Clear cell and signet-ring cell variants of follicular neoplasms may cause diagnostic difficulty.
Clear cell change can occur in nodular goitre, follicular neoplasms, papillary carcinoma and medullary carcinoma.
Frequently it represents clear cell metaplasia in a Hürthle cell neoplasm.
This change may be focal or extensive.
Cytologically, there is abundant pale diffusely vacuolated cytoplasm superimposed on the features of the underlying neoplasm.
Where the clear cell change is extensive the possibility of a non-thyroid neoplasm should be considered, in particular a parathyroid tumour or metastatic carcinoma of the kidney.
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