The Optic Strut—CBCT Pneumatization Pattern and Prevalence

(1) Background: The optic strut (OS) is a critical landmark for clinoid and paraclinoid surgical interventions. To our knowledge, the current literature only mentioned the OS as a possibility for a lesser sphenoidal wing (LSW) pneumatization path, without a proper study of the pneumatization patterns and prevalence within this structure. Thus, our aim was to fill in the missing information. (2) Methods: A retrospective study on 80 cone beam computed tomography (CBCT) files was conducted to assess the prevalence and the origins of pneumatization within the OS. (3) Results: The pneumatization patterns of the OS were: 56.25% from the sphenoid sinus, 1.25% from the posterior ethmoid air cells (PEAC), and 10% from Onodi cells (ONC). Simultaneous pneumatization of unique origin within the lesser sphenoidal wing (LSW) was found in 26.25% from the sphenoid sinus, 1.25% from PEAC, and 5% from ONC. Communication between both LSW roots through pneumatization was found in 6.25% of the files. (4) Conclusions: A careful radiological examination should precede clinical diagnosis and surgical interventions in the paraclinoid area to evaluate postoperative surgical risks and possible diffusion patterns for infection. Additionally, pneumatization within the OS alters its morphological features and thus, its utility as a landmark.

Clinoidal Meningioma with Cavernous Sinus Invasion

We present a-49-year old female presenting headache and progressive right eye visual loss in the last 6 months. Magnetic resonance imaging showed a large clinoidal meningioma on the right side, invading the superior, lateral and medial aspects of the cavernous sinus, the optic canal, and the clinoidal segment of the internal carotid artery (ICA).A cranio-orbital approach was performed. The anterior clinoid process was removed extradurally to achieve devascularization of the anterior clinoidal meningioma, followed by the peeling of the middle fossa to decompress V2 and open the superior orbital fissure. We open the dura in a standard fronto-temporal flap to access the lower portion of the skull base allowing retractorless dissection. We complete the removal of the anterior clinoid process and optic strut through an intradural approach. It allows safer dissection of the clinoidal segment of the ICA and avoids its injury by adherent and hard consistency tumor.Intraoperative neurophysiological monitoring, sharp dissection, and avoiding the use of bipolar coagulation when dissecting the cavernous sinus are essential to minimize the risk of cranial nerve injury. We also like to point that cranial nerve deficit caused by surgical manipulation without primary lesion of the nerve can be recovered postoperatively.The link to the video can be found at: https://youtu.be/ozUCsnUGxyM.

Optic Canal Decompression: Concepts and Techniques: 2-Dimensional Operative Video

The optic canal (OC) is a bony channel that transmits the optic nerve (ON) and ophthalmic artery (OphA) as they course through the lesser wing of the sphenoid bone to the orbital apex. The OC is involved in a variety of intracranial and extracranial pathologies,1 and opening of the canal may be necessary in order to achieve adequate exposure, better disease control, and vision preservation.2 Depending on the location of the pathology and its relationship with the optic nerve, the OC may be decompressed through an open transcranial approach or an endoscopic endonasal approach.1,3 OC drilling can be tailored based on the location of the pathology and its extension. Anterior clinoid process and optic strut drilling can be added based on these factors as well.4,5 In this video, we demonstrate the steps of OC drilling in both transcranial microscopic and endoscopic endonasal approaches through a combination of animated illustrations and operative videos. We present 4 cases, including 2 transcranial microscopic and 2 endoscopic endonasal approaches,6 demonstrating OC decompression and its technical nuances. Each case was selected to represent the range of pathologies relevant to OC drilling to allow for a complete understanding of the techniques and concepts required for optimal treatment. An informed written consent has been obtained from each of the patients in this publication. Video © Mayo Foundation for Medical Education and Research. All rights reserved. Copyright information: Bendok BR, Abi-Aad KR, Sattur MG, Welz ME, Hoxworth JM, Lal D. Endoscopic resection of a paraclinoid meningioma extending into the optic canal: 2-dimensional operative video. Operative Neurosurgery. 2018 September 1;15(3):356 by permission of Oxford University Press. Cadaveric images provided by courtesy of: The Rhoton Collection. http://rhoton.ineurodb.org/.

Strategies for Optic Pathways Decompression for Extra-Axial Tumors or Intracranial Aneurysms: A Technical Note

Background Different types of skull base tumors and intracranial aneurysms may lead to compression of the optic pathways. Since most of them are biologically benign conditions, the first aim of surgery is preservation of optic nerves rather than the oncologic radicality. Materials and methods Based on the progressive technical refinements coming from our institutional experience of optic nerve compression from aneurysms and extra-axial tumors, we analyzed the surgical steps to release nerves and chiasm during tumor debulking and aneurysm clipping. Results We distinguished vascular and tumor lesions according to the main direction of optic nerve compression: lateral to medial, medial to lateral, inferior to superior, and anterior to posterior. We also identified four fundamental sequential maneuvers to release the optic nerve, which are (1) falciform ligament (FL) section, (2) optic canal unroofing, (3) anterior clinoid process drilling, and (4) optic strut removal. The FL section is always recommended when a gentle manipulation of the optic nerve is required. Optic canal unroofing is suggested in case of lateral-to-medial compression (i.e., clinoid meningiomas), medial-to-lateral compression (i.e., tuberculum sellae meningiomas), and inferior-to-superior compression (i.e., suprasellar lesions). Anterior clinoidectomy and optic strut removal may be necessary in case of lateral-to-medial compression from paraclinoid aneurysms or meningiomas. Conclusions Preservation of the visual function is the main goal of surgery for tumors and aneurysms causing optic nerve compression. This mandatory principle guides the approach, the timing, and the technical strategy to release the optic nerve, and is principally based on the direction of the compression vector.

