Magnetic resonance imaging (MRI) will demonstrate a variable appearance, depending on the state of hydration of the mucocele contents. It may present as hyperintense in T1-weighted images because of the high protein content in mucus, or hyperintense in T2-weighted images because of a higher aqueous component. If the mucus becomes dehydrated, the lesion will be hypointense in T1-weighted images and absent in T2-weighted images.
Pathology
Histopathologic evaluation reveals features of respiratory mucosa with cyst walls of pseudostratified ciliated columnar epithelium. Areas of reactive bone formation, hemorrhage, fibrosis, and granulation tissue may be found. Although metaplastic changes are rare, longstanding lesions may show evidence of squamous metaplasia.13
Management
Although symptoms may be managed medically, the definitive treatment for sinus mucocele is surgical intervention. This includes evacuation of the mucocele and re-establishment of drainage of the affected sinus. This can be accomplished by marsupialization of the mucocele through an endoscopic approach or by obliteration of the sinus by mucosal stripping and packing with bone, fat, or fascia through an external approach. These have comparable rates in terms of complications and recurrence.14
The surgical approach depends on the comfort level of the surgeon and the extent of the mucosal disease. Kennedy’s landmark paper on treatment of mucoceles by endoscopic marsupialization in 1989 created a shift in the management of these cases.15 With advances in computer-guided imaging, cameras, and instrumentation, most authors in the literature now favor an endoscopic approach.14 Advantages include reduced postoperative morbidity, lack of external incision, and preserved forehead sensation. It has proven safe and effective, even with orbital extension of the mucocele.
External approaches can be used when previous endoscopic approaches have failed, for cases with difficult anatomy hampering the endoscopic approach, or when the advanced instrumentation required for endoscopy are not available.16 External approaches depend on the location of the mucocele. Frontal sinus mucoceles can be approached through a coronal incision, followed by frontal sinus obliteration or cranialization. Sphenoid sinus mucoceles can also be approached from a coronal incision. Maxillary sinus mucoceles are accessed through a Caldwell Luc or lateral rhinotomy incision and ethmoid mucoceles through a Lynch or transcaruncular incision. Complications of external approach include scar formation, numbness, longer surgical time, and infection.
The ophthalmic surgeon may be asked if an orbital approach or orbital reconstruction is necessary at the time of mucocele removal. It is not always necessary, but the decision should be made on a case-by-case basis (Figs. 27.2 and 27.3). Most orbital signs are caused by a mass effect into the orbit by the mucocele. Shah et al. demonstrated in select cases that removal of the mucocele alone is curative of the orbital signs.17 Even in cases with bone destruction, the body is capable of remodeling the bony defect. It should be noted that none of the patients in the above-mentioned study had evidence of optic neuropathy or infection on presentation. It is reasonable in the majority of cases to allow for a period of observation after mucocele removal. Orbital reconstruction can then be planned secondarily for patients with persistent globe displacement or diplopia from their orbital wall defect.
Cases where an orbital approach would be useful include those requiring drainage of an intraorbital abscess associated with a mucopyocele or cases where the sinus surgeon does not have a high comfort level evacuating a mucocele that abuts important orbital structures (optic nerve, globe, etc.). In these cases, approach from the orbital side can allow for protection of important structures and help the surgeon with intraoperative orientation. Primary reconstruction should be considered in patients with large orbital wall defects and are not good candidates for multiple surgical procedures (medical comorbidities, travel from distant location, etc.).
Prognosis and Complications
After surgical excision, mucoceles may recur in up to 26% of cases. A recent meta-analysis comparing external and endoscopic approaches in a contemporary cohort (after 2001) found a similar recurrence rate in both approaches (2.3% and 4.2%, respectively).14 Prognosis for both life and vision is typically excellent with appropriate management. Longstanding cases with compression on the optic nerve may result in optic atrophy and permanent vision loss.9,10
Meningocele/Encephalocele
Historical Background
The terms meningocele, encephalocele, and meningoencephalocele all describe herniation of cerebral tissue through a defect in the skull. Meningocele refers to only meninges herniating through the defect. Encephalocele refers to herniation of brain tissue that does not contain meninges, and meningoencephalocele refers to herniation of both meninges and brain tissue. The skull defect through which cerebral tissues herniate may be congenital or acquired. When this herniation occurs into the orbit or surrounding sinuses, ophthalmic signs and symptoms will often be present.
Pathogenesis and Etiology
Congenital meningocele results from failure in closure of the neural tube or defective basilar ossification. Bony defects usually occur in the skull midline and can occur anywhere from the nose to the occipital bone. The embryologic pathogenesis of frontonasal encephalocele is not fully understood. It may be that failure of bony fusion in the area of the defect allows prolapse of glial tissue.18 Alternatively, the abnormal neurologic stalk may develop first, resulting in abnormal bone formation around the tissue.19 Congenital absence of the orbital roof is occasionally seen in neurofibromatosis.
