Onodi Cell Mucocele-Associated Optic Neuropathy: A Rare Case Report and Review of the Literature.

PURPOSE: To present a rare case report of Onodi cell-associated optic neuropathy, conducting a review of the literature.
METHODS: A 36-year-old male presented with an 18-h history of acute deterioration of vision in his left eye (LE). Ophthalmic examination and Magnetic Resonance Imaging (MRI) were consistent with an Onodi cell-associated compressive optic neuropathy.
RESULTS: Despite immediate, successful surgical decompression, severe optic nerve atrophy and permanent visual loss occurred during early postoperative period. The reported case gives rise to different hypotheses regarding pathophysiology that may lead to irreversible blindness. A systematic review of the respective literature is provided attempting to compare different approaches in the management of Onodi cell-associated compressive optic neuropathy and assess their efficacy in the final visual outcome. Poor initial visual acuity (VA) may represent a bad prognostic factor. Moreover, age and gender do not seem to significantly influence the outcome.
CONCLUSION: This report and associated literature review highlight the importance of the radiologic characteristics and early diagnosis in the final visual outcome of the Onodi cell-associated optic neuropathy. High level of suspicion is crucial for early diagnosis of mucoceles, which must be treated promptly by surgical and medical means to enhance visual recovery. Copyright:

INTRODUCTION

Mucocele is a benign and chronic epithelial-lined cystic lesion, arising at the expense of the paranasal sinus mucosa, usually containing sterile mucus. The vast majority of mucoceles arises from the frontal (65%) and ethmoidal sinuses (25%), as they are numerous with narrow ostia, in contrary to the sphenoid sinus (only 1–2%).12345

The Onodi cell, initially described by Onodi in 1904,6 is an anatomical variant, whereby during normal embryological development, the posterior ethmoid cell enlarges and pneumatises superolaterally into the sphenoid sinus, an area closely related to the optic canal, the optic nerve and the internal carotid artery.7 It can, thus, represent a possible cause of retrobulbar optic neuropathy. Based on radiological findings, the incidence rate of the Onodi cell is calculated 8–24%, while in cadaveric studies, the prevalence rate has been reported to be up to 60%.89

Compressive optic neuropathy caused by an Onodi cell-related mucocele is an extremely rare complication with only a few reports in the literature. We herein present a rare case of unilateral, permanent visual loss, without any relevant ocular or nasal history, caused by compressive optic neuropathy due to an Onodi cell mucocele, despite urgent surgical intervention. This case highlights the importance of early diagnosis of the Onodi cell-associated optic neuropathy, based on clinical and radiologic findings, as well as prompt intervention with regards to final visual outcome.

CASE REPORT

A 36-year-old male presented to our emergency department 18 hours after a sudden deterioration of vision in his left eye (LE). The patient had a clear ophthalmic and medical history, reporting no use of medication, tobacco, or alcohol. Upon presentation, best corrected visual acuity (BCVA) was measured 20/20 in the right eye (RE) and counting fingers (CF) in the left. A prominent relative afferent pupillary defect (RAPD) was noted on the left side. Ocular motility and main cranial nerves function were undisturbed, while slit-lamp biomicroscopy was unremarkable. Dilated fundoscopy was not diagnostic for optic disc edema or vein congestion, while the rest of the retina appeared normal [Figure 1a]. Requested Magnetic Resonance Imaging (MRI) of the brain and orbits revealed a hyper-dense cystic bilobed mass in the far posterior ethmoid cell. The lesion was located in the superior aspect of the sphenoid sinus and extended to the left orbital apex in close proximity to the left optic nerve [Figure 1b and c].

