Primitive Spindle Cell Neoplasm of Ileum with Extensive Heterotopic Cartilage, Presenting as Acute Abdomen in a 6-Day-Old Neonate.

Neonatal intestinal masses with spindle cell morphology have broad differential diagnoses and require a multidisciplinary approach to make the final diagnosis. Spindle cell masses with heterotopic cartilage in the gastrointestinal tract are very rare, and, to our knowledge, have not previously been reported in the neonate. Here we present a case of intestinal primitive spindle cell neoplasm with extensive heterotopic cartilage that manifested initially as acute abdomen in a 6-day-old term infant. Plain radiography demonstrated pneumoperitoneum, prompting diagnostic laparotomy that identified a perforated mass involving the midileum. Histologic and immunohistochemical examination demonstrated an infiltrative spindle cell tumor most compatible with infantile fibrosarcoma (IFS) by a process of exclusion, with nodules of mature heterotopic cartilage. Additional staging studies did not reveal any evidence of residual or metastatic disease. Recognition of this rare variant of IFS will aid in differentiation from other neonatal intestinal mesenchymal tumors.