Acquired meningoceles or encephaloceles most commonly result from trauma, with herniation of cranial contents through a fracture in the skull base or orbital roof. Meningoceles may also result from iatrogenic damage and have been reported after sinus surgery and orbital decompression.20 A low-lying skull base is a risk factor for intracranial penetration during orbital decompression or lacrimal surgery because of transmission of rotational forces to the cribriform plate.21 Spontaneous encephalocele in the setting of idiopathic intracranial hypertension has also been reported.22
Epidemiology
Meningoencephaloceles have an incidence of 1 in 10,000 to 15,000 live births in North America. Basal encephaloceles occur in 1 in 35,000 to 40,000 live births in Western countries and are the least common of all encephaloceles with an incidence of less than 10%.23 They are classified into five anatomic subtypes: sphenoethmoidal, transsphenoidal, spheno-orbital, transethmoidal, and sphenomaxillary.24 Congenital encephaloceles are usually diagnosed in childhood, but diagnosis in middle-aged adults has been reported.23 Traumatic encephaloceles related to orbital roof fractures are a relatively rare event, with only a handful of cases reported in the literature. The first case was reported in 1951.25
Clinical Features
Anterior meningoceles occur through a defect between the lacrimal and frontal bones and present in childhood as a smooth medial canthal mass. Posterior meningoceles enter the orbit through defects in the optic foramen, superior orbital fissure, or greater wing of the sphenoid. These typically present later than anterior lesions and can cause compression at the orbital apex. Frontonasoethmoidal encephaloceles involve central herniation of glial contents through the upper central face, which can laterally displace the medial orbital contents. This results in hypertelorism, telecanthus, and medial canthal dystopia.26
In addition to the structural changes mentioned above, clinical signs present acutely or gradually as the encephalocele and bony fracture expand over time.27 Signs and symptoms include decreased visual acuity, orbital edema, subconjunctival hemorrhage, dacryocystitis, nasolacrimal duct obstruction, motility restriction, axial proptosis or globe dystopia that may be pulsatile, and, rarely, diplopia.23,28 Neurologic symptoms may include headaches, seizures, and cerebrospinal fluid leak. Alternatively, they may be asymptomatic and found on routine imaging.20
Investigations
CT is best for identification of the bony defect and secondary calcifications of the herniated tissue, when present. With a meningocele, the mass is consistent with cerebrospinal fluid (CSF) density, whereas encephaloceles often have the same density as normal cerebral tissue. MRI is the preferred imaging modality to evaluate the herniated structure because of superior differentiation of soft tissues. Both T1- and T2-weighted images are consistent with brain tissue and can differentiate brain parenchyma from ectopic or retained tissue. Both imaging modalities can demonstrate associated encephalomalacia, brain edema, and enhancement.
Pathology
Prolapsed cerebral tissue can vary from nonfunctional glial elements to vital neurologic structures. Ectopic brain tissue may be disorganized, infarcted, edematous, or calcified. Herniated tissue may also show glial proliferation. In congenital defects, herniated dural tissue is usually very thin.29 Smaller defects along the skull base may enlarge over time, possibly secondary to the pressure gradient between the intracranial vault and underlying sinuses. This is referred to as the “growing skull fracture of childhood.”30
Management
The management of meningoceles should include a neurosurgeon. Fragility of the prolapsed cerebral tissue makes it difficult to preserve and reposition it. For this reason, definitive treatment of meningoceles most often involves amputation of the prolapsed cerebral tissue.29 Occasionally, the intracranial contents can be repositioned into the cranial vault before surgical repair of the bony defect. Release of dural adhesions and repair of any dural defects are also performed at the time of excision or repositioning.
Surgical approach depends on the location of the defect but is often accessed through a frontal craniotomy. This can be combined with a superior orbitotomy, when necessary. Large frontoethmoidal meningoceles often require osteotomies of the fronto-orbital nasal bones for access and reconstruction.29 Nasal augmentation and medial canthopexy may be required as well.26 Repair of the orbital roof fracture is most commonly repaired with a bone graft or pericranial flap, but the alloplastic materials mentioned in the section on mucoceles can also be used.26 In children with a small orbital roof fracture, the defect can be managed with duraplasty alone after excision of intraorbital encephalocele.31 Endoscopic repair of meningoencephaloceles has also been reported.32
Prognosis and Complications
Prognosis is excellent unless the meningoencephalocele associated with other comorbid conditions such as Dandy-Walker syndrome, holoprosencephaly, or agenesis of the corpus callosum.33 If compression at the orbital apex is prolonged, permanent visual decline may result.
Silent Sinus Syndrome (SSS)
Historical Background
SSS was first described by Soparkar et al. who reviewed 19 cases with bone resorption and remodeling of the orbital floor resulting from otherwise asymptomatic maxillary sinus disease.34 The orbital floor remodeling leads to enophthalmos and hypoglobus, resulting in both ophthalmic symptoms and disfigurement (Figs. 27.4 and 27.5).
