Morphometric Characterization of the Foramen Lacerum and Its Relationships with Adjacent Skull Base Structures

Objective To explore the scope, feasibility and indications of extended neuroendoscopic endonasal approach to reveal the region of cranial-cervical junction. Methods Ten (20 sides) intact frozen adult cadaveric heads were used to simulate the extended neuroendoscopic endonasal approach to remove the anterior tubercle of atlas, part of the atlas anterior arch, odontoid and part of the slope. In the cranial-cervical junction area, we observed the exposed range and measured the distance from the nostril to the anterior tubercle of atlas, the height and width of the anterior arch of the atlas, the distance of bilateral medial margin of occipital condyle, the distance of bilateral medial margin of the foramen lacerum, the vertical distance from the occipital condyle to the homolateral foramen lacerum, and the height, anteroposterior diameter and transverse diameter of the odontoid. Results The exposed range of the extended neuroendoscopic endonasal approach was as follows: when the lesion was located at the foramen magnum, the medial margin of the occipital condyle was the boundary of both sides, the root of the odontoid was the lower boundary, and the lower edge of the occipital bone was the upper boundary. When the lesion was located at the region of cranial-cervical junction, the upper edge of the foramen lacerum on both sides was the upper boundary, and the foramen lacerum and the outer edge of the occipital condyle were the boundaries of both sides of the bone window. By measurement, the distance from the nostril to the anterior tubercle of atlas was 8.9-9.7 cm, with an average of 9.3±0.3 cm. The height of the anterior arch of the atlas was 2.3-3.0 cm, with an average of 2.7±0.3 cm; the width was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of occipital condyle was 1.5-2.0 cm, with an average of 1.8±0.2 cm; the distance of bilateral medial margin of the foramen lacerum was 2.1-2.9 cm, with an average of 2.4 ±0.3 cm; the vertical distance from the occipital condyle to the homolateral foramen lacerum was 1.6-2.2 cm, with an average of 1.9±0.3 cm; the height of the odontoid was 0.9-1.3 cm, with an average of 1.1±0.2 cm, its length was 0.8-1.3 cm, with an average of 1.1±0.2 cm; the transverse diameter of the dentate was 0.9-1.2 cm, with an average of 1.0±0.1 cm.The maximum exposed area of cranio-cervical junction was 6.4-9.8 cm2, with an average of 8.6±1.6 cm2. Conclusion The extended neuroendoscopic endonasal approach with removal of the anterior tubercle of atlas and part of the atlas anterior arch could effectively reveal the cranial-cervical junction area which is suitable for the treatment of odontoid deformity, skull base depression and atlantoaxial joint dislocation as well as resection of epidural tumors in the cranial-cervical junction and ventral and ventral midline tumors. Key words: Natural orifice endoscopic surgery; Anatomy; Cranio-cervical junction; Extended endonasal approach

Introduction: The foramen lacerum is located in the middle cranial fossa and transmits a number of nerves and blood vessels. Occlusion can result in the compression of the neurovascular bundle, and the foramen has been reported to be involved in the spread of tumours into the cranium. Aim: The aims of the present study was to describe the morphology of the foramen lacerum and to compare the anatomical parameters on the left and right sides of the skull. Also, the significance of the anatomical parameters in male versus female skulls and right side versus left side of the skull where studied. Materials and Methods: This cross-sectional study was conducted in May and June 2023 using 62 dry skulls (124 foramen lacerum) available in the Department of Anatomy at Gautam Buddha Chikitsa Mahavidyalay, a tertiary care teaching institute in Dehradun, Uttarakhand, India. The anatomical parameters, including the Anteroposterior (AP) and transverse diameters, were recorded using a calibrated digital Vernier caliper. The shape of the foramen was also observed. The mean and standard deviation of the recorded parameters were obtained. Results: Out of the 62 skulls, 41 were males and 21 were females, resulting in a male-to-female ratio of 1.8:1. The mean AP diameter on the Right Side (RT) and Left Side (LT) in males was 6.26 mm and 6.24 mm, respectively, while in females, the mean diameter was 4.97 mm (RT) and 5.4 mm (LT). The mean transverse diameter recorded in the present study was 6.14 mm (RT) and 6.2 mm (LT) in males, while in females, this measurement was 5.88 mm on both sides. The most common shape of the foramen lacerum observed in the study was bilaterally round, in both males and females. Conclusion: There are morphological differences in the AP diameter between male and female skulls, with males having a larger AP diameter on their right side and females having larger AP diameter on their right side. The overall size of the foramen lacerum was smaller in the present study, indicating a higher likelihood of neurovascular bundle compression with age. The recent advances in skull base surgery warrant further and larger studies on this neglected yet important foramen to gather more data on its morphometric variations in different geographical regions.

