Operative Management of a Late Presentation of Frontal Sinus Mucocele
Kibwei A. McKinney
Brent A. Senior
DEFINITION
A mucocele is a benign, cystic collection of mucus lined with respiratory epithelium that results from obstruction of the drainage pathway of a paranasal sinus ostium.
The mucus within a mucocele may become infected and is then termed a pyocele or mucopyocele.1
Mucoceles present most frequently in the frontal and ethmoid sinuses, accounting for between 54% and 73% of lesions occurring within the paranasal sinuses.2
The vast majority of mucoceles occur in the setting of preexisting sinus disease (eg, nasal polyps or sinonasal neoplasms), whereas a minority present as a long-term sequela of prior trauma to the frontal sinus drainage pathway.3
Trauma to the frontal drainage pathway is thought to result in post-traumatic scar formation, inflammation, and obstruction that prevent normal mucociliary clearance, thus resulting in mucocele formation.4,5
Frontal mucoceles can result in significant morbidity, due to their expansile, erosive nature, and close proximity to the orbit and brain. Complications include facial asymmetry, orbital proptosis, cellulitis of the orbit and facial skin, and intracranial extension.6
The treatment of mucoceles of the frontal sinus is particularly challenging due to the limitations of external and endoscopic techniques.
External approaches may result in poor appearance, hypesthesia of the facial skin, and poor access to the frontal sinus drainage pathway.
Endoscopic approaches have decreased morbidity but are limited in their ability to access lesions localized to the superior and lateral aspects of the sinus.
ANATOMY
Frontal Sinus
The frontal sinuses are paired structures of the forehead that are present in 90% of the population and exhibit different patterns of pneumatization among individuals.7
The frontal sinus arises embryologically from an anterior ethmoid furrow that evaginates into the frontal bone, forming an inverted, pyramidal-shaped, air-filled structure, along the roof of the orbit.7,8
The anterior table of the frontal sinus varies between 4 and 12 mm and thickens at its inferior extent to form the frontal “beak,” where it forms an articulation with the frontal process of the maxilla.
The anterior table is covered by skin, subcutaneous fat, frontalis muscle, and pericranium.
The posterior table is much thinner and forms the boundary between the sinus cavity and the intracranial space.
The intersinus septum is a bony partition that divides the right and left frontal sinuses into two sinus cavities with independent drainage pathways.
These cavities may be asymmetric in size and can potentially communicate via an intersinus septal cell.
Frontal Recess
This is an hourglass-shaped space through which the frontal sinus drains.
The internal frontal ostium is the narrowest segment of this space.
It is bordered anteriorly by the frontal beak and posteriorly by the skull base.
The ostium drains inferiorly into the frontal recess (previously referred to as the nasofrontal duct), a space that is defined by the following limits:
Anterior—frontal beak and posterior wall of the agger nasi cell
Posterior—anterior face of the ethmoid bulla
Lateral—lamina papyracea and lacrimal apparatus
Frontal Pneumatization Patterns
The anterior ethmoid cells may pneumatize in various patterns, thus resulting in a multitude of different orientations of the frontal sinus outflow tract.
The development of these cells may lead to displacement of the frontal recess, thus resulting in a circuitous pattern of drainage.
Agger nasi cell: the most anterior and most anatomically consistent anterior ethmoid cell, located between the lateral nasal wall and the uncinate process, directly anterior to the vertical attachment of the middle turbinate to the skull base (FIG 1)
Type 1 frontal cell: a single cell located superior to the agger nasi cell. Its posterior border displaces the frontal recess posteriorly.
Type 2 frontal cell: two or more stacked cells located superior to the agger nasi cell. These cells result in posterior displacement of the frontal recess.
Type 3 frontal cell: a single, large anterior ethmoid cell superior to the agger nasi cell that extends superiorly beyond the internal frontal ostium, into the frontal sinus. It posteriorly displaces the frontal recess.
Type 4 frontal cell: a single anterior ethmoid cell located entirely within the frontal sinus. Its anterior wall is either
the anterior table of the frontal sinus or the floor of the frontal sinus.
FIG 1 • Illustration of the named ethmoid cells, on parasagittal view. Demonstrated is the frontal recess (FR), which is bordered anteriorly by the agger nasi cell (AN) and posteriorly by the frontal bullar cell (FB). The agger nasi cell is a reliable landmark, present in virtually all sinonasal cavities. Also shown are the uncinate process (U, dashed line), suprabullar cell (SB), ethmoid bulla (B), posterior ethmoid cells (P), basal lamella of the middle turbinate (M), and the sphenoid sinus (S).
