Bony Optic Canal Research Articles

Optic nerve-associated connective tissue structures revisited: A histological study using human fetuses and adult cadavers.

Unlike the usual peripheral nerve, the optic nerve accompanies a thick "dural sheath," a thin "sheath of pia mater" (SPM), and multiple "septa," which divides the nerve fibers into fascicles. We collected specimens from 25 adult cadavers and 15 fetuses and revisited the histological architecture of the optic and oculomotor nerves. In the optic chiasma, the meningeal layer of the dura joins the pia to form a thick SPM, and the periosteum of the sphenoid is continuous with the dural sheath at the orbital exit of the bony optic canal. The septa appeared as a cluster of irregularly arrayed fibrous plates in the intracranial course near the chiasma. Thus, the septa were not derived from either the SPM or the dural sheath. In the orbit, the central artery of the retina accompanies collagenous fibers from the dural sheath and the SPM to provide the vascular sheath in the optic nerve. These connective tissue configurations were the same between adult and fetal specimens. At the optic disk, the dural sheath and SPM merged with the sclera, whereas the septa appeared to end at the lamina cribrosa. However, in fetuses without lamina cribrosa, the septa extend into the nerve fiber layer of the retina. The SPM and septa showed strong elastin immunoreactivity, in contrast to the absence of reactivity in the sheaths of the oculomotor nerve. Each S100 protein-positive Schwann sheath of the oculomotor nerve was surrounded by collagenous endoneurium. Glial fibrillary acidic protein-positive astrocytes showed a linear arrangement along the septa.

Unilateral Papilledema in Idiopathic Intracranial Hypertension: A Case Series.

Idiopathic intracranial hypertension (IIH) typically presents with bilateral papilledema; however, highly asymmetric and rare unilateral cases have been reported. We report three cases of IIH meeting modified Dandy criteria presenting with unilateral papilledema. Magnetic resonance imaging (MRI) demonstrated bilateral distention of the optic nerve sheaths and computed tomography (CT) of the orbits demonstrated a smaller diameter of the optic canal in the unaffected eye in two cases. Papilledema fully resolved in all with acetazolamide. Of postulated mechanisms, we suspect that differences in bony optic canal diameter, compliance of the lamina cribrosa, and optic nerve sheath anatomy may contribute to asymmetry.

STUDY ON THE OPTIC NERVE VARIATIONS IN RELATION TO POSTERIOR PARANASAL SINUSES USING CT IN TERTIARY CARE CENTRE

Background and objectives: Optic nerve has a close relationship with the posterior paranasal sinuses. Depending on the degrees of pneumatization of these sinuses, the optic nerve may indent the sinus wall or protrude into them, predisposing the nerve to injury during sinus surgeries. Aim was to analyse the optic nerve variations in relation to the posterior paranasal sinuses and to categorize the subjects as per DeLano's classification.
 Methods: Cross-sectional study was conducted on 336 patients above 16 years of age who underwent computed tomographic evaluation of head and brain. From volume data, multiplanar reconstructions were made in axial, coronal and sagittal planes and analysed in both bone and soft-tissue windows. Relationship of optic nerve with posterior paranasal sinuses were categorised into 4 types according to DeLano's classification. Bony dehiscence of optic canal and pneumatization of anterior clinoid process were also assessed.
 Results: 672 optic nerves were assessed, the most common optic nerve type identified was type 1 (62.6%), followed by type 2 (18.6%). Types 3 and 4 were seen equally in number (9.6% each). Dehiscence of optic nerve canal and pneumatization of anterior clinoid process (ACP) was seen respectively on 66 (9.8%) and 75 (11.2%) sides. Compared to type 1 and 4 optic nerves, dehiscence of bony optic canal was statistically more significant in type 2 and 3 nerves. 45.5% individuals with anterior clinoid process pneumatization had associated optic canal dehiscence, which was found to be statistically significant.
 Conclusion: Optic nerve variations were identified and classified according to DeLano’s classification. The range was within international limits and type 1 was the most common occurrence. When compared to other similar studies among Indian population, disparity observed in the frequency of optic nerve types and bony optic canal dehiscence in our study, were probably due to differences in ethnicity and size of study group. Association of bony optic canal dehiscence with type 2 & 3 optic nerves and ACP pneumatization with type 3 optic nerve was found to be statistically significant, making them more vulnerable to injury during surgery. Knowledge of optic nerve relation with posterior paranasal sinuses, and its identification in preoperative computed tomography (CT) scan are important to avoid injury to optic nerve.
 Keywords: Optic nerve, sphenoid sinus, posterior ethmoid cell, Onodi cell, anterior clinoid process pneumatization, optic canal dehiscence.

