Clinical History
A 13-year-old male patient presented with a history of consistently increasing pain and tenderness of the left leg over six months, he was not able to stand on his left leg anymore for the last few weeks. He had no history of trauma or any systemic disease.
Imaging Findings
A 13-year-old male patient presented with a history of consistently increasing pain and tenderness of the left leg over six months ( the delay to admit the hospital was due to the poor socio-economic status of his family), he was not able to stand on his left leg anymore for the last few weeks. He had no history of trauma or any systemic disease. MRI study of the left leg with spin-echo T1-weighted, gradient-echo T2-weighted, fat-suppressed fast spin-echo T2-weighted sequences on three planes was performed, upon detection of a lytic lesion of the tibia. A biopsy and then a following curettage of the mass were the following procedures.
Discussion
Aneurysmal bone cysts (ABC) are benign, expansile and locally aggressive lesions of the bone, containing thin-walled blood-filled cystic cavities. Approximately 75-90 % of the ABC's occur in patients younger than 20 years of age. Females are affected more than males, some authors even give a ratio of two to one for ABC's. They are most commonly found in the posterior elements of the vertebrae and the shafts of the long bones with eccentrical metaphyseal location. Histopathologically ABC's are composed of honey-comb-like spaces filled with blood, fluid, and lined by granulation tissue and osteoid, there might be areas of free hemorrhage and sometimes multinucleated giant cells are observed. ABC's may be primary or secondary. The cause of primary ABC's is unclear, they originate in bone marrow cavity with slow expansion of the cortex, and are rarely related to a history of trauma. Secondary ABC's arise from preexisting bone lesions such as giant cell tumor, osteoblastoma, chondroblastoma, angioma, fibrous dysplasia, chondromyxoid fibroma. The patients with ABC's have a pain of relatively acute onset with rapid increase of severity over 6-12 weeks, with or without a history of trauma. Roentgenograms reveal purely lytic eccentric radiolucency, aggressive expansile ballooning lesion of soap-bubble pattern with thin internal trabeculations and sclerotic inner portions, almost invisible thin cortex, tumor respecting epiphyseal plate, no periosteal reaction unless a fracture develops. MRI shows a well-circumscribed expansile, but heterogeneous lesion representing different stages of blood by-products. The lesion may have internal hypointense septations, and fluid-fuid levels due to layering of the uncoagulated blood within the lesion. Cortical bowing and septation may be seen in a low signal intensity of cortical bone. The diagnosis of aneurysmal bone cyst can be strongly suspected by correlating the radiographic and magnetic resonance imaging findings. The key findings that aid in the diagnosis of an ABC can be summarized as: 1) the patients are typically young individuals less than 20 year-old; 2) an expansile bone lesion is bordered by a thin, low signal intensity rim mass; 3) the lesion is inhomogenously increased in signal signal intensity on T2-weighted images; and 4) multiple fluid-fluid levels are seen with the mass on T2-weighted magnetic resonance imaging scans. However for definitive diagnosis, accurate histopathological evaluation is imperative to rule out many lesions simulating ABC's such as giant cell tumors, hemorrhagic cyst, enchondroma, metastases from renal cell ca and thyroid ca, plasmacytoma, chondrosarcoma, fibrosarcoma, fibrous dysplasia, hemophilic pseudotumor, telangiectatic osteosarcoma.Giant cell tumor is an expasile solitary lytic bone lesion, but not that much aggressive as ABC. Hemorrhagic cyst is not expansile, and mostly located in the epiphysis of the long bones. Enchondroma has a typical ground-glass appearance, and it is painless. Other entities listed in the differential diagnosis could be ruled out depending on the imaging findings, as well as laboratory and clinical findings.
Differential Diagnosis List
Aneurysmal bone cyst of tibia
Final Diagnosis
Aneurysmal bone cyst of tibia
