Topographic Anatomy and Pneumatization of the Posterior Clinoid Process in Chiari Type I Malformation.

OBJECTIVE: This study aimed to examine pneumatization and topographic location of the posterior clinoid process (PCP) in Chiari type I malformation (CIM) for skull base approaches. METHODS: Computed tomography images of 52 (23 males/29 females) CIM subjects aged 23.87 ± 16.09 years and 71 (26 males/45 females) healthy subjects aged 42.48 ± 21.48 years constituted the study universe. RESULTS: The distances of PCP to the foramen magnum (P = 0.037), superior orbital fissure (P < 0.001), foramen rotundum (P < 0.001), and foramen ovale (P < 0.001) were smaller, but the distance of PCP to the crista galli (P = 0.038) was greater in CIM patients, compared with normal subjects. In CIM, the fusion between PCP and the anterior clinoid process was observed in 9 sides (8.70%), while in controls it was observed in 12 sides (8.50%). PCP pneumatization was observed in 40 sides (38.50%) in CIM patients, while it was observed in 28 sides (19.70%) in normal subjects. These data displayed that PCP pneumatization was affected by CIM (P < 0.001). CONCLUSIONS: The distances of PCP to the crista galli and foramen magnum indicate the anterior fossa length and the posterior fossa depth, respectively; thus CIM patients have a longer anterior fossa and a shallow posterior fossa. In addition, the distances of PCP to the superior orbital fissure, foramen rotundum, and foramen ovale indicate the middle fossa width; hence CIM patients have less middle fossa width than normal individuals. CIM patients have an approximately 50% higher PCP pneumatization rate, and this may increase the risk of complications such as cerebrospinal fluid fistula during the application of posterior clinoidectomy.

Accuracy of sex estimation by morphometric evaluation of foramen magnum using computed tomography - a systematic review and meta-analysis.

The objective of this study is to determine whether the morphometric evaluation of the foramen magnum using computed tomography can be used as an accurate tool in estimating the sex of an individual. An extensive search of the databases, PubMed, ProQuest, Google Scholar, and Scopus, was carried out to procure articles that fulfilled the inclusion criteria. The AQUA tool was used to assess the quality of the included studies. A random effects model was used for the meta-analysis of the eligible studies using the STATA software, version 16, 2019 at 95% CI and p ≤ 0.05. Eleven eligible articles that measured the transverse and sagittal diameters of the foramen magnum using computed tomography were included in this study. The sagittal diameter of the foramen magnum was greater than the transverse diameter, and both the diameters were greater in males than in females. Meta-analysis revealed that both transverse and sagittal diameters were more reliable for male sex estimation. Since there is a dimensional variation between the male and female foramen magnum, it can be used for initial sex identification and also as an auxiliary to other advanced methods of sex estimation.

Detailed Anatomy of Bridging Veins Around the Foramen Magnum: a Multicenter Study Using Three-dimensional Angiography.

BACKGROUND AND PURPOSE: There has been limited literature regarding the bridging veins (BVs) of the medulla oblongata around the foramen magnum (FM). The present study aims to analyze the normal angioarchitecture of the BVs around the FM using slab MIP images of three-dimensional (3D) angiography. METHODS: We collected 3D angiography data of posterior fossa veins and analyzed the BVs around the FM using slab MIP images. We analyzed the course, outlet, and number of BVs around the FM. We also examined the detection rate and mean diameter of each BV. RESULTS: Of 57 patients, 55 patients (96%) had any BV. The median number of BVs was two (range: 0-5). The BVs originate from the perimedullary veins and run anterolaterally to join the anterior condylar vein (ACV), inferior petrosal sinus, sigmoid sinus, or jugular bulb, inferolaterally to join the suboccipital cavernous sinus (SCS), laterally or posterolaterally to join the marginal sinus (MS), and posteriorly to join the MS or occipital sinus. We classified BVs into five subtypes according to the draining location: ACV, jugular foramen (JF), MS, SCS, and cerebellomedullary cistern (CMC). ACV, JF, MS, SCS, and CMC BVs were detected in 11 (19%), 18 (32%), 32 (56%), 20 (35%), and 16 (28%) patients, respectively. The mean diameter of the BVs other than CMC was 0.6 mm, and that of CMC BV was 0.8 mm. CONCLUSION: Using venous data from 3D angiography, we detected FM BVs in most cases, and the BVs were connected in various directions.

Far Lateral Approach: "Trans-tumor Approach" on Huge Dumbbell-Shape Neurofibroma of Anterior Foramen Magnum Without Craniectomy-Anatomical Consideration and New Trend.

