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Foramen magnum is present on which side

The foramen magnum (from the Latin, meaning great hole) is the large opening in the base of the skull through which the spinal cord exits the cranial vault. The foramen magnum is situated in the occipital bone, and forms around the base of the brainstem (the medulla oblongata), separating the brain above from the spinal cord below Answer: The foramen magnum is the large hole on the ventral (bottom) side of the skull where the medulla, arteries, and the spinal cord exits down towards the body. The brain is able to communicate with the rest of the body using a series of nerves that are bundled together in the spinal cord, the part of the central nervous system that extends. The foramen magnum (Latin: great hole) is a large oval opening (foramen) in the occipital bone of the skull in humans and many other animals. It is one of the several oval or circular openings (foramina) in the base of the skull The foramen magnum is the largest foramen of the skull. It is located in the most inferior portion of the cranial fossa as a part of the occipital bone. Its contents include the medulla oblongata, meninges, spinal root of cranial nerve XI, vertebr..

Chiari malformations are structural defects in the base of the skull and cerebellum, the part of the brain that controls balance. Normally the cerebellum and parts of the brain stem sit above an opening in the skull that allows the spinal cord to pass through it (called the foramen magnum). When part of the cerebellum extends below the foramen. Beneath the foramen magnum, a deep concavity is present. On either side of this concavity is a prominence - occipital condyle articulates with the first vertebra, occipital crest is formed. Dicondylic skull. Beneath the foramen magnum, there are two occipital condyles. On either side of the foramen, magnum dorsolaterally exoccipital bones are. can be located on the base (inferior portion) of the skull. they are oval shaped, smooth projections located on either side of the foramen magnum. this is where the first cervical vertebra articulates with the skul there are 6 foramen on the sphenoid bone, 3 on each side that serve as a passageway for an AP axial towne method the _____ _____ should be symmetrical in size & shape and the lateral border of the foramen magnum to the lateral border of the skull should be equidistant on each side to indicate no rotation. Rotation of skull present.

Located centrally in the posterior fossa is the foramen magnum which is the large opening at the base of the skull through which the spinal cord becomes continuous with the medulla oblongata (part of the brainstem). Posterior fossa meningiomas include tentorial, clival, cerebellopontine angle and foramen magnum meningiomas Chiari type 0, a newly identified form of Chiari, describes the absence (or a zero herniation) of the tonsils below the foramen magnum. Yet Chiari 0 includes the presence of both symptoms and a syrinx in the spinal cord. This new type is under study and controversial. Chiari type II is present at birth and affects infants. It occurs with the. Definition. A foramen (plural foramina) is an opening or hole through tissue, usually bone.It allows nerves and blood vessels to travel from one side of the tissue layer to the other. Foramina are primarily found in the skull; others are located in the vertebrae, long bones, roots of the teeth, heart, and abdomen.A similarly-named aperture is also found is in the female reproductive organ of. The two lateral sections are located on either side of the foramen magnum. The foramen magnum is located at the center of the occipital bone. It acts as a passageway for the spinal cord. Medulla oblongata of the brainstem enters and exits the skull through this aperture

To their margins are attached the capsules of the atlanto-occipital joints, and on the medial side of each is a rough impression or tubercle for the alar ligament. At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal The foramen magnum is an oval-shaped opening in the occipital bone bound by the basiocciput anteriorly, the occipital condyles laterally, and the supraocciput posteriorly. If premature suture fusion occurs and/or endochondral ossification is abnormal, a small foramen magnum is the result

