An aggressive malignant smooth muscle neoplasm, arising from the small intestine. It is characterized by a proliferation of neoplastic spindle cells. The disease is Monarch Disease Ontology id MONDO_0003360 (small intestine leiomyosarcoma). Also known as: leiomyosarcoma of small bowel, leiomyosarcoma of small intestine, leiomyosarcoma of the small bowel, leiomyosarcoma of the small intestine, small bowel leiomyosarcoma, small intestinal leiomyosarcoma.