Cerebellar Differentiation in Ovarian Teratoma: A Report of 6 Cases

Ovarian teratomas potentially demonstrate a wide range of tissue elements including central nervous system differentiation. The latter can include cerebellar tissue, which in our experience remains an under-recognized phenomenon. In the current study we present a review of 6 ovarian teratomas including 4 mature cystic teratomas and 2 immature teratomas showing cerebellar differentiation. Two cases were seen in consultation because the cerebellar elements were initially misinterpreted as immature teratomas. Two mature cystic teratomas focally demonstrated a distinct cerebellar architecture including folial type structures, but in all cases the cerebellar elements usually showed a less organized anatomic appearance, and sometimes these were concerning for immature teratomas upon initial examination. This concern was exacerbated in 5 cases by the presence of a cytologically immature and mitotically active neuronal component corresponding to the external granular layer of normal fetal and neonatal cerebellum. However, careful examination demonstrated the characteristic molecular, Purkinje and (internal) granular layers of cerebellum. Furthermore, while the external granular layer in teratomas strongly expressed Ki67, corresponding to the proliferative activity of this cellular compartment physiologically, immunostaining was often helpful in highlighting the preserved zonal pattern of cellular proliferation. The absence or minimal expression of SALL4, OCT3/4, and SOX2 was also helpful in this regard. Cytoplasmic OCT3/4 expression in osteoblasts was noted incidentally in 2 tumors, but further studies are required to determine whether this is a consistent and diagnostically useful finding.