[Atrophic kidney-like lesion: a clinicopathological study of three cases]

Objective: To investigate the clinicopathological characteristics, immunophenotypes, diagnostic criteria and differential diagnosis of atrophic kidney-like lesion (AKLL). Methods: Three cases of AKLL were collected from April 2021 to October 2023 at the Xiangya Hospital of Central South University, Changsha, Zhejiang Provincial People's Hospital, Hangzhou and Ningbo Clinical Pathology Diagnosis Center, Ningbo, China. The clinical, morphological, and immunohistochemical characteristics were analyzed. Relevant literature was also reviewed. A targeted DNA-based next-generation sequencing (a panel of 150 genes) was performed on one of the three cases. Results: There were 1 female and 2 males, aged 30, 57, and 17 years (mean 34.6 years), respectively. The lesions were all incidentally identified during physical or imaging examination. Radiologically, they were all presented as a unilateral renal parenchymal mass. Grossly, the maximum diameters of the lesions were 1.8, 4.0, and 6.5 cm (mean 4.1 cm), respectively. The tumor cut-surfaces were sponge-like, multilocular cystic, and solid, respectively. At low magnification, the lesions were well-circumscribed, while a thick fibromuscular capsule was noted in cases 1 and 3. Cases 1 and 2 were composed of thin-walled cysts or follicular like structures of varying sizes, with the cyst wall lined by flattened and atrophic, or hobnail cells. The luminal spaces contained dense eosinophilic secretion and associated calcifications, while some cysts contained discohesive cells floating in the eosinophilic material. The tissue between the cysts showed predominantly small atrophic tubular structures. Case 3 was almost entirely composed of atrophic and collapsed tubular structures with focal cyst formation, imparting a solid sheets growth pattern under low magnification. Immunohistochemical staining revealed that the cyst lining cells and the intracystic floating cells were WT1 positive, PAX8 negative and CK7 negative, while the atrophic renal tubules were WT negative, PAX8 positive and CK7 positive. Targeted next-generation sequencing in case 1 showed no significant genetic abnormalities. All 3 patients underwent partial nephrectomy. No evidence of recurrence or metastasis was found with a follow-up of 17 to 36 months. Conclusions: AKLL is a rare and novel benign renal disease. It is easily misdiagnosed as a renal neoplasm grossly and histologically. Careful morphological observation combined with characteristic immunophenotypes can aid in its diagnosis and differential diagnosis.