Anatomy of the orbital apex and cavernous sinus on high-resolution magnetic resonance images

A systematic review of the surgical anatomy of the orbital apex

Purpose

The orbital apex is the narrowest part of the orbit, housing the link between the intracranial cavity and orbit. Knowledge of orbital apex anatomy is crucial to selecting a surgical approach and reducing the risk of complications. Our purpose is to summarize current knowledge on surgical anatomy and attempt to reach a consensus on definition of the orbital apex.

Methods

The online databases of Embase, the Cochrane library, Web of Science and PubMed (MEDLINE) were queried in a comprehensive bibliographic search on the (surgical) anatomy of the orbital apex and consisted of a combination of two subjects, using indexed terms and free text: “Orbital Apex” and “Orbital Anatomy.”

Results

A total of 114 relevant papers were included in this review. Numerous anatomical variations are described in the literature. Variations of the optic canal include duplication (0.64%) and keyhole anomaly (2.65%). Variations in pneumatization of the anterior clinoid process were unilateral in almost 10%, bilateral in 9%, and normal in 72%. A rare variant of the superior orbital fissure (SOF) is Warwick’s foramen, which appears as if the lowest portion of the SOF was separated from the main fissure by a transverse bony bridge.

Conclusion

The definition of the orbital apex varies in the literature, and further research would most likely identify additional variations. A universal definition reporting these variations and pathology and imaging findings is essential for determining the optimal surgical approach to the orbital apex.

Electronic supplementary material

The online version of this article (10.1007/s00276-020-02573-w) contains supplementary material, which is available to authorized users.

Thin-Section MR Imaging for Carotid Cavernous Fistula

BACKGROUND AND PURPOSE

Carotid-cavernous fistulas are abnormal vascular shunts that can cause various neurologic or orbital symptoms. The purpose of this retrospective study was to evaluate the diagnostic performance of thin-section MR imaging for carotid cavernous fistula in patients with clinically suspected carotid cavernous fistula, and to identify possible imaging predictors of carotid cavernous fistula.

MATERIALS AND METHODS

A total of 98 patients who were clinically suspected of having carotid cavernous fistula (according to their symptoms and physical examinations) between January 2006 and September 2018 were included in this study. The patients underwent pretreatment thin-section MR imaging and DSA. Thin-section MR imaging consisted of 2D coronal T1- and T2WI with 3-mm thickness and 3D contrast-enhanced T1WI with 0.6 mm thickness. The diagnostic performance of thin-section MR imaging for carotid cavernous fistula was evaluated with the reference standard of DSA. Univariate logistic regression analysis was performed to determine possible imaging predictors of carotid cavernous fistula.

RESULTS

Among the 98 patients, DSA confirmed 38 as having carotid cavernous fistula. The overall accuracy, sensitivity, and specificity of thin-section MR imaging were 88.8%, 97.4%, and 83.3%, respectively. Possible imaging predictors on thin-section MR imaging included abnormal contour of the cavernous sinus (OR: 21.7), internal signal void of the cavernous sinus (OR: 15.3), prominent venous drainage flow (OR: 54.0), and orbital/periorbital soft tissue swelling (OR: 40.4).

CONCLUSIONS

Thin-section MR imaging provides high diagnostic performance and possible imaging predictors of carotid cavernous fistula in patients with clinically suspected carotid cavernous fistula. Thin-section MR imaging protocols could help decide appropriate management plans for patients with clinically suspected carotid cavernous fistula.

Assessing the abilities of senior otolaryngology residents and graduated otolaryngologists in recognizing skull base elements in axial CT scan: proposing a new method for differentiating superior orbital fissure and optic canal

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the ability of recognizing some important elements of the skull base in axial CT-scan cuts, including the optic canal (OC), superior orbital fissure (SOF), vidian canal (VC), foramen rotundum (FR), jugular foramen (JF) and hypoglossal canal (HC).