Figure 1

(a) Fundus photograph at baseline. No signs of optic nerve compression are noticed (b and c) magnetic resonance imaging (fat-saturated post contrast T1-weighted axial and coronal cuts, respectively) at presentation depicting an iso-dense bilobed cystic lesion lateral to the ethmoid sinuses, compressing the optic nerve inferomedially (orange arrow) (d) Fundus photograph at week 4 postoperatively. Progression of optic nerve pallor is noted (e and f) magnetic resonance imaging (fat-saturated post contrast T1-weighted axial and coronal cuts, respectively) at week 1 postoperatively. The area corresponding to the evacuated cyst is marked with the orange arrow

Based on clinical and radiologic findings, an urgent surgical intervention was scheduled to facilitate decompression of the optic nerve. The Onodi cell mucocele was efficiently evacuated through a left transnasal endoscopic approach, without any iatrogenic damage to the optic nerve, while its content was sent for microbiology evaluation. Cultures revealed the growth of E. Coli, Enterobacter aerogenes and coagulase negative Staphylococcus. Postoperatively, the patient was set on intravenous steroids (500 mg Methyl-prednisolone I.V./day) and antibiotics (Ceftriaxone 1000 mg I.V./twice a day). Upon discharge, he was prescribed per oral steroids in tapering doses and antibiotics (Doxycycline and Ciprofloxacin) for 2 weeks.

BCVA of the LE was handmotion (HM) atday1, deteriorated to perception of light (LP) at day 5, and remained unchanged throughout later follow-up visits, with the last being 3 years thereafter. Fundoscopy and fundus photography at 4 weeks postoperatively showed progressively established paleness of the optic disc [Figure 1d], while MRI sequences confirmed the complete evacuation of the cystic lesion [Figure 1e and f].

DISCUSSION

There are numerous etiologies that are associated with the formation of mucoceles. Primary causes, such as secretory duct blockage and obstruction of mucus drainage, as well as secondary causes, such as sinus surgery and trauma, result in progressive accumulation of mucus and subsequent dilation of the lesion.10 All these may result to local bone destruction, deformation, and progressive remodeling of the surrounding osseous walls.1112

The potential pathophysiological mechanisms, responsible for the mucocele-associated optic neuropathy and visual loss, are not yet completely understood.13 The optic nerve inside the optic canal is not surrounded by fat or other soft tissues. Consequently, the mucocele pressure is directly transferred to the optic nerve, blood supply is thereby compromised, and subsequent optic atrophy may appear. Another possible explanation of the visual disturbances consistent with an Onodi cell mucocele is optic neuritis which can be caused by the respective inflammatory reaction. Microvascular changes and inflammatory factors are more frequently related to an acute onset and rapid progression of visual disturbances, rather than mechanical compression, which is mainly characterized by a gradual appearance of clinical symptoms.1314

Clinical manifestations of paranasal mucoceles are variable and depend not only on the size of the mucocele but also on its location and direction of expansion. The most common ocular findings of fronto-ethmoidal mucoceles include diplopia, globe displacement, and increased intraocular pressure, due to the compression exerted on the eye.1013 On the other hand, Onodi cell and sphenoidal mucoceles appear as a more common cause of retrobulbar optic neuropathy, cranial nerve palsies, and acute visual loss due to their close anatomical relation and increased pressure exerted on cranial nerves.1516 Moreover, stretching of the dura and paranasal sinus mucosa may result in trigeminal nerve-mediated periorbital pain, which is very frequently reported by patients.1317

Except for clinical symptoms and signs, imaging techniques, such as CT and MRI, play an essential role in the diagnosis of Onodi cell mucoceles, aiding in the differential diagnosis of similar clinical entities as well as optimal surgical planning.181920 Regarding MRI scans, Onodi cell mucoceles are optimally identified on axial images, where the track of the optic nerve in relation to the sphenoid sinus and the posterior ethmoid, can be better assessed.19 Mucocele appearance varies on MRI and it depends on protein concentration, which alters over time. The initial high content of water results in hypointense T1 and hyperintense T2-weighted images, while the gradual rise of protein content may lead to a reverse intensity.20

In the literature, there are several reports of Onodi cell mucoceles that resulted in optic neuropathy. Hereby we provide an up-to-date review of the literature regarding this entity. Eligible articles were identified by a search of the bibliographic database in PubMed using the following combination of search terms:” Onodi cell-associated optic neuropathy “OR” Onodi cell AND optic neuropathy “OR” mucocele AND compressive optic neuropathy “. The end date of the search period was June 3, 2019. We also checked all the references of relevant reviews and eligible articles that our search retrieved. Language restrictions were not used, and data were extracted from each eligible study by 3 investigators working independently (A.T., P.R., and A.D.). For each of the eligible studies, the following data were collected: lead investigator name; year of publication; journal name; demographic characteristics of the population being studied; symptoms at presentation; initial visual acuity; medical history; final visual outcome; final imaging outcome.

