BRAIN ABBREVIATION KEY DNET ϭ dysembryoplastic neuroepithelial tumor WHO ϭ World Health Organization Received August 30, 2018; accepted November 19, 2018. Neuroimaging Findings in Septal From the Departments of Neuroradiology (P.P.B., P.D., T.J.E.M., S.H.P., J.H.D.) and Dysembryoplastic Neuroepithelial Pathology (Neuropathology) (M.B.L.), University of Virginia Health System, Charlottesville, Tumor: Why Is It Important to Virginia. Previously presented as electronic Recognize This Entity? educational exhibit at the 56th Annual Meeting of the American Society of Neuroradiology, June P.P. Batchala, P. Darvishi, T.J. Eluvathingal Muttikkal, S.H. Patel, M.B. Lopes, and 2–7, 2018, Vancouver, British J.H. Donahue Columbia, Canada. Disclosures S. Patel—UNRELATED: Grants/grants pending: RSNA, Comments: RSNA scholar grant for ABSTRACT research unrelated to the current A dysembryoplastic neuroepithelial tumor like neoplasm of the septum pellucidum is a rare manuscript. entity that can be easily mistaken for more common pathologies, such as a colloid cyst, Please address correspondence to Prem P. Batchala, MD, Department central neurocytoma, or glioma involving the septum pellucidum. On histopathologic ex- of Neuroradiology, University of amination, these tumors can mimic central neurocytomas, subependymomas, or oligoden- Virginia Medical Center, 1215 Lee Street, Charlottesville, VA 22908; drogliomas. Here, we describe clinical and imaging findings in 4 patients with dysembryo- e-mail: [email protected]. plastic neuroepithelial tumor like neoplasms arising from the septum pellucidum. A http://dx.doi.org/10.3174/ng.1800044 systematic review of the literature follows. INTRODUCTION torial extracortical locations of DNET The term “dysembryoplastic neuroepithe- include the third ventricle, basal ganglia, lial tumor (DNET)” was originally coined and septum pellucidum.4,5,7 by Daumas-Duport et al1 in 1988. It was Septal DNETs, like their cortical coun- described as a predominantly supratento- terparts, are World Health Organization rial, cortical-based tumor with multinodu- (WHO) grade I neoplasms. But, unlike lar architecture and cellular heterogeneity cortical DNETs, they mostly present with in 39 patients with medically intractable obstructive symptoms rather than sei- partial complex seizures.1 DNETs typically zures.4 On imaging, septal DNET can have mixed glial and neuronal elements on mimic more common neoplastic and non- histology.1 Typical imaging findings in- neoplastic entities that can arise from the clude a hypoattenuated lesion on CT that septum pellucidum or the foramen of shows T1-weighted hypointensity, T2- Monro. Neoplastic mimics include central weighted hyperintensity, and a characteris- neurocytomas, subependymomas, intra- tic FLAIR hyperintense peripheral rim.2 ventricular meningiomas, and low-grade Since the original case review in 1988, our gliomas, whereas nonneoplastic mimics in- understanding of DNET has evolved. It has clude parasitic cysts (eg, neurocysticerco- been documented that DNETs can occur sis) and colloid cysts. Herein, we describe elsewhere than the typical cortical loca- the clinical and imaging findings in 4 pa- tion.3-8 DNETs can be multifocal, can in- tients with septal DNET from our institu- crease in size during follow-up imaging, tion with histologic confirmation in 3. In with occasional recurrence after resec- addition, we present a systematic literature tion, and, also, very rarely, can undergo review of septal DNET and describe imag- malignant transformation after radiation ing findings of more common mimics of therapy.9-11 The less common supraten- septal DNET. 212 ͉ Neurographics 2019 May/June;9(3):212–219; www.neurographics.org Fig 1. Surgically proved septal DNET. A 6-year-old girl presented with obstructive hydrocephalus. A, Axial CT shows a nearly imperceptible left lateral ventricle hypoattenuated septal DNET (arrow) close to the foramen of Monro, causing left lateral ventricle outflow obstruction. B, Axial T2WI shows the lesion to be homogeneously hyperintense (arrow), blending with the CSF background. C, Axial contrast-enhanced T1WI shows the absence of enhancement in the septal DNET (arrow). D, Axial ADC demonstrates facilitated diffusion in the lesion (arrow). E, Axial FLAIR better delineates the septal lesion (arrow) compared with other MR images and CT. Fig 2. Septal DNET recurrence 1 year after gross total resection. A, A high-resolution axial T2 sequence better delineates the walls of the hyperintense intraventricular mucoid recurrent septal tumor (arrow). B, Axial FLAIR sequence, showing a hyperintense rim around the recurrent tumor (arrow), a finding also previously reported with cortical DNET. C, Coronal contrast-enhanced T1WI, revealing the relation of the recurrent tumor