Pseudoprogression after proton beam irradiation for a choroid plexus carcinoma in pediatric patient: MRI and PET imaging patterns

Abstract

Pseudoprogression is a rare complication of radiation therapy, and discrimination between true progression and pseudoprogression is of paramount importance for further medical care. We present a case of intra-axial pseudoprogression following complementary proton radiation therapy for a choroid plexus carcinoma in a child. We aim to highlight radiological patterns of pseudoprogression after proton beam therapy. A 6-year-old girl presented with choroid plexus carcinoma, manifesting as change in behavior, tremor, and balance disorder. Partial resection and chemotherapy were performed. Complementary localized proton beam therapy (54Gy) was administered on the residual tumor. Eight month follow-up MRI showed an abnormal, irregular, rim-like enhancement in the pons and both temporal lobes within the field of irradiation. These lesions had a low cerebral blood volume (CBV) on perfusion MR imaging and no restricted diffusion. However, the lesions were hypermetabolic on O-(2-[18F]fluoroethyl)-L-tyrosine (FET)-PET MRI. Follow-up MRI showed disappearance of these lesions confirming the perfusion MR diagnosis of pseudoprogression. Based on this case, radiological patterns of pseudoprogression after proton beam therapy may be a low CBV and no restricted diffusion. Lesions can be hypermetabolic on FET-PET imaging.