Colloid cyst of the third ventricle: cytomorphologic features on stereotactic fine-needle aspiration

Stereotactic brain fine-needle aspiration (FNA) is a valuable diagnostic modality for evaluating space-occupying central nervous system disorders. Colloid cyst (CC) is a rare nonneoplastic lesion thought to arise from misplaced endodermal tissue in the anterosuperior portion of the third ventricle. This study summarizes cytomorphologic features of CC on FNA along with clinical, radiologic, and histopathologic correlation. Ten cases of CC of the third ventricle diagnosed on FNA were retrospectively reviewed for a period of 12 yr (1989-2000). Material was obtained under stereotactic radiologic guidance. Smears were stained with Diff-Quik and Papanicolaou stains and cell block sections with hematoxylin and eosin. The aspirates showed a characteristic sticky and viscous quality on gross examination. Smears showed abundant, amorphous, proteinaceous material with staining qualities similar to colloid aspirated from thyroid. This included a purplish, filmlike coating of the slide with occasional "cracking" artifact; thick, globular, eosinophilic fragments; and granular, ropelike, and somewhat viscous, mucinous material. Pathognomonic radiating hyphae-like structures were not seen. The cellular components varied from isolated cuboidal/columnar cells to large tissue fragments of glandular-type epithelium with focal ciliated border. Goblet cells were frequently identifiable, as were fragments of collagenous cyst wall. Stereotactic FNA of the CC of the third ventricle is an accurate and cost-effective diagnostic modality. Cytomorphology coupled with the radiologic features is sufficiently unique for the diagnosis of this rare pathologic entity.