First report of a solid variant of aneurysmal bone cyst in the os sacrum

We report on a 19-year-old woman with a rapidly growing, solid variant of aneurysmal bone cyst (solid ABC) in the right part of the lateral mass of the sacrum. On admission, the magnetic resonance imaging (MRI) scan disclosed an inhomogeneous low intensity mass right of the centre of the os sacrum with a diameter of 38 x 64 mm and a height of 56 mm on T1 and T2 weighted images. The mass showed homogenous high signal intensity on Gd-enhanced images. Computed tomography demonstrated an expansile osteolytic lesion and (99m)Tc-methylene diphosphonate bone scintigraphy revealed uniform accumulation in the lesion. The histological evaluation showed a proliferation of fibroblasts, histiocytes, chronic inflammatory cells and numerous multinucleated giant cells. Nevertheless, the cells were devoid of nuclear atypia. A cystic component was not observed. In spite of thorough curettage, the patient suffered from recurrence and severe neurological deficits. A review of the literature revealed no previous cases of solid ABC in the sacrum.