The foramen lacerum is a relevant skull base structure that has been neglected for many years. From the endoscopic endonasal perspective, the foramen lacerum is a key structure due to its location at the crossroad between the sagittal and coronal planes. The objective of this study was to provide a detailed investigation of the surgical anatomy of the foramen lacerum and its adjacent structures based on anatomical dissections and imaging studies, propose several relevant key surgical landmarks, and demonstrate the surgical technique for its full exposure with several illustrative cases. Ten colored silicone-injected anatomical specimens were dissected using a transpterygoid approach to the foramen lacerum region in a stepwise manner. Five similar specimens were used for a comparative transcranial approach. The osseous anatomy was examined in 32 high-resolution multislice CT studies and 1 disarticulated skull. Representative cases were selected to illustrate the application of the findings. The pterygosphenoidal fissure is the synchondrosis between the lacerum process of the pterygoid bone and the floor of the sphenoid bone. It constantly converges with the posterior end of the vidian canal at a 45° angle, and its posterolateral end points directly to the lacerum foramen. The pterygoid tubercle separates the vidian canal from the pterygosphenoidal fissure, and forms the anterior wall of the lower part of the foramen lacerum. The lingual process, which forms the lateral wall of the foramen lacerum, was identified in 53 of 64 sides and featured an average height of 5 mm. The mandibular strut separates the foramen lacerum from the foramen ovale and had an average width of 5 mm. This study provides relevant surgical landmarks and a systematic approach to the foramen lacerum by defining anterior, medial, lateral, and inferior walls that may facilitate its safe exposure for effective removal of lesions while minimizing the risk of injury to the internal carotid artery.

Introduction: Basiocciput is the part of occipital bone present on the inferior aspect of skull. Fossa Navicularis Magna-an osseous defect is a variation in normal anatomy of basiocciput. Lately few case reports presented this fossa as a cause of spread of infection from nasopharynx to brain resulting in meningitis and osteomyelitis.
 Objectives: This study aims to find the incidence and morphometry of this fossa in Pakistani populace to avoid any misdiagnosis or misinterpretations.
 Materials & Methods: This study was conducted on dry human skulls at King Edward Medical University Lahore. Fossa was measured in its transverse and vertical diameters and to locate the fossa its distance from various anatomical land marks such as foramen ovale, foramen Lacerum, carotid canal, occipital condyles, pharyngeal tubercle and posterior border of vomer was noted.
 Results: The incidence of this fossa was found to be 5.3% in Pakistani population. Predominantly oval shaped, fossa measured 5.5 and 3.06 mm in vertical and transverse diameters respectively. It was 12.2 mm posterior to vomer and 5.9 mm anterior to pharyngeal tubercle.
 Conclusion: This study is useful for radiologists and clinicians in avoiding any misinterpretations on radiographs and unnecessary investigations

The microanatomic details of the foramen lacerum and surrounding region are described to clarify the relationship between the internal carotid artery and the foramen lacerum. The terminology related to these structures is reevaluated. Examples of pathological abnormalities restricted to the foramen lacerum region are presented to document the clinical relevance of this region. Microanatomic dissections were performed in 12 formalin-fixed cadaveric specimens. Bony landmarks were examined in 50 dry skulls. Microscopic sections of the region were obtained from cadaveric specimens that were formalin-fixed, decalcified, and processed for histological examination. The foramen lacerum is not a true foramen. No significant structures traverse its fibrocartilage. In this region, the bony and fibrous structures surround the internal carotid artery to form an incomplete canal, which serves as the rostral extension of petrous canal. The term foramen lacerum should be restricted to that portion of the cranial base at the confluence of the petrous portion of the temporal, basioccipital, and basisphenoid bones that in vivo is filled with fibrocartilage. The region immediately above the foramen lacerum, occupied by the internal carotid artery and traditionally considered the upper portion of the foramen lacerum, should be considered, anatomically and functionally, to be the rostral extension of the petrous canal. We suggest calling this extension the lacerum portion of the carotid canal.

