Epidemiology

Mucoceles most commonly present between the ages of 40 and 60 years without any discernible sex predilection.1 Those presenting in the pediatric population are generally idiopathic, although some authors advocate cystic fibrosis screening in any child presenting with a mucocele.2 Sixty to 90% of mucoceles develop in the frontal sinus and 8 to 30% within the ethmoid sinuses. Mucoceles of the maxillary and sphenoid sinuses are rare, although some authors report an incidence of up to 5 and 10%, respectively.1,3,4

Pathophysiology

Current treatment protocols require an understanding of the underlying pathophysiology of mucocele development. Lund and Milroy5 demonstrated that the mucocele lining is composed of functional respiratory mucosa, specifically ciliated pseudostratified columnar epithelium. Thus, the development of a mucocele can be extrapolated to an event resulting in retained mucus through a loss of a normal outflow tract. Iatrogenic mucocele formation has been demonstrated in the setting of both external and endoscopic sinus surgery (ESS) secondary to trapped mucosa or scarring of a paranasal sinus ostium. One series demonstrates a 9.3% incidence of frontal sinus mucocele formation following osteoplastic flap.6 Additionally, sinus outflow obstruction resulting from intranasal neoplasm or maxillofacial trauma may contribute to formation of mucoceles.

Once mucocele formation occurs, bony remodeling often ensues through an inflammatory cascade at the bone-mucocele interface. Inflammatory mediators, including interleukin-1 (IL-1) and IL-2, as well as fibroblast-derived prostaglandin E₂ and collagenase, act to promote bone resorption. This in combination with the mass effect of the lesion itself can result in local bone destruction and subsequent displacement of adjacent soft tissue structures.5,7,8

Bacterial invasion of the cyst can also lead to the development of a mucopyocele. This can result in rapid expansion of the lesion and an increased incidence of local complications. Common culture isolates from mucopyoceles are Staphylococcus aureus, α-hemolytic streptococci, Haemophilus influenzae, Pseudomonas aeruginosa, and anaerobes, including Propionibacterium acnes, Prevotella, and Fusobacterium.2,9

Clinical Features

The presentation of an enlarging mucocele is determined by its cause and location. The general symptoms patients present with reflect those of any obstructive abnormality within the paranasal sinuses and the extent of the mucocele expansion ( Fig. 32.1 ).

Diagnostic Work-up

The diagnosis and preoperative evaluation relies primarily on history and physical examination coupled with radiographic evaluation. The previously mentioned symptoms in conjunction with a thorough physical examination including nasal endoscopy provide clues to the location and extent of the mucocele. Although plain films have been used in the past, computed tomography (CT) has become the modality of choice to characterize these lesions. Mucoceles appear as well-circumscribed cysts with homogeneous mucoid content attenuation that increases with the duration of the lesion secondary to increasing protein content (10–40 Hounsfield units [HU]).4 High-resolution images in both the axial and coronal planes provide information regarding the integrity of surrounding bony structures and aid in surgical planning.

Magnetic resonance imaging (MRI) is also useful in differentiating mucoceles from other sinonasal soft tissue lesions. It is strongly recommended in cases in which the primary lesion demonstrates skull base erosion or frank intracranial extension. Mucoceles will be low intensity on T1-weighted and gadolinium-enhanced images and appear high intensity on T2-weighted images. Over time, the MRI characteristics of the mucocele evolve as the protein concentration throughout the cyst increases. Eventually, a mucocele will demonstrate an increasing T1 signal intensity and a decreased T2 intensity. The T2 intensity may eventually drop out.4 Table 32.1 reviews the imaging characteristics of mucoceles. Note that in very thick secretions, signal intensity may drop, in both T1 and T2 MRI, resulting in a deceptive signal void ( Fig. 32.2 ).

Several systems have been devised to classify mucoceles based on the location and degree of local invasion. Intracranial extent is a critical element in most systems, as it determines surgical complexity and potential need for skull base repair or sinus obliteration during surgical intervention. Although posterior plate erosion does not in itself always require reconstruction, reconstruction is necessary in cases with both bone erosion and subsequent erosion of dura resulting in a CSF leak. In the authors’ experience, the majority of mucoceles that have eroded the skull base generally do not invade dura, instead pushing its borders secondary to expansion.

Paranasal sinus mucoceles can be classified as10

In summary, as part of the preoperative evaluation for surgical intervention of mucoceles, the surgeon should follow this checklist:

1. 
   

   Perform a complete history and physical examination, including nasal endoscopy

   
   
2. 
   

   Obtain a high-resolution CT with axial and coronal cuts (the use of image guidance for recurrent lesions is advocated)

   
   
3. 
   

   Carefully review CT with specific attention to the site of involvement, the presence of bony erosion, and the degree of intraorbital and/or intracranial extension

   
   
4. 
   

   Obtain an MRI with any significant intracranial or intraorbital involvement, in recurrent lesions or concerns about the diagnosis (including sinonasal neoplasm)

Treatment

Paranasal sinus mucoceles are primarily treated surgically. Traditionally, open resection was considered the gold standard. Approaches such as Lynch-Howarth frontoethmoidectomy and osteoplastic flap with subsequent sinus obliteration were associated with significant morbidity, cosmetic deformity, and a relatively high recurrence rate.11 An alternative, less invasive approach to open procedures has been marsupialization of the cyst. This treatment modality has been supported by subsequent studies demonstrating essentially normal mucociliary transport mechanisms within previously marsupialized cavities.12 With advances in endoscopic techniques, transnasal marsupialization has become the treatment of choice and obviated the need for external incisions in the vast majority of cases.