The foramen magnum approach is always challenging because of the relationships between vital neurovascular structures in this area. Several approaches have been described, among them, the far lateral approach remains a cornerstone for the resection of anterior or anterolateral processes of the foramen magnum. This approach displays two main steps: the first is cervical, whereas the second is cranial.We report the case of a 63 year-old woman admitted for a progressive quadriplegia with swallowing disorders revealing a process of the anterior and anterolateral part of the foramen magnum. A cervical step of a far lateral approach without opening the foramen magnum achieved a near total resection of the process via a trans-tumor corridor and confirmed a dumbbell shape neurofibroma. The postoperative period showed a resolution of swallowing disorders and a progressive improvement of muscular strength. At 8 months follow-up, she was asymptomatic and able to walk with a normal balance. The surgical technique and anatomical correlation of this trans-tumor approach are discussed.

New minimally-invasive approach in adult for Chiari I malformation.

BACKGROUND: Chiari I malformation is defined by tonsillar herniation through the foramen magnum. There is no consensus on the treatment of Chiari malformation. A simple follow-up is recommended for asymptomatic cases. The classic approach is the midline sub-occipital craniotomy. METHODS: For four years, we operated on six patients with Chiari malformation I using our endoscopic minimally invasive sub-occipital approach. We compared the results with six other patients operated by the classical sub-occipital approach. RESULTS: Patients operated by endoscopic approach had shorter hospital stays, and wounds healed faster and smoother. Mid-term results were similar in the two groups. CONCLUSION: This paper proposes a new endoscopic Minimally invasive paramedian sub-occipital approach for Chiari malformation I. Although the number of cases is limited, the results look promising. We need to gather more cases to have significant numbers to perform a global comparison between the two approaches and assess the advantages and disadvantages of each technique.

Benign Enhancing Foramen Magnum Lesions.

Benign enhancing foramen magnum lesions have been previously described as T2-hyperintense small, enhancing lesions located posterior to the intradural vertebral artery. We present the first case with pathologic correlation. These lesions are fibrotic nodules adhering to the spinal accessory nerve. While they can enlarge with time on subsequent examinations, on the basis of the imaging characteristics and location, they do not necessitate surgical resection.

A valuable subarachnoid space named the occipito-atlantal cistern.

The cisterna magna has been defined as the space between the inferior margin of the cerebellar vermis to the level of the foramen magnum, while an enlarged dorsal subarachnoid space at the occipito-cervical junction extending from the foramen magnum to the upper border of the axis (C2) is still ignored. Recently, the myodural bridge complex is proved to drive the cerebral spinal fluid flowing via this region, we therefore introduce the "occipito-atlantal cistern (OAC)" to better describe the subarachnoid space and provide a detailed rationale. The present study utilized several methods, including MRI, gross anatomical dissection, P45 sheet plastination, and three-dimensional visualization. OAC was observed to be an enlarge subarachnoid space, extending from the foramen magnum to the level of the C2. In the median sagittal plane, OAC was a funnel shape and its anteroposterior dimensions were 15.92 ± 4.20 mm at the level of the C0, 4.49 ± 1.25 mm at the level of the posterior arch of the C1, and 2.88 ± 0.77 mm at the level of the arch of the C2, respectively. In the median sagittal plane, the spino-dural angle of the OAC was calculated to be 35.10 ± 6.91°, and the area of OAC was calculated to be 232.28 ± 71.02 mm2. The present study provides OAC is a subarachnoid space independent from the cisterna magna. Because of its distinctive anatomy, as well as theoretical and clinical significance, OAC deserves its own name.

Basilar tubercles and eminences of the clivus: Novel anatomical entities.

BACKGROUND: The clivus forms the central skull base between the dorsum sellae and the foramen magnum. Although bony variations of the inferior surface of the clivus are well-recognized and have been well studied, studies of bony variations of the basilar (superior) surface of the clivus are scarce. Therefore, the present study was performed to investigate bony anatomical variations on the basilar part of the clivus. METHODS: Computed tomography scans belonging to 407 Indian subjects from the CQ500 open-access dataset were retrospectively reviewed. RESULTS: Bony tubercles on the basilar surface of the clivus were found in 40 cases (9.83%). They were classified into three types including single, double and triple. A single tubercle was found in 35 cases (8.60%) including 12 on the left (2.95%), 10 on the right (2.46%) and 13 in the center (3.19%). The tubercles were doubled in four cases (0.98%) and tripled in one case (0.25%). The average width and height of the tubercles were 4.4 ± 1.5 mm (range 1.4-7.9 mm) and 1.7 ± 0.7 mm (range 0.8-4.2 mm), respectively. Ninety-five (95%) percent of the tubercles were located on the lower half of the clivus. CONCLUSIONS: To our knowledge, these tubercles have not been previously described. Therefore, we suggest the terms "basilar tubercles of the clivus" and "basilar eminences of the clivus", depending on their sizes. Knowledge of these newly described structures is important when interpreting radiological images of the skull base.