METHODS

In this study, 25 otolaryngology residents and 25 recently graduated otolaryngologists were evaluated in terms of their recognition of skull base elements, using 30 axial CT-scan cuts. Two months later, the exam related to skull base CT scans was taken in groups after a brief anatomy courses for otolaryngology residents.

RESULTS

The percentage of correct answers from otolaryngology residents regarding OC, SOF, VC, FR, JF, and HC in the first exam were 74 ± 26, 47 ± 34, 65 ± 30, 41 ± 38, 58 ± 26, and 68 ± 32, respectively. The correct answer for each element was similar between groups, and the differences were not statistically significant (p > 0.05). p value for the differences observed regarding the percentage of correct answers for the second exam between trained otolaryngology residents and recent otolaryngology graduates regarding OC and JF was no significant (p > 0.05) but significant for the other elements with better result in trained otolaryngology residents and most for SOF (p > 0.0001).

CONCLUSION

This study showed that the ability of recognition for the mentioned elements in axial CT-scan cuts was low among otolaryngology residents and graduated otolaryngologists. The proposed novel method for distinguishing SOF from OC had a powerful and long-lasting effect on trainee.

Morphological study of the eye and adnexa in capuchin monkeys (Sapajus sp.)

The objective of this study was to describe the anatomic and histologic features of the Sapajus sp. eye, comparing similarities and differences of humans and other species of non-human primates for biomedical research purposes. Computed tomography (CT) of adnexa, eye and orbit live animal, as well as formolized pieces of the same structures of Sapajus sp. for anatomical and histological study were also performed. The anatomical description of the eye and adnexa was performed using the techniques of topographic dissection and exenteration. Histological fragments were fixated in buffered formalin 10%, processed by the routine paraffin inclusion technique, stained with hematoxylin-eosin and special stains. CT scan evaluation showed no differences between the live animal and the formolized head on identification of visual apparatus structures. Anatomic and histologic evaluation revealed rounded orbit, absence of the supraorbital foramen and frontal notch, little exposure of the sclera, with slight pigmentation of the exposed area and marked pigmentation at the sclerocorneal junction. Masson's Trichrome revealed the Meibomian glands, the corneal epithelium and Bowman's membrane; in the choroid, melanocytes and Bruch's membrane were observed; and in the retina, cones and rods as well as, optic nerve, the lamina cribrosa of the nerve fibers bundles. Toluidine blue highlighted the membranes: Bowman, Descemet and the endothelium; in the choroid: melanocytes; and in the retina: nuclear layers and retinal pigment epithelium. In view of the observed results Sapajus sp. is an important experimental model for research in the ophthalmology field, which has been shown due to the high similarity of its anatomical and histological structures with the human species.

Orbital venous pattern in relation to extraorbital venous drainage and superficial lymphatic vessels in rats

The purpose of this study was to demonstrate the normal and variant anatomy of extraorbital and intraorbital venous drainage together with retroorbital communication, and determine the lymphatic drainage from the superficial orbital region with a potential outlet of lymphatic vessel into the venous bloodstream. The study of the venous system was carried out on 32 Wistar rats by using corrosion casts methods and radiography, while the lymphatic system was studied in 12 Wistar rats following ink injection. Superficially, orbital veins are connected with extraorbital veins running through angular vein of the eye and the superficial temporal vein, and via the pterygoid plexus with the maxillary vein, which provide readily accessible communication routes in the spread of infection. The extent of intraorbital and periorbital venous drainage was ensured by the dorsal and ventral external ophthalmic vein through the infraorbital vein, which together formed the principal part of the ophthalmic plexus. Venous drainage of the eyeball was carried out mainly by the vortex veins, ciliary veins and internal ophthalmic vein. The highest variability, first presented by differences in structural arrangement and formation of anastomoses, was observed within the ventral external ophthalmic vein (22 cases) and the medial vortex vein (10 cases). Four vortex veins, one vein in each quadrant of the eye, were observed in rats. The vortex vein located on the ventral side of the eyeball was occasionally found as two veins (in four cases) in the present study. The lymphatic vessel from the lower eyelid entered into the mandibular lymph centre, and from the upper eyelid entered into the superficial cervical lymph centre, but both drained into the deep cranial cervical lymph node. The direct entry of lymph entering the veins without passing through lymph nodes was not observed.

