Non-enhancing de novo glioblastoma: report of two cases

Malignant gliomas arise from two distinct pathways, as de novo lesions or from secondary transformation from low-grade lesions. Herein, we describe the cases of two patients to illustrate the proposition that de novo malignant gliomas can originate as non-enhancing tumors and rapidly progress to a pattern of ring enhancement characteristic of a glioblastoma. Both patients presented with new-onset seizures (simple partial and generalized). Their neurological examinations were unremarkable. Initial MRI evaluations revealed a right precentral gyrus and right medial temporal lobe lesions in each case, respectively. These lesions demonstrated increased T2 signal changes without contrast enhancement. The biopsy of the right frontal lesion in the first patient was consistent with an anaplastic astrocytoma; the second patient was followed expectantly. Repeat MRI for both patients within 17 weeks disclosed ring-enhancing lesions, consistent with an unusually rapid evolution to glioblastoma multiforme (GBM). Subsequent resection of the right medial temporal lesion in the second patient revealed a GBM. Neither tumor displayed abnormal overexpression of P53 by immunohistochemistry. Early MRI of de novo glioblastomas may demonstrate a non-enhancing tumor suggestive of a low-grade lesion. These tumors can rapidly evolve into ring-enhancing lesions more consistent with the traditional imaging findings.