Abundant intracytoplasmic hemosiderin in both histiocytes and neoplastic cells: A diagnostic pitfall in fine-needle aspiration of cystic papillary renal-cell carcinoma

Benign renal tubular cells and renal-cell carcinomas (RCC) may have intracytoplasmic hemosiderin (ICH). The RCC subtype most commonly reported to contain ICH is papillary carcinoma (PRCC). PRCC, usually a low-grade neoplasm, may be associated with cystic degeneration, hemorrhage, and presence of abundant hemosiderin-laden macrophages (HLM). We report a case of PRCC with massive ICH and HLM that created a diagnostic challenge to differentiate from a hemorrhagic cyst. Review of 14 additional nephrectomy specimens with PRCC disclosed ICH in 3 cases. All had coexisting cystic change and hemorrhage. Preoperative FNA had been performed in one of these cases, and both ICH and HLM were found. Papillary epithelial cell features, however, were well-defined in this case. PRCC should be considered in the differential diagnosis of cystic renal lesions with hemosiderin-laden cells. Differentiation of HLM from neoplastic cells with massive ICH may be difficult, especially when epithelial fragments are scanty.