A cooperative approach to diagnosis of rare diseases: primitive myxoid mesenchymal tumor of infancy.

Primitive Myxoid Mesenchymal Tumor of Infancy (PMMTI) is a recently recognized locally aggressive myofibroblastic tumor. It is a low- to intermediate-grade fibroblastic malignancy with a high local recurrence rate but low metastatic potential and is composed of primitive spindled cells in a myxoid background. We present the eleventh reported case of PMMTI, occurring in the sinonasal tract of a 3-year old child. This case is novel in both the relatively older age of the child, the location of the tumor, and the role that immunohistochemical stains, and cytogenetic analysis played in differentiating it from similar diagnoses that differ considerably in their chemosensitivity and recurrence rates. Close collaboration between the pathologist and surgeon was crucial as different diagnoses would have led to vastly different treatment strategies for the patient.