Frontal sinus pneumocele caused by a maxillary sinus mucocele

Abstract

A sinus pneumocele is a rare entity caused by obstruction of a paranasal sinus ostium. It is characterised by dilation and expansion of the sinus, with subsequent bony erosion. The most probable mechanism is air trapping in the paranasal sinus, via a one-way valve mechanism. The case presented concerns a 68-year-old Caucasian man, with recurrent episodes of acute rhinosinusitis. Clinical examination and subsequent imaging of the face, revealed a large pneumocele of the right frontal sinus that significantly eroded the posterior sinus wall. A large mucocele of the right maxillary sinus was also noted, extending to the middle meatus, causing full obstruction of the ostiomeatal complex. Endoscopic sinus surgery was performed, the mucocele was removed and the pneumatisation pathway of the frontal sinus was restored. The patient reports full resolution of symptoms and shows no evidence of recurrence, 6 months postoperatively.

Background

Sinus pneumocele is a rare entity characterised by dilation and expansion of a paranasal sinus with corresponding bony erosion.^{1 2} The bony erosion is a consequence of pressure necrosis.³ Pneumocele most commonly affects the frontal sinus (63%) followed by the sphenoid sinus, the ethmoid sinuses and the maxillary sinuses.^{1 3 4} Although its aetiology is unclear, it is most often associated with head trauma, sinus surgery and chronic rhinosinusitis (CRS), most commonly with nasal polyps.¹ We present a unique case of a pneumocele of the frontal sinus caused by a concurrent mucocele of the maxillary sinus.

Case presentation

A 68-year-old Caucasian man was referred to the outpatient clinic due to unilateral acute exacerbations of chronic rhinosinusitis (AECRS). The patient had been diagnosed with CRS 5 years ago and has been treated with intranasal steroids. He had never undergone sinus surgery. The patient described more than three episodes of worsening of his symptoms, during the past 6 months. These involved, mainly, nasal blockage, purulent nasal discharge and headache. On two occasions the patient had been hospitalised due to preseptal cellulitis. During these hospitalisations, he was treated with intravenous antibiotics, developing no further complications.

Investigations

Nasal endoscopy revealed mucosal oedema, especially in the right nasal cavity and purulent discharge in the right middle meatus. A CT scan was ordered, which demonstrated opacification of the right maxillary sinus. The ipsilateral frontal sinus was well pneumatised and an erosion of the frontal bone at the roof of the orbit, adjacent to the obstructed frontal recess was also deemed probable (figure 1A). A remarkable erosion of the posterior frontal sinus wall was noted (figure 1B). A MRI was performed in order to differentiate intracranial involvement and to further characterise the unilateral opacification. The MRI revealed a mucocele in the right maxillary sinus that completely blocked the ostiomeatal complex (figure 1C). Specifically, the mucocele fully occupied the maxillary sinus, demonstrating extension, through the maxillary ostium, to the ipsilateral anterior ethmoid cells and the frontal recess. Moreover, a pneumocele that fully eroded the posterior wall of the frontal sinus and extended intracranially, was noted (figure 1D). However, the dura seemed to be unaffected.

Figure 1.

(A) Coronal plane of the preoperative CT in which significant pneumatisation of the right frontal sinus is noted. A probable erosion of the frontal bone at the roof of the orbit, adjacent to the obstructed frontal recess is also noted (*). Note the deviated septum. (B) Axial plane of the preoperative CT demonstrating the extensive erosion of the posterior frontal sinus wall (white arrows). (C) Coronal plane of the preoperative MRI in which the mucocele of the right maxillary sinus is shown. (D) Axial plane of the preoperative MRI showing the pneumocele of the right frontal sinus, extending intracranially. The dura, however, seems to be unaffected.

Treatment

Endoscopic sinus surgery was opted and informed consent was obtained from the patient. A septoplasty was necessary in order for the proper manoeuvring space to be created. A right medial maxillary antrostomy was subsequently performed. The mucocele was recognised and removed following ethmoidectomy, including the cell septa in the region of the frontal recess (figure 2A). In order to fully evaluate the defect of the posterior frontal sinus wall and establish extended drainage, the floor of the right frontal sinus was resected, between the lamina papyracea and the nasal septum (Draf type IIb). Intraoperative intermittent pressure of the right globe confirmed the defect on the lateral aspect of the frontal ostium (figure 2B, video 1). When the frontal sinus was properly visualised a protruding pulsating mass, covered by normal mucosa was found in the anatomic area of the posterior wall (figure 2C, video 1). There were no intraoperative findings of cerebrospinal fluid leak. Since no radiological findings of dura involvement were noted neither clinical signs of intracranial complications were documented, we decided to proceed without restoration of the bony defect. Nasal packing was not applied.

Figure 2.

