Skull base ligamentous mineralisation: evaluation using computed tomography and a review of the clinical relevance

The Coexistence of Carotico-Clinoid Foramen and Interclinoidal Osseous Bridge: An Anatomo-Radiological Study With Surgical Implications

BACKGROUND AND OBJECTIVES

The coexistence of complete carotico-clinoid bridge (CCB), an ossification between the anterior (ACP) and the middle clinoid (MCP), and an interclinoidal osseous bridge (ICB), between the ACP and the posterior clinoid (PCP), represents an uncommonly reported anatomic variant. If not adequately recognized, osseous bridges may complicate open or endoscopic surgery, along with the pneumatization of the ACP, especially when performing anterior or middle clinoidectomies.

METHODS

According to Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews guidelines, a systematic scoping review was conducted up to June 5, 2023. PubMed, Scopus, Web of Science databases, and additional citations were searched. Two hundred high-resolution noncontrast computed tomography (CT) scans (400 sides) and 41 dry skulls (82 sides) were analyzed to identify the different morphology of sellar bridges, focusing on the coexistence of complete CCF and ICB. Two embalmed latex-injected heads with coexisting CCF and ICB were dissected step-by-step to show the anatomic relationship with the surrounding structures from an endoscopic and microscopic perspective.

RESULTS

A total of 19 articles were included. The review identified a complete CCF and ICB rate ranging from 4.92% to 6.3%. The analysis of 200 CT scans revealed a rate of coexistence in 4% of the cases, all encountered in White women. Two different types of interclinoid bridges were identified based on the degree of bone mineralization. Both endoscopic and macroscopic step-by-step dissections highlighted variability in morphology and consistency of the sellar bridges and the close relationship with the cavernous sinus neurovascular structures.

CONCLUSION

The coexistence of CCF and ICB is an anatomic variation found in 4% of cases. Preoperative knowledge of the degree of mineralization and its relationship with surrounding structures is essential to performing safe surgery and minimizing cranial nerve and vascular injuries. Preoperative high-resolution CT scans can adequately identify these anatomic variations.

The posterior or tubal sphenoidal plate extending into the tympanosquamous fissure - A novel finding

OBJECTIVE

The tympanic plate typically joins the articular tubercle in the medial glenoid wall. It is aimed to report a peculiar anatomic variant of the latter.

METHODS

The computed tomography scans of two adult male cases were documented for the anatomical details of the temporomandibular joint.

RESULTS

The absence of the tubal processes of the tympanic plates was found bilaterally. The medial glenoid walls were penetrated by posterior or tubal sphenoidal plates extending posteriorly from the sphenoidal spines, 6.6 mm/12.2 mm on the right/left sides in the first case, and 9.8/8.4 mm on the right/left sides in the second case. These plates formed the lateral tubal walls and modified the tubal sulci on the sphenopetrosal fissures into musculotubal pseudo-canals. On the sides of the tubal sphenoidal plates formed in the medial wall of the glenoid fossa additional fissures, an anterolateral sphenotemporal one and a postero-medial sphenotympanic one.

CONCLUSION

As far as the authors know, the tubal plate of the sphenoid bone was not observed previously to participate in the glenoid fossa's medial wall. It could be regarded as a rare anatomic variation.

A morphological study on the sphenoid bone ligaments' ossification pattern

PURPOSE

The sphenoid bone (SB) extracranial ligaments (ECRLs) are the pterygoalar and pterygospinous ligaments (PTAL and PTSL) that are located at the SB lateral pterygoid plate, and inferior to the foramen ovale (FO). Their ossification may affect the mandibular nerve's distribution. The intracranial ligaments' (ICRLs) ossification (the caroticoclinoid ligament-CCLL, the anterior and posterior interclinoid ligaments-AICLL and PICLL) may impede the approaches to the sella. This study highlights the incidence of the ossified ECRLs and ICRLs location, their type (partial, or complete), considering laterality, gender, age, and ligaments' simultaneous presence.

METHODS

The sample consisted of 156 Greek adult dried skulls of both genders and variable age.