Traumatic “TERSON SYNDROME PLUS”: Pneumocephalocele with optic atrophy

Introduction. Terson Syndrome is subarachnoid hemorrhage (SAH) with sub retinal hemorrhage flowing through channel. Reduced vision in such fresh case is due to hemorrhage itself, blocking macula/other photo receptors in the long run macular cellophane retinopathy which causes profound visual loss. SAH causes neurological problems which can become a risk factor for evacuating blood from vitreous. Hypertension is commonest cause to cause Terson Syndrome, but trauma is also devastating cause as it can lead to irreversible visual consequences like total loss of perception of light or blindness. Aim. Here we describe a case of Terson Syndrome plus disease features SAH in frontal lobe. Description of the case. When there is traumatic pneumocephalocele, it gives space to blood to imbibe towards bony optic canal and form hematoma around nerve sheath which causes compression around the same and leads to optic atrophy. Optic nerve can be injured by direct traumatic dissection during road traffic accidents (RTA), but even without that blood may accumulate around optic nerve and in turn leads to formation of hematoma and subsequently pressure induced optic atrophy. Moreover, blood can slowly travel to sub hyaloid space/sub retinal space (beneath internal limiting membrane or sub ILM) with probable gliosis covering typical boat shaped blood as seen in this case. This sub ILM hemorrhage or gliosis may have resolved through three injections of Triamcinolone in the orbital floor (OFTA) near apex, but optic atrophy snatches vision. This protocol was followed to treat traumatic compressive (peri optic hematoma) optic neuropathy and traumatic retinopathy associated with sub hyaloid hemorrhage. Conclusion. Diagnosis of Terson syndrome plus disease was established by addressing all features on computed tomography (CT) scan and magnetic resonance imaging (MRI). Plus, features include pneumocephalus, optic nerve sheath hematoma, optic atrophy and gliosis over sub-hyaloid hemorrhage, typical boat shaped. The part of hemorrhage still endured as seen on optical coherence topography, but vision was lost by virtue of optic atrophy. OCT shows clot in sub hyaloid space.

The relationship between optic canal size and severity of papilledema in children with intracranial hypertension

Bony optic canal size has been proposed to affect the dynamics of cerebrospinal fluid pressure from the cranium to the subarachnoid space within the optic nerve sheath. This may contribute to variations in clinically observed optic nerve edema (ONE) in patients with intracranial hypertension (IH). The purpose of this study was to determine if a relationship exists between optic canal size and the grade of clinically observed ONE in pediatric IH patients.

Optic canal size in idiopathic intracranial hypertension and asymmetric papilledema

ObjectiveAsymmetric papilledema (AP) is a rare condition in idiopathic intracranial hypertension (IIH). As the pathophysiology of papilledema developement in IIH remains unclear, the study of AP could clarify some etiologic aspects. We aimed to evaluate bony optic canal size in IIH patients with AP. Patients and methodsAll IIH patients based on modified Dandy criteria in our referral tertiary eye hospital underwent neuro-opthalmologic exams and grading of papilledema according to modified Frisén scale. Very asymmetric papilledema (VAP) defined as a ≥2 grade difference between the two eyes. Clinical features, cerebrospinal fluid opening pressure (CSF OP), best corrected visual acuity, Humphery visual field, and brain magnetic resonance imaging (MRI) and MR venography was performed for all patients. Spiral orbital computed tomography (CT) scan which is the choice method for details of bony structures with axial, coronal and sagittal planes was done in patients with VAP. Result59 patients with IIH were diagnosed that 18.6% of them (n = 11) had VAP. There was no IIH patient with strictly unilateral Papilledema. Presenting symptoms and CSF OP was not significantly different between patients with symmetric and asymmetric papilledema. In patients with VAP, bony optic canal size was not statistically significant different in axial, coronal and sagittal plane when comparing the eye with higher grade edema to the fellow eye. ConclusionOur study showed that bony optic canal size evaluated by orbital CT scan was not different in VAP in IIH patients. Finding the exact pathophysiology of AP need further studies.

