A morphologic classification of peripheral neuroblastic tumors has been established by the International Neuroblastoma Pathology Committee in 1999 and subsequently revised in 2003. It divides the tumor into two prognostic groups – favorable histology and unfavorable histology. This classification is based on patient age, degree of Schwannian stroma development (stroma-poor, stroma-rich, and stroma-dominant), histologic grade (undifferentiated, poorly-differentiated, and differentiating), and Mitotic-Karyorrhectic Index (low, intermediate, high). The upper part of the image shows a band of residual adrenal cortex. The lower two-thirds shows neuroblastoma, undifferentiated subtype, composed of a uniform population of small cells with round hyperchromatic nuclei and little cytoplasm.