Primary micro neuroendocrine tumor arising in a horseshoe kidney with cyst: report of a case and review of literature

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2121156944757267 webciteNeuroendocrine (NE) tumours include a heterogeneous group of neoplasms arising from NE cells, which are either present in endocrine organs or dispersed through the body, including the gastrointestinal tract, lung, kidney, ovary, testis, et al. The World Health Organization (WHO) classification scheme places neuroendocrine tumors into three main categories: well-differentiated, well-differentiated (low grade) and poorly differentiated (high grade) [1]. The classification of the NE tumours largely depends upon the anatomical site and organ of origin. NE tumours in the lung include four groups of neoplasms with diverse prognosis, i.e. typical and atypical carcinoid, large-cell NE carcinoma (LCNEC) and small cell carcinoma (SCC) [2]. A new classification system for the gastroenteropancreatic NE tumours considers the proliferative activity, with well-differentiated NE tumours and carcinomas being classified as grades 1 and 2, and poorly differentiated NECs are defined as grade 3 [3]. The neuroendocrine (NE) tumours are subdivided into two basic types as carcinoid tumour and neuroendocrine carcinoma in the urinary system and male genital organs. Carcinoid is a rare tumour and similar to its counterpart in other organs, such as lung or gastrointestinal tract. NE carcinoma is extremely rare and also similar to NE carcinoma arising in other organs, which is highly aggressive [4]. Carcinoid tumors in kidney are characteristically low grade malignant tumors with neuroendocrine differentiation. Primary renal neuroendocrine tumors are extremely rare in the world because neuroendocrine cells are not found in normal renal parenchyma, pelvis, and ureter. In the literature, the smallest neuroendocrine tumor is about 2？cm in all cases reported so far.A 45-year-old Chinese man was found a microscopic hematuria incidentally by routine urine examination in a med