A rare case of eosinophilic cystitis involving the inside and outside of the urinary bladder associated with an infected urachal cyst

Abstract Background Eosinophilic cystitis is a rare inflammatory disease of the bladder characterized by eosinophilic infiltration of the bladder wall. Most Eosinophilic cystitis cases present with mucosal lesions of the urinary bladder. We present a very rare case of large mass-forming eosinophilic cystitis, involving the inside and outside of the bladder associated with an infected urachal cyst. Case presentation A 59-year-old man presented with gross hematuria, fever, dysuria, and suprapubic pain. Computed tomography showed a heterogeneously enhancing mass that measured 7.6 cm × 4 cm located on the anterosuperior portion of the bladder with an internal fluid collection. Cystoscopy revealed a raspberry-like mass lesion on the bladder dome. Transurethral resection of the bladder was initially performed. The mass lesion protruding from inside the bladder was removed, and pus-like fluid was drained. The pathologic diagnosis was eosinophilic cystitis. Follow-up computed tomography showed a remnant mass outside the bladder and urachal cyst. To eliminate the remnant lesion, robot-assisted partial cystectomy was performed. The patient showed no evidence of recurrent disease on follow-up cystoscopy and computed tomography for up to 2 years. Conclusions Clinicians should consider the possibility of eosinophilic cystitis in patients who present with hematuria, fever, and suprapubic pain and have both intravesical and extravesical masses