LAUSR

arms 1p and 19q were examined by interphase fluorescence in situ hybridization (iFISH). The presence of KIAA1549BRAF fusion transcripts was also tested by reverse transcription polymerase chain reaction (RT-PCR). We collected relevant clinical information and follow-up radiologic studies to characterize the tumors’ clinical behavior and tendency for leptomeningeal dissemination. DLGNT presents most commonly in children and young adults [6]. Similarly, among the five patients in our series, four were children (5–14 years old) and one was a young adult (20 years old). There was no apparent gender predilection, although female patients were older in our series. Pre-operative imaging was not available for one child. While diffuse leptomeningeal enhancement was not identified by MRI in any of the five cases, extensive intramedullary involvement across multiple segments was typical (Supplemental Figure). Except for one distal thoracic tumor spanning three segments, all tumors spanned ≥7 segments, with holospinal involvement from obex to conus in two cases. All four pre-operatively imaged tumors appeared central within the cord, filling and expanding the central canal (Fig. 1). All were multicystic, with peripheral variably solid or nodular enhancement. This mixed solid/cystic appearance, with T1 hypointensity and T2 hyperintensity, matches the imaging characteristics of DLGNT with a spinal cord mass [3, 6, 8–10]. None of the five patients had documented leptomeningeal metastasis during follow-up (2 months – 7.5 years). Tumor cells in DLGNT have a characteristic oligodendrocyte-like morphology and express OLIG2. The expression of GFAP or synaptophysin is more variable. Signs of neurocytic or ganglion cell differentiation are present in 10–20% of cases [6, 10]. Neuropil-like hypocellular zones and glial foci that resemble a pilocytic astrocytoma are sometimes seen [10]. Mimicking DLGNT, the five spinal Concurrent KIAA1549-BRAF fusion and chromosome 1p deletion with or without concomitant chromosome 19q loss are recurrent molecular alterations in the diffuse leptomeningeal glioneuronal tumor (DLGNT) [6, 7, 10], in which widespread leptomeningeal dissemination is a diagnostic feature [1, 6, 10]. We have reviewed five spinal cord tumors (Table 1) that show the morphologic and molecular genetic characteristics of DLGNT, but in which radiographically apparent leptomeningeal dissemination was not identified at presentation. At the initial review, we sought to understand the relationship between these tumors and DLGNT by undertaking immunohistochemical analyses with a panel of neural markers: GFAP, OLIG2, and synaptophysin, and with antibodies to the BRAF V600E, histone H3.1/H3.3 K27 M, and IDH1 R132H mutant proteins. Duplication of chromosome 7q34 (a surrogate marker for the presence of KIAA1549-BRAF fusion) and deletion of chromosome