Patient went on to have a resection.
Histology
Sections show a thin walled cyst lined by a layer of ciliated cuboidal epithelium. No goblet cells are identified. The epithelial lining is arranged on a layer of loose fibrous tissue. The cyst contents comprise acellular amorphous material. The features are of a colloid cyst.
FINAL DIAGNOSIS: Third ventricle colloid cyst and contents.