Cytomorphologic features of myxopapillary ependymoma: A review of 13 cases

Objective: To describe the cytologic features of myxopapillary ependymoma (MPE) on intraoperative smears, to analyze cytomorphologic parameters that may help in reaching the diagnosis and to discuss differential diagnosis. Study Design: Touch imprint smears of 13 MPE cases were reviewed and graded semiquantitatively for 14 cytomorphologic parameters; cellularity, myxoid background, isolated/dispersed tumor cells, "hyaline globules (HGs)," fibrillary cytoplasmic processes, papillary structures, perivascular pseudorosettes, epithelioid tumor cells (ETCs), intracytoplasmic mucin, intranuclear inclusions, nuclear grooves, mitosis, cytologic atypia and hemosiderin-laden macrophages. Results: Cytologic examination revealed variably cellular specimens composed of isolated and loosely aggregated tumor cells with round to oval or occasionally spindle-shaped nuclei; evenly distributed, finely granular chromatin; and fibrillary processes admixed with occasional ETCs. Most of the cases showed prominent fibrillary processes and occasional ETCs with at least a focal myxoid background. HGs and hemosiderin-laden macrophages were often seen. Papillary structure, a histologic hallmark of MPE, was rarely observed. Conclusion: Dual glial and epithelioid properties of tumor cells, well-known features of "regular" ependymomas, and a distinctive myxoid background with HGs strongly support a diagnosis of MPE and are of great help in excluding other mimics (e.g., other variants of ependymoma, metastatic mucinous adenocarcinoma, metastatic adenoid cystic carcinoma and chordoma).