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SUMMARY: The foramen magnum is an important topographic opening which connects cranial cavity and spinal canal. The analysis of the bone material established that there are differences in the shape of the foramen magnum between individuals. The aim of this study was to determine sex based on shape and size of foramen magnum using geometric morphometrics method. A study was performed on three-dimensional models (3D models) of 214 human skulls of known sex and known age (141 male skulls and 73 female skulls). The skulls are located at the museum of Medical Faculty, University of Sarajevo. Skulls belong to Bosnian population from the mid-twentieth century. All examined skulls were scanned with a laser scanner to obtain their 3D models. On 3D models of the examined skulls, four landmarks were marked on foramen magnum. Analysis of sex determination was performed using the MorphoJ program. Results of this study showed that there are sex differences in the shape and size of the foramen magnum. Sex determination based on the shape and size of the foramen magnum was showed 65.25 % accuracy for male and 63.01 % accuracy for female using geometric morphometrics method. Examination of the effect of size of foramen magnum on sexual dimorphism of shape of foramen magnum showed a statistically significant effect. Sex determination based just on the shape of foramen magnum using geometric morphometrics method was possible with 62.41 % accuracy for male and 58.90 % accuracy for female on examined sample. Sex differences on shape and size of foramen magnum were found using geometric morphometrics method on three-dimensional models of the examined skulls. The percentage of accuracy was higher for male based on the shape and size of the foramen magnum than for female.

El foramen magno es una importante abertura topográfica que conecta la cavidad craneal y el canal espinal. El análisis del material óseo estableció que existen diferencias en la forma del foramen magno entre individuos. El objetivo de este estudio fue determinar el sexo en función de la forma y el tamaño del foramen magno utilizando morfometría geométrica. El estudio se realizó en modelos tridimensionales (modelos 3D) de 214 cráneos humanos de sexo y edad conocidos (141 cráneos masculinos y 73 cráneos femeninos). Los cráneos se encuentran en el museo de la Facultad de Medicina de la Universidad de Sarajevo. Los cráneos pertenecen a población bosnia de mediados del siglo XX. Todos los cráneos examinados fueron escaneados con un escáner láser para obtener sus modelos 3D. En los modelos 3D de los cráneos examinados, se marcaron cuatro puntos de referencia en el foramen magno. El análisis de determinación de sexo se realizó utilizando el programa MorphoJ. Los resultados de este estudio mostraron que existen diferencias de sexo en la forma y el tamaño del foramen magno. La determinación del sexo basada en la forma y el tamaño del foramen magno mostró una precisión del 65,25 % para los hombres y del 63,01 % para las mujeres utilizando morfometría geométrica. El examen del efecto del tamaño del foramen magno sobre el dimorfismo sexual de la forma del foramen magno mostró un efecto estadísticamente significativo. La determinación del sexo basada solo en la forma del foramen magno utilizando morfometría geométrica fue posible con una precisión del 62,41 % para los hombres y del 58,90 % para las mujeres en la muestra examinada. Se encontraron diferencias de sexo en la forma y el tamaño del foramen magno utilizando morfometría geométrica en modelos tridimensionales de los cráneos examinados. El porcentaje de precisión fue mayor para los hombres en función de la forma y el tamaño del foramen magno que para las mujeres.

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SUMMARY: The foramen magnum (FM) is the key component of the craniovertebral junction, which connects the brain stem and medulla spinalis and is closely related to vital structures. FM dimensions are of great clinical importance. Considering the similarity in shape between FM and orbita, we thought that there might be a relationship between the lengths (sagittal diameter) and widths (transverse diameter) of these structures. Since it is not possible to reach FM directly, we set up our hypothesis as can we calculate the foramen magnum dimensions from orbital measurements before proceeding to costly tests. We also investigated this harmony in the skulls we used in the study. In the study, 21 dried skull bones from the Turkish population were used. FM and right Orbital length and width measurements were made. Precision digital caliper was used for measurements. Statistical validity and reliability analyzes were performed to prove the agreement between the measurements. We found that the length of the orbit and FM in the sagittal plane is close to each other, with 34.74±2.11 mm and 34.99±3.0 mm, and the width of the orbit in the coronal plane is approximately 1.40 times the width of the FM. We proved that the estimation of FM dimensions based on orbital measurements is also statistically valid and safe. Using orbital measurements, it is possible to estimate FM dimensions which are difficult to reach directly in living humans.