Refining Operative Strategies for Optic Nerve Decompression: A Morphometric Analysis of Transcranial and Endoscopic Endonasal Techniques Using Clinical Parameters.

Various approaches can be considered for decompression of the intracanalicular optic nerve. Although clinical experience has been reported, no quantitative study has yet compared the extent of decompression achieved by an endoscopic endonasal versus transcranial approach. Toward this aim, our morphometric analysis compared both approaches by quantifying the circumferential degree of optic canal decompression that is possible before any meningeal violation, which would result in cerebrospinal fluid (CSF) leak. From 10 cadaver heads, 20 optic canals were sequentially decompressed using an endoscopic endonasal approach and pterional craniotomy with extradural clinoidectomy. Dissections ended before violation of the sphenoid sinus during the transcranial approach, and before intracranial transgression from the endonasal corridor. Based on our study criteria, decompressions were not maximal for either approach, but were maximal before violating the other compartment. Decompression achieved from each approach was quantified using CT scans for each stage. Greater circumferential bony optic canal decompression was obtained from transcranial (245.2°) than endonasal (114.8°) routes (P < .001). By endonasal perspective, the anatomical point where the optic nerve traverses intracranially was approximated by the medial border of the anterior ascending cavernous internal carotid artery. Our morphometric analysis comparing optic canal decompression for endonasal and transcranial corridors provides important guidance for this location. Ample visualization and wide exposure can be achieved via a transcranial approach with limited risk of CSF leak. A landmark, where the intracanalicular segment ends and optic nerve traverses intracranially, can mark the extent of decompression safely obtained before risking CSF leak.

Surgical Freedom Evaluation During Optic Nerve Decompression: Laboratory Investigation.

Various surgical routes have been used to decompress the intracanalicular optic nerve. Historically, a transcranial corridor was used, but more recently, ventral approaches (endonasal and/or transorbital) have been proposed, individually or in combination. The present study aims to detail and quantify the amount of bony optic canal removal that may be achieved via transcranial, transorbital, and endonasal pathways. In addition, the surgical freedom of each approach was analyzed. In 10 cadaveric specimens (20 canals), optic canals were decompressed via pterional, endoscopic endonasal, and endoscopic superior eyelid transorbital corridors. The surgical freedom and circumferential optic canal decompression afforded by each approach was quantitatively analyzed. Statistical comparison was carried using a nonpaired Student t test. An open pterional transcranial approach allowed the greatest area of surgical freedom (transcranial, 109.4 ± 33.6 cm2; transorbital, 37.2 ± 4.9 cm2; endonasal homolateral, 10.9 ± 5.2 cm2; and endonasal contralateral, 11.1 ± 5.6 cm2) with widest optic canal decompression compared with the other 2 ventral routes (transcranial, 245.2; transorbital, 177.9; endonasal, 144.6). These differences reached, in many cases, statistical significance for the transcranial approach. This anatomic contribution provides a comprehensive evaluation of surgical access to the optic canal via 3 distinct, but complementary, approaches: transcranial, transorbital, and endonasal. Our results show that, as expected, a transcranial approach achieved thewidest degree of circumferential optic canal decompression and the greatest surgical freedom for manipulation of surgical instruments. Further surgical experience is necessary to determine the proper surgical indication for the transorbital approach to this disease.

The Optic Canal Size Is Associated With the Severity of Papilledema and Poor Visual Function in Idiopathic Intracranial Hypertension.