Accessing the petrous apex (PA) via an endoscopic endonasal approach (EEA) is challenging due to its posterior and lateral anatomical relationship with the paraclival carotid artery. Typically, the EEA requires the mobilization or compression of the vessel and the use of angled-lens endoscopes and instruments. A sublabial contralateral transmaxillary (CTM) corridor has been used to overcome these challenges. Still, it requires extensive osteo-meatal disruption and drilling of the medial pterygoid process, which risks the vidian nerve and increases nasal morbidity. Furthermore, the CTM corridor positions the endoscope in the same horizontal plane as the instruments passing through the nostrils, leading to fencing. The authors propose a novel minimally invasive route to the PA, the precaruncular contralateral medial transorbital (cMTO) corridor, to address these issues. This anatomical study compares the EEA+CTM and EEA+cMTO corridors in accessing the PA. The authors dissected 14 fresh, preinjected cadaveric specimens (28 sides) using neuronavigation to complete EEA, cMTO, and CTM on each side. In addition to qualitative analysis, they measured and compared the working distance between the entry point (nose, orbit, maxilla) and the petrosal process of the sphenoid bone (PPSB), superomedial PA, and foramen lacerum (FL); angle of attack (AoA); area of surgical freedom; endoscope-instrument fencing angle; and visual angle for each approach. The cMTO corridor provided the shortest working distance to the petroclival region (PA = 67.4 ± 4.47 mm, PPSB = 67.57 ± 4.33 mm, and FL = 66.30 ± 4.77 mm) compared to the CTM (PA = 75.85 ± 3.63 mm, PPSB = 76 ± 3.96 mm, and FL = 74.52 ± 4.26 mm) and to the EEA (PA = 85.16 ± 3.16 mm, PPSB = 84.55 ± 3.02 mm, and FL = 83.42 ± 3.21 mm, p < 0.001). Both CTM and cMTO corridors had a similar visual angle to the PA (20.72° ± 2.16° and 21.63° ± 1.84°, respectively), offering a similar but significantly better visualization than EEA alone (44.71° ± 3.24°, p < 0.001). The cMTO corridor provided better instrument maneuverability than the CTM, as evidenced by a significantly greater fencing angle (30.9° ± 4.9°) than with the CTM (21.7° ± 4.02°, p < 0.001). The vertical AoAs for the EEA, cMTO, and CTM corridors were 9.79° ± 1.75°, 10.65° ± 0.82°, and 9.82° ± 1.43°, respectively (p = 0.009), whereas in the horizontal plane, these were 9.29° ± 1.51°, 9.10° ± 0.73°, and 10.49° ± 1.43° (p < 0.001), respectively. Both the CTM and cMTO corridors offered similar areas of surgical freedom (678.06 ± 99.5 mm2 and 673.59 ± 104.8 mm2, p = 0.986), but they were more significant than that provided by the EEA 487.29 ± 112.9 mm2 (p < 0.001). The EEA+cMTO multiport technique may be a better alternative than the EEA+CTM multiport approach for targeting the petroclival region. However, clinical validation is required to confirm these laboratory findings.