Surgical anatomy of the superior orbit on ultra-high-resolution MRI at 9.4 Tesla

BACKGROUND

A good understanding of the anatomical details is required to ensure optimal results during surgery of the orbit. Several indications for orbital surgery require biopsy, resection, or reconstructive procedures. The intricate relationships between the orbital septum and adjacent structures of the upper orbit can cause difficulties in interpreting the surgical anatomy of this region. The purpose of this study was to acquire further insight into the anatomy of the superior part of the orbit, with special attention paid to the orbital septum.

METHODS

An ex-vivo study was performed using magnetic resonance imaging (MRI) at 9.4 Tesla (isotropic resolution = 20 μm) on six human cadaver specimens to examine the superior-medial half of the orbit. To visualise the posterior layers of the upper orbit, a dissection of three of the orbits was performed prior to the MRI examination, and a flexible PVC sheet was introduced above the levator muscle.

RESULTS

The technique enabled a visualisation of anatomically important landmarks of the anterior and posterior parts of the upper orbit at a resolution near histological levels; to the authors' knowledge, this visualisation has not been reported previously. A posterior continuation of the orbital septum, which forms a distinct anatomical structure, is revealed.

CONCLUSIONS

The posterior aspect of the orbital septum separates the levator muscle and the orbital fat pad. Between these two structures, a surgical corridor is formed using MRI, enabling alternative access to the superior part of the orbit; this alternative access might be less invasive because the orbital septum remains undamaged.

High-resolution MRI of uveal melanoma using a microcoil phased array at 7 T

High-field MRI is a promising technique for the characterisation of ocular tumours, both in vivo and after enucleation. For in vivo imaging at 7 T, a dedicated three-element microcoil array was constructed as a high-sensitivity receive-only device. Using a dedicated blink/fixation protocol, high-resolution in vivo images could be acquired within 3 min in volunteers and patients with no requirement for post-acquisition image registration. Quantitative measures of axial length, aqueous depth and lens thickness in a healthy volunteer were found to agree well with standard ocular biometric techniques. In a patient with uveal melanoma, in vivo MRI gave excellent tumour/aqueous body contrast. Ex vivo imaging of the enucleated eye showed significant heterogeneity within the tumour.

Brainstem pathways for horizontal eye movement: pathologic correlation with MR imaging

Horizontal eye movements are conducted by the medial rectus and the lateral rectus muscles, which are innervated by the oculomotor nerve (cranial nerve III) and the abducens nerve (cranial nerve VI), respectively. The oculomotor and the abducens nuclei are interconnected by a tract in the brainstem named the medial longitudinal fasciculus (MLF). Through the MLF, the actions of the oculomotor and the abducens nuclei are coordinated, generating conjugate horizontal eye movements. The disorders of horizontal eye movement that are caused by brainstem lesions are classified into three groups: (a) lateral gaze palsy, (b) internuclear ophthalmoplegia, and (c) one-and-a-half syndrome. Lateral gaze palsy is caused by a lesion involving the paramedian pontine reticular formation (PPRF) or the abducens nucleus. Internuclear ophthalmoplegia occurs as a result of a lesion involving the MLF. One-and-a-half syndrome is a combination of lateral gaze palsy and internuclear ophthalmoplegia and is caused by a lesion involving both (a) the ipsilateral PPRF or the ipsilateral abducens nucleus and (b) the ipsilateral MLF. The pathologic lesions depicted on magnetic resonance images were topographically well correlated with the brainstem pathways and each type of horizontal eye movement disorder. Most of the lesions were tiny acute infarctions and were found in the most posterior region of the pons, which corresponded to the location of the brainstem pathways. Therefore, awareness of the brainstem pathways controlling horizontal eye movement is important to avoid missing a small pontine lesion.