to the foramen of Monro (arrow). A small, postsurgical, interhemispheric subdural collection is also present (white star). PATIENT 1 A 6-year-old girl presented with headaches. An initial CT was suspicious for a septal mass that was causing obstruc- tive hydrocephalus. On MR imaging, a cystic lesion was evident at the foramen of Monro, initially reported as a possible atypical colloid cyst (in view of the absence of typical CT hyperattenuation) or a parasitic or glioependy- mal cyst (Fig 1). The patient underwent gross total resection with histopathology that showed a low-grade glioma. Fol- Fig 3. Surgically proved septal DNET. A 22-year-old woman with ob- structive hydrocephalus. A, Axial T2WI, showing an elliptical, hyperin- low-up imaging after a year demonstrated recurrence (Fig tense septal DNET located between the leaves of the anterior inferior 2). Histopathologic examination of the repeated resection septum (arrow). B, Axial FLAIR sequence reveals a hyperintense rim was characteristic for a septal DNET-like lesion. The pa- around the centrally hypointense septal DNET (arrow). A correct preop- tient’s postoperative course was complicated by pituitary erative diagnosis was made in this case. insufficiency and persistent hydrocephalus that required a ventriculoperitoneal shunt. There was no recurrence in the lucidum. There was no evidence of progression in the 6-year 9-year follow-up after the second resection. follow-up. PATIENT 2 PATIENT 3 A 22-year-old woman presented with acute-onset severe A 14-year-old girl presented with acute-onset headaches, headaches, nausea, and emesis. MR imaging revealed a sep- nausea, and vomiting. MR imaging revealed an intraven- tal mass that caused obstructive hydrocephalus (Fig 3), tricular mass in the left lateral ventricle along the septum and a preoperative diagnosis of septal DNET was made. pellucidum, which caused obstructive hydrocephalus and The patient underwent subtotal resection with histology was reported as a colloid cyst (Fig 4). The patient under- consistent with a DNET-like neoplasm of the septum pel- went gross total resection with histopathology initially re- Neurographics 2019 May/June;9(3):212–219; www.neurographics.org ͉ 213 Fig 4. Surgically proved septal DNET. A 14-year-old girl presented with Fig 6. Septal DNET. A, Low-magnification (40x) and (B) high-magnifica- obstructive hydrocephalus. A, Axial T2WI, showing a homogeneously tion (100x) images, showing oligodendrocyte like cells (large arrows) hyperintense, rounded septal DNET in the left lateral ventricle attached aligned in columns in a background of mucoid matrix with floating neu- to the anterior-inferior aspect of the septum pellucidum (arrow). B, Axial rons (small arrow) (H&E). Cortical DNET shows similar findings. FLAIR sequence reveals a homogeneously hypointense tumor (arrow). There is no hyperintense FLAIR rim in this patient. The initial histopatho- logic diagnosis was low-grade glioma in this patient, and a local recur- septum pellucidum is a relatively preferred site. The other rence (not shown) after 2 years was treated by gamma knife. A retro- reported sites are the basal ganglia, third ventricle, brain spective review of the histopathology was consistent with a DNET-like 5,7,8 neoplasm of the septum pellucidum. stem, and cerebellum. A systematic review of the Eng- lish literature conducted using PubMed and internet search identified 11 peer-reviewed publications that detailed 30 patients with DNET that involved the septum pellucidum near the foramen of Monro, which, in conjunction with our 4 reported patients, yielded a total of 34 patients (Table 1).3-5,9,12-19 In a large series of 51 DNETs, only 2 patients had lesions that occurred within the ventricles.9 Baisden et al4 reported the single largest series of septal DNET in the English literature to date, with 10 patients. In contradistinction to cortical DNETs, patients with Fig 5. MRI, suggestive of a septal DNET. A 62-year-old woman with head- septal lesions overwhelmingly presented with headache or ache. A, Axial T2WI, showing a homogeneous T2-hyperintense tumor splaying the septal leaves (arrow), an appearance similar to the patient other obstructive symptoms, with only 3 patients who pre- illustrated in Fig 3. B, A hyperintense rim is present around the tumor in sented with seizure and 3 tumors identified incidentally. this axial FLAIR image (arrow). The tumor remained stable for 6 months, The mean age of diagnosis was 22.6 years (range, 3–62 and the patient remains on a serial follow-up protocol. years) and the male-to-female ratio was 10 to 23. The mean imaging follow-up among the 17 patients for whom fol- ported as a low-grade glioma (oligodendroglioma versus low-up was reported was 4.1 years, during which time 3 oligoastrocytoma).