Supraorbital ethmoid cell: one or more anterior ethmoid cells that pneumatize superiorly into the frontal sinus. This is typically posterior and lateral to the frontal recess, resulting in anteromedial displacement of the drainage pathway. It may result in a septate appearance of the frontal sinus on coronal imaging.
Frontal bullar cell: an anterior ethmoid cell located above the ethmoid bulla that extends into the frontal sinus. It borders the skull base and posterior table of the frontal sinus, causing anterior displacement of the frontal recess. It is thought to arise from pneumatization of the lamella of the anterior ethmoid bulla (see FIG 1).
Suprabullar cell: an anterior ethmoid cell located above the ethmoid bulla that borders the skull base. Similar to the frontal bullar cell, it forms from pneumatization of the bulla lamella and displaces the frontal recess anteriorly. It does not, however, extend into the frontal sinus (see FIG 1).
Soft Tissue Anatomy
The afferent innervation of the frontal region is supplied by distal ramifications of the ophthalmic branch of the trigeminal nerve, the supratrochlear and supraorbital nerves.
The supratrochlear nerve is the medial branch of the frontal nerve.
It courses superior to the trochlea (within the orbit) and penetrates the orbital septum at the medial aspect of the orbit.
The nerve then traverses the corrugator muscle to provide sensory innervation to the soft tissues of the inferomedial aspect of the forehead.
The supraorbital nerve is the lateral division of the frontal nerve.
It exits the orbit through the supraorbital foramen, at the junction between the medial one-third and lateral twothirds of the orbital rim.
It courses superiorly deep to the corrugator muscle and penetrates the frontalis muscle to provide sensory innervation to the upper and lateral forehead.
Its distal branches enter retrograde through the anterior table of the frontal sinus (along with the diploic veins) to provide afferent innervation to the sinus cavity.
PATHOGENESIS
The function of the frontal sinus is not known, but is thought to increase the surface area of respiratory mucosa for air humidification and serves as a protective barrier to forces directed toward the anterior cranium.
The frontal sinus is lined by pseudostratified, ciliated, columnar epithelium.
Mucoceles are lined by the same respiratory-type epithelium, but their exact pathogenesis remains unknown.
They are believed to arise from mucosal inflammation causing obstruction of the natural drainage pathway of the sinus in which they originate. This leads to retained secretions and osteolysis of the surrounding bone, thus resulting in the expansion that is often noted radiographically.2,6,9
Insults that lead to ostial obstruction vary considerably and include9
Trauma
Chronic sinusitis
Nasal polyposis
Iatrogenic (postsurgical)
Neoplasm
NATURAL HISTORY
Due to their pathogenesis, frontoethmoidal mucoceles tend to be slow-growing, with clinical manifestations occurring late in the disease process.2
Alternatively, some mucoceles remain completely asymptomatic and are only discovered incidentally through radiographic imaging for unrelated issues.
Various series that have looked at postoperative complications from sinus surgery support the indolent nature of frontal mucocele formation. They have found a mean duration to symptom onset of 5 years following the initial surgery.10
Because of this, many of these lesions go unrecognized and may present dramatically with serious complications, due to intraorbital or intracranial extension.
Mucoceles occurring secondary to antecedent trauma to the frontal sinus have been reported up to 50 years following the initial injury.1,11,12
The peak incidence of these lesions remains unknown. Therefore, all patients who have had any history of frontal sinus trauma are at risk for this late stage complication.
PATIENT HISTORY AND PHYSICAL FINDINGS
Because of indolent growth patterns, frontal mucoceles tend to be asymptomatic for many years prior to their clinical presentation.
They typically become clinically evident only after extensive expansion and erosion, due to compression of surrounding structures.
Symptomatically, patients most often present with proptosis (61.5%), frontal pain/pressure (38.5%), and nasal drainage (38.5%).6
IMAGING
Imaging is typically obtained in the axial, coronal, and sagittal planes, in order to demonstrate the location of the lesion and its relationship to the surrounding anatomical structures.
CT scan of the maxillofacial skeleton with fine cuts through the paranasal sinuses is the standard imaging modality used in the diagnosis of frontal mucoceles.
Contrast enhancement may be utilized to better delineate the degree of intracranial or intraorbital extent and to differentiate these lesions from other pathologic entities.
CT provides excellent bony definition and typically demonstrates a cystic, homogenous, fluid-filled structure with thinning of the surrounding bone (FIG 2A,B).
MRI may be used in tandem with computed tomography, particularly if the diagnosis remains in question.
The T2 sequence will reveal a hyperintense signal, consistent with a mucocele’s high fluid content.4,11Related posts:
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