Multiple Unilateral Subcapsular Cortical Hemorrhagic Cystic in the Left Kidney Disease: A Case Report of a Potential New Clinical Entity in Young Adults.

Introduction: Unilateral renal polycystic disease is a rare condition, first described in 1964, with over 60 cases reported worldwide. In 2019, Yoshida et al. [Eur Radiol. 2019;29(9):4843-50] identified 14 patients with unilateral renal cysts, who exhibited distinctive clinical and radiological features: young adults with multiple unilateral subcapsular cortical hemorrhagic (MUCH) cysts in the left kidney. The epidemiology, etiology, clinical significance, and prognosis of this condition remain largely unknown. Case Presentation: We report a 36-year-old male who presented with nephrotic syndrome, generalized edema, and impaired renal function, requiring renal replacement therapy. Magnetic resonance imaging revealed unilateral subcapsular hemorrhagic cysts in the left kidney, with nearly normal renal size. A percutaneous biopsy of the right kidney showed acute tubular necrosis and focal segmental glomerulosclerosis, tip lesion variant. The patient achieved complete remission shortly after initiating immunosuppressive therapy, with full recovery of renal function. Whole exome sequencing did not reveal any pathogenic variants. A 99Tcm-DMSA scintigraphy, performed 20 months after the initial presentation, showed a renal uptake of 11.3% (reference range: 30 ± 6%) in the affected kidney, with normal uptake in the right kidney. Conclusion: MUCH cysts in the left kidney, observed in young adults, may represent a novel clinical entity. However, the epidemiology, etiology, clinical implications, and prognosis of this condition remain to be fully elucidated.