Retroperitoneal ectopic brain: Case report and literature review.

Heterotopic neural tissue (HNT) has been identified in many sites. In our literature review, we have found only two cases of HNT located in the retroperitoneum. As far as we know, cytological features of HNT have not been described. We here report a case of retroperitoneal HNT diagnosed by fine-needle aspiration (FNA) cytology and subsequent resection. Our patient was a male infant born at 26 weeks' gestation. A retroperitoneal solid-cystic lesion measuring 3.8 cm was identified by abdominal ultrasound. FNA was performed and cytology showed highly cellular smears with single cells and masses of fibrillary material. Cells were small with rounded irregular nuclei and variable cytoplasm. Multinucleated cells, cells with neuronal morphology, calcifications, and hemosiderophages could also be seen. The lesion was excised and histology showed fibrillary areas, glial cells, neurons, and ependymal cells. Synaptophysin, GFAP, and EMA were expressed in distinct areas and cell types. No recurrences were observed.