Computer-aided three-dimensional reconstruction and measurement of the optic canal and intracanalicular structures

Three-dimensional anatomical analysis of the optic nerve canal with virtual model based on CBCT

The optic nerve canal (ONC) is a fine skeletal structure that contains the optic nerve. However, it has not been thoroughly examined. This necessitates establishing a baseline knowledge of the geometrical and volumetric parameters of the ONC. The data of twenty patients who received a cone beam computed tomography examination were prepared using a voxel-based segmentation. The measurement was performed separately by two examiners on virtual skull models in stereolithography format in Geomagic Wrap®. The results showed that the volume of the ONC varied between 92.48 mm3 and 162.7 mm3 (M = 123.46 mm3, SD = 26.61 mm3). Sex-specific statistically significant differences in volume were detected only for the right side. The angle of the ONC to the skull base was independent of the diameter of the canal. Both the intrarater and interrater comparisons of the measurements showed high values of reproducibility of the results. This study showed that a virtual anatomical model provides a feasible and reliable method to investigate the ONC. The examination technique could have a wider range of application in anthropology and application in clinical medicine. Advances in the automation of radiological diagnostics and the digital analysis of X-ray images could help to reduce examination times.

Assessment of the Optic Foramen Shape and Size in Human Fetuses

OBJECTIVE

This study was aimed to obtain data on the dimensions of the optic foramen in human fetuses for early childhood surgeries.

METHODS

Twenty-five formalin-fixed fetuses (16 boys and 9 girls) with average age 21.68 ± 3.12 gestational weeks (range, 16-28 weeks) in the inventory of Anatomy Department, Faculty of Medicine were included in the study. The surface area, width, and height of the optic foramen were bilaterally measured using a digital image analysis software.

RESULTS

The forms of the optic foramen were described as oval shaped (72%, 36 foramina) and round shaped (28%, 14 foramina). The surface area, width, and height of the optic foramen were found as 2.40 ± 1.02 mm, 1.83 ± 0.59 mm, and 1.58 ± 0.36 mm, respectively. The measurements of the parameters related to the optic foramen were not statistically different in terms of sides and sexes (P > 0.05). Linear functions for the height, width and surface area of the optic foramen were calculated as: y = 0.711 + 0.040 × weeks, y = -0.019 + 0.086 × weeks, and y = -0.400 + 0.129 × weeks, respectively.

CONCLUSION

The linear functions in this study can be used to estimate the dimensions of the optic foramen. The calculated regression equations, representing the growth dynamic of the optic foramen showed that the surface area, width, and height were increasing according to gestational ages between 16 and 28 weeks. Microanatomical knowledge related to the optic foramen may be beneficial for surgeons to avoid iatrogenic injury in infants and for anatomists to understand the development of the fetal skull base.

Anatomic features of the cranial aperture of the optic canal in children: a radiologic study

OBJECTIVE

This study aimed to peruse anatomic features of the cranial aperture of the optic canal (CAOC) for obtaining an extended morphometric dataset in children.

METHODS

Computed tomography images of 200 children were included in this retrospective work to analyze the shape, location and diameters of the CAOC.

RESULTS

The CAOC area, width and height were observed as 17.53 ± 2.80 mm², 6.12 ± 0.84 mm, and 4.35 ± 0.64 mm, respectively. The angle of the optic canal in axial plane was found as 39.28 ± 5.13°, while in sagittal plane as 16.01 ± 6.76°. The distance between the CAOC and the midsagittal line was 7.17 ± 1.48 mm. The CAOC was measured as 54.04 ± 5.23 mm and 42.55 ± 3.28 mm away from the anterior and lateral boundary of the anterior skull base, respectively. The CAOC shape was described as the tear-drop (186 foramina, 46.5%), triangular (156 foramina, 39%), oval (47 foramina, 11.8%), and round (11 foramina, 2.8%).

