Three cases of retroperitoneal schwannoma diagnosed by EUS-FNA

Schwannomas are peripheral nerve tumors that are typically solitary and benign. Their diagnosis is largely based on surgically resected specimens. Recently, a number of case reports have indicated that retroperitoneal schwannomas could be diagnosed with endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). We report the diagnosis of three cases of schwannoma using EUS-FNA. Subjects were two males and one female, ages 22, 40, and 46 years, respectively, all of whom were symptom-free. Imaging findings showed well-circumscribed round tumors. However, as the tumors could not be diagnosed using these findings alone, EUS-FNA was performed. Hematoxylin-eosin staining of the resulting tissue fragments revealed bland spindle cells with nuclear palisading. There was no disparity in nuclear sizes. Immunostaining revealed S-100 protein positivity and all cases were diagnosed as schwannomas. Ki-67 indexes were 3%-15%, 2%-3%, and 3%, respectively. No case showed any signs of malignancy. As most schwannomas are benign tumors and seldom become malignant, we observed these patients without therapy. All tumors demonstrated no enlargement and no change in characteristics. Schwannomas are almost always benign and can be observed following diagnosis by EUS-FNA.