(A) Intraoperative photograph of the right frontal ostium, following ethmoidectomy and excision of the cell septa in the region of the frontal recess. (B) intraoperative photograph showing the right frontal sinus, following type IIb Draf sinusotomy. The white arrows show the defect on the lateral aspect of the frontal ostium. (C) Intraoperative photograph demonstrating the visualised right frontal sinus. The protruding, pulsating mass covered by normal mucosa corresponds to the eroded posterior frontal sinus wall (*).

Video 1.

Download video file ^{(80.7MB, mp4)}

DOI: 10.1136/bcr-2021-242477.video01

Outcome and follow-up

Postoperative course was uneventful and the patient was discharged 24 hours after surgery. No signs of recurrence have been noted in the subsequent 6-month follow-up period. Ostia of both the maxillary and the frontal sinus remain open. The patient reports improvement of his CRS symptoms, with no episodes of exacerbation in the aforementioned period.

Discussion

Several conditions can resemble a pneumocele in the frontal sinus, all of which are characterised by an abnormal expansion of the sinus. Hypersinus, pneumosinus dilatans and pneumocele have already been classified and defined accordingly in literature.² The main characteristic that differentiates a pneumocele from the other abnormal dilations of the paranasal sinuses, is the variable thinning of the sinus wall, which could be either focal or generalised and may lead to bony erosion.⁵ It is important to be able to identify each entity, since their differences in terminology correspond to variations in aetiology that are crucial for their diagnosis.⁵

Six different mechanisms that could lead to pneumocele formation are reported in the literature. However, it is unclear which of them better describes the actual pathogenesis.^{1 5} These mechanisms include one-way valve air entrapment in the ailing sinus, local growth disturbances, spontaneous drainage of a mucocele, hormonal deregulation, pathologic osteoclastic and osteoblastic activity and preceding trauma.^{1 4 5} The one-way valve mechanism is caused by sinus outflow obstruction, through which air is trapped in the sinus, followed by an increase in sinus pressure.1 3 5 6 The obstruction can occur due to developmental, neoplastic, inflammatory or post-traumatic causes.¹ In our case the presence of a large maxillary sinus mucocele, which protruded in the middle meatus and totally blocked the ostiomeatal complex, thus causing impaired air flow to the ipsilateral frontal sinus, was noted. This seems to be the most probable explanation for the formation of the pneumocele. Clinicians should bear in mind that concurrent existence of a pneumocele and a mucocele is possible and can have a causative relation. Therefore, therapeutic actions should be planned accordingly.

Pneumoceles are usually asymptomatic or present with frontal bossing and prominence of the supraorbital ridge, sinus pressure, diplopia and headache.^{1 4 5} Interestingly, our patient had unilateral AECRS, as well as two episodes of preseptal cellulitis without any of the aforementioned typical pneumocele symptoms. This fact can demonstrate the connection between chronic rhinosinusitis and pneumocele formation, which has already been proposed in the literature.¹

It has been previously mentioned that the main characteristic of a pneumocele is thinning or even bony erosion of the sinus wall. There are only three cases in the literature presenting with such an erosion. In the first two cases the erosion was located at the posterior wall of the frontal sinus, with coexisting pneumocephalus.^{1 4} The third case concerned a partial defect of the orbit wall, due to a pneumocele of the frontal sinus, which resulted in orbital emphysema and consequent exophthalmos.⁷ All cases suggest that, when extensive bone erosion is present, surrounding structures at the site of the erosion could be seriously affected.⁴ In our case, despite the significant erosion of the posterior frontal sinus wall there were no signs of intracranial involvement.

Several treatment modalities have been suggested, including direct sinus needle puncture, creation of a nasoantral window through a Caldwell-Luc operation or endoscopic sinus surgery (ESS).⁸ ESS is considered the most suitable option, when no cosmetic deformities are present.⁹ ESS is also preferable, when the nasofrontal duct is involved in the pathogenesis of the pneumocele, as it restores sinus drainage.⁵ Ramprasad et al suggested observation as a sole treatment option in those cases where no bony erosion of the sinus wall is present.⁴ In our case ESS was selected in order to restore frontal sinus drainage and evaluate the bony defect of the posterior frontal sinus wall, which was subsequently decided not to be restored.

Learning points.

• A pneumocele is a rare clinical entity of the paranasal sinuses with unclear pathogenesis.

• Paranasal sinus ostium blockage leading to an air trapping one-way-valve mechanism seems to be important for its formation.

• Variable symptoms, ranging from sinus pressure to neurological involvement can be reported.

• Clinicians should be aware of the possible causes of a pneumocele and plan therapeutic actions accordingly.

• Endoscopic sinus surgery is proven to be an effective way to restore sinus drainage and aeration, especially in cases where cranial deformity restoration is not necessary.