JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
was cauterized to remove the remainder of the tumor. A small septostomy was performed to promote flow of cerebrospinal fluid between the right and left ventricles. The patient was admitted to the pediatric intensive care unit postoperatively. PostopearativeMR showed gross total resection (Figure 2). The patient was discharged to home on postoperative day four without any new neurological deficit.
• Lipoma • Hamartoma • Cavernous hemangioma • Vascular malformation with hemorrhage • Cysticercosis • Colloid cyst • Central Neurocytoma • Subependymoma • Subependymal giant cell astrocytoma • Low grade astrocytoma • Pilocytic astrocytoma • Oliglioglioma • Dysembroplastic neuroepithelial tumor
Non-Neoplastic
PATHOLOGY
Neoplastic
The specimen was received in two parts. The first part consisted of gelatinous soft tan tissue that measured 0.5x0.3x0.1 cm. The second part consisted of fragments of pink tan tissue that measured in aggregate 0.8x0.5x0.2 cm. Microscopically both parts of the neoplasms consisted of disorganized microcystic architecture with hypocellular neuronal growth without cytological atypia, findings consistent with a low-grade primary neuronal lesion. Subsequent immunohistological staining with glial fibrillary acidic protein (GFAP) and neurofilament highlighted the glial component of the neoplasm. Immunohistochemical staining was also positive for synaptophysin , a synaptic vesicle glycoprotein present in all neurons. In summary, the pathological diagnosis was consistent with dysembryoplastic neuroepithelial tumor (DNET) with presence of both glial and neuronal components and positive immunohistochemical staining for GFAP, neurofilament and synaptophysin (Figure 3).
Table 1: Differential diagnosis of lesions in the septum pellucidum
distinguishing features make preoperative diagnosis extremely difficult. A few differential points may help in diagnosis (Table 2). On MRI, DNETs appear as a gyriform enlargement of involved cortex. 17 They are hypointense onT1-weighted and hyperintense on T2-weighted images, and these tumors do not enhance with contrast. Some tumors may show iso/hypointensity on FLAIR with characteristic hyperintense rim. Among other MRI sequences, apparent diffusion co-efficient (ADC) sequences have been reported to be of clear differentiating value because of high cellularity. In the tumor series by Yamasaki et al, DNETs had much higher ADC values than other WHO grade 1 and grade 2 tumors, including ganglioneural tumors like central neurocytomas. 18 DNETs localized in the septum pellucidummay mimic colloid cysts; however, DNETs may be differentiated from colloid cysts by their clear origin above the foramen of Monro. Still, final diagnosis solely depends upon histopathological analysis. Histologically, DNETs resemble other ganglioneural tumors because of the presence of oligodendroglial like cells (OLC). A multinodular architecture is characteristic especially in cortical locations. Small, round OLC cells along with floating neurons in a gelatinous matrix form a microcystic or alveolar pattern. 11 On immunohistochemistry staining, the OLCs are positive for S-100 and Oligo-2 protein. They also express other neuronal markers like synaptophysin, Neu N, NSE and MAP2. 11 DNETs in theseptumpellucidumdonot differmuchhistologically from cortical DNETS; however, occasional irregularity from the classical pattern has been observed. Firstly, the characteristic multinodular pattern is less frequently observed in DNETs of septum pellucidum. 6,23 Secondly, we observed a less cellular growth in our specimen. Similar to Baisden et al, 6 we also noted single OLCs with a uniform round nuclei floating in a fibrillary background. In 50% of patients in Baisden et al series, synaptophysin positivity was noted on immunohistochemical staining. A possible genetic association has been suggested by Saito et al who found a familial occurrence of DNETs in the septum pellucidum. 24 Recently, Gessi et al studied molecular
DISCUSSION
The septum pellucidum is a midline structure with uncertain functional importance that separates the two halves of the lateral ventricles. Though its role in the limbic system and its connection with the hippocampus and hypothalamus has been demonstrated in few studies, 1 surgeons consider it as a benign membranous structure that may be divided if need arises. The occurrence of de-novo tumors in the septum pellucidum is rare. Tumors of the septum arise either from direct tumor extension from the corpus callosum or via subependymal spread from adjacent periventricular structures. Table 1 lists a differential diagnosis of tumors of the septum pellucidum. DNETs of the septum pellucidum are extremely rare and only sixteen cases have been reported to date. 6-10 Generally, DNETs are located in the supratentorial cortex andpresent with epilepsy in children and young adults. 11 In children with primary CNS tumors, the frequency of DNET is estimated to be 0.6-0.8 %. 12,13 Amongst extracortical locations, DNET has been reported to occur in periventricular white matter, foramen of Monro and the caudate nucleus. DNET origin from midline septum pellucidum location, thought to arise from subpial and subependymal germinal layers, 22 is distinctly rare as a primary location. DNETs of the septum pellucidum may simulate multitudes of lesions that can range from simple benign colloid cysts to high-grade atypical gliomas. Lack of clinical or radiological
12 J La State Med Soc VOL 170 JANUARY/FEBRUARY 2018
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