The sinus involved and the degree of extrasinus extension noted on preoperative imaging largely dictate current surgical management of these lesions. The overall goal of intervention includes complete adjacent sinusotomy followed by wide-field marsupialization of the cyst wall to minimize the risk of scarring and entrapment of residual secretory mucosa.

The use of stereotactic image guidance navigation is determined on a case-by-case basis. Stereotactic image guidance navigation is especially beneficial in revision cases and those with extrasinus extension. If the technology is available, intraoperative CT scanning with real-time update of computer-aided systems is valuable for difficult cases, especially when the confines of the mucocele are more difficult to visualize ( Fig. 32.3 ).

Frontal Sinus Mucoceles

A clear understanding of the frontal recess anatomy and its variants is necessary to establish adequate drainage of frontal sinus mucoceles and establish long-term patency. All air cells encroaching on the frontal sinus outflow tract, such as agger nasi and suprabullar cells, are completely removed to increase the chances of long-term frontal patency.

Evacuating a frontal sinus mucocele using image guidance-based suction without performing a complete frontal recess dissection invites recurrence ( Fig. 32.4 ). A complete frontal sinus dissection can be completed with a 0- or 30-degree 4-mm nasal endoscope; we additionally routinely use a 70-degree endoscope for visualization during dissection. If minimal osteoneogenesis is present, the frontal recess can be dissected with frontal sinus instruments. Care must be paid to preserving the mucosa surrounding the outflow tract to help increase long-term patency. In cases with abundant osteoneogenesis, a 70-degree diamond bur may be helpful to aid in dissection. When drilling is required or in cases with small frontal openings, an intraoperative decision must be made to extend the operation to a Draf IIb or Draf III (modified endoscopic Lothrop) procedure. Stenting after frontal sinusotomy is controversial and based on surgeon preference. In all cases after frontal sinus dissection, we place a rolled Silastic stent. If the decision to place a stent is made, it should be a soft, comfortable material, such as Silastic or other inert material, and removed within 2 weeks to prevent bacterial biofilm formation on the stent itself, which can create a nidus for inflammation.13

Maxillary Sinus Mucoceles

Maxillary mucoceles are also best approached endoscopically. Any residual uncinate process is resected to identify the natural ostium. A wide maxillary antrostomy is then created by resection of the posterior fontanelle flush with the posterior wall of the sinus. Angled endoscopes can be used to assist in visualization into the sinus.

Patients with prior Caldwell-Luc procedures typically had their maxillary mucosa stripped, often resulting in a contracted, hypoplastic maxillary sinus with multiple recurrent, well-loculated mucoceles. Patients with a history of facial trauma can also develop laterally located mucoceles within the maxillary sinus. These patients typically require a modified endoscopic medial maxillectomy, often in conjunction with a Caldwell-Luc procedure for effective drainage and marsupialization of the mucoceles ( Fig. 32.5 ).

Ethmoid and Sphenoid Mucoceles

Ethmoid mucoceles are approached with a complete ethmoidectomy and removal of the anterior, inferior, and medial aspects of the mucoceles. The numerous bony partitions within the ethmoid sinus pose an increased risk of developing mucoceles in the postsurgical cavity as scarring and secondary obstruction develop. In patients with isolated ethmoid mucoceles along the skull base, especially in the setting of prior paranasal sinus surgery, the diagnosis of an isolated encephalocele must be entertained. Carefully evaluating a high-resolution CT scan as well as obtaining an MRI will help with this evaluation.

Sphenoid mucoceles may be approached via either a transnasal/transseptal or traditional transethmoid approach ( Fig. 32.6 ). Locating the natural ostium of the sphenoid is the ideal entry point. Commonly, in postsinus and/or pituitary surgery patients, the anatomy is significantly altered. In such instances, the superior turbinate is the most reliable landmark if present. The inferior one-third is removed to identify the natural ostium, and a wide sphenoidotomy is performed ( Fig. 32.7 ).

Postoperative Care

Postoperatively, nasal saline irrigation and topical nasal steroids are critical in helping to clear the operative site of debris and maintain patent ostia. Packing is generally not required. In the setting of mucopyocele or positive intranasal cultures, patients are placed on a culture-directed antibiotic regimen. Patients are monitored and débrided postoperatively until healing and reestablishment of normal mucociliary clearance pathways are complete, which takes a minimum of 6 weeks and often can take months.

Outcomes

In 1989, Kennedy et al14 reported a series of 18 patients treated with endoscopic marsupialization with a 0% recurrence at an 18-month average follow-up period. This success was replicated in several subsequent studies, and in 2000 Har-El and DiMaio12 reported the largest series to date of 103 patients with 108 paranasal sinus mucoceles with a 0.9% recurrence rate and a median follow-up of 4.6 years. In this series, only one major complication was reported, and this consisted of a CSF leak in the setting of marsupialization of a large frontoethmoidal mucocele with intracranial extension. Based on these datasets, it is clear that marsupialization with drainage is the gold standard of treatment for sinus mucoceles.