An eight-year-old boy presented with a swelling on the posterior aspect of the head since two months associated with headache off and on. The patient had a history of fall during play two years back with resultant torticollis, which subsided on its own. On local examination, there was an 8 x 6 cm, ill defined, high occipital swelling with mild pulsatility.

CNS examination was unremarkable with no focal neurological deficit. Routine hematological examinations were normal.

RADIOLOGICAL FINDINGS:

A CT scan of the brain (plain) done two years back at the time of injury was normal.

Fig. 1

A CT scan of the brain at the time of the present admission revealed an expansile, permeative destructive pattern of the parietal bone involving both the inner and outer tables associated with a subgaleal soft tissue swelling. The plain scan revealed a hyperdense mass lesion involving the posterior high parietal region predominantly on the left side with multiple calcifications within. There was associated perilesional white matter edema. Post contrast CT in the early venous phase revealed multiple tortuous vessels suggestive of a vascular malformation. The proximal superior sagittal sinus revealed contrast within it. However, the distal one- third showed no contrast - suggesting thrombosis. Post contrast CT reconstructed in the coronal plane confirmed destruction of the bone with aneurysmal dilatation of the venous channels suggestive of vascular malformations.

Fig. 2			Fig. 3
Fig. 4			Fig. 5

MRI study of the brain with contrast showed a large dural AVM at the vertex. Multiple enlarged draining veins were seen. The superior sagittal sinus and the right transverse sinus were enlarged. An underlying solid-cystic soft tissue mass was noted at the vertex. This mass was predominantly on the left side and appeared to be extra axial. It caused destruction of the adjacent bony calvarium. The mass protruded into the scalp through the bony calvarial defect. The mass measured 11.4 x 10.9 x 8.9 cms in maximum craniocaudal, transverse and AP diameters. It was associated with perilesional edema and mass effect. The lesion caused compression of the left lateral ventricle, posterior corpus callosum and brainstem with mild subfalcine herniation to the right side. Subacute intralesional hemorrhage could be seen.

Fig. 6	Fig. 7
Fig. 8	Fig. 9

A four-vessel angiogram showed a large, highly vascular, dural-based mass on the vertex displacing the superior sagittal sinus inferiorly and extending out of the skull. This superior component of the lesion was seen to extend on both the sides of midline. There was another large component of this lesion, which was seen, inferior to the superior sagittal sinus in the left temporo - parieto - occipital regions. The lesion derived its supply from multiple small branches of both middle meningeal arteries, occipital arteries, dural twigs of dysplastic cortical branches of both middle cerebral arteries, anterior cerebral arteries and posterior cerebral arteries. The draining veins are hypertrophic and dysplastic with multiple ectasias and drained into the hypertrophic superior sagittal sinus.

Fig. 10	Fig. 11	Fig. 12

The child complained of productive cough since two weeks. A chest radiograph revealed a well-defined nodular soft tissue mass lesion in the right mid zone. A CT scan of the chest was performed. This showed an isodense nodular mass lesion in the right upper lobe with amorphous calcification and lobulated margins. On post contrast examination, the lesion showed heterogenous enhancement with HU of 35 - 55.

Fig. 13	Fig. 14	Fig. 15

In view of the age of the child and pattern of bone destruction, a diagnosis of Ewings sarcoma was made. The child underwent a biopsy of the skull lesion. The histopathology and immuno histo chemistry confirmed it to be an EWINGS SARCOMA. We believe that the vascularity is related to the tumor though it is difficult to be certain that this is not a separate dural AVM secondary to the trauma.

FINAL DIAGNOSIS: EWINGS SARCOMA OF THE SKULL WITH UNDERLYING DURAL ARTERIO VENOUS FISTULAS WITH LUNG METASTASES.

DISCUSSION:

INCIDENCE: Ewing sarcoma is a rare, highly malignant neoplasm of bone accounting for about 5% of biopsied bone tumours. Common sites of primary Ewing's sarcoma are long bones (47%), pelvis (19%) and ribs (12%). Ewing's sarcoma of skull vault is rare. It constitutes less than 1% of all the brain tumours. Frontal, parietal and occipital bones are common sites in the skull. Skull base and facial bones are less commonly involved. Seventy five percent of cases are under the age of 20 years, with peak incidence between 5 to 13 years.

PRESENTATION: Usually patients with primary skull vault Ewing's sarcoma present with pain and swelling. Rarely, the patient may present with a neurosurgical emergency. Neurological signs and symptoms may be present when the tumour is large, compressing or invading the brain parenchyma. These signs and symptoms vary according to size of tumor and region of brain parenchyma involve

HISTOPATHOLOGY: On FNAC, Ewing's sarcoma shows a cluster of monomorphic tumor cells with round vesicular nuclei and ill-defined vacuolated cytoplasm. Many dissociated cells present with naked nuclei. Demonstration of glycogen in the cytoplasm is usually a consistent finding in Ewing's sarcoma. Histologically, Ewing's sarcoma is a highly anaplastic tumour with solidly packed small round cells. Light microscopic, ultrastructural and immunohistochemical features differentiate Ewing's sarcoma from neuroblastoma, lymphoma and rhabdomyosarcoma

SITES: The most common sites for primary Ewing's sarcoma is long bones. Diaphysis is more commonly involved, although in 25% cases metaphyses may also be involved. Ewing's sarcoma in long bones presents with a permeative pattern of medullary destruction a having wide zone of transition, destruction of cortex, multilamellar periosteal reaction and presence of soft tissue.


RADIOLOGICAL FINDINGS:
Primary skull lesions present with osteolytic lesion with erosion of inner and outer table associated with soft tissue swelling as seen on plain films.. Similar osteolytic lesions in the skull vault are noted in eosinophilic granuloma; Hand Schuller Christian syndrome, metastasis, Burkitt's lymphoma, fibrous dysplasia, aneurysmal bone cysts, osteoclastoma and giant cell reparative granuloma. Radiologically it is difficult to distinguish them however, they can be distinguished by different pattern of destruction of skull vault, presence of soft tissue, calcification, cystic component and septations. However histopathology is more specific for their differentiation. Ewings sarcoma of the skull has a tendency to create a significant epidural mass and push in to brain. The epidural mass is well seen on CT scans .The mass is usually iso to hyperdense on plain scanned with heterogenous enhancement on post contrast study. MRI is useful in precise delineation of different tumour components such as extent of bone, dural and parenchymal involvement. Epidural masses rarely invade the dura and invade the brain parenchyma. Primary Ewing's sarcoma of the skull has lesser tendency to metastasize to lung and bones (one of few bone tumors metastasizing to bones). From remote primary sites like pelvis and long bones Ewing's sarcoma may metastasize to skull, spine, meninges and brain parenchyma. Extensive workup is indicated in all cases of Ewing's sarcoma of skull to search for extracranial primary sites. Radionuclide scanning is most sensitive in early detection of the primary lesion and metastatic deposits. Metastasis to brain parenchyma and dura is less frequent. CNS parenchymal involvement is more common due to primary bone tumour rather than metastatic disease. Most primary Ewing's sarcomas have good prognosis because they can be totally or subtotally excised. However, those arising from skull base may involve vital structures prohibiting surgical excision.

TREATMENT:
Surgical removal and /or radiotherapy with adjuvant chemotherapy are treatment of choice. Isolated radiotherapy is indicated in inoperable cases .High risk cases should receive combined radiotherapy and surgical treatment, preferably preoperative irradiation to the lesion Patients with primary skull vault Ewing's sarcoma have excellent prognosis with 2-5 years of disease free survival in 50-80% cases.