Mesocolic myxoid hamartoma showing neural differentiation: an ultrastructural and immunohistochemical study.

A myxoid mesocolic tumor in a 4-month-old female infant is described. The tumor weighed 190 g and measured 8 cm in diameter and presented as a single mass composed of stellate and round cells with vesicular nuclei and prominent nucleoli in a myxoid, well-vascularized stroma. Electron microscopy showed mesenchymal cells with dilated rough endoplasmic reticulum, cell projections with primitive and desmosome-like cell junctions, and basal membrane-like material. Immunohistochemical studies demonstrated immunoreactivity with antibodies against vimentin and S-100 protein. The infant is well and without evidence of disease 3 years after surgery. This is an example of a peripheral myxoid hamartoma with neural differentiation, and the tumor is expected to have a benign clinical course.