A 16-year-old male presented for evaluation of an indentation of his right parietal skull. The patient had first noted the indentation 2 weeks prior with no recent change in size. He had been involved in a 4-wheeler accident 2 years before and was evaluated for a possible concussion during a football game about one and a half years prior to presentation. The patient described having occasional headaches, but had no local tenderness or other neurological symptoms.
On examination, the patient was noted to have a palpable defect and indentation of the right parietal bone. The overlying scalp was unremarkable and he was neurologically intact.
The patient's previous imaging was reviewed. The first study, from 2 years prior, showed a skull defect in the right parietal bone [Figure 1a]. The second and third computed tomography (CT) scans showed progressive erosion of the skull [Figure 1b and c]. The defect did not appear to involve the dura or scalp. A magnetic resonance imaging (MRI) was obtained and confirmed the localization of the lesion to the skull [Figure 1e-f].
Excision of the skull defect and right parietal cranioplasty with titanium plate was performed. The overlying tissue was grossly abnormal, measuring approximately 5 cm in diameter, and was removed en bloc. The underlying bone was thin and eggshell like with a trabeculated pattern, especially in the center. Peripherally, the bone was thickened with a sponge-like appearance. The abnormal tissue portion could be seen replacing the diploic space while leaving the inner and outer table intact at the periphery. The dura was not involved and was stripped from the bone and left intact. The abnormal bone was then removed and a mesh titanium plate was used to replace the cranial defect [Figures 1d and 3].
The patient tolerated the operation well and had no immediate operative or perioperative complications. The right parietal indentation was corrected and the patient was discharged on postoperative day 2.
On gross examination, the soft tissue lesion appeared rubbery, yellow, and avascular. The tissue consisted predominantly of dense fibrous tissue with a few foci of woven bone at the periphery adjacent to the eroded bone. Angulated spicules of bone were rare, some of which lacked osteoblastic rimming while others were rimmed. There was minimal inflammation. The final diagnosis was that of a benign fibro-osseous lesion most in keeping with a DF. The case was reviewed at the Mayo Clinic where it was felt to be an atypical FD. Conflicting pathology interpretations of these lesions is not uncommon.