Atrophic kidney-like lesion: A rare benign entity and mimicker of thyroid follicular-like carcinoma of kidney

ABSTRACT

Atrophic kidney like lesion (AKLL) is a recently described benign entity with only 14 cases reported so far. Genitourinary Pathology Society proposed inclusion of AKLL as a provisional entity in 2021. It mimics thyroid follicular-like carcinoma of kidney as it has a follicular architecture. We report a case of an 18-year-old female with detection of renal mass, while the patient was being investigated for abdominal pain. Mediastinal nodes were also enlarged with detection of necrotizing granulomas on biopsy. Histology revealed a tumor enveloped by a thick capsule with smooth muscle fibers, varying sized follicles, interspersed atrophic tubules, and calcifications. Immunohistochemically, the “cystic follicles” show WT1 +/PAX8 -/CK7-phenotype, while atrophic tubules present between “cystic follicles” harbor WT1 -/PAX8 +/CK7 + phenotype. Morphological diagnosis and differential diagnosis will be discussed.