcinom
Page 57 and 58: Fig. 57. Undilferentiated carcinoma
Page 59 and 60: Fig.67. Undffirentiated carcinoma.
Page 61: Fig. 65. Undifferentiated carcinoma
Page 65 and 66: Fig.1 4, Malignant haemangioendothe
Page 67 and 68: Fig.78. Intrathyroid paraganglioma.
Page 69: Fig.87. Metastasis of a renal clear
Page 72 and 73: X IJ) Fig. 87. Hyperplastic goitre
Page 75 and 76:
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