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 .