Extreme Lateral Approach to the Craniocervical Junction, Operative Technique and Approach Essentials: 2-Dimensional Operative Video.

INDICATIONS CORRIDOR AND LIMITS OF EXPOSURE: The extreme lateral approach is useful for both extradural and intradural anterior and anterolateral lesions at the lower clivus down to the level of C2. ANATOMIC ESSENTIALS NEED FOR PREOPERATIVE PLANNING AND ASSESSMENT: The patient is evaluated with MRI, computed tomography (CT), and an angiogram. Special attention is given to vascular (vertebral artery course, dominance, tumor feeders) and bony (occipital condyle, jugular tubercle, foramen magnum and extent of bony involvement) anatomy. ESSENTIALS STEPS OF THE PROCEDURE: The patient is positioned lateral with the head flexed and tilted down without axial rotation. A hockey-stick incision is performed, and the myocutaneous flap is raised. A retrocondylar craniectomy is performed. The extradural vertebral artery is exposed for proximal control. A C1 hemilaminectomy is performed. Cephalad/caudal exposure and drilling of the occipital condyle are determined per case. The dura is opened, and the vertebral artery is released at the dural entry point to facilitate the tumor removal. The tumor is debulked and delivered inferoventrally away from the neuroaxis and cranial nerves. After removing the tumor, the dura is closed using an allograft.The patients consented to the procedure and to the publication of their images. PITFALLS/AVOIDANCE OF COMPLICATIONS: • Cranial nerve deficits• Craniocervical instability• Postoperative hydrocephalus• Postoperative pseudomeningocele. VARIANTS AND INDICATIONS FOR THEIR USE: A transmastoid extension of the craniectomy allows access further rostrally in the clivus. For C1-2 chordomas, the approach is extended inferiorly, and the vertebral artery is mobilized out of the C1-2 transverse foramina. For tumors involving the joints, an occipitocervical stabilization is required.Images in video reused with permission as follows: image at 00:16 from Revuelta Barbero et al, Endoscopic endonasal transclival-medial condylectomy approach for resection of a foramen magnum meningioma: 2-dimensional operative video, Oper Neurosurg , 16(2), 2018, by permission from the Congress of Neurological Surgery; images at 00:30, and top image at 00:52 reused from Wen et al, Microsurgical anatomy of the transcondylar, supracondylar, and paracondylar extensions of the far-lateral approach, J Neurosurg , 87(4), 1997, with permission from JNSPG; bottom images at 00:52 from Muthukumar et al, A morphometric analysis of the foramen magnum region as it relates to the transcondylar approach, Acta Neurochir , 147(8), 2005, by permission from Springer Nature.

Retrospective evaluation of the morpometric and morphological anatomy of the occipital condyle, hypoglossal canal and foramen magnum in Turkish populaton with CBCT.

PURPOSE: The aim of this study is to morphometrically and morphologically examine the occipital condyle, which is an important anatomical region in terms of surgery and forensic medicine, and its surrounding structures, to evaluate the change in mean values according to gender and age, and to evaluate the correlation of the measurements obtained. METHODS: 180 (90 men, 90 women) CBCT images selected from the archive of Ankara University Faculty of Dentistry. Occipital Condyle length and width, Hypoglossal Canal-Basion distance, Hypoglossal Canal-Opistion distance, Hypoglossal Canal-Occipital Condyle anterior and posterior border distance, Occipital Condyle thickness, Hypoglossal Canal length, the widest diameter of Hypoglossal Canal, the narrowest diameter of the Hypoglossal Canal, the length of the Jugular Tubercle, the width of the Jugular Tubercle, the anterior intercondylar distance, the posterior intercondylar distance, and the Foramen Magnum index were measured. At the same time, the presence of septum or spicule in the hypoglossal canal and protrusion of the occipital condyle were evaluated. The relationship of age, gender, anterior and posterior intercondylar distance, and foramen magnum index measurements with all measurements were examined. RESULTS: In our study, all measurements were repeated 1 month after the first measurements to evaluate the intra-observer agreement, and the agreement between the obtained measurements and the first measurements was evaluated by calculating the intraclass correlation coefficient and 95% confidence intervals. Men's measurements were found to be significantly higher than women's measurements. When the coefficients of concordance in all measurements were examined, it was observed that there was a perfect concordance. CONCLUSION: When the results of the study are evaluated, it is seen that the values ​​obtained are generally close to the studies related to CT. Considering this, an idea can be gained as to whether CBCT, which has a lower dose and less cost, can be used as an alternative to CT in studies to be conducted with more comprehensive and different methods in skull base surgical planning.

