Cytoplasmic RNA in nervous system tumours in children: a fluorochromic histochemical study using acridine orange

Acridine orange was used as a fluorochromic histochemical stain of nucleic acids, applied to 78 neoplasms of the central and peripheral nervous systems of 60 children. Some cases were compared with 5 adults and 4 other cases of chronic reactive gemistocytic gliosis. Opposite concentration gradients of cytoplasmic ribonucleic acid (RNA) was demonstrated in tumours of the neuronal/neuroectodermal series, and those of the glial/neuroepithelial series. Minimal AO-RNA fluorescence was seen in 8 cerebellar medulloblastomas and in a retinoblastoma; strong AO-RNA fluorescence occurred in one cerebellar medulloblastoma and in 3 primitive neuroectodemal tumours of the cerebral cortex. Intermediate intensity of fluorescence was found in neuroblastomas, and strong fluorescence was shown in well differentiated ganglioneuroma cells and in cells of chromaffin tumours. Among glial tumours, by contrast, the most anaplastic cells displayed the most RNA fluorescence, while better differentiated astrocytoma cells showed much less. Gradients also were found within some astrocytomas, corresponding to zones of relative anaplasia. Minimal or no fluorescence was detected in reactive gemistocytes or in oligodendroglioma cells. Ependymomas were weakly fluorescent and choroid plexus papillomas showed more fluorescence, similar to the findings in normal ependyma and choroid plexus. Several non-neuroepithelial tumours of the nervous system and Schwannomas also were studied. The acridine orange technique applied to either frozen or paraffin sections of nervous system tumours, has value as an adjunct in the diagnosis and grading of these neoplasms and perhaps in distinguishing reactive gliosis from benign astrocytoma.