Quantitative computed tomographic predictors of compressive optic neuropathy in patients with thyroid orbitopathy: a volumetric analysis

PURPOSE

To evaluate the relationship between orbital bony geometry and the volume of the intraorbital structures in predicting compressive dysthyroid optic neuropathy (DON).

DESIGN

Retrospective, consecutive case series.

PARTICIPANTS

Images of 198 orbits from 99 patients suffering from thyroid-related orbitopathy were reviewed.

METHODS

Clinical examination and computed tomography of the orbits, including volumetric analysis, were performed on all patients.

MAIN OUTCOME MEASURES

Clinical and radiologic predictors of DON.

RESULTS

Significant volumetric univariate predictors of compressive optic neuropathy included medial rectus volume (P = 0.005), lateral rectus volume (P = 0.011), superior muscle group volume (P = 0.04), and total rectus muscle volume (P = 0.015). Inferior rectus muscle volume, orbital volume, bony orbital apex angle, globe diameter, and bony medial wall contour were not associated with optic neuropathy. Multivariate modeling found medial rectus volume the only independently significant predictor. Univariate modeling of simple rectus diameter measurements found medial rectus axial diameter (P = 0.003) and total recti diameter (P = 0.016) predictive of optic neuropathy. Lateral rectus, superior rectus, and inferior rectus diameters were not predictive. Multivariate modeling found only medial rectus diameter to be a significant independent predictor of optic neuropathy. The area under the receiver operating characteristic curve was not different between the volumetric and rectus diameter curves.

CONCLUSIONS

Medial rectus size was found to be the most important quantifiable predictor of compressive optic neuropathy in patients with optic neuropathy. In this study, simple maximum medial rectus diameter, as measured on axial scans, was equally predictive of compressive optic neuropathy as the more involved volumetric calculation. Assessment of orbital geometry, including bowing of the medial wall, orbital apex angle, globe diameter, and orbital volume, were not found to be predictive of DON.

Visualization of the oculomotor cranial nerves by magnetic resonance imaging

MRI is the imaging method of choice in patients with cranial nerve palsies. However, the nerves are often not seen on MR images and smaller lesions may not be diagnosed on routine brain MRI. The purpose of this study is to show that the oculomotor cranial nerves can be visualized by standard MR sequences and to present an update on clinical applications of cranial nerve imaging. In MR images of normal subjects, it is demonstrated that the oculomotor nerve, the trochlear nerve and the abducens nerve can be identified not only in the subarachnoid space and cavernous sinus, but also in the orbit. However, a precondition is the use of appropriate imaging sequences and planes (e.g., subarachnoid cisterns: T2-weighted fast spin-echo or T2*-weighted three-dimensional sequences in oblique-axial and sagittal planes; cavernous sinus: contrast-enhanced T1-weighted coronal images; orbit: T1-weighted images without contrast agent in the coronal plane obtained using surface coils). The capability of imaging cranial nerves is clinically important not only for diagnostic purposes in eye muscle palsies but also for planning surgical procedures at the cranio-orbital junction.

The oculomotor cistern: anatomy and high-resolution imaging

BACKGROUND AND PURPOSE

The oculomotor cistern (OMC) is a small CSF-filled dural cuff that invaginates into the cavernous sinus, surrounding the third cranial nerve (CNIII). It is used by neurosurgeons to mobilize CNIII during cavernous sinus surgery. In this article, we present the OMC imaging spectrum as delineated on 1.5T and 3T MR images and demonstrate its involvement in cavernous sinus pathology.

MATERIALS AND METHODS

We examined 78 high-resolution screening MR images of the internal auditory canals (IAC) obtained for sensorineural hearing loss. Cistern length and diameter were measured. Fifty randomly selected whole-brain MR images were evaluated to determine how often the OMC can be visualized on routine scans. Three volunteers underwent dedicated noncontrast high-resolution MR imaging for optimal OMC visualization.