How I do it - The "drum skin" duraplasty technique after foramen magnum decompression for Chiari malformations.

BACKGROUND: Chiari malformations are a spectrum of posterior cranial fossa anomalies characterized by herniation of the cerebellar tonsils through the foramen magnum. Surgery is the treatment of choice for selected patients with good postoperative outcomes. METHODS: We describe foramen magnum decompression (FMD) with dural opening and a "drum skin" duraplasty technique. CONCLUSIONS: In our experience, FMD with "drum skin" duraplasty is a safe and effective procedure, reducing the risk of CSF leakage and arachnoidal adhesions and yielding better long-term clinical and radiological outcomes than other traditional techniques.

Detection of sexual dimorphism of the foramen magnum in cats using computed tomography.

The foramen magnum is a large round or oval opening surrounded by parts of the occipital bone. It connects the cranial cavity with the vertebral canal. The foramen magnum is an important structure having various applications in veterinary practice and forensic medicine. The variability of its shape and sexual dimorphism allow it to be exploited for sex and age identification in different species. This retrospective study used computed tomographic (CT) images of the caudal region of the 102 mixed-breed cat heads (55 males and 47 females). Eight linear measurements of the foramen magnum (FM) and occipital condyles were performed on CT images. The aim of the study was to find out if the linear measurements of the CT images of the foramen magnum showed variability between the sexes of the cats. In general, the values of the linear measurements in male cats were higher than in females. The mean maximum length of the foramen magnum (MLFM) was 11.18 ± 0.84 mm and 10.63 ± 0.72 mm in male and female cats, respectively. The mean maximum internal width of the foramen magnum (MWFM) was 14.43 ± 0.72 mm in males and 13.75 ± 1.01 mm in females. The difference between FM measurements in female and male cats was statistically significant (p value; FML: 0.001, FMW: 0.000). The MLFM confidence interval was 10.41 mm to 10.86 mm in female cats and 10.97 mm to 11.39 mm in males. The confidence interval of MWFM was 13.5 mm to 14.0 mm in female cats and 14.2 mm to 14.66 mm in male cats. With these intervals, we can predict the probability of sex in cats with 95% confidence. It was noted that measurements of the occipital condyles were not sex-determining. The difference in foramen magnum index in female and male cats was statistically insignificant (p value; 0.875). As a result of the study, it was seen that the linear measurements of the foramen magnum were sex-determining.

Natural History of Chiari 1 Deformity.

PURPOSE: Chiari type 1 deformity (Ch1) is associated with bony deformity of the skull base and herniation of cerebellar tonsils more than 5 mm below the foramen magnum. Magnetic resonance imaging (MRI) is used for diagnosis and surgery is advised for symptomatic children. We present a case series using MRI including cerebrospinal fluid (CSF) flow, in children with Ch1 to demonstrate a variety of outcomes, both surgical and spontaneous: spontaneous resolution, spontaneous worsening, postsurgical improvement, and postsurgical deterioration. CASE: A 2-week-old female newborn underwent brain MRI demonstrating an ectopic neurohypophysis, under opercularization suggesting brain immaturity and a normal craniocervical junction (CCJ). Follow-up (F/U) MRI at 6 years of age showed interval spontaneous development of Ch1 with decreased CSF spaces at CCJ. CASE: A 6-year-old girl referred for imaging with short stature and growth hormone deficiency demonstrated incidental findings of Ch1 without syringomyelia. There was 15-mm protrusion of pointed cerebellar tonsils through the foramen magnum and a reduced CSF space at the craniocervical junction. No surgery was performed, and F/U MRI at the age of 7 years demonstrated spontaneous resolution of the tonsillar ectopia (cerebellar tonsils now 3 mm right and 6 mm left) and expansion of the CSF spaces at CCJ. CASE: A 7-year-old boy with headaches and staring spells underwent an MRI demonstrating 6-mm protrusion of pointed cerebellar tonsils and CSF space reduction at CCJ. No surgery was performed, and F/U imaging at the age of 9 years demonstrated spontaneous improvement in cerebellar tonsillar position and increased bidirectional CSF flow at CCJ. CASE: A 17-month-old boy underwent brain MRI for unsteady gait and poor vestibular response, which showed Ch1 and narrow CSF spaces at the foramen magnum and with reduced CSF flow. At the age of 3 years, after posterior fossa decompression, F/U MRI showed postsurgical improvement of the position of the cerebellar tonsils and increased CSF space at CCJ. CASE: A 4-month-old male infant with a history of 34-week prematurity, prior germinal matrix hemorrhage, and neonatal subdural hemorrhage was referred for MRI of the cervical and thoracic spine for evaluation of developmental delay and hypotonia with torticollis. Magnetic resonance imaging of the spine demonstrated mild protrusion of inferiorly pointed cerebellar tonsils up to the foramen magnum, with visible CSF and without retroflexion of the dens. Follow-up MRI scans demonstrated progressive worsening of the Chiari 1 deformity, even after multiple surgeries. CONCLUSIONS: It is important to be aware of a variety of different outcomes with Ch1, including spontaneous resolution, spontaneous worsening, improvement with surgery, and even deterioration after surgery. More research is required to determine objective criteria for predicting outcome, which include both anatomic measures and physiologic measures of CSF flow, so that better surgical decisions can be made and for evaluating patients who have undergone surgery.