Table 1 summarizes all published relevant cases, presented in chronological order, providing additional information on the course of each case. Twenty-four cases (our case included) were identified according to the aforementioned inclusion criteria and were further analyzed. Patients' age at the time of presentation varied from 28 to 79 years with a mean age of 51.6 years. Nine cases were reported in female patients (37.5%) and 15 in males (62.5%), yielding no statistically significant difference in the mean age or final visual outcome between genders (P > 0.05, Mann-Whitney test). All visual acuities were converted to decimal system in order to facilitate comparison between cases.

Table 1

Epidemiology and clinical characteristics of published cases

	Author, year	Age, sex	Presenting symptoms	Initial VA	Medical history	Course	Final VA
1	Ogata et al., 199817	63, male	Recurrent optic neuropathy with visual lossInferior VF defect	0.8		Improvement with steroids temporarilyAfter surgery (ESS): VA=1.0, No VF defect (1 week later)Follow-up (6 months later): Stable	1.0
2	Klink et al., 200021	41, male	Sudden VA lossRAPDCentral scotoma of 20o	HM		After 1st surgery (ESS): VA=0.67, Small paracentral scotoma (9d later)Recurrence of mucocele, VA and VF: stable (3 months later)After 2nd surgery (ESS): VA=1.0, No paracentral scotoma (1 year later)	1.0
3	Kitagawa et al., 200322	73, male	HeadacheDecreased visionRAPDCentral scotoma	CF	Cataract surgery - phacoemulsification (1 week before)	After surgery (ESS) (7 days delay): VA=1.0 (1 month later)Follow-up (6 months later): Stable	1.0
4	Yoshida et al., 200423	53, female	Retroorbital dull painBlurred visionInferomedial VF defect	CF		After surgery (pterional craniotomy) (3 weeks delay): Immediate VA recovery, VA=1.0, Normal VF (2 weeks later),	1.0
5	Yoon et al., 24 2006	43, female	Sudden visual loss over 2 daysRAPDCentral scotoma	HM		After immediate surgery (ESS) and intravenous Methylprednisolone: VA=0.67, Mild temporal VF defect (6 months later)	0.67
6	Fukuda et al., 20065	79, male	Bilateral visual lossFrontal headacheNausea	LP in both eyes	Glaucoma	Methylprednisolone: Visual Improvement (0.6 RE, 0.4 LE)After surgery (ESS): 0.9 RE, 0.8 LEFollow-up (5 years later): No recurrence	0.9 RE0.8 LE
7	Toh and Lee 20072	61, male	Sudden blurring of visionPale optic nerve disc	0.2	Nasopharyngeal Ca treated with radiotherapyPolyps treated with endoscopic surgery	Amoxycillin-Clavulanate-Dexamethasone: VA=0.5 (3 days later)After surgery (ESS) (1 week delay): VA=0.67 (1 week later)Follow-up (1 year later): Stable - no further improvement	0.67
8	Toh and Lee 20072	40, female	HeadacheBlurring of vision over 2 weeksRAPDPale optic nerve discMild red desaturation	0.5		Amoxycillin-Clavulanate-Prednisolone (10 days course): No improvement (10 days later)After surgery (ESS): VA=0.8 (1 day later), 1.0 (2 week later), Normal color visionFollow-up (1 year later): Stable	1.0
9	Nonaka et al., 20073	41, male	PainVA decreaseOptic disc edema	LP		Steroids: No improvement (5 days later)After surgery (ESS) (2 week delay): No VA improvementFollow-up (6 months later): Stable	LP
10	Lim et al., 200825	60, male	Sudden VA lossColor vision decreasedPainRAPD Temporal VF defect	0.2	NasopharyngealCa treated with Radiotherapy	After immediate surgery (ESS): VA=1.0, Normal color vision, Normal VF (Content: Purulent material)	1.0
11	Loo et al., 200815	53, male	First visit Intermittent blurring HeadacheSecond visit (5 months later) Loss of vision RAPD Proptosis  Decreased motility	NLP	Endoscopic sinus surgery	After immediate surgery (ESS) and intravenous steroids-antibiotics: VA=NLP, Optic nerve atrophy (2 months later) (Content: Abscess)	NLP
12	Chee and Looi 200926	63, female	Acute horizontal diplopia - 6th nerve palsySudden VA loss RAPDPainless proptosisDecreased corneal sensation	CF		After surgery (lateral orbitotomy): VA 1.0, full recovery with antibiotics (Content: Abscess)	1.0
