Primary Intracranial Extraosseous CNS Ewing's Sarcoma: A Distinct Entity.

Dear Sir,

Ewing's sarcoma (EWS)/peripheral primitive neuroectodermal tumor (pPNET) is an aggressive malignant small round blue cell neoplasm that frequently manifests in the second decade of life, accounting for 4% of childhood and adolescent Ewing’s sarcoma (EWS)/peripheral primitive malignancies.[1] Primary extraosseous EWS of the central neuroectodermal tumor (pPNET) is an aggressivel nervous system (CNS-EES) is an extremely uncommon malignant small round blue cell neoplasm that entity with only a handful of cases reported till date.frequently manifests in the second decade of life, CNS-EES is histologically similar to central PNET (cPNETs), however, differs in histogenesis, molecular characteristics, and clinical behavior.[23]

We discuss case of an 18-year-old boy who presented with complaint of gradually increasing head size for 5 months along with persistent headache. On examination, the patients’ vitals were stable and his Glasgow Coma Scale was 15 (E4V5M6). There was no sensory neural or motor deficit. Magnetic resonance imaging revealed a 10 cm × 6.7 cm × 6.5 cm bilobed heterogeneously enhancing mass lesion in the right parietal region [Figure 1a]. The lesion was extradural but intracranial and eroding the overlying calvarial bone. The mass was variegated in appearance with heterogenous signal intensity. Peroperatively, bicoronal, midsagittal, and lambdoid incisions were made with gross total decompression of tumor and artificial cranioplasty. A clear plane could be achieved between the tumor and brain parenchyma. The gross specimen in histopathology laboratory was received in multiple fragments measuring 2 cm to 9 cm in maximum dimension. The tumor fragments had a glistening outer surface and grayish-brown firm to soft cut surface [Figure 1b]. Microscopy revealed a cellular tumor comprising sheets of monotonous small round cells with hyperchromatic nuclei and scant cytoplasm [Figure 1c and d]. No rosettes were seen. Entrapped bony trabaculae noted. Many thin walled vascular channels were seen traversing through the tumor, of which, an occasional vessel showed tumor emboli. Large areas of necrosis were evident. Cells were positive for intracytoplasmic glycogen on periodic acid-Schiff stain and showed strong membranous positivity for product of MIC-2 antigen, CD99. Interphase FISH revealed ESWR1 gene rearrangement [Figure 1e]. A final diagnosis of CNS-EES was given. On metastatic workup, CT Scans of the thorax, abdomen, and a technetium bone scan were negative for tumor. The patient received 2 weeks of chemotherapy including vincristine, doxorubicin, and cyclophosphamide. He was stable for initial 2 weeks but subsequently developed fever and signs of sepsis and eventually succumbed to his illness.

Figure 1

(a) Magnetic resonance imaging: Bilobed intracranial extradural heterogeneously enhancing mass lesion in right parietal region (b) Gross: Soft gray-brown with areas of hemorrhage. External surface; glistening encapsulated (inset) (c) Small round cell sheets with intervening vascular channels (H and E, ×100) (d) Monotonous tumor cells with indistinct cytoplasm, vesicular nuclei, and clumped chromatin (H and E, ×400). Focal intracytoplasmic glycogen (PAS stain) (e) Interphase FISH with the ESWR1 (22q12) break-apart probe. Fused red/green signal indicate ESWR1 gene rearrangement. CD99 immunostain positive (inset)

CNS-EES shows CD99 expression and EWS/FLI1 translocation, which is specific and sensitive marker for diagnosing EWS family of tumors. These markers are often not found in cases of cPNET.[1] Minimally invasive techniques such as fine needle aspiration as well as onsite squash smear preparation and assessment have limited roles in this diagnosis as the morphological overlap exists between CNS-EES and c-PNET. However, the cytology smears can be triaged for ancillary FISH testing later on.[4] The prognosis of CNS-EES is favorable, and management is similar to EES elsewhere in the body and includes treatment comprising surgery, chemotherapy, and radiation. Patients with c-PNET require more aggressive therapy and wider surgical resection and have a relatively dismal prognosis when compared to patients of CNS-EES; however, there are limited cases reported in the literature of this entity.[15] Dedeurwaerdere et al.[3] in their series discussed five patients, of which follow-up was available in four. Only one of these patients died 10 years after the first diagnosis while all others showed no evidence of disease posttherapy. Sato et al. reported a young adult who was managed postoperatively by whole cranial irradiation and chemotherapy. Their patient was disease-free after 1 year of follow-up.[6]

Primary intracranial EWS is a rare entity and is essential to diagnose because of a better outcome. Immunophenotypical as well as genetic analysis plays a key role in the diagnosis and the distinction from central PNET.

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