Foramen Magnum Placement Center for Academic Research

The foramen is paired with another on the medial wall of the orbit of the other side of the skull MRI of brain & cervical spine showed an intra-dural extra medullary lesion measuring about 5 x 3.5cm at foramen magnum extending both up and down situated posteriorly more on left side (Figures 4A-C). There was no other lesion on further cranial & spinal screening MRI The black arrows show the foramina of Vesalius on the same side. The short black arrow shows the foramen of Vesalius, which is divided into 2, by a septum. The long black arrow shows the second.. Occipital bone - Location, Anatomy, and Function. Located at the lower back part of the skull, the occipital bone is categorized into 4 areas, i.e., basioccipital, squama occipitalis, and ex-occipitalis with 2 condylar parts. These 4 regions occur around the foramen magnum and are integral to the anatomy of the occipital bone foramen magnum, in the cistern ventral to the medulla oblongata (prebulbar); one placed at the foramen mag-num, dorsal aspect; and two placed below the foramen magnum, in the ventral and in the dorsal SSS at the C-5 level. Cerebrospinal fluid flow was also evaluated at the fourth ventricle/aqueduct level and, when present, inside the syrinx

What is the structure and function of the foramen magnum

Abstract ABSTRACT Aim: The two bony projections that are present in the inferior surface of the occipital bone in the skull are called as Occipital condyles. They are present on either side of the.. Here, we present a patient with HMEs who developed cervical myelopathy due to an osteochondroma arising from the foramen magnum. Due to the cartilaginous ossification of the foramen magnum, clinicians should be aware that osteochondromas can occur in this location and potentially give rise to cervical myelopathy measuring about 3.5 x 2.7cm at foramen magnum extending both up and down.it was placed more on right side crossed the midline and almost touched the opposite margin of the foramen magnum. Another intra-dural extra-medullary lesion was also noticed at the level of C4/5 region (Figure 1) & (Figure 2). There was no other lesion on furthe

Foramen magnum - Wikipedi

  1. 100% (1 rating) Answer: option b---> Chimpanzee Position of foramen Magnum is indicative of the posture of anorganism. We all know that in the lineage of human evolution, all the speciesof H view the full answer
  2. Our series showed that foramen magnum DAVFs may present with a confusing clinical presentation that may result in a delay in diagnosis and appropriate therapy. There are 2 distinct patterns of clinical presentations, intracranial hemorrhage or myelopathy, which depend upon the venous outflow
  3. diameter. The anterior margin of the foramen magnum is encroached on each side by the occipital condyles which project down to articulate with the superior articular facets of the atlas. Anterior and posterior atlanto occipital membranes are attached to the corresponding margins of the foramen
  4. The foramen magnum is situated in the occipital bone, and forms around the base of the brainstem (the medulla oblongata), separating the brain above from the spinal cord below. The foramen magnum in apes and humans is formed by the fusion of the four individual parts of the occipital (pars squama, left and right pars lateralis, and pars basilaris)
  5. Foramen Magnum is the largest foramen situated on the base of the skull through which multiple structures pass including the Spinal Cord. It acts as a passage between the cranial vault and the base of the skull. So let us look at all the other details regarding the Foramen Magnum like its location and the [&helli
  6. Identifying the foramen magnum on brain CT. The foramen magnum is at the bottom of the skull where the brain joins the spinal cord. Normally, you should be able to see the cerebellar tonsils and the medulla as separate structures within the foramen magnum. Figure 12. Brain computed tomography (CT) scan featuring a normal foramen magnum with the.

foramen magnum canal on the medial side of the petrous part through which nerves and vessels supplying the inner ear and the facial nerve pass. Pterygoid canals are present at the base of these processes The foramen magnum is the hole in the skull through which the spinal cord attaches to the brain. To determine this distance, place a ruler on the base of the skull, starting at the back most edge of the foramen magnum and measure the distance to the end of the skull (see diagram below) Note and measure: Foramen magnum on the inferior aspect of the occipital bone. This large hole allows passage of the spinal cord. To quantify the position of the foramen magnum and evaluate how centered it is in relation to the entire skull, measure the following on the human skull and the other primate skulls The foramen magnum is the largest of the cranial foramina. A human skull contains two pterygopalatine fossae—one on the left side, and another on the right side. It is the indented area medial to the pterygomaxillary fissure leading into the sphenopalatine foramen. present in the fetus but usually closed soon after birth, is the.