CONCLUSION

The depth, angle and diameter measurements belonging to the CAOC were changing according to its shape or demographic data (e.g., sex and age). Therefore, preoperative radiologic evaluation containing the shape, location and size of the CAOC should be considered by multidisciplinary operating teams in terms of surgical interventions such as implant positioning.

The deformable most-likely-point paradigm

In this paper, we present three deformable registration algorithms designed within a paradigm that uses 3D statistical shape models to accomplish two tasks simultaneously: 1) register point features from previously unseen data to a statistically derived shape (e.g., mean shape), and 2) deform the statistically derived shape to estimate the shape represented by the point features. This paradigm, called the deformable most-likely-point paradigm, is motivated by the idea that generative shape models built from available data can be used to estimate previously unseen data. We developed three deformable registration algorithms within this paradigm using statistical shape models built from reliably segmented objects with correspondences. Results from several experiments show that our algorithms produce accurate registrations and reconstructions in a variety of applications with errors up to CT resolution on medical datasets. Our code is available at https://github.com/AyushiSinha/cisstICP.

Evaluation and Stability Analysis of Video-Based Navigation System for Functional Endoscopic Sinus Surgery on In Vivo Clinical Data

Functional endoscopic sinus surgery (FESS) is one of the most common outpatient surgical procedures performed in the head and neck region. It is used to treat chronic sinusitis, a disease characterized by inflammation in the nose and surrounding paranasal sinuses, affecting about 15% of the adult population. During FESS, the nasal cavity is visualized using an endoscope, and instruments are used to remove tissues that are often within a millimeter of critical anatomical structures, such as the optic nerve, carotid arteries, and nasolacrimal ducts. To maintain orientation and to minimize the risk of damage to these structures, surgeons use surgical navigation systems to visualize the 3-D position of their tools on patients' preoperative Computed Tomographies (CTs). This paper presents an image-based method for enhanced endoscopic navigation. The main contributions are: (1) a system that enables a surgeon to asynchronously register a sequence of endoscopic images to a CT scan with higher accuracy than other reported solutions using no additional hardware; (2) the ability to report the robustness of the registration; and (3) evaluation on in vivo human data. The system also enables the overlay of anatomical structures, visible, or occluded, on top of video images. The methods are validated on four different data sets using multiple evaluation metrics. First, for experiments on synthetic data, we observe a mean absolute position error of 0.21mm and a mean absolute orientation error of 2.8° compared with ground truth. Second, for phantom data, we observe a mean absolute position error of 0.97mm and a mean absolute orientation error of 3.6° compared with the same motion tracked by an electromagnetic tracker. Third, for cadaver data, we use fiducial landmarks and observe an average reprojection distance error of 0.82mm. Finally, for in vivo clinical data, we report an average ICP residual error of 0.88mm in areas that are not composed of erectile tissue and an average ICP residual error of 1.09mm in areas that are composed of erectile tissue.

Multimodality-evoked potential study of anti-aquaporin-4 antibody-positive and -negative multiple sclerosis patients

Neuromyelitis optica (NMO) is claimed to be a distinct disease entity from multiple sclerosis (MS) because of its strong association with NMO-IgG/anti-AQP4 antibody; however, the in vivo role of the antibody remains unknown. Therefore, we aimed to clarify whether the presence of anti-AQP4 antibody is associated with any abnormalities in multimodality-evoked potentials in 111 patients with relapsing-remitting or relapsing-progressive MS, including the opticospinal form of MS, 18 of whom were seropositive for anti-AQP4 antibody. More patients with anti-AQP4 antibody showed a lack of the P100 component on visual-evoked potentials (VEPs) than those without the antibody (11/17, 64.7% vs. 20/84, 23.8%, p=0.003), whereas the frequency of delayed P100 latency was significantly higher in the latter group than in the former (1/17, 5.9% vs. 28/84, 33.3%, p=0.021). The frequencies of non-responses and delayed central sensory conduction times in median and posterior tibial nerve somatosensory-evoked potentials (SEPs) were not significantly different between anti-AQP4 antibody-positive and -negative patients. In terms of upper and lower limb motor-evoked potentials (MEPs), the frequencies of non-responses and delayed central motor conduction times did not differ significantly based on the presence or absence of anti-AQP4 antibody. The frequency of optic nerve lesions on MRI was significantly higher in anti-AQP4 antibody-positive patients than in anti-AQP4 antibody-negative patients (p=0.0137). Multiple logistic analyses revealed that anti-AQP4 antibody positivity (OR=8.406, p=0.02) and unevoked VEP responses (OR=35.432, p<0.001) were significantly related to development of severe visual impairment. Such an association of anti-AQP4 antibody with disability was not found for either severe motor or sensory impairment. These findings suggest a distinctive nature of optic nerve lesions between anti-AQP4 antibody-positive and -negative patients; lesions are supposed to be more necrotic in the former group and more demyelinating in the latter.

