Primary thyroid-like follicular carcinoma of the kidney is a rare but newly emerging histological variant of renal cell carcinoma RCC, with only nine cases reported in the literature to date. We present a further case of this unique condition, discuss the workup and typical histological findings, and review the literature regarding this rare histological variant. 1. Introduction Renal cell carcinoma (RCC) accounts for 2-3% of all cancers, and its incidence is increasing worldwide [1]. It is the commonest solid renal malignancy, accounting for approximately 90% of all renal cancers, and comprises a number of distinct pathological entities. The World Health Organisation Classification of Tumours [2] introduced several new entities in 2004, such as RCC associated with neuroblastoma and mucinous tubular and spindle cell carcinoma. However, a more recently described histological entity has emerged for which there is currently very little clinical data—thryoid-like follicular carcinoma of the kidney (TLFCK). This rare tumour morphologically resembles follicular carcinoma of the thyroid gland, with follicular structures containing abundant colloid-like material, and currently only nine cases have been reported in the world literature [3–6]. We describe a further case of this rare histological entity and provide a review of the literature. 2. Case Report A 29-year-old woman presented to her General Practitioner with a long history of left-sided abdominal pain. She had no haematuria, urinary tract infections, or lower urinary tract symptoms, and apart from one previous normal vaginal delivery, no relevant past medical or family history of note. Physical examination of the thyroid and abdomen was normal. Laboratory data, including thyroid-function tests, were within normal limits, and an ultrasound scan revealed a complex multiseptated, and partly cystic, mass arising from the lower pole of the left kidney. Subsequent investigation with a computed tomography (CT) scan confirmed a lobulated, low-attenuation lesion in the lower pole of the left kidney, with no measurable enhancement following contrast administration (see Figure 1). There was no evidence of renal vein involvement, lymphadenopathy, or metastatic disease. Figure 1: (a) Noncontrast coronal CT scan showing mass in lower pole of left kidney (see arrow). (b) Postcontrast coronal CT scan showing no measurable enhancement. A magnetic resonance imaging (MRI) scan was performed to determine whether there was a haemorrhagic component, but this was not seen. There was no enhancement following gadolinium
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