Non-urothelial lesions of the urinary bladder A 14.5-year, single-institution review

Context: In contrast to urothelial cancers, non‐urothelial neoplasms involving the bladder are uncommon and often diagnostically challenging. These lesions include a variety of benign and malignant tumors often presenting with a combination of hematuria and the presence of a polypoid lesion at cystoscopy that may lead to an erroneous diagnosis of urothelial cancer. Objective: We set out to quantify and classify the spectrum of non-urothelial lesions diagnosed in our institution, and briefly review the relevant literature on each lesion, with a focus on differential diagnosis and potential pitfalls. Design: We performed a retrospective review (Jan 2008 – Jun 2022) of the cases diagnosed on TURB material at our institution. Results: Out of 4071 TURB specimens, a total of 66 (1.62 %) non-urothelial lesions were identified. Most of these lesions were malignant (n = 51, 77 %), with metastases being the most common (n = 40, 60.6 %), followed by non-Hodgkin lymphoma (n = 8, 12 %). The remaining cases were benign lesions (n = 15, 22.7 %), with the most common being inflammatory myofibroblastic tumor (n = 4, 6.1 %) and endometriosis (n = 3, 4.5 %). Conclusions: In this retrospective case series, we identified various malignant and benign entities, some of which have been rarely reported in the bladder, such as paragangliomas, inflammatory myofibroblastic tumor, and leiomyosarcoma. These lesions may macroscopically and histologically mimic urothelial carcinoma. Because of their relative rarity and diagnostic overlap with conventional urothelial tumors, the pathologist should always keep in the mind the possibility of non-urothelial lesions.