Malignant gastrointestinal neuroectodermal tumor (GNET) presenting as Ileocaecal intussusception: A rare cause of acute intestinal obstruction in adults

GNET is an exceptionally rare and aggressive mesenchymal tumor of the gastrointestinal tract, characterized by EWSR1 gene rearrangements. This report describes a unique case of GNET originating from the ileum of a 52-year-old male, presenting as acute intestinal obstruction due to ileocaecal intussusception. The patient experienced abdominal distension, pain, and vomiting for three days. Imaging revealed intussusception, prompting emergency laparotomy. Intraoperatively, a polypoidal mass was identified in the distal ileum as the lead point. Surgical resection of tumor with ileo-ileal anastomosis was performed successfully, and the post-operative course was uneventful. Gross pathology showed a well-circumscribed, submucosal mass arising from the muscularis propria of the ileum, with hemorrhagic and necrotic changes. Histologically, the tumor showed spindle cells with pleomorphic nuclei, arranged in fascicles and interspersed with stag horn-type vasculature. Immunohistochemistry ruled out differential diagnosis such as GIST and leomyoma, with negative DOG1, CD117, and DESMIN markers. Strong CD34 positivity confirmed the diagnosis of Solitary Fibrous Tumor. Risk stratification classified the tumor as low risk. Interestingly, on postoperative follow-up after 4 months, the patient presented with multiple subcutaneous swellings of various sizes over the extremities. FNAC of the swellings surprisingly revealed histopathological features positive for S100, CK8/18 (scattered cells). Tumor cells were negative for SMA, DESMIN, HMB45, SOX10, MELAN A, CD117, DOG1, CK, GATA3, PAX8, HEPAR, CDX2, SATB2, ALK, Synaptophysin, and WT1. KI67 index showed 50%, leading to differential diagnosis of malignant GI neuroectodermal tumor, Malignant peripheral nerve sheath tumor, and sarcomatoid carcinoma. This case underscores the importance of considering rare neoplastic etiologies in adult intussusception. Comprehensive diagnosis involved clinical assessment, radiological imaging, histopathology, and immunohistochemistry. Due to its rarity and aggressive nature, GNET poses diagnostic and therapeutic challenges, necessitating awareness and a multidisciplinary approach.