Introduction:A thorough understanding of skull base anatomy is imperative to perform safely and effectively any skull base approach. In this article, we examine the microsurgical anatomy of the skull base by proposing a modular topographic organization in the median, paramedian, and lateral surgical corridors in relation to transcranial and endoscopic approaches.Methods:Five dry skulls were studied focusing on the intracranial and exocranial skull base. Two lines were drawn parallel to the lateral border of the cribriform plate of the ethmoid bone and foramen lacerum, respectively. Lines 1 and 2 delimited the median, paramedian and lateral corridors of the skull base. The bony structures that formed each corridor were carefully reviewed in relation to the planning and execution of the skull base transcranial and endoscopic approaches.Results:The midline corridor involves the crista galli, cribriform plate, planum and jugum sphenoidale, chiasmatic sulcus, tuberculum sellae, sellar region, dorsum sellae, clivus, and foramen magnum. The paramedian corridor includes the fovea ethmoidalis, the root of the lesser and greater sphenoid wing, anterior clinoid process, foramen lacerum, the upper half of the petro-occipital suture, and jugular tubercle. The lateral corridors include the orbital plates, sphenoid wings, squamosal and petrous parts of the temporal bone, caudal aspect of the petro-occipital suture, internal auditory canal, jugular foramen, the sulcus of the sigmoid sinus.Conclusion:In-depth three-dimensional knowledge of skull base anatomy based on the modular concept of the surgical corridors is critical for the planning and execution of the transcranial and endoscopic approaches.

Surgeries via the transoral approach are widely used to deal with lesions near the craniovertebral junction. For this approach, the pharyngeal tubercle is an important landmark to identify the midline. The foramen lacerum, another important anatomic area where some crucial structures pass, is close to the pharyngeal tubercle. In the current study, we measured relevant distances and angles on 120 adults without brain diseases to estimate the safety range of the transoral approach. Distances between the pharyngeal tubercle and the foramen lacerum were expressed as mean (SD) and 95% confidence interval. Angles between the straight lines, which pass through the pharyngeal tubercle and the foramen lacerum, and the sagittal plane, as well as the horizontal plane, were also presented as mean (SD) and 95% confidence interval. As regards the 95% confidence intervals of the angles and the distances, which were used to define the safety range, no differences were observed between the right side and the left side. During such surgeries, if the midline is defined as a datum line, it is less likely for surgeons to destroy adjacent structures when moving within 36.30 degrees on the sagittal plane and 45.00 degrees on the horizontal plane once they find the pharyngeal tubercle. It is also safe to move within 16.20 mm from the pharyngeal tubercle. With these data, we have successfully defined the safety range of the surgery, which may help operators choose proper instruments in surgery and avoid injuries to important structures. Moreover, operators may use these data to position the pharyngeal tubercle so as not to deviate from the midline.

The petrosal process of the sphenoid bone (PPsb) is a relevant skull base osseous prominence present bilaterally that can be used as a key surgical landmark, especially for identifying the abducens nerve. The authors investigated the surgical anatomy of the PPsb, its relationship with adjacent neurovascular structures, and its practical application in endoscopic endonasal surgery. Twenty-one dried skulls were used to analyze the osseous anatomy of the PPsb. A total of 16 fixed silicone-injected postmortem heads were used to expose the PPsb through both endonasal and transcranial approaches. Dimensions and distances of the PPsb from the foramen lacerum (inferiorly) and top of the posterior clinoid process (PCP; superiorly) were measured. Moreover, anatomical variations and the relationship of the PPsb with the surrounding crucial structures were recorded. Three representative cases were selected to illustrate the clinical applications of the findings. The PPsb presented as a triangular bony prominence, with its base medially adjacent to the dorsum sellae and its apex pointing posterolaterally toward the petrous apex. The mean width of the PPsb was 3.5 ± 1 mm, and the mean distances from the PPsb to the foramen lacerum and the PCP were 5 ± 1 and 11 ± 2.5 mm, respectively. The PPsb is anterior to the petroclival venous confluence, superomedial to the inferior petrosal sinus, and inferomedial to the superior petrosal sinus; constitutes the inferomedial limit of the cavernous sinus; and delimits the upper limit of the paraclival internal carotid artery (ICA) before the artery enters the cavernous sinus. The PPsb is anterior and medial to and below the sixth cranial nerve, forming the floor of Dorello's canal. During surgery, gentle mobilization of the paraclival ICA reveals the petrosal process, serving as an accurate landmark for the location of the abducens nerve. This investigation revealed details of the microsurgical anatomy of the PPsb, its anatomical relationships, and its application as a surgical landmark for identifying the abducens nerve. This novel landmark may help in minimizing the risk of abducens nerve injury during transclival approaches, which extend laterally toward the petrous apex and cavernous sinus region.

