increased intraspinal pressure exerted by an expanding mass such as a slow - growing intraspinal tumor is a common cause of erosion ( scalloping ) of the posterior vertebral wall [ 18 ] . as for other causes of scalloping , communicating hydrocephalus , marfan syndrome , ehlers  danlos syndrome , ankylosing spondylitis , neurofibromatosis , achondroplasia , morquio syndrome , hurler syndrome , acromegaly , tuberculosis , and fungal infections have been reported [ 4 , 815 ] . erosion of the spinal osseous structure by herniated nucleus pulposus ( hnp ) has rarely been reported . only 10 hnp cases with scalloping we describe an uncommon case of hnp causing erosion of the vertebral body , the pedicle , and the lamina , which was initially diagnosed to be a tumorous lesion located in the spinal canal . the patient was an 81-year - old woman with 3-year history of low - back pain and left leg radiating pain . her symptoms had gradually worsened until she was not able to walk unaided . finally , she was referred to our hospital for surgical intervention . neurological examination showed a positive straight - leg raising test at 20 and positive femoral nerve stretching testing on the left side . muscle weakness found in the left quadriceps was 4-/5 , and that of the left tibialis anterior was 4/5 . plain ap and lateral radiographs of the lumbar spine are shown in fig .  1 . there was no spinal abnormality except for osteoporosis ( fig .  1 ) . dual - energy x - ray absorptiometry ( dxa ) demonstrated an l2l4 t - score of 2.5 . computed tomographic ( ct ) myelography following myelography at l3l4 showed a tumorous mass with partial calcification in the spinal canal , and erosion of the adjacent l4 vertebral body , pedicle , and lamina . the right panel in fig .  2 shows the slice corresponding to the cranial aspect of the l4 pedicle , and the left panel shows the one corresponding to the caudal aspect of the l4 pedicle . red arrows indicate the location of scalloping , and white arrows , the calcification in the mass.fig . 2ct myelography following myelography at l3l4 showing a tumorous mass with partial calcification in the spinal canal . the right panel shows the slice corresponding to the cranial aspect of the l4 pedicle . the left panel shows the slice corresponding to the caudal aspect of the l4 pedicle . red arrows indicate the location of scalloping , and white arrows , the calcification in the mass plain ap and lateral radiographs of the lumbar spine ct myelography following myelography at l3l4 showing a tumorous mass with partial calcification in the spinal canal . the right panel shows the slice corresponding to the cranial aspect of the l4 pedicle . the left panel shows the slice corresponding to the caudal aspect of the l4 pedicle . red arrows indicate the location of scalloping , and white arrows , the calcification in the mass magnetic resonance ( mr ) sagittal images showed a mass at l3l4 ( fig . axial mr images showed that the mass was located on the right side and caused scalloping ( fig . b axial mr images showing the mass located on the right side and the scalloping ( red arrows ) a mr sagittal images showing a mass at l3l4 . b axial mr images showing the mass located on the right side and the scalloping ( red arrows ) because of the long clinical history and the mr images , we considered the tumor to be not malignant , but rather most likely to be an hnp , and therefore did not perform biopsy prior to removing it . however , we should have done a biopsy for differential diagnosis of slow - growing malignant tumors to ensure safer treatment . after removal of the mass , erosion of the vertebral body was noted . figure  4 shows the removed tissue 3  days after fixation in 10% formic acid . scalloping was also clearly seen on postoperative mri ( arrows in the right panel ) . the patient was asked whether data concerning her case could be submitted for publication , and she consented.fig . 4the surgical specimen shown after fixation in 10% formic acid . on macroscopic examination , it seems to be an hnpfig . scalloping was also clearly seen on postoperative mri ( arrows in the right panel ) the surgical specimen shown after fixation in 10% formic acid . on macroscopic examination , it seems to be an hnp postoperative mr images revealed that the thecal sac was totally decompressed . it is well known that increased intraspinal pressure exerted by an expanding mass such as an intraspinal tumorous lesion may cause erosion ( scalloping ) of the spinal osseous structures . ependymoma , dermoid cysts , epidermoid cysts , schwannoma , lipomas , and lymphomas frequently show thinning of laminae and pedicles [ 4 , 7 , 8 , 20 ] . dural ectasia , associated with inherited disorders such as marfan syndrome , and ehlers  danlos syndrome , and neurofibromatosis is also a cause of scalloping of vertebral bodies [ 4 , 8 , 9 , 11 , 12 , 15 ] . there have been few reports , however , of scalloping of the spinal osseous structures caused by hnp . the present case showed erosion of the l4 vertebral body , pedicle , and lamina by a calcified herniated mass of the l3l4 intervertebral disc . there have been 10 cases of bone erosion due to hnp reported in the literature [ 1620 ] . most cases showed erosion in the posterior wall of the vertebral bodies ( table  1 ) . .   stated that thinning of the laminae and pedicles was commonly seen associated with a tumorous lesion , and that this kind of scalloping was not observed in cases with hnp . an hnp would usually cause scalloping of the vertebral bodies only , if there were any . in the present case , no previous report showed such wide erosion of the spinal osseous structure by hnp as shown in the present case.table  1summary of the characteristics of previous casescaseauthorssex , age ( years)clinical historylocation of herniationlocation of scallopingcalcification1vadala et  al . female , 39more than 1  yearl5vertebral body2male , 457  yearsl5vertebral body3male , 41several yearsl5/svertebral body4female , 553  yearsl5vertebral body5norfray et  al . female , 433  yearss1vertebral body6male , 487  yearsl4neural foramen7male , 413  yearsl5vertebral body+8briceno et  al . male , 61several weekst10vertebral body+present caseyoshioka et  al.female , 823  yearsl4vertebral body , pedicle , and lamina+ summary of the characteristics of previous cases several authors have advocated that long clinical history of pain and chronic pressure due to large - size hnp could cause bone erosion [ 1620 ] . nine of the 11 cases reported so far , including the present case , had history of pain longer than 1  year ( table  1 ) . .   also suggested that old hnps might cause a mechanical irritating action on the small vascular structures of the bone cortex . we supposed that an elderly patient with osteoporosis suffering for a long period from pain caused by an hnp was likely to show erosion of spinal osseous structures .