Biometric study of the optic canal during cranial development

To study optic canal dimensions and symmetry during cranial development, 146 silicon rubber left- and right-side models of the optic canal were cast from 51 dry skulls and 22 individual bones. The sample was divided in three age groups: fetuses (including newborns), children and adults with ages ranging from seven months of fetal life to 68-year-old. A digital caliper was used to measure the optic canal orbital and cranial diameters as well as model length. Results for the right and the left sides were, respectively, in millimeters: a) Maximum diameter of the orbital opening: fetuses, 4.68/4.47--children, 5.51/5.41--adults, 5.43/5.34; b) Minimum diameter of the orbital opening: fetuses, 2.89/2.84--children, 3.54/3.61--adults, 3.78/3.73; c) Diameter of the cranial opening: fetuses, 3.79/3.76--children, 4.67/4.72--adults, 5.24/5.43; d) Length of the optic canal: fetuses, 3.27/3.05--children, 3.93/3.71--adults 4.94/5.21. The diameter of the cranial opening of the optic canal increases significantly (p < 0.001) during the fetal period and throughout child and adulthood. The greater and smaller orbital apertures increase during the fetal period and during childhood, keeping the same size in adulthood. Optic canal length increases at some point between childhood and adulthood. Concerning symmetry, the only significant difference found was greater right than left optic canal diameter on the orbital side.

Correlation of cephalic anthropometric parameters and microsurgical anatomy of the optic nerves: a cadaveric morphometric study

BACKGROUND

This study was designed to elucidate the possible correlation of cranial anthropometric measurements with the chiasm to limbus sphenoidale distance to facilitate preoperative estimation of this distance and to choose a better surgical approach.

METHODS

Thirty-three fresh adult cadaver heads (22 males and 11 females) were evaluated for cranial anthropometric measurements. The precraniotomy anthropometric measurements included (A) inion to nasion distance and (B) the longest intermeatal meridian. Subsequently, with a standard craniotomy, the following intervals were measured: (C) optic chiasm to falciform ligament, (D) anterior aspect of optic chiasm to limbus sphenoidale, and (E) limbus sphenoidale to inner nasion. A combined ratio parameter, labeled as (F), was calculated from the following equation: F = B/E x 10.

RESULTS

The mean values and standard errors of the mean of parameters A to F were 195.8 +/- 14.53 mm, 374.7 +/- 25.29 mm, 10.47 +/- 1.89 mm, 9.93 +/- 2.01 mm, 38.46 +/- 3.17 mm, and 9.81 +/- 1.11, respectively. The parameter D had significant correlation to the parameters B, C, E, and F. The most significant correlation was seen between parameters D and F (p < 0.001). According to linear regression assessment between parameters D and F, the following regression equation was obtained: D = 4.24 + 0.58F.

CONCLUSIONS

Optic nerve topography and dimensions show inter-personal variations that may be anticipated to some extent with cranial anthropometric data. Calculating of F ratio gives us an acceptable estimation of the actual distance of chiasm to limbus sphenoidale, which in turn can help the surgeon to select the approach to tumors of intrasellar region. However, the role of meticulous imaging studies cannot be overemphasized to confirm the anticipated estimations.