aneurysmal bone cysts ( abcs ) are rare entities which cause expansile and destructive bone lesions characterized by reactive proliferation of connective tissue1,5 ) . they are benign lesions and can occur in any part of the skeleton and the spine can be affected up to 30% of the cases . abcs can cause symptoms such as back and/or dorsal pain , neurological deficitis , and pathological fractures . although abcs mostly occur in the distal part of femur and/or proximal part of the tibia , some cases have been reported in pelvis and posterior elements2,4,5 ) . abcs can occur rarely in the sacrum and this location has some difficulties in treatment because of the relations with the sacral nerves . togetherness of abc and fibrous dysplasia , giant cell tumors and/or osteoblastomas are defined as secondary abc by some authors and this association was seen aproximately in 20 - 30% of cases . diagnosis can be verified by ct scans and mri . in this paper , authors reported two rare cases with thoracic and sacral aneurysmal bone cysts . a 14-year - old male admitted to neurosurgery department with suffering of being unable to walk for 15 days . thoracic mri images and ct scans demonstrated a mass which causes mass effect on spinal cord ( fig . 2 day he was mobilised and his neurological examination was enough for walking with arm holder on postoperative 7 day . on the 5 months control of the patient there were no suffering and no instable images on x - ray and mr images ( fig . an 8-year - old male pateint admitted to us with right hip and back pain . in his history , he had fallen down from 2 meters . spinal mri revealed abc on the right side of the 3 sacral vertebra with an enlargement of 2419mm(fig . the second case is under control and no surgical treatment is suggested because of the patient 's age and observing no neurological deficits at the patient . a 14-year - old male admitted to neurosurgery department with suffering of being unable to walk for 15 days . thoracic mri images and ct scans demonstrated a mass which causes mass effect on spinal cord ( fig . 2 day he was mobilised and his neurological examination was enough for walking with arm holder on postoperative 7 day . on the 5 months control of the patient there were no suffering and no instable images on x - ray and mr images ( fig . an 8-year - old male pateint admitted to us with right hip and back pain . in his history , he had fallen down from 2 meters . spinal mri revealed abc on the right side of the 3 sacral vertebra with an enlargement of 2419mm(fig . the second case is under control and no surgical treatment is suggested because of the patient 's age and observing no neurological deficits at the patient . known as a non - neoplastic expansile bone lesion , abc has a consistance of blood - filled spaces separated by connective tissue septa containing bone and osteoclastic giant cells . discussions about thoracic and sacral aneurysmal bone cysts are limited and only a few cases have been reported3,7 ) . papagelapoulos et al described 44 pelvis abcs and 12 of them were in the sacrum6 ) . it is well known that total extirpation of sabc is so difficult and surgical results in treatment of sabc are excellent . these clinical findings include leg weakness and numbness , bowl or bladder dysfunctions . in our cases up to 60 - 70% of abc cases that occured in spine present with neurological deficits . the clinical aspects are pain due to the destruction and neurological deficits due to the fractures and compression . in our case the diagnostic problems are because of the expeditious growth of abc and its expansive destruction of bone . the diagnosis becomes more complicated if there is an extra - osseous and soft - tissue tumour mass . it also helps to evaluate the fluidfluid level , which is characteristic for abc on mr images1 ) . our first case was evaluated as a pathological fracture , and the patient underwent urgent surgery because of the compression on spinal cannal . but the second case was so typical for abc on the radiological examinations as if in the literature . the primary option for treatment is surgery . enneking classified 3 surgical types : 1-intralesional ( curettage and bone grafting ) , 2-marginal ( en bloc ) resection , 3-wide resection ( segmental resection)3,4,5,6,7 ) . the most important factors in preoperative planning are the location and the growing pattern of the abc . if abc is growing superficially and besides if it is not involving the one - third of the bone , in this case it will be more advantageous . this is really a good intervention for abc and local recurrences occur less com- monly . besides this , if the abc is so large and located in pelvis or spine extraperitoneal excision and bone grafting could be more difficult and risky . in similar cases like this , curettage and bone grafting remain a choiceable surgical technique . low - dose radiotheraphy can be performed after curettage and bone grafting as an other option for treatment5 ) . age , location , size and number of mitotic figures have been suggested for recurrence treatment of abc is difficult and histological examination should be done to prevent overlooked of an underlying more aggressive neoplasm .
aneurysmal bone cysts are rare entities which causes expansile and destructive bone lesions characterized by reactive proliferation of connective tissue . 
 they usually grow rapidly with hypervascularity . in clinical practice 
 they can be easily misdiagnosed due to the rare occurance and having no such typical findings as radiologically . 
 most cases have uncommon pain symptoms , but rarely , if fractures occur , neurological findings can be seen and the surgical treatment , if needed , could be difficult . 
 we will discuss our evaluations to two cases that we experienced in our clinic in this report .