Giant Size Intra-Cranial Osteoma of Anterior Cranial Fossa Skull Base in a 19 Year Old

Symptomatic skull base osteomas are extremely rare. The enostotic form (arising from inner-table) of osteoma reaching this large size (5.5 × 5.5 × 5.0 cm) and extending via the dura to depress brain parenchyma, as reported in our case is even more prominently rare. We present a case of a healthy 19-year-old female presenting with a generalized tonic-clonic seizure. On examination she had no neurological deficits and no blood work abnormalities. MRI showed a large calcified extra-axial mass in the left anterior cranial fossa skull base measuring 5.5 × 5.5 × 5.0 cm and extending into the cribriform plate. To our knowledge, this is the largest inner-table skull base osteoma reported in a 19-year-old female. Management of such cases can be complex and needs thorough pre-operative planning and excellent intra-operative problem solving skills, especially with piecemeal resection of the bony lesion with multiple drill and saw machines. The first step in tumor excision is to reach the tumor site safely with minimal to no brain retraction by utilizing the available surgical approaches (the orbitozygomatic approach). Second breeching into sinus and nasal cavity by error can lead to CSF leak and subsequent meningitis. As such every step needs to be taken to avoid penetrating into the nasal cavity. Our patient underwent surgery with a bicoronal skin flap and left-sided craniotomy using the orbitozygomatic surgical approach for tumor excision with craniplasty and zygomatic reconstruction. Intra-operatively the entire tumor was found to be bony hard. Tumour’s rock solid consistency makes resection tedious, time consuming and dangerous with the potential risk of a bony sharp edge lacerating the brain parenchyma. Multiple different drills including matchstick and oscillating saw were used to cut through the tumor slowly using egg-shelling shaving technique to attain complete tumor resection. Prior to closure, dural defects were repaired with pericranium and bony defects in the skull were reconstructed. Pathology showed fragments of dense cortical bone with markedly thickened bony trabeculae comprised of mature lamellar bone with focal rimming of bony trabeculae by hyperplastic osteoblasts. These findings are consistent with Osteoma. Our patient recovered with no complications. 6-week follow up CT was normal and did not show tumor recurrence. To our knowledge, this is the largest pure intracranial inner-table skull base osteoma reported in a young adult. Our patient had an excellent post-operative outcome, which was achieved via a complete resection of the osteoma with no intra-operative complications. Our case is a good example of highlighting the intricate complexity required for complete tumor excision with nice case images.