Solitary Bone Cyst in the Skull

Solitary bone cysts are relatively common in long bones, but rare in skull bone. A rare case of the solitary bone cyst (unicameral bone cyst) in the skull is reported. A 7-year-old boy was referred to the department for painless swelling of the left parietal region. On admission, the patient revealed no physical or neurological abnormality except for a mild circumscribed swelling of the left parietal region. Plain skull X-ray films and tomograms showed a radiolucent lesion about 4 cm in diameter, within the left parietal bone, but no hyperostotic area could be noted in this lesion. Computed tomographic scan also revealed a low density lesion in the left parietal bone which showed no contrast enhancement. Left parietal craniotomy was undertaken and total removal of the cystic lesion was performed. The cyst was single, multiloculated and was lined by thin granular tissue. The cavity was filled with bloody fluid. The postoperative course was uneventful. Histological examination revealed that loose connective tissue was lining the cavity wall and no epithelial or endothelial lining cells. Osteoid tissue and osteoclast-type giant cells were found in the cavity wall. When a roentgenogram shows a well-circumscribed radiolucent lesion, the solitary bone cyst should be taken into consideration, and surgical exploration is necessary in order to confirm the diagnosis.