Pilocytic astrocytomas are the most common gliomas (World Health Organization (WHO) grade 1) in children. According to many authors, stereotactic irradiation (radiotherapy and radiosurgery) is an effective method that provides a prolonged, recurrence-free survival in patients who have had partial tumor removal or in patients with an unresectable tumor. We present a case of a patient with midbrain pilocytic astrocytoma that enlarged considerably in the first six months after irradiation and then diminished in size during the next six months without any antitumor treatment. The clinical and radiological follow-up data for this patient, the surgery results for similar patients, and the data from other authors led us to the conclusion that early tumor volume enlargement after irradiation is usually pseudoprogression.
Keywords: irradiation; pilocytic astrocytoma; pseudoprogression; radiotherapy.