13	Fukuda et al., 201027	45, female	Gradual visual loss over 1 year	0.67		After surgery (pterional craniotomy): VAImprovement (3 days later)	1.0
14	Wu et al., 201028	28, male	VA lossOcular pain and HeadacheRAPDConstricted VF on confrontationPale optic nerve disc	0.2		Initial improvement with intravenousMethylprednisolone-CeftriaxoneAfter surgery (ESS) and intravenousMethylprednisolone-Ceftriaxone (5 weeks delay): VA=1.0, Clear VF (3 weeks later)Follow-up (1 year later): Stable (Content: Purulent fluid)	1.0
15	Nickerson et al., 201029	51, female	Complete visual lossDiagnosis 5w laterOptic nerve atrophy	NLP	Orbital fracture 38 years ago	After surgery (ESS) and steroids (7 weeks delay): Anatomical success, No VA improvement	NLP
16	Victores et al., 201230	46, male	Blurring over 3 daysSudden VA loss	NLP	Chronic sinusitisPrevious endoscopic sinus surgery	After surgery (ESS): No VA improvement (1 month later)Recurrence (eye pain and headache) (6 year later)(Content: Purulent and mucoid)	NLP
17	Taflan et al., 201331	61, female	Acute visual lossPainOptic nerve edemaMacular star	0.1		After surgery (ESS) and intravenous antibiotics: VA=0.5 (10 days later)	0.5
18	Fleissig et al., 201432	53, female	Sudden VA lossPain in ocular movementsRAPDEyelid edemaDiplopiaParesthesia V1 and V2Eye movement limitation	CF	Chronic rhinosinusitis treated with endoscopic sinus surgery	After surgery (ESS) and methylprednisolone: NLP, Normal eye movements	NLP
19	Cheon et al., 201433	60, male	HeadacheVisual loss	NLP	Brain infraction for 5 year	After surgery (ESS): No headaches, No visual improvement (Content: Fungal ball - Aspergilloma)	NLP
20	Rueping et al., 201434	39, male	Acute visual lossRAPDDull orbital headache	NLP	Endoscopic surgery 20 yeara. for chronic sinusitis	After surgery (ESS): VA=NLP	NLP
21	Yen Nee See et al., 201635	50, male	Acute painless loss of visionRAPDPale optic nerve disc	CF		After surgery (ESS) and steroids (6 weeks delay): VA=0.1, No RAPD (5 months later)	0.1
22	Lee and Au 201636	39, female	Progressive visual lossRetro-orbital painOptic disc edemaDecrease in color vision	0.08	Endoscopic surgery 10 years before for chronic sinusitis	After surgery (ESS): VA=0.67, Normal color vision, No optic disc edemaFollow-up (6 months later): Stable	0.67
23	Kwon et al., 201937	62, male	Double visionTrochlear nerve palsyPathological ocular motility test	1.0		After surgery (ESS) and intravenousDexamethasone: Orthotropia, Improvement of ocular motility (4 months later)	1.0
24	Tzamalis A. 2019	34, male	Sudden VA lossRAPD	CF		After surgery (ESS) and intravenous antibiotics/steroids: VA=HM, optic nerve palenessFollow-up (3 years later): VA=LP, Stable (Content: Purulent fluid)	LP

VF: Visual field; VA: Visual accuity measure in decimal system; RAPD: Relative afferent pupil defect; HM: Hand motion; CF: Counting fingers; LP: Light perception; NLP: No light perception; ESS: Endoscopic sinus surgery; RE: Right eye; LE: Left eye

In most of the reported cases, despite an initial visual decrease, a certain amount of visual recovery was noted after immediate surgical intervention and evacuation of the compressing mucocele.25172122232425262728313637 However, it is of note that 37.5% of the reported cases in the literature (9/24, 7 males, 2 females, P > 0.05, Chi-square test) resulted in very poor visual acuity despite medical or/and surgical treatment.315293032333435 In 6 of those cases, final VA was no LP, in two cases LP, and in one case 0.1 (decimal VA). In all the above-mentioned patients, initial VA upon presentation was extremely poor (≤ CF). On the other hand, the rest (62.5%) of the reported cases (15/24) demonstrated a complete (10/15) or fair (5/15) recovery of vision with or without peripheral visual field defects. In those cases, initial VA varied significantly between LP and 0.8 (decimal VA).

