Intrasellar primitive neuroectodermal tumor (PNET) in familial retinoblastoma: a variant of "trilateral retinoblastoma".

An infant with bilateral familial retinoblastomas was found at age 6 months to have a large mass within the region of the sella turcica. The histology, immunoreactivity and ultrastructure of the tumor showed primitive neuroectodermal cells. A small number of cells showed positive immunostaining to retinal S antigen. This represents a rare form of so-called trilateral retinoblastoma. In most cases of trilateral retinoblastoma, the intracranial non-metastatic tumor is within the pineal gland. The occurrence of such a tumor in the region of sella turcica is very unusual and its possible significance is discussed in regard to our current understanding of the susceptibility to carcinogenesis conferred by inheritance of the mutant retinoblastoma gene, Rb-1.