RESULTS

Ossified ligaments were identified in 57.05%, predominantly extracranially (42.31%, P = 0.003). ECRLs were predominantly identified unilaterally (30.13%, P < 0.001). The majority of the ossified ICRLs were predominantly identified in male skulls (31.1%, P = 0.048) and the majority of the ECRLs (52.8%, P = 0.028) were predominantly identified at the age of 60 years and above. The PTAL was the most ossified (32.69%), followed by the CCLL (24.36%), the PTSL (16.03%), the PICLL (6.41%), and the AICLL (4.49%).

CONCLUSIONS

Detailed knowledge of the SB morphology and ligaments' ossification extent is essential to improve the technique of the FO percutaneous approach, and sellar approaches, to minimize complications.

The "candy wrapper" of the pituitary gland: a road map to the parasellar ligaments and the medial wall of the cavernous sinus

PURPOSE

The anatomy of the medial wall of the cavernous sinus (MWCS) and parasellar ligaments (PLs) has acquired increasing importance in endoscopic endonasal (EE) surgery of the cavernous sinus (CS), including resection of the MWCS in functioning pituitary adenomas (FPAs). Although anatomical studies have been published, it represents a debated topic due to their complex morphology. The aim is to offer a description of the PLs that originate from the MWCS and reach the lateral wall of the cavernous sinus (LWCS), proposing the "candy wrapper" model. The relationships between the neurovascular structures and histomorphological aspects were investigated.

METHODS

Forty-two CSs from twenty-one human heads were studied. Eleven specimens were used for EE dissection; five underwent a microscopic dissection. Five specimens were used for histomorphological analysis.

RESULTS

Two groups of PLs with a fan-shaped appearance were encountered. The anterior group included the periosteal ligament (55% sides) and the carotico-clinoid complex (100% sides), formed by the anterior horizontal and the carotico-clinoid ligaments. The posterior group was formed by the posterior horizontal (78% sides), and the inferior hypophyseal ligament (34% sides). The periosteal ligament originated inferiorly from the MWCS, reaching the periosteal dura. The anterior horizontal ligament was divided in a superior and inferior branch. The superior one continued as the carotid-oculomotor membrane, and the inferior branch reached the CN VI. The carotico-clinoid ligament between the middle and anterior clinoid was ossified in 3 sides. The posterior horizontal ligament was related to the posterior genu and ended at the LWCS. The inferior hypophyseal ligament followed the homonym artery. The ligaments related to the ICA form part of the adventitia.

CONCLUSION

The "candy wrapper" model adds further details to the previous descriptions of the PLs. Understanding this complex anatomy is essential for safe CS surgery, including MWCS resection for FPAs.

A Newly Discovered Dural Venous Sinus of the Skull Base: The Anterior Petroclinoid Sinus

INTRODUCTION

Neurosurgeons must master microanatomy and its variants that occur at the skull base. To the best of our knowledge, we describe a previously unreported dural venous sinus (DVS) within the anterior petroclinoid fold and discuss its potential surgical relevance.

METHODS

Fifteen latex-injected human cadaveric heads (30 sides) underwent skull base dissection using a surgical microscope. The anterior petroclinoid fold was opened in search of evidence of an embedded DVS. When identified, this sinus was documented, photographed, and measured with microcalipers.

RESULTS

An anterior petroclinoid sinus (APCS) was identified in 67% of sides. These DVSs had a mean diameter of 0.65 mm and a length ranging from 8 to 15 mm (mean: 12.5 mm). The APCS ran from the anterior aspect of the cavernous sinus, arising just lateral (60%), posterior (20%), or medial (20%) to the anterior clinoid process, to the superior petrosal sinus (65%) or the posterior aspect of the cavernous sinus (35%), at the level of the posterior clinoid process. Along the course of the APCS, the oculomotor nerve was located medially at the oculomotor porus. Although slightly more common and larger on the right side, there was no statistically significant side difference.

CONCLUSIONS

An improved knowledge of variant DVSs can lower the risk of intraoperative complications and increase our understanding of the venous outflow from the cavernous sinus. Future neuroimaging techniques might also seek to identify the APCS. This is the first description of a DVS contained within the anterior petroclinoid fold.

Morphological Measurements of Innominate Foramina and Bony Spurs along the Base of Sphenoid as a Potential Risk Factor for Neurovascular Entrapment, Radiological Interpretation and Surgical Access

Background

Restricted access and compression of neurovascular structures at various anatomic variations at the skull base poses a challenge to surgeons, neurologists and anesthetists. The present study was performed with the objective of providing morphometric analysis of innominate foramina, and anomalous bony bars and spurs along the infratemporal surface of the greater wing of the sphenoid and reviewing the practical significance of dealing with this region.

