Main Menu Pathology | Bladder II - [click on image(s) below] Inverted Papilloma Etiology remains uncertain: some people think this is a neoplastic phenomenon, others think it is reactive. Clinical features: middle-aged men, presenting with hematuria or irritative symptoms Gross: usually single, small, and involve the trigone where they appear as smooth domed masses Histologic features: Trabecular type consists of anastomosing cords and sheets or urothelium that arises from the overlying mucosal surface Glandular type consists of nests of urothelium with pseudoglandular differentiation (i.e., lined by urothelium) or glandular differentiation (i.e., lined by goblet cells) may be associated with non-keratinizing squamous metaplasia cytologic atypia is minimal, and mitoses are rare or absent The differential diagnosis here is invasive TCC; check the overlying mucosa to help distinguish the two: if the mucosa is normal, favor inverted papilloma; if it is abnormal, think about invasive TCC.