Synchronous Schwannoma and Gastrointestinal Stromal Tumor in Small Intestine – A Rare Case

Introduction/Objective Small bowel Schwannoma is a benign neoplasm of nerve sheath cells. The Gastrointestinal stromal tumor (GIST) constitutes only about 1-2% of small bowel spindle cell tumors. The simultaneous presence of two tumors in the small bowel is extremely uncommon. Methods/Case Report We report a case of small bowel GIST co-existing with Schwannoma. A 64-year-old female with a known history of Neurofibromatosis was admitted for excision of a small bowel tumor. MRI of the abdomen revealed two enhancing lesions in the left upper quadrant adjacent to the small bowel. Differential considerations included GIST versus Neurofibroma. Left hemicolectomy with small bowel resection was performed. The proximal small bowel revealed GIST, spindle cell type, low risk (3.5 cm), low grade (<5 mitoses/ 5mm2). Tumor cells were diffusely reactive to CD34, CD117, and DOG1 immunostains and were nonreactive to S100 and SOX10 immunostains confirming the diagnosis of GIST. Another segment of the small bowel revealed a 1.5 cm well-circumscribed, predominantly spindle cell tumor with abundant myxoid stroma and prominent cyst formation. Tumor cells were diffusely reactive to S100 and SOX10 immunostains but nonreactive to CD34, CD117, and DOG1, favoring a diagnosis of Schwannoma. Gastrointestinal Schwannomas may be associated with Neurofibromatosis in some cases. GIST, a KIT- or PGDFRA-signaling driven mesenchymal tumor has also rarely been reported to be associated with Neurofibromatosis type 1. However, synchronous small bowel Schwannoma and GIST represent a rare co-existence of two different histopathologic subtypes of spindle cell tumors. Results (if a Case Study enter NA) NA Conclusion In summary, we present the rare co-existence of two different spindle cell lesions in Neurofibromatosis patient.