The Key role of MRI modalities in En Plaque Meningioma

En plaque meningioma is at frontal region is difficult to be differentiated from osteoma, based on CT scan only. En plaque meningioma represents in 2-9% of all meningioma cases. Usually en plaque meningioma grows on the sphenoid wing, whereas only 1 % grows on the frontal and temporal bone. This case is female 37 yearold who presents with chronic headache and huge lump on her right forehead that she believes it slowly enlarges for the last 5 years. The Computerized Tomography scan (CT scan) shows thickening of the right fronto-temporal bone (3-4 cm) with the diameter of 12 cm and bony hard. Initial impression suggests it could be osteoma or fibrous dysplasia. After the MRI (Magnetic Resonance Imaging) with contrast, it shows a carpet like tumor underline the thickening bone, and it suggest an en plaque meningioma. For en plaque meningioma, we have to remove the abnormal duramater. We suggest that for a case with a wide thickening calvarian bone, it’s better to get the MRI of the head with contrast.


INTRODUCTION
En plaque meningioma is a rare type of meningioma and characterized by a carpet or sheet like lesion that infiltrates the dura mater and sometimes invades the bone or so called hyperostosis. 1 En plaque meningioma is mainly located in the sphenoid wing, juxtaorbital, fronto-parietal and rarely spinal region. 2 - --------------------------------------------------------------------------- In meningioma, hyperostosis is a well-known sign of tumor, but is more frequently present in en plaque meningioma.However, hyperostosis of the bone in en plaque meningioma is often confused with other disease such as fibrous dysplasia or osteoma. 3Some cases, such as this case report, the hyperostosis bone could be such significant with minimal intracranial pathology and often be missed on regular CT Scan.MRI with contrast would be able to visualize the pathologic duramater underneath the overgrowth bone.We report a case of En plaque meningiomais that located in the fronto-temporal bone, who initially was considered as osteoma but the contrast MRI suggest En plaque meningioma.

CASE REPORT
A 37 year old woman came with a five years history of intermittent headache and a mass on her right forehead.She usually took pain-killer to relieve the pain, but the symptoms worsened and the mass slowly grow bigger.She concerns about her performance.
On physical examination revealed a hard mass in the right fronto-temporal region.The Size of the mass was about 12 cm in diameter.There is no evidence of neurological deficit.Laboratory study on blood was normal.CT Scan findings from previous hospital showed a thickening of the right fronto-temporal bone (figure 1) that suggest an osteoma.Then we arrange her for further investigation with contrast MRI.After the contrast admission, it showed a sheet like (carpet like) lesion underneath the thickening bone (Figure 2&3).The feature is suitable for en plague meningioma.Surgery was performed by removing all the thickening bone and the infiltrated durameter (Figure 4).The duramater is replaced with synthetic duramater.The bone is replaced with titanium mesh and covered with the bone cement.The en plague meningioma was completely removed (figure 4).She did very well after the surgery and make a good recovery without any deficit.

DISCUSSION
Meningioma en plaque is a rare biological type of meningioma, which infiltrates the dura and associated with hyperostosis of the bone.En plague meningioma mainly located in the sphenoid wing. 4It is three to six times more frequent in females than in males and more common in the sixth to seventh decade of life. 5ll types of meningioma usually develop after high dose irradiation of glioma, lymphoma, leukemia or metastases. 6e development of en plague meningioma or hyperostosis still remains unclear, but Cushing's conclusion proposed that infiltration of the bone by meningioma cells stimulates osteoblastic activity.The tumor invasion will stimulates periosteal to grow a new bone.On the histopathological examination of hyperostotic bone showed that tumor cells apparently invading the Haversian system of the overlying bone. 7e clinical manifestations are defined by the en plague meningioma's location which compressing the adjacent structures.Generally the symptoms consist of proptosis, declined visual acuity, visual field deficits, headache, temporal swelling, diplopia, seizures and blindness.Diagnosis of en plague meningioma determined by radiological and clinical features rather than histological appearance. 7 Scan and MRI are chosen when it comes to diagnosing meningioma en plaque.But unfortunately, relying on CT Scan alone can sometimes poses diagnostic problems.En plague meningioma can be easily confused with fibrous dysplasia, osteoma, Paget's disease, chronic osteomyelitis and sclerotic metastases of the skull.Therefore, MRI must be done if there is any suspicion to en plague meningioma. 4MRI features of en plague meningioma will show linear dural thickening and enhancing soft tissue around the affected bone.Although CT shows better details of the bone, MRI precisely demonstrates dural enhancement and soft tissue components of the tumor. 8In this patient the early diagnosis was osteoma or fibrous dysplasia, but after the MRI results was seen, the diagnosis was changed.
Total removal of the tumor is the treatment of choice for en plague meningioma.In some cases, total removal is not an easy thing to do because of its extensive bone and dural involvement, also the chances of recurrence rates is high. 9But in this patient, craniotomy tumor removal and cranioplasty with titanium mesh have been performed successfully and The pathology review confirm the diagnosis of meningioma.

CONCLUSION
A wide thickening calvarian bone should be further investigated with contrast MRI.

Figure 1 .
Figure 1.Plain CT Scan of head shows a thickening of the right fronto-temporal bone.

Figure 2 .
Figure 2. T1-MRI Brain with contrast (axial) shows an extra axial carpet like lesion with enhancement in the right frontal (size : 6 x 0,6 x 0,8 cm), just underneath the hyperostosis and compressing the frontal lobe.

Figure 4 .
Figure 4. Meningioma en plaque (gross findings).Macroscopically.Left: showing the thickening part of the bone and the surface is filled up with many small little hole with tumor invasion.Right: inner surface of the bone, and duramater that is attached firmly to the inner table.It is very difficult to separate the dura from the bone.