In our case, vision worsened rapidly, and despite immediate and efficient optic nerve decompression along with rapid administration of I.V. steroids and antibiotics, no visual improvement was reported. This condition led to unilateral visual loss along with established optic nerve atrophy. The rapid and painless visual loss may be suggestive of microcirculatory and inflammatory mechanisms involved in the optic neuropathy seen in our case. Moreover, the normal fundus findings at presentation, only 18 hours after acute visual loss was noticed, give additional evidence for minor mechanical optic nerve compression. One could also assume that an intraoperative, direct optic nerve trauma may have led to permanent visual loss. However, endoscopic videos of the operation were thoroughly reviewed and were not found to be suggestive of any iatrogenic optic nerve violation.

Apart from visual disturbance, the second most common symptom of Onodi cell mucocele was pain (13/24; 54.2%) appearing either as dull headache or as periorbital pain. Interestingly, RAPD was reported only in half of the cases (12/24; 50%), given the fact that almost all cases presented with visual acuity reduction possibly due to compressive optic neuropathy. Other less frequent symptoms were visual field constriction and double vision, which were reported in 7/24 (29.2%) and 3/24 (12.5%) cases, respectively. Interestingly in one case, reported by Fleissig et al.,32 the patient complained not only about loss of vision, pain and diplopia, but also about eyelid edema and paresthesia in the region of V1 and V2 cranial nerves.

The mainstay of treatment in Onodi cell-associated optic neuropathy is urgent surgical decompression. Regarding surgical techniques, endoscopic transnasal approach is the most commonly used due to its less invasive nature related to lower complication rates and quicker patient recovery.27 In our review, the majority of patients (21/24; 87.5%) underwent endoscopic sinus surgery (ESS), 2 patients (8.3%) underwent pterional craniotomy, and just one patient (4.2%) was treated with lateral orbitotomy and drainage of the abscess.

A very important issue that needs to be further investigated is whether, and to which extent, delay of the surgical decompression could determine the final visual outcome. Kitagawa et al.22 and Yoshida et al.23 reported a complete visual recovery despite the fact that decompression surgery was delayed approximately 1 and 3 weeks after initial diagnosis, respectively. Moreover, Wu et al.28 reported a postoperative visual acuity of 20/20 in their patient despite a 5 week delay of surgery. On the other hand, there are some reports with no visual recovery, despite early surgical decompression and intravenous treatment with steroids and/or antibiotics.

Furthermore, the role of corticosteroids and antibiotics in visual rehabilitation remains unclear, and future studies may investigate whether their use is beneficial in Onodi cell-associated optic neuropathy. Our systematic review has not identified any strong evidence for the efficacy of intravenous treatment with steroids or antibiotics with regards to the final visual outcome, which also may differ in cases of purulent mucoceles. In 7 cases with purulent content reported in the literature, only 3 of them (42.9%) achieved a complete visual acuity restoration, despite appropriate medical and surgical treatment.252628

All the aforementioned reports give rise to further questions regarding pathophysiology of Onodi cell mucoceles that may lead to irreversible blindness despite early surgical intervention. Poor initial VA may represent a factor associated with poor prognosis. Moreover, age and gender do not seem to significantly influence the outcome. Further work needs to be carried out to establish the usefulness of steroids and antibiotic treatment regarding the final visual outcome. In conclusion, a high level of suspicion is crucial for early diagnosis of mucoceles, which must be promptly treated in order to enhance visual recovery.

Informed consent

The study was performed with informed consent and following all the guidelines for experimental investigations required by the Institutional Review Board of Ethics Committee of which all authors are affiliated.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understand that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.