To determine whether the size of the bony optic canal is associated with the severity of papilledema and poor visual function in idiopathic intracranial hypertension (IIH). We performed a retrospective review of definite patients with IIH with requisite brain magnetic resonance imaging allowing for optic canal measurement. Clinical characteristics and automated (Humphrey) visual field results were reviewed; papilledema was graded according to the modified Frisén scale. Cross-sectional area of the optic canals was measured independently by 2 readers and averaged for each canal. Logistic regression modeling was applied. Sixty-nine patients with IIH were included (mean age: 33; 91% women; 65% black). Controlling for age, sex, body mass index, race, and cerebrospinal fluid (CSF) opening pressure, each mm increase in canal size was associated with a 0.50 dB reduction in Humphrey visual field mean deviation (P = 0.006); this was likely mediated by the increased odds of Grade 4-5 papilledema or optic atrophy in patients with larger canals (odds ratio: 1.30 [95% CI: 1.10-1.55; P = 0.003] for Grade 4-5 papilledema or atrophy vs grade <4 papilledema per mm increase in canal size). Poor visual function and severe papilledema or optic atrophy were associated with a larger optic canal. Potential mechanisms include alteration of local CSF flow or bony remodeling at the optic canals.

Asymmetric papilledema in idiopathic intracranial hypertension.

Very asymmetric papilledema in idiopathic intracranial hypertension (IIH) is rare, and few studies have dealt with this atypical presentation of IIH. Our aim was to describe the clinical and radiologic features of patients with IIH and very asymmetric papilledema. We identified all adult patients from our IIH database with very asymmetric papilledema defined as a ≥2 modified Frisén grade difference between the 2 eyes. Demographic data and initial symptoms were collected, and all brain imaging studies performed at our institution were reviewed. Of the 559 adult patients with definite IIH, 20 (3.6%; 95% confidence interval [CI], 2.3-5.6) had very asymmetric papilledema at initial evaluation. They were older (39 vs 30 years; P < 0.001), had lower cerebrospinal opening pressure (35.5 vs 36 cm of water; P = 0.03), and were more likely to be asymptomatic compared with patients with symmetric papilledema (27% vs 3%; P < 0.001). Visual fields were worse on the side of the highest-grade papilledema (P = 0.02). The bony optic canal was smaller on the side of the lowest-grade edema in all 8 patients (100%) in whom the imaging was sufficient for reliable measurements (P = 0.008). IIH with very asymmetric papilledema is uncommon. Very asymmetric papilledema may result from differences in size of the bony optic canals, supporting the concept of compartmentation of the perioptic subarachnoid spaces.

Readout-segmented diffusion-weighted imaging in a critical anatomic area - diagnosing posterior ischemic optic neuropathy (PION).

Posterior ischemic optic neuropathy (PION) is a rare condition characterized by blindness following ischemia of the retrobulbar segment of the optic nerve. It is usually bilateral, involving both optic nerves, but can be unilateral. Most cases of PION occur due to surgical complications or following trauma (Hayreh SS et al. Prog Retin Eye Res 2009; 28: 34). In the perioperative setting, PION occurs in non-ophthalmic surgery that is prolonged, performed in a prone position or associated with a very large blood loss (or a combination of these factors). These conditions can lead to low blood pressure and resulting hypoxia with edema of the nerve. The optic nerve is also prone to develop a compartment syndrome as it is confined within the narrow bony optic canal. In cases of non-ophthalmic head trauma, two different factors may lead to optic nerve ischemia. The nerve may be stretched resulting in compression of the supplying vessels and disruption of its blood supply. Volume loss due to trauma-related hemorrhage can also occur.

Colour Doppler imaging evaluation of blood flow parameters in the ophthalmic artery in acute and chronic phases of optic neuritis in multiple sclerosis