Methods

A total of 100 dry-aged human adult skulls from the archives of the osteology library of the Department of Anatomy were studied. A detailed morphometric analysis of such innominate foramina and anomalous osseous structures along the base of the sphenoid was performed using a sliding digital vernier caliper.

Results

Anomalous bony bar was found in 22 skulls (25.28%). A complete bar was observed at eight (9.1%). An innominate foramen was located inferomedial to foramen ovale (5 unilateral and 3 bilateral) with a mean anteroposterior diameter of 3.44 mm and a mean transverse diameter of 3.16 mm.

Conclusion

Neurovascular structures may be compressed by abnormal bony outgrowths or while traversing through such unnamed bony foramina. The latter may also be overlooked and mistaken during radiological interpretation leading to delayed diagnosis. Such unnamed foramina and bony outgrowths need to be documented in the literature due to their surgical, and radiological implications and limited citations.

Osseous Bridges of the Sphenoid Bone: Frequency, Bilateral and Sex Distribution

Sellar (caroticoclinoid and interclinoid), pterygospinous and pterygoalar bridges are osseous bars of the sphenoid bone, which enclose additional foramina in the skull base and could cause entrapment of nerves, occlusion of vessels and obstruction of surgical corridors. This study aimed to investigate the frequency of sphenoid bone bridges in Bulgarians and to assess the bilateral and sex differences in their distribution. This study was performed on head CT scans of 315 Bulgarians, 148 males and 167 females. The sellar bridges were the most common type of sphenoid bridging; particularly the caroticoclinoid bridge. The pterygospinous bridge was a relatively common finding and the pterygoalar bridge was the most infrequent type of bridging. The total frequency of sellar bridges did not differ significantly between both sides and sexes. The pterygospinous bridge did not indicate significant bilateral differences but showed considerable sex differences concerning the left-side occurrence, which was significantly higher in the male series. There were no considerable bilateral and sex differences in the distribution of the pterygoalar bridging. There were no significant correlations between the different types of sphenoid bone bridges, but each type of bridging showed significant positive correlations between the right and left side co-occurrence in males and females.

Prevalence, Laterality, and Classification of Ossified Petroclival Ligaments: An Anatomical and Histological Study With Application to Skull Base Surgery

Background The petroclival ligament (PL) forms the roof of Dorello's canal (DC). In humans, partial and complete ossification of this ligament have been reported. When completely ossified, DC is transformed into a bony foramen for the abducens nerve and accompanying vascular structures. As this osteological finding might have an impact on skull base surgery, this anatomical study was performed. Methodology Using 100 adult human skulls, the presence of an ossified PL was noted and classified. The diameter of the resultant bony foramen and laterality were documented. Additionally, PL was evaluated histologically in 10 heads. Results Overall, 8% of the sides were found to have partial or complete ossification of the PL. Partial ossification (type I) was noted on 3% of the sides. Completely ossified PL was identified on 5% of the sides. Some ossified ligaments (2.5%) were seen as an ossified bridge (type II), and others (2.5%) were converted into small foramina (type III). Three skulls (3%) were found to have a completely ossified ligament bilaterally. The mean diameter of the underlying DC was 0.8 mm. Partially ossified ligaments were statistically more likely to be on the right sides, and the diameter of the underlying DC was statistically smaller in type III. Histologically, the PL was found to have bone within it on three skull sides. Conclusions An ossified ligament can be found on imaging of the skull base. Moreover, during surgical approaches to the petroclival region and, specifically, DC, skull base surgeons should be cognizant of this anatomical variation.

Anatomy of the Calvaria and Skull Base

A thorough understanding of the skull anatomy is of key importance to radiologists as well as specialist physicians and surgeons. We describe the anatomy of the neurocranium comprising calvaria (the skull vault) and the skull base and discuss the most common and clinically relevant anatomic variants.

