Mucoceles of the Paranasal Sinuses: Causes and Treatment

What is Mucocele?

• A mucocele is an epithelium-lined mucus-filled sac within one of the paranasal sinuses with the expansion of the sinus cavity and remodeling of the sinus walls. 
• In the above CT image, a mucocele is seen within a concha bullosa. 
• Concha bullosa is the pneumatization of the middle turbinate.

Pathogenesis of Mucocele

• The above diagram shows the orbit, nasal cavity, and Maxillary sinus. 
• Maxillary Sinus is the least commonly affected sinus in mucocele. 
• The most commonly affected sinus is the frontal sinus. 
• So, there is an epithelium-lined sinus, and within the sac, there is an accumulation of mucus. 
• This accumulation happens because of the obstruction of the drain. 

Site of Development 

• The frontal sinus is the most common place of the mucocele. 
• Because the frontal recess is a very narrow and hourglass-shaped area, and the surrounding area also has many cells that can complicate the drainage of the fluid. 
• The frontal recess can be damaged by trauma or it can narrow down because of CRS or because of polyposis. 
• Due to the obstruction in the frontal recess area, the frontal sinus can no longer drain into the nasal cavity. 
• This leads to the entrapment of the mucus, and over a long time, like a few years, it develops into mucocele. 
• The frontal, ethmoid, maxillary and Sphenoid sinuses are involved in descending order of frequency 
• Mucocele can occur in any other aerated structure, like concha bullosa of the middle or superior turbinate. 
• Mucocele can occur due to obstruction in the nasolacrimal duct. 
• The nasolacrimal duct opens in the inferior meatus (IM). 
• When there is an obstruction in the opening, then mucocele can happen in the lacrimal duct. 

Also read: Understanding the Serious Complications of Rhinosinusitis

Etiology  

• Sinus surgery is now the leading cause (66–86%) of mucocele formation following surgery, mostly for chronic sinusitis and nasal polyposis.
  • If there is a mucosal trauma 360º around the frontal recess, there can be adhesions that can form eventually. 
  • Over time, this can result in stenosis or narrowing of the recess. 
  • When there is no sinus injury but an ethmoidectomy, it automatically touches the frontal recess.
  • So, while doing these kinds of surgeries, full attention should be paid so that there is no injury or trauma to the circumferential area of the frontal sinus.
• Surgery in the region of the frontal recess during functional endoscopic sinus surgery can cause circumferential injury to the frontal sinus outflow tract with subsequent stenosis and mucocele formation. 
• External frontoethmoidectomy/Lynch-Howarth operation is a leading cause of mucoceles because of loss of lateral bony support of the frontal recess, which causes herniation of the periorbital tissue into the frontal sinus outflow tract. 

Pathogenesis

Two factors are essential to form mucocele 

1. An obstructed sinus outflow tract. 
2. Inflammatory process within the sinus.
   • Due to the obstruction in the sinus, there is cystic degeneration of the mucosa over time with a mucous-containing epithelial sac surrounding it. This is called mucocele. 
   • In a patient with acute sinusitis along with some complications, then the osteoclastic activity is higher than the osteogenetic activity, resulting in the spread of complications. 
   • However, osteogenesis is also associated with mucocele. 
   • In mucocele, bone remodeling is an important associated event. 

Also read: Anatomy of Paranasal Sinuses: Maxillary & Ethmoid Sinuses

Clinical Features Of Paranasal Sinuses

• Depends on the site where the mucocele has developed. 
• Cosmetic: A visible mass is often seen on the forehead, medial canthus, gingivobuccal sulcus, or cheek. 
• In frontoethmoidal mucocele, orbital findings are very common. 
• Ophthalmologic symptoms: Most common
  • Periorbital swelling
  • Pain
  • Exophthalmos 
  • Displacement of the orbital contents can lead to limited ocular mobility, visual disturbance, and diplopia. 
• Diplopia is a characteristic feature of mucocele. 
• Optic neuropathy occurs in the sphenoid sinus mucocele. 
• A mucocele within a concha bullosa may present with nasal obstruction and/or secondary sinusitis. 
• Epiphora and a cystic swelling in the medial canthus suggest the presence of a dacryocele. 
• They can also cause swelling of the cheek, loosening of the teeth, etc. 
• While examining a patient, swelling is a very important feature. 
• While touching the swelling, there is an eggshell-cracking feeling. This is a specific diagnostic feature in mucocele. 
• Local tenderness may be present.