Introduction: Foramen Ovale (FO) is an important aperture present in the middle cranial fossa which transmits delicate neurovascular structures, especially the mandibular nerve. Morphological and morphometrical variations of this foramen are seen in literature and this knowledge is important as it is used for cannulation in rhizotomy for trigeminal neuralgia. Aim: To analyse the foramina of the middle cranial fossa by emphasising on morphometry and morphology of FO as mandibular nerve passes through it. Materials and Methods: This observational study was conducted in the Department of Anatomy, Vydehi Institute of Medical Sciences and Research,Banglore, Karnataka,India from January 2020 to June 2020. Fifty-one fully ossified adult skulls were utilised for this observational study. Antero-Posterior (AP) diameter, transverse diameter, area, and different shapes of the FO, distance between FO and other foramina, presence of foramen of Vesalius and accessory bony structures were studied. Independent sample t-test was done to compare the mean values of all the diameters. Results: The AP and transverse diameter of FO on the right and left side was found to be almost symmetrical. AP diameter on the right and left side was found to be 6.79±1.4 mm and 6.78±1.3 mm, respectively and transverse diameter was 3.58±0.90 mm on the right and 3.45±0.99 on left side. Distance between FO and Foramen Spinosum (FS), foramen lacerum and Meckel’s cave were similar on both the sides. The distance between FO and rotundum was greater on the right side i.e., 11.09±1.9 mm than left side which showed a diameter of 10.68±1.6 mm. The different shapes of the FO observed were oval, almond, D-shaped, elongated, round, slit and irregular. Oval shape (22 skulls on the left side and 27 skulls on the right) was the most common type. Foramen of Vesalius was observed in four skulls and accessory bony structures like bony septum, plate and spurs were also seen in the current study. Conclusion: The knowledge regarding the shape and distance between the FO and various foramina might benefit the neurosurgeons and radiologists during surgical procedures.

The carotid canal (CC) located in the petrous temporal bone transmits the internal carotid artery, internal carotid venous plexus and sympathetic nerve plexus from the neck into the cranial cavity. It is an accessible passage into the cranial cavity and is considered an important anatomical landmark for neurosurgeons. The aim of this study was to investigate the topographical, morphometric and morphological parameters of the CC. An examination of the CC and related adjacent structures in 81 dry skull specimens was performed. Distribution of sample by sex was 34 females and 47 males, and by race 77 African and 4 Caucasian. The mean age was 50 years (range: 14-100 years). The external opening of the CC was found to be round-shaped, oval-shaped and tear-drop-shaped in 28.4%, 49.4% and 22.2% of the specimens, respectively. (1) Mean diameters [mm]: (a) medio-lateral 7.52 mm and (b) antero-posterior 5.41mm. Statistically significant difference in the vertical diameter was recorded in the race groups and laterality of the samples. (2) Mean distances [mm] between: (a) medial margins of external opening of CC was 50.03 mm, (b) lateral margins of external opening of CC was 62.73 mm and (c) external openings of CC and foramen lacerum was 15.6 mm. There was a statistically significant correlation between race and location of the opening of external CC in relation to foramen lacerum (viz. postero-lateral, lateral and diagonal, and lateral). The present study corroborated previous reports on the CC; however, the tear-drop shaped external CC opening was a unique finding. The knowledge of the reference measurements pertaining to the CC and its relationship to adjacent structures may postulate a suitable surgical "safe-zone" range within the CC area.

The sphenoid is a bone that is part of the neurocranium and is located in the middle cranial fossa. A lot of anatomic structures go through its foramina. The typical foramina found in the sphenoid bone are the following seven: optic canal, superior orbital fissure, foramen rotundum, inferior orbital fissure, foramen ovale, foramen spinosum and foramen lacerum. However, in a skull belonging to the collection of the anatomic laboratory of an university of the South of Brazil, it was found an unusual foramen in the body of the sphenoid bone, below the optic canal, connecting the middle cranial fossa with the nasal cavity; a foramen not yet described in the literature. The goal of this paper was to check the presence of this foramen in dry skulls that had their base exposed, verifying their prevalence in the collection of the anatomic labs of the participating universities. Therefore, a search was made in all of the skulls, following the inclusion criteria, in three universities of Rio Grande do Sul, looking for the same observed foramen. The analysis was performed in other 71 skulls, finding the uncommon foramen in another 3 skulls, making a total of 5.4%. Among them, two had this foramen unilaterally and the other two presented the foramen bilaterally (2.7 %). The analysis was performed in dry skulls. It was not possible to see what structures could go through it. The knowledge of the existence of this foramen entails the need to, in the future, research in other cadavers in gross anatomy available in these institutions in order to identify possible anatomic structures that cross this foramen as well as their functions. The discovery of this anatomic variations can benefit neurosurgeons, antropologists, radiologists and others professionals in the health field, as well as showing itself as a variation depending on other variables. Future perspectives of this study will be concentraded on the observation of the existence of this foramen in cadavers during dissection and removal of the brains.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

