Retroperitoneal cellular schwannoma (CS): a potential pitfall of malignancy. Report of a case and review of the literature

Cellular Schwannoma (CS) is a well-recognized morphological variant of schwannoma, which has been reported in many usual and unusual sites. We herein report a rare case of a bulky, retroperitoneal cellular schwannoma showing challenging radiological and morphological features. Due to large size and ill-defined margins at CT examination a malignant soft tissue tumor (sarcoma) was suggested. At histological examination high cellularity and co-existence of several growth patterns, such as fascicular, storiform and herringbone patterns, contributed to make difficult its recognition as schwannoma. The present case emphasizes the possibility that retroperitoneal CS can represent a potential diagnostic pitfall of malignancy. Awareness of the possibility that this unusual variant of schwannoma may occur in the retroperitoneum is crucial to avoid potential confusion with malignant tumors, especially when evaluating small biopsies.