Investigation of the calcification at the petroclival region through Multi-slice Computed Tomography of the skull base

Twenty Intracranial Skull Base Variations in the Same Specimen

Anatomists and clinicians often encounter single bony anatomical variations in dry skulls and on imaging. However, a constellation of 20 such variants some that, to our knowledge, have not been previously described is noteworthy. Here, we describe an adult skull with multiple bony variations, and these are detailed and discussed. These included clival canals, an interclinoid bar with resultant foramen at the uppermost aspect of the clivus, middle clinoid process, posterior petroclinoid ligament, pterygoalar plate, septated hypoglossal canal, foramen through the anterior clinoid process, septated foramen ovale, shortened superior orbital fissure, and crista muscularis. Knowledge of individual differences in the structure of the skull may be of use to both anatomists and clinicians in the treatment of intracranial procedures as well as cranial imaging studies. Taken together, such a unique specimen is of archival value.

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.

Microanatomical study of arachnoid granulations and meningeal architecture around Meckel's cave

Although the microanatomy of Meckel's cave (MC) has been well studied, there are still controversies regarding the meningeal architecture of the space. Moreover, there are only general mentions of the arachnoid granulations near MC in just a few sources. This study is aimed at determining the frequency, location, and anatomical variability of the main clusters of arachnoid granulations around MC. The dissection involved 26 isolated specimens of MC fixed in formalin (neutral buffered, 10%). This number included five freshly harvested specimens examined histologically. Additional paraffin block with MC horizontal section was taken from our neuroanatomical collection. Carefully selected anatomical and histological techniques were applied to assess the complex relationships between the arachnoid granulations and adjacent structures. Arachnoid granulations were found around MC in all specimens with different anatomical variations. The main clusters of arachnoid granulations were close to the trigeminal ganglion and its divisions. The dorsolateral wall of MC was a thick layer formed by interweaving bundles of collagen fibers arranged in various directions. The entire MC was surrounded by a dural sleeve (envelope). This sleeve separated MC from the lateral sellar compartment. At its anterior (rostral) end, it formed a cribriform area pierced by individual fascicles of the trigeminal nerve's primary divisions. The connective tissue forming the sleeve was not only continuous with the epineurium but also shifted to the perineuria surrounding individual nerve fascicles. The meningeal architecture around MC has a complex and multilayer arrangement with a collagenous sleeve closely related to the trigeminal ganglion. Arachnoid granulations are typically found around MC.

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 effect of morphological variability of Dorello's canal on surgical procedures - a review

Dorello's canal is an arched structure of bone-fibrous character located in the petroclival venous confluence atop the petrosal bone in the petroclival region. It is bordered by the petrosphenoidal ligament, the petrous part of the temporal bone and the lateral border of the upper part of clivus. Its content in the vast majority of variants comprises the abducens nerve, the inferior petrosal sinus, the venous drainage and the dorsal meningeal artery or its medial branch. With the development of microsurgical techniques, this area has gained huge clinical importance, mainly concerning the order in which the above-mentioned elements (especially the position of the abducens nerve) are arranged in relation to each other. These structures appear in different variant forms and necessitate an individual clinical approach. The main purpose of this review is to present condensed information about possible intercorrelations among them and to indicate, on the basis of the available literature and research, possible surgical approaches and the need to consider the variability when treatments in this region are planned.

Review of the Petroclinoid Ligament

An ossified left petroclinoid ligament was found during routine dissection of the skull base in an adult male cadaver. The petroclinoid ligament is clinically and surgically important given its anatomical relationships to cranial nerves III, V, and VI, so its ossification is a risk factor for injuries due to trauma, increased intracranial pressure, and vascular and tumor compression resulting in abducens and oculomotor palsies. The causes of petroclinoid ligament ossification are yet to be completely elucidated although several reports have associated them with age-related and physiological processes. Assessing the integrity of the petroclinoid ligament is important during skull base surgical interventions to avoid postoperative complications. Therefore, this paper reviews the petroclinoid ligament and its variation, the ossified petroclinoid ligament.

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 Petroclinoid Ligament: Its Morphometrics, Relationships, Variations, and Suggestion for New Terminology

The anatomy and definition of the petroclinoid ligament (PCL) and its relationship with the abducens nerve are variably described. The goal of this study was to clarify the anatomy of the PCL and better elucidate its relationship with the abducens nerve. Thirty-six sides from 18 fresh-frozen adult cadaveric heads were used in this study. Specimens were all Caucasian and derived from 10 males and 8 females. The mean age at death was 79 years. Dissection of the PCL and abducens nerve was performed using a surgical microscope. The anterior and posterior attachments of the PCL, and position of the abducens nerve were noted. Subsequently, the width, thickness, and length of the ligament, and diameter of the abducens nerve were measured. Thirty-one sides (86.1%) were found to have a PCL, on two sides (5.6%), the PCL was ossified, and on three sides (8.3%), the PCL was absent. The width, thickness, and length of the PCL ranged from 0.54 to 3.39, 0.07 to 0.49, and 3.27 to 17.85 mm, respectively. No PCL had an anterior attachment onto the posterior clinoid process but rather, the clivus. Therefore, based on our findings, the PCL would be better described as the petroclival ligament.

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

Objectives

To determine the frequency, morphologic and demographic characteristics, and clinical relevance of the mineralisation of six skull base ligaments (interclinoid, caroticoclinoid, petrosphenoid, posterior petroclinoid, pterygospinous, and pterygoalar).

Methods

This is a retrospective review of 240 CT scans of the paranasal sinuses (ages 6–80 years). A limited systematic review was performed primarily using Embase and Medline databases.

Results

Ligamentous mineralisation was well delineated on CT and occurred at ≥ 1 location in 58.3% of patients. There was a nonsignificant trend towards a greater incidence with advancing age. The interclinoid and posterior petroclinoid ligaments were most commonly mineralised (22.1% and 18.3%, respectively); the petrosphenoid and pterygoalar ligaments were least frequently mineralised (10.8% and 6.3%, respectively). The mean age of patients with posterior petroclinoid mineralisation was significantly greater than those with interclinoid and petrosphenoid mineralisation and was not seen in patients aged 6–20 years. The literature review highlighted the clinically relevant potential for mineralised ligaments to cause barriers to surgical access (e.g. to the foramen ovale), increase the risk of neurovascular injury during surgery at the skull base (e.g. during anterior clinoidectomy), and predispose to neural impingement.

Conclusions

Skull base ligamentous mineralisation is commonly encountered on CT imaging. Given the potentially significant clinical implications, an understanding of the morphological appearances is of importance to those planning interventions at the skull base. To the authors’ knowledge, this study is the first to comprehensively evaluate such a wide range of skull base ligaments using CT. For some ligaments, the incidence on CT has not been previously described.