Pathogenesis and Etiology
Several mechanisms have been described to explain the findings in SSS. Maxillary sinus atelectasis from chronic sinusitis results in inward displacement of the sinus walls and impaired ventilation through the natural ostium. Gas resorption continues through the sinus, creating a negative pressure gradient that further bows the sinus walls.35 However, many patients with chronic sinus disease with outflow obstruction do not develop SSS, which gives rise to the question about the existence of another mechanism. It has been proposed that a communication between the sinus and the pterygopalatine fossa acts as a pressure gradient during mastication, resulting in wall “implosion.”36
Secondary causes of SSS include trauma, nasogastric tube insertion, nasotracheal intubation, cosmetic rhinoplasty, and septoplasty with inferior turbinate fracture.37–40 It has also been reported after orbital decompression for thyroid eye disease caused by prolapsed orbital fat obstructing the sinus ostium.41
Epidemiology
SSS is a relatively rare clinical condition, which has been diagnosed in patients in the second to ninth decades but peaks toward the end of the fourth decade.19 There is no race or gender predilection, and SSS almost exclusively presents unilaterally, with only three case reports of bilateral presentation.42–44 Mid-sinus hypoplasia is found in many patients with SSS, but it is unclear if this hypoplasia is a cause of SSS or a result of it.34 Other predisposing anatomic features include congenitally narrow or slit-shaped ostium, nasal septal deviation, polyps in the nasal cavity or sinus antrum, chronic inflammation, and retention cysts near the ostium.34
Clinical Features
The inward displacement of the maxillary sinus roof (downward displacement of the orbital floor) results in increased orbital volume. Clinical signs include painless, slowly progressive unilateral enophthalmos and hypoglobus. Associated findings often include deepening of the superior sulcus, lagophthalmos, and audible clicking when blinking.45 The globe displacement can result in decreased extraocular motility and resulting diplopia.46 Nasal examination may demonstrate septal deformity, a lateralized uncinate process, and an enlarged middle meatus.
In rare cases, the orbital floor becomes thickened, resulting in proptosis. The mechanism of this alternative presentation is not well understood but is most likely caused by osteoblastic response to chronic maxillary inflammation.47 Other reported presentations include dental pain, bilateral involvement, and dry eye disease.
SSS of the frontal and ethmoidal sinuses have also been reported. Frontal sinus involvement results in hyperglobus, whereas ethmoid sinus involvement results in medial displacement of the globe.48,49
Differential Diagnosis:
When extraocular motility is diminished, diagnosis may be confused with myasthenia gravis or cranial nerve palsy.
Investigations
The diagnosis is usually suspected during clinical examination and confirmed with radiologic imaging. Typical findings on CT include maxillary sinus opacification, volume loss of the maxillary sinus, downward bowing of the orbital floor, and increased orbital volume. In a review of the imaging characteristics of 14 patients with SSS, all were observed to have depression of the orbital floor with hypoglobus. Thickness of the maxillary walls was variable, but concavity of the medial and lateral maxillary walls was universal. Sinus opacity was present in all but one patient, and only one had disease in another sinus.50
Management
The primary goals of treatment include improved maxillary sinus drainage and restoration of normal orbital anatomy. Sinus surgery typically involves opening the maxillary antrum, re-establishing appropriate drainage, and aspiration and culture of residual sinus secretions.51 The Caldwell-Luc approach has largely been replaced by endoscopic surgery. Functional endoscopic sinus surgery (FESS) may begin with a septoplasty to improve exposure. An uncinectomy is commonly performed to gain access to the osteomeatal complex. Once the maxillary ostium is visible, a wide antrostomy is performed to enlarge the osteum. Balloon sinuplasty has recently been described as a less invasive alternative to FESS.52
Controversy: There is some debate as to the need for and timing of orbital reconstruction. Options include a single-stage operation done concurrently with the FESS, delaying the orbital reconstruction for 2 to 6 months, or no orbital reconstruction at all. Several studies have documented return of normal orbital anatomy after FESS alone.53,54 In a review of 23 cases of SSS, Sivasubramaniam et al. showed that 22 patients had resolution of symptoms with FESS alone. One patient required delayed orbital reconstruction without complication.54 Other authors have recommended combined FESS and orbital reconstruction, citing the advantages of avoiding morbidity associated with a second hospital stay and second anesthesia event.55 Delayed orbital reconstruction may also avoid overcorrecting the globe position and placing an implant near a potentially infectious process.56
When indicated, orbital floor reconstruction should follow the basic surgical principles of orbital floor fracture repair. Exposure is obtained either through a transconjunctival or subciliary approach to the inferior orbit.45 After the depressed orbital floor is identified, an appropriately sized implant is placed. Implant material is determined by the surgeon and may include alloplastic materials or autogenous grafts. Alloplastic materials include titanium, porous polyethylene, combined titanium and porous polyethylene, hydroxyapatite, supramid, nylon, and silicone. Autogenous grafts include septal cartilage, split calvarial bone grafts, anterior maxillary bone, and costochondral cartilage.45,55–57 Mavrikakis described injection of 2 mL of hyaluronic acid gel filler into the intraconal and posterior extraconal orbital space, improving globe position, with stable results seen at 6 months after injection.57
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