Medulloblastomas with extensive posttherapy neuronal maturation

The authors report on two patients with classic medulloblastoma, each of wh om underwent extensive therapy-associated neuronal maturation. The first pa tient presented at 3 months of age with hydrocephalus caused by a 5-cm tumo r in the cerebellar vermis. He underwent a gross-total resection of a desmo plastic medulloblastoma. No mature elements were identified. Despite adjuva nt chemotherapy, a 1.5-cm recurrent tumor developed 6 months later. Section s from the subtotally resected tumor demonstrated exclusively mature neuron al elements, ranging from neurocytes to ganglion cells. Four months later, a second recurrent tumor was resected. The specimen collected this time dem onstrated classic medulloblastoma morphological characteristics. The patien t was subsequently treated with radiation therapy, which seemed to have an effect; however, the tumor eventually progressed and the patient died. The second patient presented at 3 years of age with a midline medulloblastoma a nd was treated with subtotal resection, radiation therapy, and chemotherapy . Although the tumor remained stable on radiographic imaging, a second rese ction was performed 8 years later to alleviate hydrocephalus. Histological examination revealed predominantly small mature neurons with scattered gang lion cells and extensive calcification. No adjuvant therapy was given and t he patient is alive and well as of his last follow-up examination. The matu re neuronal neoplasms resected in both patients demonstrated negligible pro liferative indices and stained appropriately with neuronal immunohistochemi cal markers. The smaller neuronal population resembled those of a central n eurocytoma and medullocytoma/cerebellar neurocytoma. Analogous to neuroblas toma, our cases suggest that adjuvant therapy can induce extensive or compl ete neuronal maturation in medulloblastoma. Additional cases must be studie d to determine the prognostic significance of this rare phenomenon.