Key-words:
Fronto-ethmoidal - giant - osteoma - subdural empyema - surgery
Introduction
Frontoethmoidal osteomas represent slow-growing benign tumors with potentially serious
complications. They are rare with an incidence of 0.43% in the general population.[[1]] These encapsulated bony tumors are most commonly asymptomatic or may remain silent
without causing neurological deficit, and are detected incidentally in 3% of computed
tomography (CT) scans and 1% of plain sinus radiographs.[[2]] However, depending on their size and location, they may become symptomatic due
to direct mass effect or erosion of the posterior sinus wall.[[3]] Thus, surgery is necessary as the main treatment option for symptomatic frontal
osteomas and intracranial complication.
We conducted a focused literature review of PubMed and MEDLINE databases for similar
contemporary cases of osteoma, restricting our focus to frontal sinus osteomas complicating
subdural empyema requiring surgical management. To the best of our knowledge, only
two cases of frontal osteoma complicated by subdural empyema have been reported in
the literature.[[4]],[[5]] Through this observation and the review of the literature, we aim to discuss the
etiology of intracranial infection, complicating sinusal osteomas, their pathogenesis,
and the treatment strategy.
Case Report
A 34-year-old man presented with a prolonged history of progressive right frontal
bony swelling, headaches, and new-onset seizure. The patient denied any history of
fever, chills, or nasal liquorrhea. On physical examination, he was afebrile, alert,
and oriented without focal neurologic deficit. Initial CT scan demonstrated a large
bony lesion of the right frontal bone, growing inside the right frontal sinus, breaking
the posterior wall of the sinus cavity and compressing the frontal lobe. The osseous
lesion was associated to right frontobasal pneumocephalus. The CT scan patterns suggested
a giant fronto-ethmoidal osteoma [[Figure 1]]. Subsequently, the patient was advised that the lesion was most likely present
from birth, and given the lesion's apparent growth and risk of further seizures, surgical
resection was recommended. During a prolonged hospitalization, the patient presented
a progressive left hemiparesis 4/5 strength, with 38.5°C of fever, and he complained
aggravation of headache. Brain magnetic resonance imaging (MRI) was performed in emergency
and revealed a right fronto-parietal subdural empyema causing a noticeable mass effect
to the midline structures. It demonstrated also the known giant right fronto-ethmoidal
osteoma [[Figure 2]]. Because of the presence of subdural empyema, surgery was performed in emergency.
Figure 1: Axial cerebral computed tomography scan (in bony and parenchymal windows) showing
a large right fronto-ethmoidal osseous lesion (a), compressing the frontal lobe with
pneumocephalus (b)
Figure 2: Axial brain magnetic resonance imaging weighted T1 with gadolinium (a) and weighted
T2 (b), demonstrating a right frontoparietal compressive subdural empyema associated
to giant right fronto-ethmoidal osteoma
Operation
The patient underwent right decompressive fronto-parietal craniotomy, with en bloc
resection of the fronto-ethmoidal osteoma which was sent for frozen and permanent
pathology [[Figure 3]]. At operation, it was noted that the bony tumor had eroded the posterior wall of
the frontal sinus and the basal dura, with extension into the frontal brain parenchyma.
The right frontal sinus cavity was fully cranialized by resecting all remaining respiratory
mucosa, and the residual sinus cavity was packed with a pedunculated periosteal flap.
The dura mater in contact with the osteoma was expanded and thin harboring a large
dural defect behind surrounding inflammatory changes, and adhered closely to the brain
surface. After dural incision, meticulous removal of yellowish pus with irrigation
was done. The dural defect was then reconstructed with an autologous periosteal flap
and fibrin glue.
Figure 3: Intraoperative picture of the giant osteoma totally resected
Postoperative course
Surgical pathology revealed bony tumor consistent with mixed osteoma, cortical, and
cancellous type [[Figure 4]]. In addition, the bacteriological examination and culture of pus were negative.
Thereby, the patient received intravenous antibiotics ceftriaxone (200 mg/Kg/day)
and metronidazole (1.5 g/day) for 3 weeks associated to antiepileptic treatment. His
neurological status improved to baseline after the surgery, and the patient experienced
no postoperative complications with total recovery at 2 months postoperatively. At
the last follow-up, the patient is doing well but had epilepsy well equilibrated by
400 mg of carbamazepin well taken three times daily.
