meningiomas are one of the most common neoplasms arising from cellular elements of the meninges , in particular , from arachnoid villi structures .
commonly , meningiomas are attached to the dura and grow in the cranial cavity or intraspinal region . however , ectopic locations of meningiomas can not be excluded . in this report , we present a rare case of this special tumor entity in the mandibular bone of a young woman .
a 20-year - old woman was referred to our department with the suspicion of a radicular cyst resulting from a periapical infection of tooth 36 in the mandibular bone .
on radiographic examination , panoramic x - ray and computed tomography ( ct ) imaging showed a 2  1.8-cm radiolucent lesion of the left posterior mandible .
the lesion involved both apical roots of the first molar and the mesial apical root of the second molar .
it showed an expansive character and penetrated the medial corticalis of the mandibular bone ( figs 1 and 2 ) . 

the lesion involved both apices of the first molar and the mesial apex of the second molar and extended to the caudal border of the mandibular bone . 

figure 2:axial , sagittal and coronar ct showing a 2  1 x 1.8-cm lesion in the left posterior mandible , its expansive and destructive character , and its penetration of the medial corticalis .
the lesion involved both apices of the first molar and the mesial apex of the second molar and extended to the caudal border of the mandibular bone .
axial , sagittal and coronar ct showing a 2  1 x 1.8-cm lesion in the left posterior mandible , its expansive and destructive character , and its penetration of the medial corticalis .
after completion of a discussion of the results , the patient was treated under general anesthesia by intraoral subtotal incisional biopsy by using piezosurgery ( mectron , cologne , germany ) .
the tumor had a high cell density including fascicular , storifom and spindle - shaped patterns .
the cells were ordered into cell cords , but also into whorls . additionally , collagenous and hard matter areas were present evoking psammom bodies , and the cells clearly formed reticulin fibers .
biotin complex immunostaining , we found a strong positive reaction with antibodies for vimentin , epithelial membrane antigen ( ema ) and somatostatin and also a positive reaction for desmoplakin in a smaller amount of tumor cells ( < 20% ) ( fig .
the final histopathological results of the biopsy revealed a mesenchymal tumor classified as an ectopic meningioma who grade i. 
 figure 3:(a ) spindle - shaped cells arranged in cell cord and in whorls with no mitotic figures ( hematoxylin  eosin , original magnification 400 ) .
immunhistochemical stains with immunopositive reaction for ( b ) vimentin ( 100 ) , ( c ) ema ( 400 ) and ( d ) somatostatin ( 400 ) .
( a ) spindle - shaped cells arranged in cell cord and in whorls with no mitotic figures ( hematoxylin  eosin , original magnification 400 ) .
immunhistochemical stains with immunopositive reaction for ( b ) vimentin ( 100 ) , ( c ) ema ( 400 ) and ( d ) somatostatin ( 400 ) .
meningiomas are one of the most common tumor entities in the central nervous system , are generally benign and have their origin in the arachnoid villoid structures of the meningocytes . however , in rare cases , ectopic forms of this tumor entity can appear extracranially and extraosseously in the head and neck region . with respect to the jaws , we have found only eight cases including two meningiomas of the maxilla [ 1 , 2 ] and six meningiomas of the mandible [ 37 ] in the current literature .
we have found the seventh case of an extracranial meningioma of the mandible in a young woman who presented with a cystoid - like lesion in the left mandibular bone and no specific clinical symptoms . because of the absence of typical radiographic features , no clear diagnosis was possible either with a panoramic x - ray or 3d imaging .
however , the role of ct is seen significantly to assess the relationship between the tumor and the bony surfaces and to exclude potential malignancy .
several hypotheses have been proposed for the occurrence of extracranial meningiomas , including extradural enclosing of arachnoid cell nests during embryogenesis , ectopic migration , and the development of arachnoid cells in combination with the peripheral nerves , or metaplasia of the mature peripheral nerve sheath cells or progenitor cells .
however , ectopic meningiomas have also been postulated to be mesenchymal tumors that arise from multipotential mesenchymal cells , particularly if no associations to the cranial nerves are apparent . in the head and neck region , this tumor entity
is often associated with cranial nerves and , therefore , is considered to be derived from ectopic arachnoid tissue present around these nerves .
therefore , the origin of the tumor arising in our patient seems to be the perineural cells of the mandibular nerve .
however , ectopic arachnoid cells within the mandibular bone as a source of tumor growth can not be excluded .
the histopathologic and immunhistochemical features of ectopic meningiomas are seen similar to those of their more frequent intracranial counterparts [ 4 , 8 ] .
the general histologic diagnosis of meningiomas describes spindle - shaped cells that can be arranged in whorls , rosettes and interconnecting fascicles .
mitotic figures or atypia is generally rare , and psammom bodies might be present . because of the differential diagnosis from other tumor entities of peripheral nerve origin , an immunhistochemical analysis is useful or even necessary . in meningiomas ,
the positive expression of ema , desmoplakin , somatostatin and vimentin is a characteristic feature [ 3 , 4 , 10 ] and demonstrates the epithelial and mesenchymal patterns of cells within this tumor .
epidemiologically , ectopic meningiomas are slightly more frequent in females with a ratio of 1:1.2 , i.e. ~55% . the average age of patients is 43.4 years , whereby females are older ( 48.7 years ) than males ( 36.9 years ) . on closer consideration of extracranial meningiomas of the mandibular bone , all previously described cases in the current literature were women with an average age of 45.7 years . in our case ,
the gender was the same , but the age of the patient was , at 20 years , considerably younger than the average .
the therapy of choice for extracranial meningiomas in the jaw bones is surgical excision [ 3 , 4 , 8 ] .
the prognosis of extracranial meningiomas after complete surgical tumor resection is good with disease - free rates of 82 and 78% at 5 and 10 years , respectively . in cases of subtotal resection or aggressive histopathologic features such as mitotic figures or foci of necrosis ,
close follow - up is necessary . despite the strong recommendation for surgical treatment in the current literature
, we decided on close follow - up examinations without any therapeutic interventions at the time of diagnosis , considering potential tooth loss or surgical damage of the inferior alveolar nerve as a potential complication of surgery .
the follow - up examinations at 12 months including panoramic x - ray ( fig .
5 ) showed no significant progression of the tumor lesion and no new clinical symptoms were apparent .
this case remains under review and is the first case of an ectopic mandibular meningioma that has not initially been surgically removed after diagnosis . 

