Granular cell tumor of the infundibulum: a systematic review of MR-radiography, pathology, and clinical findings

Introduction: Granular cell tumors (GCTs) of the infundibulum are rare in practice and literature, resulting in a lack of evidence-based standard of care. We present two characteristic cases from our institution and perform a systematic review of the existing literature to further elucidate the presentation of this tumor and guide management. Methods: A systematic literature search was conducted according to PRISMA guidelines, yielding 42 total individual reported GCTs suitable for evaluation. Available clinical presentation, magnetic resonance imaging (MRI) characteristics, pathology, surgical approaches, and outcomes were charted. We measured frequencies of clinical characteristics and performed an outcome comparison of open versus endoscopic surgical treatment. Results: In this pooled dataset, GCT incidence was higher in females than males (3:1). Clinical presentation peaked in the fourth decade with tumor-related symptoms. MRI appearance was characterized by T1 isointensity (50%) and T2 hypointensity or isointensity (52%) with gadolinium contrast enhancement (74%). Histopathology demonstrated positive staining for PAS, PAS-D, S100, CD68, and TTF1. In a simple uncontrolled analysis, patients who underwent endoscopic surgery experienced more symptom improvement (p = 0.006) and lower incidence of new diabetes insipidus postoperatively (p = 0.047) versus patients who underwent open microsurgery. Conclusions: This first comprehensive review of GCTs of the infundibulum corroborates existing data and adds significant new MR-radiological information to the literature, notably a typical tumor appearance of T1 isointensity, T2 iso- to hypointensity, and gadolinium contrast enhancement. Future prospective studies should be conducted to validate our findings.