Immature teratoma (malignant):
– Adult and primitive or embryonal-type tissues seen
microscopically
– Grossly solid, solid and cystic, or mostly cystic
– Immature neural type tissue most often seen but
any immature tissue from ectoderm, mesoderm, or
endoderm can be encountered
– The amount of immature tissue should be reported
relative to all tissues examined
– GFAP can be useful to identify glial tissues, both
mature and immature.
– Prognosis based on amount and type of immature
components; best when a predominance of neural
tissues is seen
– Grading:
• Grade 1: predominantly mature tissues with loose
mesenchymal tissue, immature cartilage, and
tooth anlagae
• Grade 2: fewer mature tissues; focal neuroepithe-
lial tissue with mitotic figures <3/HPF
• Grade 3: few to no mature tissues and abundant
neuroepithelium
– Cellular stroma occupies ≥ 4 low power fields
– Malignant neuroectodermal tumors are tumors with
an exclusive malignant neural component
– Teratomas exclusively composed of ependymal
structures are designated as ependymomas