RESULTS

One or both OMCs were visualized on 75% of IAC screening studies. The right cistern length averaged 4.2 +/- 3.2 mm; the opening diameter (the porus) averaged 2.2 +/- 0.8 mm. The maximal length observed was 13.1 mm. The left cistern length averaged 3.0 +/- 1.7 mm; the porus diameter averaged 2.1 +/-1.0 mm, with a maximal length of 5.9 mm. The OMC was visualized on 64% of routine axial T2-weighted brain scans.

CONCLUSION

The OMC is an important neuroradiologic and surgical landmark, which can be routinely identified on dedicated thin-section high-resolution MR images. It can also be identified on nearly two thirds of standard whole-brain MR images.

Orbital apex syndrome in a child

A 8-year-old male presented with visual loss, diplopia, ptosis, pain behind the left eye, facial numbness and vomiting of one week duration. The ophthalmological, neurological and radiological examination showed a lesion of the left orbital apex with extension into the cavernous sinus. Examination of the nose and paranasal sinuses did not reveal any abnormality. Transnasal Endoscopic orbital decompression was performed and inflamed granulation tissue found in the orbital apex was removed. Microbiology showed fungal elements which on culture grew Aspergillosis flavus. Antifungal therapy with new generation oral drug (voriconazole) resulted in complete resolution of symptoms. Relevant literature is reviewed and discussed.

High-resolution microscopy coil MR-Eye

The eye is involved in several pathologies where precise identification of the underlying condition is essential for the optimal patient care. This preliminary report presents the potential of high-resolution microscopy coil magnetic resonance imaging (HR-MRI) to undertake this task being actively used in the clinical setting. We used a commercially available MRI scanner and a microscopy surface coil. Exquisite anatomic detail of the eye and orbit with depiction of previously unobserved structures and clear demonstration of the underlying pathology was achieved. This report supports the idea that orbital imaging can be revolutionized with the introduction of HR-MRI with broad clinical implications.

Myoneural Junctions of Extraocular Muscles: Distances from the Orbital Rim and Widths

PURPOSE

To examine both the distances from the orbital rim to the myoneural junctions (MNJs) and the widths of the MNJs of all extraocular muscles.

METHODS

Six orbits of 3 post-mortem cadavers were used. The cadavers (1 female and 2 males) were all Japanese with an average age of 76.3 years. The MNJs of the extraocular muscles and their motor nerves were exposed, and then the distance from the orbital rim to each MNJ and the width of each MNJ were examined.

RESULTS

The distance from the orbital rim to each MNJ in the 6 extraocular muscles ranged from 24.4 to 33.6 mm and the width of each MNJ ranged from 5.0 to 8.5 mm.

CONCLUSIONS

It is essential for orbital surgeons to understand both the distance from the orbital rim to MNJs and the widths of MNJs. This information not only aids the understanding of MNJ damage, but also prevents iatrogenic nerve impairment during orbital surgery.

Cavernous sinus anatomy as a basis for interpretation of the clinical picture and radiological investigations in a case of Entomophthorales infection

Several cranial nerves traverse the cavernous sinus producing the typical symptom complex seen during cavernous venous sinus thrombosis in Mucorales infection. Fungi of the order Entomophthorales display different pathological and histological characteristics although belonging to the same class of fungi. A case is presented, wherein the anatomy of the cavernous sinus forms the basis in explaining the presenting symptoms of a patient with Entomophthorales infection. The anatomical explanation for the presenting neurological symptoms is confirmed by radiological investigations and further supports the diagnosis of Entomophthorales infection.

Imaging the sella and parasellar region

The anatomy of the sella and parasellar region is discussed. Pertinent ophthalmologic findings and syndromes relating to this anatomic region are described. Pathologic processes, such as pituitary adenoma, pituitary apoplexy, craniopharyngioma, Rathke's cleft cyst, lymphocytic adenohypophysitis, and other such parasellar lesions are discussed along with their ophthalmologic manifestations.

