Spontaneous dissolution of a renal pelvic stone with intrastone gas: A case report with serial CT findings.

Spontaneous dissolution of a large renal pelvic stone is extremely rare. We report the case of a 65-year-old man with paraplegia below Th6 who experienced recurrent febrile urinary tract infections beginning in May 2016. Noncontrast computed tomography (CT) in August 2016 revealed a right renal pelvic stone measuring 26 × 13 mm. During long-term follow-up, serial CT imaging demonstrated structural homogenization, central cavitation, progressive rim thinning associated with intrastone gas, and complete disappearance by November 2020. CT attenuation analysis suggested a uric acid-dominant core surrounded by a calcium-containing shell. Extremely low attenuation values within the central cavity (mean -364 HU) supported the presence of intrastone gas rather than fluid. These observations may suggest that dynamic interactions among urinary pH, stone composition, and intrastone bacterial activity may promote progressive internal weakening and spontaneous dissolution of mixed-composition renal stones.