Teaching Case

A 7-year-old female patient presented with left sided painless proptosis and diplopia, developing over the last 3-4 months. Ophthalmologic examination revealed left sided papilledema and loss of vision.

A 7-year-old female patient presented with left sided painless proptosis and diplopia, developing over the last 3-4 months. Ophthalmologic examination revealed left sided papilledema and loss of vision. MRI study of the orbits with spin-echo T1-weighted, fast spin-echo T2-weighted, post-gadolinium fat-suppressed spin-echo T1-weighted sequences on three planes was performed. The lesion was excised following MRI study of the patient.

Aneurysmal bone cyst (ABC) is a benign fibroosseous lesion which very rarely occurs in the orbit. ABC's are 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. 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. 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. 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.