Atlas invagination through the foramen magnum: expanding the spectrum of craniovertebral junction malformations.

PURPOSE: Malformations of the craniovertebral junction (CVJ) range from mild, asymptomatic conditions to severe forms of instability with basilar invagination. Rarely, there have been accounts of forms of so-called paramedian basilar invagination, with abnormal bone masses invading the lateral portion of the foramen magnum. All these entities have been comprehensively classified both from an anatomical and embryological standpoint. METHODS: Here, we report a case of a unique CVJ malformation which is not included in any existing classification framework and could represent a novel pathologic entity. We also provide an overview of the pertinent literature. RESULTS: The patient was a 14-year-old boy with a recent onset of spastic tetraparesis. Radiological studies documented a malformation of the atlas which invaginated through the foramen magnum, causing anterolateral medullary incarceration. Surgical treatment involved posterior decompression with resection of the abnormal bone and occipito-cervical fusion. CONCLUSION: Our report enriches the panorama of CVJ malformations, showing how anatomical knowledge and embryological insights constitute the basis for the correct assessment and treatment of these complex entities.

Radiologic Evaluation of the Fossa Navicularis on Dry Skull: A Comparative CBCT Study.

Fossa navicularis (FN) is defined as bony depression that is not always present and is located anterior to the foramen magnum and pharyngeal tubercle on the inferior aspect of the basilar part of the occipital bone. It has been reported that FN can create an infection spread path from the pharynx to the intracranial structures. Therefore, the diagnosis of this variation is important. Although cone beam computed tomography (CBCT) diagnostic accuracy has mostly been verified in detection and quantification particularly on human skulls, there is no study comparing morphometric measurements between direct measurement on the skull and CBCT measurement. The main object of this study is to evaluate the presence of FN on dry bones and CBCT images of the same dry skull and to examine the morphometric and morphological features of this formation. Thirty-two random craniums that were made available for this study that did not have any fractures or deformities of the cranial base were examined. The sagittal diameter, transverse diameter, and depth of the FN was measured both directly on dry skulls and radiologically on CBCT images of dry skull. In addition, the shape of FN (SFN) was determined. FN was detected in 10 (31.25%) of 32 craniums examined with both modalities. It was determined that sagittal diameter of the FN, transverse diameter of the FN, depth of the FN, and the shape of FN did not show a statistically significant difference between the 2 measurements. Unlike the literature, FN was investigated on dry bones both directly and in CBCT images in this study. In contrast to previously thought the FN may be smaller according to this findings, and this small variation can be detected with CBCT images. According to this findings, it can be said that morphometric evaluations on CBCT are accurate and reliable, and CBCT is a safe method for clinical diagnosis and treatment.

Morphometric analysis of the skull of Hamdani sheep via Three-Dimensional modelling.

The aim of the present study was to determine the craniometric characteristics of the crania of Hamdani sheep, one of local breeds of Turkey, by using computed tomography (CT). In the study, 13 (six female and seven male) skulls were used. After CT images of the skulls were taken, their three-dimensional models were created by MIMICS 20.1 (The Materialise Group, Leuven, Belgium) program. Thirty-eight craniometric measurements were taken over the models created and nine indices were calculated by using these measurements. All the characteristics examined were expressed as mean ± SE. In the study, statistically significant differences were found between females and males in terms of greatest neurocranium breadth, facial breadth, greatest palatal breadth (p < 0.05) and height of the foramen magnum (p < 0.01) parameters. No statistically significant difference was observed between the sexes in the calculated index values (p > 0.05). In conclusion, it is thought that the findings obtained from the study will contribute to the zooarchaeology and sheep taxonomy of Mesopotamian region.