Original Article Dysembryoplastic neuroepithelial tumor (DNT)-like oligodendrogliomas or DNTs evolving into oligodendrogliomas: Two illustrative cases Michael Gonzales, 1,2 Susan Dale, 2 Marleen Susman, 2 Prudence Nolan, 2 Wai Hoe Ng, 3 Wirginia Maixner 4 and John Laidlaw 4 Departments of 1 Anatomical Pathology and 4 Neurosurgery, Royal Melbourne Hospital, 2 NeuroPath, TissuPath Pty. Ltd, Melbourne, Victoria, Australia, and 3 Department of Neurosurgery, National Neuroscience Institute, Singapore A review of dysembryoplastic neuroepithelial tumors (DNTs) in 14 patients over a 12-year period revealed four patients re-operated because of changes on magnetic reso- nance imaging (MRI) suggesting tumor recurrence or pro- gression. In three of these, the histological features were identical to the initial DNT. In the fourth patient, persistent DNT was surrounded by WHO grade 2 oligoastrocytoma. In one of the other 10 patients, WHO grade 2 oligodendro- glioma was present in white matter deep to and completely separate from a cortically based DNT. Fluorescence in situ hybridization showed codeletion of 1p and 19q in both the DNT and oligodendroglioma and oligoastrocytoma com- ponents. Deletions were not identified in any other tumor. Our findings corroborate other studies that 1p and 19q deletions are uncommon in DNT. These two unusual tumors also raise the possibility that rare DNTs may evolve into oligodendroglioma or oligoastrocytoma. DNTs with this altered biology can be identified by 1p and 19q dele- tion analysis. Key words: 1p/19q deletion, DNT, FISH, oligoastrocytoma, oligodendroglioma. INTRODUCTION Dysembryoplastic neuroepithelial tumors (DNTs) are regarded as benign glioneuronal neoplasms. 1 They are usually cortically located and occur in children and young adults with chronic partial and complex partial seizures that often become refractory to medical treatment. The majority of patients have a good response to surgical removal even if this is incomplete. 2 Tumor recurrence or progression is unusual.Two examples of putative malignant transformation have been reported. 3,4 Apart from the char- acteristic glioneuronal element, most DNTs have a glial component.This is usually composed of either astrocytes or oligodendrocytes, forming small nodules. Theoretically at least, this may explain synchronous or metachronous development of astrocytoma or oligodendroglioma in or near an otherwise classical DNT. We reviewed the pathology of DNTs in 14 patients over a 12-year period. The histopathological features in the initial 14 tumors were of classical DNT with all containing a glioneuronal element. Four of the 14 patients underwent re-operation, 125, 98, 64 and 40 months after initial surgery, because of changes on magnetic resonance imaging (MRI) that suggested tumor recurrence or progression. In the patient re-operated at 40 months, residual corti- cally based DNT was surrounded by WHO Grade 2 oli- goastrocytoma. In one of the 10 other patients, WHO Grade 2 oligodendroglioma was present in the white matter underlying, but separate from, a cortically based DNT. Deletions of both chromosomes 1p and 19q were found by fluorescence in situ hybridization (FISH) in both the DNT and oligodendroglioma/oligoastrocytoma com- ponents in these two patients. None of the remaining DNTs showed 1p or 19q deletion. Although the two tumors may be examples of oligodendroglial tumors closely mimicking DNTs, they raise the alternative possibility that rare DNTs have the potential to evolve into oligodendroglioma or oligoastrocytoma. This propensity can be identified by 1p and 19q deletions. Correspondence: Michael Gonzales, FRCPA, NeuroPath, 165 Burwood Road, Hawthorn, Melbourne, Vic. 3122, Australia. Email: m.gonzales@neuropath.net Received 24 August 2006; revised 3 October 2006 and accepted 4 October 2006. Neuropathology 2007; 27, 324–330 doi:10.1111/j.1440-1789.2007.00783.x © 2007 Japanese Society of Neuropathology