Optic neuritis (ON) is a common manifestation of multiple sclerosis (MS). It is caused by the immune-mediated inflammation of the optic nerve. Some vascular factors that may influence blood flow in the ophthalmic artery (OA) have also been suggested as factors in the pathogenesis of ON. The purpose of our study was to evaluate blood flow velocities and resistance (RI) and pulsatile (PI) indices in the OA in both orbits in patients in the acute and chronic phases of unilateral ON and to compare these with equivalent findings in healthy control subjects. Orbital colour Doppler imaging (CDI) was performed in 40 consecutive MS patients during acute unilateral ON prior to corticosteroid treatment. Optic neuritis was diagnosed on the basis of clinical presentation and facultative assessment of visual evoked potentials (VEPs). The peak systolic (PSV) and end-diastolic (EDV) velocities and RI and PI were measured in the OA in both eyes. We compared results from affected and unaffected orbits using the paired t-test. The same measurements were performed in 114 MS patients with a history of acute unilateral ON that occurred > 1 year prior to ultrasound examination. We also measured the same parameters in the middle cerebral arteries (MCAs) on both sides in all subjects in both groups. The same measurements were obtained in healthy controls. The PSV (p < 0.0001), RI (p < 0.0001) and PI (p < 0.0001) in the OA in the eye affected with acute ON were significantly higher than in the unaffected eye. There was no difference in EDV in the OA between affected and unaffected eyes (p > 0.05) in the group with acute ON. We did not observe any significant differences between eyes in either blood flow velocities or the RI or PI (p > 0.05) in the group in the chronic phase of ON or in the control group. All the parameters in the MCAs on both sides were normal in both the acute and chronic groups, as well as in the control group. Pathophysiological changes during acute unilateral ON influence orbital haemodynamics, as is indicated by increased PSV, RI and PI in the OA in eyes affected with ON. However, these changes do not persist over longer periods.

Computed Tomography Anatomy of the Optic Canal

Objective (1) Analyze the radiographic anatomy of the optic canal in relationship to the sphenoid sinus. (2) Understand the role variation in optic canal anatomy may have in the variability of outcomes in optic nerve decompression. Methods Fine cut computed tomography images of the sinuses were obtained with an IRB waiver. Optic canal dimensions were measured on sinus computed tomography images of 96 patients. 191 optic canals were analyzed (111 females, 80 males). Student T-test calculations were performed for statistical analysis on computer software. Results The average medial canal wall length was 1.48 centimeters (range 0.7–2.3). The length in males was 1.61 centimeters (1.1–2.3) as compared to 1.39 centimeters (0.7–2.0) in females (p=8.0–7). The average degree of exposure of the optic canal exposed to the sphenoid sinus was 101.3 degrees (56–176). The degree of exposure was 105.6 in males versus 98.2 in females (p=.01). The potential area of canal exposed to the sphenoid sinus was 0.66 centimeters squared or 28% of the total surface area. The potential area exposed to the sphenoid sinus in males was 0.76cm2 (28%) and 0.58 centimeters squared (27%) in females. Conclusions A wide range in medial canal wall length and exposure of the bony optic canal to the sphenoid sinus exists on CT images. The variation in medial canal wall length and in optic canal exposure to the sphenoid sinus may contribute to the variability in success rates of endoscopic optic nerve decompression for optic neuropathy.

This Issue of Acta

This Issue of Acta

Surgical decompression in traumatic optic neuropathy.

The management of traumatic optic neuropathy remains controversial. This retrospective study presents the results of 19 cases of indirect optic neuropathy where surgical decompression represented the primary mode of treatment. Nineteen patients (20 optic nerves) with traumatic optic neuropathy underwent primary surgical decompression. The surgery was performed using the transethmoidal technique. The extent of bony optic canal injury documented during surgery indicated that this had been underestimated in this series by CT findings. Vision improved in eight patients, five of whom had had no light perception preoperatively. Primary surgical decompression of the optic nerve within 48 h of injury produces beneficial results. Testing of visual acuity 6 weeks after surgery does not serve as a reliable predictor of final outcome.

Optic nerve decompression via the lateral facial approach

Two cases of visual loss after lateral orbital wall fracture are presented: one with retrobulbar hematoma and evidence of optic nerve compression who failed to respond to lateral canthotomy and high-dose corticosteroid administration, and the second with immediate, total blindness associated with fracture of the bony optic canal. In both, extradural decompression of the orbit and optic nerve was achieved through the lateral facial approach with partial return of visual acuity and without surgical complications. The role of orbital and optic nerve decompression in the management of patients with blindness following orbital trauma is controversial. Orbital decompression may be of value for cases of post-traumatic visual loss unresponsive to medical management. If optic nerve injury is suspected as the cause, the additional step of decompression of the optic nerve is a logical but unproven procedure. The indications for optic nerve decompression are not established and should be considered only within the context of the specific needs of the individual patient.