Surgical Relevance of Pediatric Anterior Clinoid Process Maturation for Anterior Skull Base Approaches

BACKGROUND Removal of the anterior clinoid process (ACP) can expand anterior skull base surgical corridors. ACP development and anatomical variations are poorly defined in children. OBJECTIVE To perform a morphometric analysis of the ACP during pediatric maturation. METHODS Measurements of ACP base thickness (ACP-BT), midpoint thickness (ACP-MT), length (ACP-L), length from optic strut to ACP tip (ACP-OS), pneumatization (ACP-pneumo), and the presence of an ossified carotico-clinoid ligament (OCCL) or interclinoid ligament (OIL) were made from high-resolution computed-tomography scans from 60 patients (ages 0-3, 4-7, 8-11 12-15, 16-18, and >18 yr). Data were analyzed by laterality, sex, and age groups using t-tests and linear regression. RESULTS There were no significant differences in ACP parameters by laterality or sex, and no significant growth in ACP-BT or ACP-MT during development. From ages 0-3 yr to adult, mean ACP-L increased 49%, from 7.7 to 11.5 mm. The majority of ACP-L growth occurred in 2 phases between ages 0-3 to 8-11 and ages 16-18 to adult. Conversely, ACP-OS was stable from ages 0-3 to 8-11 but increased by 63% between ages 8-11 to adult. Variations in ACP morphology (OCCL/OIL/ACP-pneumo) were found in 15% (9/60) of scans. OCCL and OIL occurred in patients as young as 3 yrs, whereas ACP-pneumo was not seen in patients younger than 11 yrs. CONCLUSION The ACP demonstrates stable thickness and a complex triphasic elongation and remodeling pattern with development, the understanding of which may facilitate removal in patients <12. Clinically relevant ACP anatomic variations can occur at any age.

Reproducibility of a new classification of the anterior clinoid process of the sphenoid bone

Background: Pneumatization of the anterior clinoid process (ACP) affects paraclinoid region surgery, this anatomical variation occurs in 6.6–27.7% of individuals, making its preoperative recognition essential given the need for correction based on the anatomy of the pneumatized process. This study was conducted to evaluate the reproducibility of an optic strut-based ACP pneumatization classification by presenting radiological examinations to a group of surgeons. Methods: Thirty cranial computer tomography (CT) scans performed from 2013 to 2014 were selected for analysis by neurosurgery residents and neurosurgeons. The evaluators received Google Forms with questionnaires on each scan, DICOM files to be manipulated in the Horos software for multiplanar reconstruction, and a collection of slides demonstrating the steps for classifying each type of ACP pneumatization. Interobserver agreement was calculated by the Fleiss kappa test. Results: Thirty CT scans were analyzed by 37 evaluators, of whom 20 were neurosurgery residents and 17 were neurosurgeons. The overall reproducibility of the ACP pneumatization classification showed a Fleiss kappa index of 0.49 (95% confidence interval: 0.49–0.50). The interobserver agreement indices for the residents and neurosurgeons were 0.52 (0.51–0.53) and 0.49 (0.48–0.50), respectively, and the difference was statistically significant (P < 0.00001). Conclusion: The optic strut-based classification of ACP pneumatization showed acceptable concordance. Minor differences were observed in the agreement between the residents and neurosurgeons. These differences could be explained by the residents’ presumably higher familiarity with multiplanar reconstruction software.

Identification of the Distal Dural Ring and Definition of Paraclinoid Aneurysms According to Bony Landmarks on 3-Dimensional Computed Tomography Angiography: A Cadaveric and Radiological Study

BACKGROUND Determining if paraclinoid aneurysms are intradural or extradural is critical for surgical planning. OBJECTIVE To create an easily reproducible diagnostic method based on bony anatomy that precisely locates the distal dural ring (DDR) to determine the position of paraclinoid aneurysms as intradural, transitional, or extradural. METHODS Bilateral anatomic dissections of 10 cadaveric heads (20 sides) were performed to evaluate DDR anatomy. We observed a plane that reflects the position of the DDR passes through 4 bony landmarks: 1) The anterior clinoid-internal carotid artery intersection, 2) the optic strut, 3) the optico-carotid elevation, and 4) the base of the posterior clinoid process. This landmark-based plane can thus define the location of the DDR using 3-dimensional computed tomography angiography (CTA). This was confirmed in 27 surgical patients with intradural/transitional aneurysms and 7 patients with extradural aneurysms confirmed with magnetic resonance imaging (MRI). The DDR plane method easily classified aneurysm locations as intradural (above the DDR plane), extradural (below the DDR plane), or transitional (the DDR plane crosses the aneurysm). The aneurysm's location was subsequently confirmed intraoperatively or with MRI. RESULTS The DDR plane method determined if paraclinoid aneurysms were intradural, transitional, or extradural in all 34 cases examined. The visibility of the anatomic features that define the DDR plane was also verified in 82% to 89% of CTA images from 100 patients. CONCLUSION The DDR plane method provides a useful diagnostic tool to evaluate the position of the DDR and determine the anatomic location of paraclinoid aneurysms.