Presentation
Recent onset of meningism
Patient Data
Non contrast CT demonstrates a large very dense bony mass, with no discernible medullary cavity, arising from the frontal sinus and extending through the inner table into the left anterior cranial fossa. A large pocket of intracranial gas (pneumocephalus) is present.
MRI demonstrates the large mass to distort the left frontal lobe, with intervening pockets of fluid which do not fully attenuate on FLAIR. The sulci, especially superiorly, demonstrate high signal also on FLAIR. Contrast enhancement is seen at the margins of the mass as well as faintly involving the leptomeninges.
Surprisingly the air containing cavity does not have significant enhancement, nor does the fluid within it restrict on DWI, and as such it does not represent an established abscess.
Case Discussion
Osteomas of the paranasal sinuses are common, especially of the frontal sinus, and they can grow quite large and result in obstruction to normal mucociliary drainage. Erosion into the intracranial cavity with pneumocephalus and meningitis is distinctly uncommon.
The patient went on to have this mass excised and his anterior cranial fossa repaired. The diagnosis of osteoma was confirmed histologically.
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