Cystic bone lesions: histopathological spectrum and diagnostic challenges.

OBJECTIVE Bone cysts are benign lesions occurring in any bone, regardless of age. They are often asymptomatic but may cause pain, swelling, fractures, and local recurrence and may be confused with other bone lesions. MATERIAL AND METHOD We retrospectively re-evaluated 143 patients diagnosed with aneurysmal bone cyst (n=98, 68.5%), solitary bone cysts (n=17 11.9%), pseudocyst (n=10.7%), intraosseous ganglion (n=3, 2.1%), hydatid cyst (n=2; 1.4), epidermoid cyst (n=1, 0.7%) and cysts demonstrating "mixed" aneurysmal-solitary bone cyst histology (n=12, 8.4%), and compared them with nonparametric tests. RESULTS Aneurysmal bone cyst, solitary bone cysts and mixed cysts were frequently seen in the first two decades of life while the others occurred after the fourth decade. Aneurysmal bone cysts, intraosseous ganglion and pseudocysts were more common in women contrary to solitary bone cyst and mixed cysts (the female/male ratio was 1.22, 2 and 1.5 versus 0.7 and 0.5, respectively). Aneurysmal bone cyst, solitary bone cysts and "mixed" cysts were mostly seen in long bones, predominantly the femur, while epidermoid, hydatid and pseudocysts were all seen in flat bones like the vertebra, pelvis and mandible (p=0.001, chi-square). Repeat biopsies were performed in 19 cases (13.3%), 84.2% of which were aneurysmal bone cyst (5 conventional, 9 solid, 1 secondary and 1 subperiosteal) and three (15.8%) were mixed cysts (p=0.02, chi-square). Notably, some of them were located in inaccessible areas of pelvis (n=3), femur (n=3) and maxilla (n=2). CONCLUSION The most common and challenging intraosseous cysts are aneurysmal bone cysts, particularly the "solid" variant. The "mixed" aneurysmal-solitary bone cyst "subgroup" requires further research with larger series to be defined more thoroughly.