Thyroid papillary carcinoma in lateral neck cyst: missed primary tumour or ectopic thyroid carcinoma within a branchial cyst?

Dear Sirs, I read with great interest the report by Sidhu et al. which described a papillary thyroid carcinoma arising in a branchial cyst. The authors indicate ve points which show that their diagnosis is correct. I disagree with each of these ‘‘proofs’’ as follows 1. ‘‘The ne needle aspirate yielded cholesterol crystals and foamy macrophages typical of a branchial cyst. Fine needle aspiration of a lymph node replaced by papillary thyroid carcinoma characteristically yields dark brown uid. ’’ In my experience cystic papillary carcinomas both in the thyroid and in cystic nodal metastases can contain cholesterol crystals and macrophages. This is a reection of old haemorrhage into the cyst. ,3 2. ‘‘The cyst lining consisted of an epithelial layer and a subepithelial collection of lymphoid tissue typical of a branchial cyst. ’’ I suggest rather that the lymphoid tissue represented lymph node. No mention is made of the presence or absence of nodal architecture, such as a subcapsular sinus; admittedly if a lymph node is totally or almost totally replaced by tumour, underlying architecture may be difcult to discern. However, if lymphoid tissue was present careful examination should be helpful in dening whether it was a lymph node. The cyst lining was columnar and not squamous or respiratory. I suggest that the columnar lining is part of the thyroid tumour which became cystic. Indeed this epithelium did stain for thyroglobulin. 3. ‘‘Normal thyroid was found within the cyst wall adjacent to the focus of papillary carcinoma. ’’ Metastatic papillary carcinoma can show normal appearing thyroid follicles in nodes. This is not ‘‘normal’’ thyroid but very well differentiated thyroid carcinoma. Did the authors perform immunostains for high molecular weight cytokeratin which may help if positive to dene this ‘‘normal thyroid’’ as cancer. 4. ‘‘There was no evidence of carcinoma in the total thyroidectomy specimen which was embedded and ‘‘examined at 1 mm cuts’’. There was no connection noted between the cystic neck mass and the pharynx or hyoid bone. ’’ In my experience, the primary tumour in the thyroid in patients such as the one described can be submillimeter in size. Alternatively, the primary may have regressed so that only an area of scar or brous tissue remains. Without serial sectioning of all the blocks of the totally embedded thyroid the authors cannot be sure there was no thyroid primary. 5. ‘‘The other possibility was a laterally placed thyroglossal duct cyst. ’’ This explanation is not valid since the lining of a thyroglossal cyst is respiratory and/ or squamous and the thyroglossal duct cyst should not contain lymphoid tissue. In summary, I believe that the diagnosis in this reports is open to question. I fear that such reports might lead to inadequate therapy of patients presenting as in this case with a cystic lateral neck mass containing papillary cancer. Hence no thyroidectomy would be performed if the gland were clinically and radiologically without nodules. The ve-year survival in this patient is not unexpected since appropriate therapy was given (total thyroidectomy); in fact he may be cured. However, ve years may be insufcient follow-up. I have personally seen a patient who had a cystic papillary carcinoma metastasis in a lateral cervical lymph node. No thyroidectomy was undertaken because no lesions were identied in the gland. Nine years later recurrent cervical node metastases were found. Total thyroidectomy disclosed two separate papillary microcarcinomas (1 mm and <1 mm in size). Hence, very small papillary carcinomas can metastasize, be unrecognizable in the thyroid gland and be very slowly growing. The intriguing biological question is why this happens in some patients.