Mucocele of the sphenoidal sinus--a report of 26 cases

Twenty six sphenoidal mucoceles are classified into two types according to the location and extent of the mucoceles. Two types are Ala parva type (mucoceles extending to the Ala parva) and common type (other than Ala parva type). Ala parva type comrises 8 cases and common type 18 cases. Ala parva type showed a more limited area of distribution at the superior posterior aspect of the sinuses and were provided with more frequent destruction of the bony optic canals. The average age at onset was 42.2 years old, male preponderance (81%) and left preponderance (69%) were seen. Postoperative cases were 77% with the average years after the initial sinus surgery (Caldwell-Luc surgery) of 19.8 years. Visual disturbance was seen in 58% and more than half showed an advanced degree (blind, sense of light only, or discrimination of finger movement only). Average duration from the onset of visual disturbance to surgery was 2.0 months. Improvement in visual disturbance was seen in the half of the cases, and the prognosis was poor when the disturbance was of advanced degree and the duration of the disturbance exceeded 1 to 2 months. Destruction of the bony optic canal was seen in 73% and medial portion (37%) and superior portion (32%) were commonly affected. Among cases with optic canal destruction, 79% were complicated with visual disturbance. Postoperative cases differ from non-operative cases in no aspects. A bibliographical study for the pneumatization of the lesser wing was also included in discussion.

Optic Nerve Meningioma

An obese white woman presented with a 10-month history of progressive loss of vision in the right eye associated with a moderate proptosis. Examination of the fundus revealed marked congestion of the retinal vasculature with dilation of both the arteries and the veins. Numerous blot hemorrhages were scattered throughout the retina. The retina was elevated and appeared to be displaced anteriorly by solid tissue, but B-scan ultrasonography demonstrated only a serous detachment of a thickened, markedly convoluted retina. A diagnosis of optic nerve meningioma was considered, but definitive treatment was deferred because of medical problems. One month later the patient returned with a blind, painful right eye associated with neovascular glaucoma. High resolution CT coronal sections of the orbit showed generalized thickening of the optic nerve. The blind eye was enucleated facilitating exposure of the optic nerve which was found to be diffusely thickened by meningioma. The orbital portion of the optic nerve was subsequently removed and meningioma was demonstrated along its entire length to the bony optic canal. A transfrontal craniotomy was later performed to rid the patient of residual tumor.

Clinical observations on the isolated optic nerve injury.

The optic nerve can be injured indirectly by blunt trauma to the frontoorbital region. The mechanism of injury is related to trauma of the nerve in the tight, bony optic canal. Neurovisual transmission in the canal is interrupted by pressure on the nerve. The conventional management includes careful observation and supportive treatment. Recent interest in this unique clinical problem has prompted the development of new techniques to decompress the injured optic canal extracranially; these approaches have produced encouraging results. Another dividend of the method has been the mapping of the optic nerve region under magnification using the operating room microscope. Any gain of vision, partial or complete, is well appreciated by the patient and the physician.

VARIOUS FINDINGS OF RHINOGENOUS NEURITIS RETROBULBARIS

Clinical diagnosis of rhinogenous optic neuritis is very difficult. To make the diagnosis sure, operative findings of posterior ethmoidal and sphenoidal sinus which situate near the nerve, and its postoperative progress are very important.The rhinogenous neuritis was classified into 3 types as follows:I. type: Syndrom of orbital apex (serious type).II. type: Optic neuritis with papilloedema (medium serious type).III. type: Optic neuritis without papilloedema (slight type).4 cases of I. type and 2 cases of II. type were reported. Among these 6 cases 5 cases of good results were obtained. Among these 6 cases in 3 cases removal of medial wall of optic canal by Niho-Sato's operation were performed and bony optic canal were histo-pathologically examined. By this histological observation serious pathologic changes were proved adjacent to the optic nerve and the etilogy as rhinogenous became very sure.The cases of the slight type are now still under investigation and although its diagnosis is still uncertain, it seems to be very probable to believe in the frequent presence of this type.For the treatment of the rhinogenous optic neuritis, complete removal of the pathologic mucous membrane thru transantral and extranasal route is very important and opening of optic canal by Niho-Sato's operation is effective.