Intra-abdominal spindle cell lesions: a review and practical aids to diagnosis

Intra‐abdominal spindle cell lesions: a review and practical aids to diagnosis Intra‐abdominal spindle cell lesions are uncommon and often present a diagnostic challenge. An important group of such lesions are the gastrointestinal stromal tumours. Other intra‐abdominal spindle cell lesions include fibromatosis, various sarcomas—in particular, leiomyosarcoma, liposarcoma, and malignant peripheral nerve sheath tumour—and, in women, endometrial stromal sarcoma. Less common lesions are inflammatory myofibroblastic tumours, the mesenteric spindle cell reactive lesions, retroperitoneal fibrosis, and solitary fibrous tumour. A variety of intra‐abdominal tumours of nonmesenchymal origin may have a spindle cell/sarcomatoid morphology; these include sarcomatoid carcinoma, malignant melanoma and, in women, sarcomatoid granulosa cell tumour. Finally, metastatic sarcomas from pelvic or extra‐abdominal organs need also be considered. A set of practical aids to the diagnosis of intra‐abdominal spindle cell lesions is presented to assist pathologists dealing with such lesions, particularly with regards to the consideration of differential diagnoses.