El foramen magno (FM) es el componente clave de la unión craneovertebral, que conecta el tronco encefálico y el bulbo raquídeo y está estrechamente relacionado con las estructuras vitales. Las dimensiones FM son de gran importancia clínica. Teniendo en cuenta la similitud de forma entre FM y órbitas, consideramos que podría haber una relación entre las longitudes (diámetro sagital) y las anchuras (diámetro transversal) de estas estructuras. Dado que no es posible llegar al FM directamente, establecimos nuestra hipótesis y calculamos las dimensiones del foramen magno a partir de mediciones orbitales antes de proceder a costosas pruebas. También investigamos esta armonía en los cráneos que usamos en el estudio. En el estudio, se utilizaron 21 huesos de cráneo secos de la población turca. Se realizaron mediciones FM y de longitud y anchura orbitales. Para las mediciones se utilizó un calibrador digital de precisión. Se realizaron análisis estadísticos de validez y confiabilidad para probar la concordancia entre las mediciones. Encontramos que la longitud de la órbita y FM en el plano sagital es cercana entre sí, con 34,74±2,11 mm y 34,99±3,0 mm, y el ancho de la órbita en el plano coronal es aproximadamente 1,40 veces el ancho de la FM. Demostramos que la estimación de las dimensiones FM basadas en mediciones orbitales también es estadísticamente válida y segura. Empleando mediciones orbitales, es posible estimar dimensiones FM que son difíciles de alcanzar directamente en humanos vivos.

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SUMMARY: The foramen magnum (FM) is a transition zone between the spine and skull. There is a study in the literature showing the golden ratio (4.62) and harmony between both FM and the anteroposterior and transverse diameters of the skull. The aim of this study is to examine the existence of this ratio on CT images and to investigate whether this ratio changes according to the FM shape types. In this study, 402 adult CT images belonging to the Turkish population were examined. Maximum cranial length (MCL), maximum cranial width (MCW) and the FM length (FML) and FM width (FMW) were measured. The different shapes of the FM were macroscopically classified. The number and incidence of each type in the studied skull was registered. In the 402 CT images used in the study, 12 FM shapes were detected. Three of the shape types observed in our study have not been reported in the literature until now, and were found in our study for the first time. In addition, our data supported that by using the ratio of 4.62, there was a great harmony between the skull and FM. The results obtained from the research show that there is a ratio of 4.62 between the basic cranial measurements and FM dimensions in all shapes except triangular shape. It is thought that repeating the calculated coefficients over more different FM shapes will contribute to the effectiveness of the proposed golden ratio.

RESUMEN: El foramen magno (FM) es una zona de transición entre la columna y el cráneo. Existe un estudio en la literatura que muestra la proporción áurea (4,62) y la armonía entre el FM y los diámetros anteroposterior y transversal del cráneo. El objetivo de este estudio fue examinar la existencia de esta relación en las imágenes de TC e investigar si esta relación cambia según los tipos de forma del FM. Se examinaron 402 imágenes de TC de adultos pertenecientes a la población turca. Se midieron la longitud craneal máxima, el ancho craneal máximo y la longitud del FM y la anchura del FM. Las diferentes formas del FM se clasificaron macroscópicamente. Se registró el número e incidencia de cada tipo en el cráneo estudiado. En las 402 imágenes de TC utilizadas en el estudio, se detectaron 12 formas de FM. Tres de los tipos de formas observados en nuestro estudio no se han reportado en la literatura consultada describiéndose por primera vez. Además, nuestros datos respaldaron que al usar la proporción de 4,62, había una armonía importante entre el cráneo y el FM. Los resultados obtenidos de la investigación muestran que existe una relación de 4,62 entre las medidas craneales básicas y las dimensiones de la FM en todas las formas excepto en la triangular. Se cree que la repetición de los coeficientes calculados en más formas de FM diferentes contribuirá a la eficacia de la proporción áurea propuesta.