Radiology Of Paranasal Sinuses

• A CT scan should be done for the diagnosis of mucocele. 
• The above scan shows a homogeneous, opaque region in the inward sinus. 
• It can be frontal ethmoid or maxillary, or it can also involve the surrounding bones. 
• It can be seen in the scan that the swelling extends into the orbit and causes an outward protrusion of the orbit. 
• CT findings suggestive of a mucocele are a homogenous, isodense lesion within an expanded sinus with bony remodeling of the sinus walls. 
• Contrast enhancement only occurs with a pyocele. 
• A bony defect of the lamina papyracea and/or superomedial part of the orbital rim is often seen in frontoethmoidal mucoceles. 
• The globe may be displayed laterally and/or inferiorly with evidence of proptosis.
• MRI should be done in cases of significant bony erosion of the posterior table of the frontal sinus or the orbital lamina papyracea in order to delineate the mucocele from the adjacent soft tissue, e.g., cerebral tissue. 
• Mucoceles generally have high water content and are hyperintense on T1; pyoceles have higher protein content and greater variability of signal intensity on both T1 and T2 weighted areas. 
• So, MRI shows hyperintense T1 and extremely hyperintense T2 areas if the water content is high. 
• These MRI findings are important for the surgery. 
• MRI is also important for the intracranial and orbital extensions.

The above image shows the frontal sinus mucoceles with bony remodeling of the surrounding bones with more osteolysis. 

• The sagittal view also shows extreme remodeling of the bone. 
• It can also cause the compression of the frontal lobe of the brain. 
• In these cases, patients experience raised intracranial pressure, seizures, vomiting, loss of memory, and behavioral problems as well.
• If MRI shows variable intensities, it is because of the content of the mucoceles.

Also read: Understanding Myringitis: Types, Symptoms, and Treatment

Differential Diagnosis

• Benign or malignant tumors 
• Allergic fungal sinusitis/other fungal disease. 
• Cholesterol granuloma (rare). 

Surgical Management

• Widely marsupial the sac to provide permanent ventilation and sinus drainage and to relieve pressure on vital structures. 
• Cosmetic deformities often settle with time as bony remodeling takes place.

Frontal-Ethmoidal Mucoceles

• Endoscopic surgery with the marsupialization/nasalization is the first line treatment for simple mucoceles; a modified but endoscopic Lothrop procedure (MELP) is often required for more complex frontal sinus mucoceles. 
• The modified procedure includes the removal of the superior part of the septum; the floor of the frontal recess area is removed completely so the right and the left frontal can communicate through each other, allowing good ventilation and a wide drainage area. 
• The MELP is useful whenever there is a loss of lateral support in the frontal recess due to bony erosion or previous removal of the superior aspect of the laminar papyracea. 
• Combined approaches are often required for laterally located mucoceles, as thick bony separations might not allow for endoscopic techniques alone.
• While the Lynch-Howard approach can be used to access laterally located frontal sinus mucoceles and to assist with the drilling down of bony separations, the approach is associated with the risk of long-term frontal outflow obstruction.
• An osteoplastic frontal flap, in combination with a MELP, may be required for those mucoceles lying far laterally in the frontal sinus. 
• Transorbital neuroendoscopic surgery (TONES)—and specifically the superior eyelid approach—allows for an alternative, less invasive approach to address the pathology of the lateral frontal sinus. 
• Stents are usually small, pipe-like structures placed into the frontal recess area. Stenting remains controversial; most authors do not advocate the use of stents to maintain patency except in smaller unilateral marsupializations. 
• If a stent is placed, it is important that it is loose fitting to prevent circumferential pressure necrosis that could eventually lead to stenosis.

Also read: Granulomatous Conditions of the Nose

Maxillary Sinus Mucoceles

• It is important to allow for wide drainage of the maxillary sinus into the nasal cavity; a wide middle meatal antrostomy will usually suffice. 
• A partial medial maxillectomy with preservation of the lacrimal system may be required to gain access to laterally located mucoceles. 
• Medial maxillectomy basically involves the removal of the lateral wall of the nose and the inferior turbinate so the maxillary sinus and the floor of the nasal cavity come into the same plane. This leads to a wide opening of the sinus. 
• The Caldwell-Luc approach is only offered in centers where endoscopic surgery is not an option.

Complications 

• Great care needs to be taken when decompressing a large, tense frontal mucocele that displaces the frontal lobe of the brain, as the sudden expansion of the cranial contents can disrupt the dural vessels and cause a subdural hematoma or disrupt the dura and cause a CSF leak. 
• Close post-operative monitoring is, therefore, essential in such patients. Because recurrence can occur decades later, long-term follow-up is required.

Also read: Understanding Rhinosporidiosis and Rhinoscleroma

Best Clinical Practice

• CT is the imaging modality of choice and must be performed preoperatively. 
• Wide endoscopic marsupialization is the first line treatment for simple mucoceles. 
• MELP is a good alternative to obliteration procedures. 
• Combined approaches may be required with laterally located frontal sinus mucoceles.
• Long-term follow-up is required to assess the need for further surgery to correct cosmetic deformities and to ensure patency of the marsupialized sac

Future Research

• The pathogenesis of idiopathic mucoceles needs further investigation to ascertain if factors exist that make certain people more susceptible to mucoceles.
• Although cosmetic deformities can settle with time as bony remodelling takes place, no studies have been done to assess the long-term cosmetic outcome with marsupialization alone.

Key points

• Sinus surgery is now the leading cause of mucoceles. 
• Wide marsupialization is required for all mucoceles. 
• Bone remodelling can take place after surgery, and cosmetic deformities will improve with time.

Also read: Nasal Septal Deviation: Causes, Types, Clinical Features and

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