Magnetic susceptibility artifact in orbital magnetic resonance imaging

Case report of a 16-year-old boy presenting with total hyphema due to blunt trauma to the left eye. During a subsequent cinematic MRI scan to identify salvageable lateral rectus muscle, the attachment of the left lateral rectus was obscured by a 20-mm diameter signal void. A subsequent CT scan for a suspected metallic foreign body revealed the muscle attachment after all. The theoretical explanations for this finding are discussed.

In vivo 3D analysis of the adipose tissue in the orbital apex and the compartments of the parasellar region

As tissue dissections carried out on formaldehyde-fixed anatomical specimens demonstrate, the parasellar region (PSR), traditionally referred to as the cavernous sinus, is composed of three distinct compartments: orbital, pterygopalatine, and lateral sellar. The aim of our study was to identify and measure these compartments in the living and to describe the topography of their adipose body tissues. For this purpose data sets of 35 patients, who had undergone thin-section multislice computed tomography (CT), were examined using 3D-reconstruction software. The pterygopalatine and orbital compartments of the PSR could be identified in the images by their adipose bodies. We provide more exacting measurements of their size than have been presented in earlier studies. Furthermore, we include data about the uni- and bilateral presence of the single compartments and analyze the topography of the adipose tissue bodies in the orbital apex region. Our quantitative data and topographical descriptions confirm the compartmentalization concept of the PSR, allow for correct interpretation of CT scans of the orbital apex and anterior PSR, and provide baseline information for individual planning of surgical and radiological interventions.

Orbital apex injury: trauma at the junction between the face and the cranium

Orbital apex injury is usually seen in multiply and severely injured patients who are subject to high-energy trauma. Orbital apex injury rarely occurs in isolation. By proximity, the face, the skull base, or their combination are the most likely regions to be injured in association with orbital apex trauma. The vast majority of these injuries occur as an extension of orbital, LeFort, naso-orbito-ethmoid, panfacial, sphenoid, or temporal bone fractures of the skull. Complex osseous anatomic structures with intimately related multiple neurovascular organs make injuries to the orbital apex diagnostically and therapeutically challenging. Often other facial fractures extend into the orbital apex, or the orbital apex is damaged in conjunction with fractures of the skull base. Therefore abnormal imaging findings within the orbital apex may be indicators of traumatic injury to the entire junctional zone of face and cranium. In this article, we will give an overview of normal CT anatomy, review clinical syndromes, which may indicate traumatic injury of the orbital apex and present an imaging strategy for evaluation of the orbital apex.

Analysis of the morbidity of submerged deciduous molars: the use of imaging techniques

A case is presented of a 13-year-old patient who had a class I occlusion on a class I skeletal base but with a retained and submerged deciduous molar causing impaction of the second premolar. Diagnostic imaging illustrates the potential challenges of the removal of the retained deciduous molar. Magnetic resonance imaging used to identify the path of the inferior alveolar neurovascular bundle clearly delineates its intimate association with the impacted teeth and underscores the risk of trauma during extraction. This is discussed with regard to other cases of submerged molars, and a strategy is outlined.

Magnetic resonance imaging of the orbit: Basic principles and anatomy

This review article gives a basic introduction to the technical principles of magnetic resonance imaging for ophthalmologists and orbital surgeons and describes the anatomical structures that can be identified on high-resolution magnetic resonance images of the orbit. The meaning of general imaging parameters, specific weighting of the images, and the use of contrast agents, fat suppression techniques and surface coils is explained. Possible artifacts are also described. The advantages and disadvantages of MRI in comparison with computed tomography (CT) are discussed in order to give recommendations for the use of the appropriate imaging modality in patients with orbital disorders. Apart from delineating the course of the extraocular muscles, high-resolution MRI is able to depict not only all important blood vessels and cranial nerves of the orbit but also major septa of the orbital connective tissue system. Clinical applications are also mentioned to show that high-resolution MRI may contribute to a specific diagnosis in orbital disease.