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Introduction: The foramen magnum is located in the occipital bone and communicates the cranial cavity with the spinal canal of the vertebral column. Variations in the shape and size of this foramen, such as the presence of a notch in its dorsal contour, characterize occipital dysplasia and may occur due to a defect in the supraoccipital bone ossification process during the gestational period. Occipital dysplasia has been reported primarily in small, toy, and brachycephalic breeds, and its clinical relevance remains controversial. The aim of the present study was to evaluate the size of the foramen magnum in asymptomatic dogs of small and toy breeds. Materials, Methods & Results: The study was conducted at the Veterinary Hospital of the Center for Rural Health and Technology of the Federal University of Campina Grande (UFCG), Patos Campus, located in Paraíba state, Brazil. Twelve (n = 12) asymptomatic, small and toy breed dogs, with variable sex and over 10 months of age, were referred to the Veterinary Hospital for elective surgical procedures and were used in this study. All dogs underwent complete neurological examination to confirm the asymptomatic status and were radiographed in rostrocaudal position, with their mouths closed and the hard palate at an angle of approximately 70º to 80º with the table of the X-ray apparatus. The foramen magnum of each specimen was evaluated in the radiographs using a precision caliper. The analyzed parameters included height (H), the height of the dorsal notch (N), total height (H+N), and width (W), and the obtained data were used to establish the degree of occipital dysplasia and determine the shape of the foramen magnum. Of the 12 animals studied, 75% (n = 9) exhibited a dorsal notch in the foramen magnum, which varied between 3.00 and 10.00 millimeters (mm) in height, characterizing occipital dysplasia. Among the affected animals, 77.77% (n = 7) were classified as grade 1 for the alteration, 11.11% (n = 1) as grade 2 and one animal (11.11%) as grade 3. The prevalent shape observed for the foramen magnum was oval (83.3%). Discussion: Although occipital dysplasia has been associated with the occurrence of nonspecific neurological clinical signs, such as tremors, ataxia, and epileptic seizures, the presence of this alteration in asymptomatic dogs indicates that the formation alone is just an anatomical variation, as demonstrated herein and in previous studies conducted over the past few years. This hypothesis has been increasingly supported by scientific evidence through publications that portray occipital dysplasia in dogs of various breeds and sizes without clinical manifestations. The clinical signs attributed to occipital dysplasia may originate in situations where there is a coexistence of other conditions. Occipital dysplasia has been reported several times in conjunction with other pathologies, such as occipital hypoplasia and syringomyelia, in symptomatic dogs. The dorsal notch-shaped occipital defect is covered by a fibrous tissue membrane in dogs affected by occipital dysplasia. The presence of this soft tissue membrane has been related to the late onset of syringomyelia due to the decompressive effect that it provides to the flow of cerebrospinal fluid. When occipital dysplasia is identified in symptomatic dogs, it is suggested that the lesion be correctly located within the nervous system and that, according to its neurolocalization, a thorough investigation of other underlying causes for the occurrence of the neurological clinical manifestation be carried out. To date, there is no evidence characterizing occipital dysplasia as a single entity causing neurological deficits.

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Introducción: Los meningiomas de la fosa posterior representan el 20% de todos los meningiomas intracraneales. Cada subtipo tiene una base de implantación, abordaje quirúrgico y morbimortalidad postoperatoria muchas veces diferente. Advertimos que en reuniones científicas y publicaciones no se sigue una forma de clasificar uniforme, sencilla y clara con orientación netamente quirúrgica. Esto genera que el neurocirujano en formación no cuente con herramientas suficientes para la toma de decisiones. Objetivos: Proponer una clasificación sencilla de los meningiomas de la fosa posterior con un fundamento anatomo-quirúrgico y presentar casos ilustrativos de cada subtipo. Materiales y métodos: Se estableció una nomenclatura considerando reportes previos, el criterio anatómico y la experiencia quirúrgica de los autores. Se presentaron casos revisando las historias clínicas y los archivos de imágenes correspondientes a cada subtipo de la clasificación. Resultados: Representamos a la fosa posterior como un compartimento con 3 anillos: el superior se divide en medial, lateral-anterior y lateral-posterior; el medio se divide en 6 variantes: clivales puros, esfeno-petro-clivales, petrosos anteriores, petrosos posteriores y de la convexidad suboccipital medial y lateral; el inferior se divide en anterior, lateral derecho, lateral izquierdo y posterior. Conclusión: Los meningiomas del anillo superior pueden resolverse mediante una vía suboccipital medial o lateral; los del anillo medio tienen un espectro de opciones más diverso; los del anillo inferior -siguiendo el esquema de división en cuadrantes de un reloj- pueden resolverse por medio de un abordaje suboccipital medial o extremolatera

Introduction: Posterior fossa meningiomas represent 20% of all meningiomas, being each location associated with a specific approach, morbidity and mortality. The actual classifications are focus on the dural attachment, without associating the anatomical with the surgical aspects, useful to the young neurosurgeons for decision making. Objectives: To propose a classification of the posterior fossa meningiomas with an anatomical-surgical view including the presentation of cases. Materials and Methods: A nomenclature was established concerning previous reports, the anatomical criteria and the surgical experience of the authors. Cases were presented by reviewing the medical records corresponding to each subtype of the proposed classification. Results: We represent the posterior fossa as a 3 rings compartment: the upper one is divided into medial, anterior-lateral and posterior-lateral; the middle ring is divided into 6 variants: pure clival, spheno-petro-clival, anterior petrosal, posterior petrosal, and medial and lateral suboccipital convexity; the lower ring is divided into anterior, right lateral, left lateral, and posterior. Conclusion: Superior ring meningiomas can be resolved by a medial or lateral suboccipital approach; middle ring meningiomas have a more diverse spectrum of options; while meningiomas of the inferior ring - following the scheme of division into quadrants of a clock - can be resolved by means of a medial or extreme-lateral suboccipital approach.

