Case of the Month August, 2010, Page 3

Answer

• Aneurysmal Bone Cyst

Findings

• CT demonstrates large, lytic lesion centered at L2 with areas of cortical thinning and breakthrough.  Internal patchy hyperdensities representing fluid-fluid levels and hemorrhage
• MRI exam confirms multiple fluid-fluid levels most notable on T2 weighted sequences as well as involvement of the pedicle and vertebral body best appreciated on the axial cut

Differential Diagnosis

• Unicameral Bone Cyst
• Aneurysmal Bone Cyst (ABC)
• Mets
• Telangiectatic Osteosarcoma

Diagnosis

• Aneurysmal Bone Cyst (ABC)

Aneurysmal Bone Cyst

• Benign lesion characterized by cyst-like walls of fibrous tissue filled with blood
• Can be easily mistaken for malignant neoplasm (pathologically and radiographically)
• Represents neither cyst nor neoplasm
• Represents reparative process triggered by tumor or trauma induced vascular process
• Primary ABC
  • Arises de-novo in bone without recognizable pre-existing lesion
  • Can be caused by trauma
• Secondary ABC
  • Arises in preexisting lesion (benign or malignant neoplasm)
  • Benign tumors: Giant cell tumor, osteoblastoma, chondroblastomas, fibrous dysplasia
  • Malignant tumors: Osteosarcoma, chondrosarcoma, malignant fibrous histiocytoma (MFH)
• Epidemiology: 6% of primary bone lesions
• Most common signs/symptoms: Progressive pain and swelling
• Clinical profile
  • Rapid increase of pain over 6-12 weeks
  • Spinal lesions may cause cord compression (radiculopathy, quadriplegia), nerve root impingement
  • Scoliosis: 10%
  • Pathologic fracture: 20%
  • Limited range of motion if close to joint
  • History of trauma