Figure 4: Histologic features of osteoma: higher-power view with compact cortical bone with
Haversian-like systems evident, consistent with mixed osteoma, cortical and cancellous
type
Discussion
Epidemiology, clinical symptoms, and histology
Giant osteomas are uncommon slow-growing tumors, defined as being larger than 3 cm,
with an overall growth rate estimated at 1.84 mm 2 per year.[[6]],[[7]] Ocular and neurological symptoms result from the proliferation of osteomas located
in the frontoethmoidal region and causing exophthalmia, dacryorrhea, even lead to
intracranial complications such as meningitis, pneumocephalus, mucocele, cerebral
abscess, or subdural empyema.[[3]],[[8]],[[9]],[[10]],[[11]]
The etiology of osteomas still remains unclear. Indeed, three theories have been suggested
as cause of osteomas; infectious, traumatic, and genetic.[[12]] Osteomas occur more commonly in men with a male-to-female ratio of 2,[[8]] and a peak incidence in the 4th to 6th decades of life.[[1]] This greater prevalence of osteomas in men is attributed to the larger size of
their sinuses and more frequent exposure to injuries. Histologically, four acknowledged
pathological types of osteomas have been described: the ivory osteoma dense and mature
bone; the compact osteoma with small Haversian canals, the osteoma spongiosum; and
finally the mixed osteoma.[[2]]
Pathogenesis
The pathogenesis of subdural empyema associated to osteoma is unclear. However, some
authors have proposed the role of osteoma in the development of intracranial infection.[[4]],[[5]] In fact, a giant osteoma may progress to trigger bone crack in the posterior wall
of the sinus concomitantly with traumatism, leading thus to meningeal erosion. Although
rarely reported, the tumor may also grow gradually intradurally with dural defect,
resulting in a fistula between the sinuses and the intracranial compartment.[[10]] In up to 50% of cases, osteomas are associated with the secondary growth of mucoceles
because they can cause chronic obstruction of outlet ostia.[[13]] The intracranial rupture of these mucoceles through bony and dural defect can lead
to severe complications such as meningitis, cerebrospinal fluid fistula, seizures,
abscesses, and subdural empyema. Another suggestion is that the cranial infection
may occur directly or indirectly, via the venous system giving rise to a life-threatening
evolution of this benign entity. In our case, we believe that the occurrence of subdural
empyema was caused by the break of the posterior wall of the sinus generated by the
huge volume of the osteoma. The illustrative CT scan and MRI of our patient are supporting
our hypothesis.
Surgery
Many authors agreed with the “wait-and-see policy” for asymptomatic osteomas, small
sized or those discovered accidently. Nevertheless, surgery is recommended for significant
tumor growth associated to the appearance of clinical symptoms or in cases of orbital
involvement and/or intracranial extension.[[12]] Depending on the location and extension of the tumor, open surgery techniques as
well as endoscopic transnasal approaches might be considered. Conversely, the surgical
method seems to be independent of the osteoma size thereby, the decision is rather
based on the past surgeon's experience and operator skill, knowledge of different
surgical techniques and available equipment.[[2]],[[14]] In case of giant frontal osteomas or associated with intracranial extensions, as
reported in our case, the transfrontal approach is safer, more effective, and remains
the standard treatment.[[15]] However, endoscopy can be considered for all fronto ethmoidal neoplasms with median
localization.[[16]],[[17]] Some authors suggest that combined surgical treatment associating endoscopy and
open surgery in one stage allowing the frontal sinus obliteration followed by osteoma
and empyema removal through craniotomy may be a good treatment strategy.[[4]],[[18]] Matter of course, postoperative antibiotics therapy for sufficient period has to
follow surgical intervention.
Conclusion
Although osteomas are usually considered as benign slow-growing lesions, they may
cause neurological and/or ophthalmological complications whenever they reach sizeable
volume. Subdural empyema should be taken in mind in a giant fronto ethmoidal osteoma
presented with seizure and neurological deficit. We emphasize the importance of early
operative management of giant osteoma before endocranial complications.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
