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|Year : 2014 | Volume
| Issue : 6 | Page : 669-673
Primary intracranial peripheral PNET" - A case report and review
Kiranchand Velivela1, Alugolu Rajesh1, Megha Shantveer Uppin2, Anirrudh Kumar Purohit1
1 Department of Neurosurgery, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad, Telangana, India
2 Department of Pathology, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad, Telangana, India
|Date of Submission||08-Sep-2014|
|Date of Decision||03-Oct-2014|
|Date of Acceptance||05-Dec-2014|
|Date of Web Publication||16-Jan-2015|
Department of Neurosurgery, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad-500 082, Telangana
Source of Support: None, Conflict of Interest: None
The site of origin of primitive neuroectodermal tumors (PNETs) is quite varied and has significant influence on the prognosis. We report a case of intracranial peripheral PNET/Ewing's sarcoma arising from the superior tentorial surface in a 13-year-old girl. Gross total excision of the tumor was done. We have discussed the distinction between central nervous system PNET (CNS PNET) and Intracranial Peripheral PNET (pPNET/ES) as their treatment and prognosis varies radically. A review of literature shows that prognosis is better in intracranial pPNET/ES.
Keywords: CD 99, central nervous system PNET, intracranial, peripheral PNET (pPNET/ES), tentorium
|How to cite this article:|
Velivela K, Rajesh A, Uppin MS, Purohit AK. Primary intracranial peripheral PNET" - A case report and review. Neurol India 2014;62:669-73
| » Introduction|| |
Primitive neuroectodermal tumors (PNET) of the central nervous system (CNS) are a heterogeneous group of embryonal tumors that occur predominantly in children and adolescents and show aggressive clinical behavior., They may arise in the cerebral hemispheres, brain stem, or spinal cord.  PNETs arising outside the CNS are grouped into peripheral PNET/Ewing's sarcoma family of tumors (pPNET/ES). They can occur in both osseous and extraosseous tissues, including intracranial (extraparenchymal), showing characteristic translocation t(11;22) (q24;q12). 
A 13-year-old girl presented with occipital headache of 3 months duration, which increased with coughing and was associated with blurred vision. Neurologic examination revealed normal visual acuity, loss of color vision and bilateral papilledema. Magnetic resonance imaging (MRI) demonstrated a solid-cystic lesion in the left temporoparietal and occipital regions attached to tentorium. The solid component was isointense on both T1W and T2W and enhanced on Gd-enhanced T1W images. There was mass effect over the midbrain and ipsilateral temporal and occipital horns with midline shift. Perilesional edema was minimal [Figure 1]a-f.
|Figure 1: MRI T2W imaging (a) axial, (b) sagittal and (c) coronal showing lesion in the left temporoparietal and occipital regions, attached to the tentorium which is heterogenous with cystic component and causing mass effect over the midbrain. MRI contrast scans (d) axial, (e) sagittal and (f) coronal show heterogenous enhancement of the lesion|
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With the patient in prone position supported with horseshoe headrest, occipito-temporo-parietal craniotomy was performed. The tumor was attached to the tentorium and was grayish white, firm and moderately vascular with well-defined plane of cleavage from the surrounding brain parenchyma. Cysts were noted medially and laterally which were dissected along the plane of cleavage. Gross total excision of the tumor was done. The tumor was found to be attached to the tentorium. Postoperative period was uneventful. Postoperative MRI revealed no residual tumor [Figure 2]a-f. Bone scan performed in the postoperative period was negative for any hotspots. Postoperatively the patient received local radiotherapy (50 Gy in 25 fractions over 30 days to the tumor bed) and was doing well with no evidence of disease after 24 months. Chemotherapy was not given as the parents did not give consent for chemotherapy.
Microscopically the tumor showed small round blue cells with oval to elongated nuclei having vesicular chromatin [Figure 3]a and b. There was no evidence of neuroblastic differentiation with rosettes/necrosis/calcification. Immunohistochemical examination demonstrated CD99 and NSE positivity in tumor cells [Figure 3]c. Immunohistochemistry with CD34, GFAP, EMA, Synaptophysin was negative and INI-1 expression was retained. Fluorescence in situ hybridization with a EWSR1 break apart probe (Vysis, Abbott diagnostics) showed > 15% of split signals confirming the diagnosis of pPNET [Figure 3]d.
CNS and peripheral PNETs though cannot be distinguished on morphology have distinct genetic features [Table 1]. The MIC2 gene product (CD99), although expressed in nearly all pPNET,  is not specific and can also be detected in other small, blue round cell tumors like rhabdomyosarcoma, desmoplastic small round cell tumor, lymphoblastic lymphomas. However, the pattern of staining is often cytoplasmic, rather than the distinct membranous staining typical of pPNET. Central PNETs are reported to be negative for CD99 staining.
|Figure 2: Postoperative MRI T2W imaging (a) axial, (b) sagittal and (c) coronal showing gliotic changes with enlargement of left occipital horn and no residual tumor. MRI contrast scan (d) axial, (e) sagittal and (f) coronal shows no tumor suggesting gross total excision of tumor|
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|Figure 3: (a) The cells lining the leptomeninges. (b) The cells are small round with vesicular nuclei H and E x400. (c) Immunohistochemical positivity for CD 99. HRP Polymer CD 99; 400. (d) FISH with EWS-FLI break apart probe showing the positive breakapart signals. (Arrowheads)|
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Cytogenetic and molecular biologic characterization of ES/pPNET has revealed a consistent chromosomal translocation t(11;22) (q24;q12) found in up to 90-95% of all cases, resulting in a chimeric fusion of the EWS gene on the long arm of chromosome 22 and the human homolog of the FLI1 gene on the long arm of chromosome 11. , Variant translocations include t(21;22), t(7;22), and t(17;22), all of which involve the EWS gene on 22q12.  It is important to differentiate pPNET/ES from central PNETs because the treatment and prognosis are radically different. The 5-year progression-free and overall survival in supratentorial PNETs is 37% and 53%.  In contrast, many patients with pPNETs as reported in literature achieved long-term disease-free survival [Table 2]. Long-term disease-free survival could be achieved with aggressive surgical resection, local radiotherapy and chemotherapy in primary intracranial pPNET/ES.
| » References|| |
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]
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