Frontal sinus osteoma with osteoblastoma-like histology and associated intracranial pneumatocele

Abstract

Osteomas of the cranial sinuses are rare, benign bony tumors that can be complicated by the formation of an intracranial pneumatocele. If not treated promptly, a pneumatocele can lead to abscess formation, meningitis, or ventriculitis. In the present case, an intracerebral pneumatocele was formed when an 18 cm(3) osteoma breached the posterior wall of the frontal sinus creating a one-way valve through which air could enter the intracranial cavity. The patient presented after forceful sneezing with nonspecific symptoms of headache, nausea, and vomiting. CT demonstrated a frontal collection of loculated air with mass effect within the left cerebral hemisphere. A partly mineralized mass occupied the left superior nasal ethmoid sinus and left frontal sinus. Of interest pathologically in this case, the tumor had a substantial osteoblastoma-like component. Surgical repair involved frontal craniotomy to remove the osteoma and debride frontal sinus mucosa, plugging the frontal nasal ducts and sinus with fat and bone wax, and dural restoration using an underwater closed drainage system to vent intracranial air and stabilize the patient.

Fig. 1

a Preoperative lateral plain film radiograph indicates an anterior location of the air accumulation that abuts the posterior surface of the frontal bone. b, c Preoperative CTs display a cyclone-shaped pneumatocele displacing substantial amounts of frontal lobe. A short blunt projection of the air accumulation (arrow) indicates the point of air entry. d Postoperative sagittal CT indicates that by postoperative day three, the pneumatocele is less than half its former size

Fig. 2

Transverse CT, frontal sinus a a preoperative axial CT scan presents a vague granular/trabecular density pattern correlating with the fibro-osseous and osteoblastoma-like areas that predominated in the pathologic specimen (Fig. 3). The comma-shaped fleck of density in the left anterior portion of the bean-shaped frontal mass corresponds to the limited amount of dense compact, concentrically laminated osteoma in it. b Postoperative CT study: the osteoma is gone. The defect in the posterior table of the frontal bone has been surgically sealed

Fig. 3

a Dense, compact bone of a classic frontal sinus osteoma has concentric laminations brought out by polarized light (×200, H&E), b the majority of the mass was fibro-osseous, resembling fibrous dysplasia but lacking the woven bone structure and prominent peripheral osteoblasts (×100; polarized light, H&E), c 10% of the mass had histopathology identical to osteoblastoma; plump atypical osteoblasts redundantly encircle their irregular bone product (×400, H&E)