1. SOLITARY METASTASIS OF RENAL CLEAR CELL CARCINOMA TO HÜRTHLE CELL ADENOMA OF THYROID GLAND: REPORT OF A CASE RITA PASSANTINO - LORENZO MARASA’ Department of Pathology, A.R.N.A.S. Civico, Palermo RITA PASSANTINO - LORENZO MARASA’ Department of Pathology, A.R.N.A.S. Civico, Palermo

2. INTRODUCTIONINTRODUCTION  Metastases to the thyroid gland are a common finding at autopsy in patients who died of malignancy and are often misdiagnosed as primary thyroid neoplasms clinically.  Metastatic Renal Cell Carcinoma (RCC) to the thyroid gland is a rare occurence but must be considered in the differential diagnosis of Clear Cell Tumours (CCT) of the thyroid gland to prevent misclassification, potentially resulting in inappropriate clinical management.  We present a patient with a rare, unusual case of RCC metastatic to a Hürthle cell adenoma of the thyroid gland.  Metastases to the thyroid gland are a common finding at autopsy in patients who died of malignancy and are often misdiagnosed as primary thyroid neoplasms clinically.  Metastatic Renal Cell Carcinoma (RCC) to the thyroid gland is a rare occurence but must be considered in the differential diagnosis of Clear Cell Tumours (CCT) of the thyroid gland to prevent misclassification, potentially resulting in inappropriate clinical management.  We present a patient with a rare, unusual case of RCC metastatic to a Hürthle cell adenoma of the thyroid gland.

3. CASE REPORT  The patient was a 77-year-old sicilian woman who was referred to our department after a thyroid tumour was identified in February 2008.  She had a history of RCC of the left kidney, which had been resected 3 years previously.  Ultrasound sonography demonstrated a well- demarcated hypoechoic mass which measured 3.5 cm in greatest diameter and occupied the left lobe.  A total thyroidectomy was performed on March 2008.  A solitary, well circumscribed, encapsulated, bright yellow to reddish-tan mass with hemorrhage and degenerative changes, which measured 3.5 cm in greatest diameter and occupied the left lobe of the thyroid gland.  The patient was a 77-year-old sicilian woman who was referred to our department after a thyroid tumour was identified in February 2008.  She had a history of RCC of the left kidney, which had been resected 3 years previously.  Ultrasound sonography demonstrated a well- demarcated hypoechoic mass which measured 3.5 cm in greatest diameter and occupied the left lobe.  A total thyroidectomy was performed on March 2008.  A solitary, well circumscribed, encapsulated, bright yellow to reddish-tan mass with hemorrhage and degenerative changes, which measured 3.5 cm in greatest diameter and occupied the left lobe of the thyroid gland.

4. HISTOLOGICAL EXAMINATION  A Hürthle cell adenoma containing large clusters of cells with abundant clear cytoplasm and round nuclei.  The predominant histologic pattern was characterized by the presence of small nests, cords and “pseudofollicles” made up of neoplastic cells separated by a prominent vascular stroma with sinusoidal-type blood vessels and intraluminal fresh hemorrhage.  Metastatic cells contained variable amounts of PAS- positive material which was indicative of glycogen in the cytoplasm of the clear cells.  Metastasis showed morphological characteristics identical to the RCC resected 3 years previously.  A Hürthle cell adenoma containing large clusters of cells with abundant clear cytoplasm and round nuclei.  The predominant histologic pattern was characterized by the presence of small nests, cords and “pseudofollicles” made up of neoplastic cells separated by a prominent vascular stroma with sinusoidal-type blood vessels and intraluminal fresh hemorrhage.  Metastatic cells contained variable amounts of PAS- positive material which was indicative of glycogen in the cytoplasm of the clear cells.  Metastasis showed morphological characteristics identical to the RCC resected 3 years previously.

9. IMMUNOHISTOCHEMICAL EXAMINATION  Specific markers of Hürthle cell adenoma such as thyroglobulin, CK14, CEA, S-100 protein and HMB-45 stained negatively in the clear neoplastic cells.  Specific markers of RCC such as EMA and vimentin stained positively.  Specific markers of Hürthle cell adenoma such as thyroglobulin, CK14, CEA, S-100 protein and HMB-45 stained negatively in the clear neoplastic cells.  Specific markers of RCC such as EMA and vimentin stained positively. THYROGLOBULIN VIMENTIN EMA

10. CONCLUSIONSCONCLUSIONS  The thyroid gland is a rare site of tumour metastasis.  RCC is one of the more common neoplasm to metastasize to the thyroid gland (<0.1%).  Metastatic RCC to a thyroid neoplasm is extremely rare, with only three reports found in the international literature.  The possibility of metastatic RCC should always be taken under consideration, especially when nests of clear cells are seen infiltrating into the thyroid parenchyma or neoplasm.  The thyroid gland is a rare site of tumour metastasis.  RCC is one of the more common neoplasm to metastasize to the thyroid gland (<0.1%).  Metastatic RCC to a thyroid neoplasm is extremely rare, with only three reports found in the international literature.  The possibility of metastatic RCC should always be taken under consideration, especially when nests of clear cells are seen infiltrating into the thyroid parenchyma or neoplasm.

11. CONCLUSIONSCONCLUSIONS  Our report shows that the architectural, cytologic, hi- stologic, histochemical, and immunohistochemical fea- tures are sufficiently distinctive to allow differentation of a primary thyroid epithelial neoplasm with clear cell changes from metastatic RCC.  This distinction is important to correctly manage the patient.  Surgical treatment is recommended as the patient may enjoy a prolonged survival. MAIN REFERENCE: Qian L. Renal cell carcinoma metastatic to Hürthle cell adenoma of thyroid. Ann Diagn Pathol. 2004 Oct; 8(5): 305-8. Qian L. Renal cell carcinoma metastatic to Hürthle cell adenoma of thyroid. Ann Diagn Pathol. 2004 Oct; 8(5): 305-8.  Our report shows that the architectural, cytologic, hi- stologic, histochemical, and immunohistochemical fea- tures are sufficiently distinctive to allow differentation of a primary thyroid epithelial neoplasm with clear cell changes from metastatic RCC.  This distinction is important to correctly manage the patient.  Surgical treatment is recommended as the patient may enjoy a prolonged survival. MAIN REFERENCE: Qian L. Renal cell carcinoma metastatic to Hürthle cell adenoma of thyroid. Ann Diagn Pathol. 2004 Oct; 8(5): 305-8. Qian L. Renal cell carcinoma metastatic to Hürthle cell adenoma of thyroid. Ann Diagn Pathol. 2004 Oct; 8(5): 305-8.