We report the case of a 41-year-old man who presented with progressive right-sided ear pressure, otalgia, hearing loss, tinnitus, and intermittent otorrhea. Computed tomography and magnetic resonance imaging detected a soft-tissue mass in the right mastoid with intracranial invasion and erosion through the tegmen tympani and mastoid cortex. Histopathologic examination was consistent with an inflammatory pseudotumor (plasma cell granuloma). These lesions rarely occur in the temporal bone. When they do, they are locally destructive and can erode bone and soft tissues. Aggressive surgery is recommended as a first-line treatment, with adjunctive steroid or radiotherapy reserved for residual or refractory disease. Our patient subsequently experienced multiple recurrences, and his treatment required all of these modalities. At the most recent follow-up, he was disease-free and doing well.

Objective To explore the improved method of precisely locating related bony structures in intradural anterior transpetrosal approach. Methods On the 10 dry skulls, the highest point of arcuate eminence (A), the petrous apex (P), the most lateral point of groove for the greater petrosal nerve (B), foramen spinosum (C), foramen ovale (D), trigeminal impression (E) and t foramen lacerum (F)were marked. Using point A as reference point and the line AP as the baseline, the distances of AB, AC, AD, AE and AF and the angles of ∠BAP, ∠CAP, ∠DAP, ∠EAP and ∠FAP were measured. Samples were analyzed by mean and standard deviation, and the data on both sides were compared by t test. Results 1．AB: (11.61±2.31) mm (left), 10.44±2.31 mm (right), t=1.084; AC: (23.14±3.07) mm (left), (21.08±2.67) mm (right), t=1.596; AD: (24.95±2.82) mm (left), (24.38±3.44) mm (right), t=0.408; AE: (18.98±3.11) mm (left), (19.21±3.09) mm (right), t=-0.164; AF: (29.68±2.62) mm (left), (29.25±2.77) mm (right), t=0.725. 2. ∠BAP: (49.15±12.10)° (left), (52.78±14.27)° (right), t=-0.624; ∠CAP: (43.98±6.95)° (left), (48.73±8.02)° (right), t=-1.418; ∠DAP: (38.68±4.81)° (left), (41.48±3.14)° (right), t=-1.543; ∠EAP: (21.93±5.29)° (left), (25.94±6.43)° (right), t=-1.523; ∠FAP: (15.96±2.78)° (left), (17.20±3.44)° (right), t=-0.882. There were no significant differences between the left and right sides (P>0.05). Conclusion Using point A and P as referent indexes, the bony structures which represent the corresponding nerves and blood vessels can be precisely located for grinding Kawase triangle via intradural anterior transpetrosal approach. Key words: Intradural anterior transpetrosal approach; Arcuate eminence; Petrous apex; Location

Unlike most bullet wounds which are damaging, this one had a beneficial result. In this respect, as well as in its anatomical relations, the present case has rarely if ever been duplicated. The bullet had entered through the right nostril, penetrating the cranium through the right maxillary antrum and base of the right middle cranial fossa and was lodged over the fractured right foramen lacerum in direct contact with the gasserian ganglion, cavernous sinus, and precavernous portion of the internal carotid artery, without seriously injuring any of these structures. Its removal was followed by relief of a long-standing pre-existing hightone deafness on the same side. Of the 7,662 cases of gunshot injuries of the skull and facial bones compiled by the Surgeon General of the US Army during the war of the Rebellion, 1861-1865, 1 none was identical with the present case. The report of the Surgeon General from World