Physiologic intracranial calcifications incidentally detected on cone beam computed tomography

OBJECTIVES

This study aims to determine the incidence of physiologic intracranial calcifications on cone beam computed tomography (CBCT) and to contribute to the differentiation between physiologic and pathologic intracranial calcifications by sharing their characteristic appearances, with the largest number of patients in the literature and many different types of physiologic calcifications.

STUDY DESIGN

CBCT images of 996 patients admitted to the clinic between 2018 and 2019 were scanned retrospectively. Petroclinoid (PCL) and interclinoid ligaments (ICL), pineal gland, coronoid plexus, falx cerebri, tentorium cerebelli, and other dural calcifications were evaluated in each radiograph.

RESULTS

Physiologic calcification was present in 49.4% of the cases, and pineal gland calcification was the most common (47.6%) type. PCL calcification was detected in 22.1%, and it was mostly bilateral partial. There were complete ICL in 1.2%, coronoid plexus in 11.3%, falx cerebri in 6.3%, tentorium cerebelli in 1.1%, and other dural calcifications in 3.6%. Only PCL calcifications differed between sexes and were more common in males. PCL, pineal gland, and coronoid plexus calcifications were most detected in the third decade of the cases.

CONCLUSIONS

Intracranial calcifications are detected incidentally in CBCT examinations. Some calcifications may indicate pathologic conditions, and patients may need to be referred for further evaluation.

The surgical management of intraoperative intracranial internal carotid artery injury in open skull base surgery-a systematic review

Intraoperative internal carotid artery (ICA) injury during open skull base surgery is a catastrophic complication. Multiple techniques and management strategies have been reported for endoscopic skull base surgery; however, the literature on managing this complication in open skull base surgery is limited. To perform a systematic review and give an overview of the different techniques described to manage this complication intraoperatively, a systematic review was conducted in PubMed, Ovid Medline, Ovid Embase and Scopus for literature published until July 2021. Titles and abstracts were screened. Studies meeting prespecified inclusion criteria were reviewed in full. PRISMA guidelines were strictly adhered to. Out of 4492 articles, only 12 articles could be included, reflecting an underreporting of open skull base ICA injuries. Multiple techniques can be used depending on the location and size of the injury as well as the surgeon's experience. Described techniques include the following: a primary repair via a micro-suture or nonpenetrating clips; wrapping or plugging; coating; occlusion of the parent artery with or without a bypass; packing with further endovascular management. A treatment algorithm is proposed.

Microsurgical Anatomy of the Inferomedial Paraclival Triangle: Contents, Topographical Relationships and Anatomical Variations

The inferomedial triangle is one of the two surgical triangles in the paraclival subregion of the skull base. It is delineated by the posterior clinoid process, the dural entrance of the trochlear nerve and the dural entrance of the abducens nerve. The aim of the present article is to describe the anatomical variations within the inferomedial triangle. Measurements of the triangle’s borders and area were supplemented by detailed observations of the topographical anatomy and various arrangements of its contents. Nine adult cadaveric heads (18 sides) and 28 sagittal head sections were studied. The mean area of the inferomedial triangle was estimated to be 60.7 mm². The mean lengths of its medial, lateral and superior borders were 16.1 mm, 11.9 mm and 10.4 mm, respectively. The dorsal meningeal artery was identified within the inferomedial triangle in 37 out of 46 sides (80.4%). A well-developed petrosphenoidal ligament of Grüber was identified within the triangle on 36 sides (78.3%). Although some structures were variable, the constant contents of the inferomedial triangle were the posterior petroclinoid dural fold, the upper end of the petroclival suture, the gulfar segment of the abducens nerve and the posterior genu of the intracavernous internal carotid artery.

The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 2

The article continues the anatomical review of the anterolateral myofascial connections of the five diaphragms in osteopathic manipulative medicine (OMM), with the most up-to-date scientific information. The postero-lateral myofascial relationships have been illustrated previously in the first part. The article emphasizes some key OMM concepts; the attention of the clinician must not stop at the symptom or local pain but, rather, verify where the cause that leads to the symptom arises, thanks to the myofascial systems. Furthermore, it is important to remember that the human body is a unity and we should observe the patient not as a series of disconnected segments but as multiple and different elements that work in unison; a dysfunction of tissue will adversely affect neighboring and distant tissues. The goal of the work is to lay solid foundations for the OMM and the five-diaphragm approach showing the myofascial continuity of the human body.