figure 4:follow - up panoramic x - ray imaging at 12 months after initial diagnosis showing no significant progression of the tumor lesion . 

figure 5:likewise to panoramic x - ray , follow - up ct after 12 months showing no significant progression of the lesion .
follow - up panoramic x - ray imaging at 12 months after initial diagnosis showing no significant progression of the tumor lesion . likewise to panoramic x - ray ,
the conclusion of this case is that unclear lesions of the jaws , even if they seem to be clear following diagnostics , should be evaluated by incisional biopsy and histopathological evaluation .
 abstractectopic meningiomas are a very rare tumor entity . 
 we present a case of a meningioma arising in the mandible of a young woman and initially supposed to be a radicular cyst . 
 histopathological and immunhistochemical evaluation showed typical cell characteristics of a meningioma . 
 only six cases of ectopic meningiomas in the mandible have been described in the literature until now , mainly in women at an advanced age and with surgical removal of all tumors . 
 for the first time , no surgical excision has been performed in this case and follow - up control after 12 months showed no significant progression or increasing clinical complaints . 
 hence , surgical removal seems non - urgent . in conclusion , 
 unclear lesions of the jaws , even if they seem to be clear following diagnostics , should be evaluated by incisional biopsy and histopathological evaluation . 
INTRODUCTION
CASE REPORT
DISCUSSION
CONFLICT OF INTEREST STATEMENT
FUNDING