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Among the posterolateral corridors to the ventral foramen magnum (FM), the transcondylar fossa (supracondylar transjugular tubercle) approach (TCFA) is indicated for lesions lying anteriorly to the dentate ligament and above the jugular foramen and hypoglossal canal.1-13 It involves the drilling of the condylar fossa, namely the exocranial surface of the jugular tubercle. Despite the anatomic variability of the condyle and posterior condylar emissary vein,14,15 they are important landmarks for the TCFA. The extradural jugular tuberculectomy has no risk of iatrogenic mechanical instability compared with the transcondylar approach. This 2-dimensional operative video (Video 1) aims to show the key technical aspects of the TCFA through the case description of an anterolateral FM meningioma. A 35-year-old male patient with a left anterolateral FM meningioma underwent TCFA in a semisitting position. Drilling of the condylar fossa led to an extradural resection of the jugular tubercle. Posterior condylar emissary veins connecting the sigmoid sinus/jugular bulb with the vertebral venous plexus marked the lateral limit of the approach. Through a suprahypoglossal working corridor, the meningioma was debulked and dissected. Postoperative magnetic resonance imaging confirmed complete resection of the tumor, and the patient was discharged neurologically intact on the third postoperative day. TCFA is a valuable technical option for selected anterolateral FM meningiomas. The perfect knowledge and intraoperative use of specific anatomic landmarks are critical to safely perform the TCFA while maximizing the exposure of the surgical target and decreasing the risk of postoperative mechanical instability of the craniovertebral junction.

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Objective To describe our surgical techniques, analyze their safety and their postoperative outcomes for foramen magnum tumors (FMTs). Methods From 1986 to 2014, 34 patients with FMTs underwent surgeries using either the lateral suboccipital approach, standard midline suboccipital craniotomy, or the far lateral approach, depending on the anatomic location of the lesions. Results In the present series, there were 22 (64.7%) female and 12 (35.2%)male patients. The age of the patients ranged from12 to 63 years old.We observed 1 operativemortality (2.9%). A total of 28 patients (82.3%) achieved a score of 4 or 5 in the Glasgow Outcome Scale (GOS). Gross total resection (GTR) was obtained in 22 (64.7%) patients. After the surgery, 9 (26%) patients developed lower cranial nerve dysfunction (LCNd) weakness. The follow-up varied from 1 to 24 years (mean: 13.2 years). Conclusion Themajority of tumors located in the FMcan be safely and efficiently removed usingeither thelateral suboccipital approach, standardmiddlelinesuboccipital craniotomy, or the far lateral approach, depending on the anatomic location of the lesions.

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Resumen Los meningiomas son tumores del sistema nervioso central que representan alrededor del 14,3% a 19%, de ellos solo un 1.8% a 3,2% surge en el foramen magno, por años el abordaje de esta clase de tumores conllevaba una gran morbimortalidad asociada debido a que el foramen magno contiene una serie de estructuras anatómicas y neurovasculares críticas, sin embargo con el progreso de las técnicas quirúrgicas, el manejo de la anestesia neurológica y la formación de neurocirujanos con experiencia en cirugías de base de cráneo, ha podido revertir estos resultados y hacer de la cirugía una alternativa segura con bajas tasas de complicaciones. El presente trabajo pretende revisar la literatura acerca de la morbimortalidad asociada a los meningiomas de foramen magno y presentar un caso abordado en nuestro centro.

The meningiomas are tumors of the central nervous system that represent around 14.3% to 19%, of them only 1.8% to 3.2% arise in the foramen magnum, for years the approach of this class of tumors entailed a great associated morbidity and mortality because the foramen magnum contains a series of critical anatomical and neurovascular structures, however with the progress of surgical techniques, the management of neurological anesthesia and the training of neurosurgeons with experience in skull base surgeries, it has been able to reverse these results and make surgery a safe alternative with low complication rates. The present work aims to review the literature about morbidity and mortality associated with meningiomas of foramen magnum and present a case addressed in our center.

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