What is a foramen magnum? - Quor

The foramen magnum is a large opening at the bottom of your skull. Nerves from the brain go through it and into the spinal canal, joining the spinal cord. Chiari malformation is a condition that causes brain tissue to settle into the spinal canal The structures present around Stylomastoid foramen are Styloid process are - mastoid process, jugular surface and stylopharyngeus. Clinical significance Bell's Palsy is a form of facial paralysis that is caused due to either dysfunction or the inflammation of the facial nerve (7th cranial nerve) If too small, the effects can be crowding of the brainstem and cerebellum, as well as herniation of the tonsils through the foramen magnum (Fig. 3B). • Sometimes the occipital bone is misshaped or thickened. • Basilar invagination is a condition where the top of C2 (odontoid) pushes upward into the foramen magnum magnum in almost all of the shapes. The perimeter of foramen magnum is maximum in egg shape 102.01mm and least in round shape 77.50mm. The width of foramen magnum is directed related to transverse distance of posterior fossa (0.366).Using signed 2 tailed test it was found to be significant (.020). The Pearson correlatio The present study was undertaken to provide data on foramen magnum and occipital condyles (OCs) for the purpose of sex determination, which can be used as a reference sample for establishing the identity in cases of unknown fragmentary skulls

In a biped, the foramen magnum is positioned more: A. anteriorly at the base of the skuli. B. posteriorly at the back of the skull. C. laterally to the side of the skull. D. dorsally at the rear of the skull. 5. The shape of the human vertebral column is formed by two curves. Describe where these two curves are located. 6 The outer and posteroior side is the formed bythe premaxilla and the vomers. A lachrymal bone is present between the frontal and the maxilla. 5. The upper jaw of each side consists of an anterior premaxilla and a posterior maxilla. They bear different types of socketed teeth. Incisor-1, premolar-1 and molar-3. A diastema is present (canine is. While a fetus develops in the womb, a small opening exists between the two upper chambers of the heart called the atria. This opening is called the foramen ovale. The purpose of the foramen ovale.

Located side-by-side in front of skull providing excellent binocular vision. Is there a gap present on the upper jaw between the canines and incisors? : Do the incisors rise vertically from the jaw or do they slant out? 11. FORAMEN MAGNUM: The foramen magnum is a large opening in the back or bottom of the skull through which the spinal. The foramen magnum is the hole in the skull through which the spinal cord attaches to the brain. To determine this distance, place a ruler on the base of the skull, starting at the back most edge of the foramen magnum and measure the distance to the end of the skull (see Figure 10). Be sure to demonstrate this measurement to your students

Background: Current study examines morphometric alterations of the foramen magnum (FM), occipital condyles (OCs) and hypoglossal canals (HCs) and highlights all the morpho-metric parameters of the FM area that present side asymmetry, gender dimorphism and are affected by the ageing Foramen magnum meningiomas are rare tumors, accounting for only 0.5 percent to 3 percent of all meningiomas, and usually appearing in men and women ages 40 through 70. With our experienced fellowship-trained skull base surgeons, Mount Sinai serves as a major center in the New York City and the tri-state area for foramen magnum meningioma. The foramen magnum lies in the occipital bone. Anterolateral to it, the occipital condyles articulate with the lateral masses of the atlas (C1) to form the atlanto-occipital joint [4, 15, 22, 25].The VA runs around the atlanto-occipital joint from the extracranial to the intracranial side (Figs. 16.1 and 16.2).The extracranial VA, which courses in a groove on the posterior arch of the atlas. On the base of the skull, the occipital bone contains the large opening of the foramen magnum, which allows for passage of the spinal cord as it exits the skull. On either side of the foramen magnum is an oval-shaped occipital condyle. These condyles form joints with the first cervical vertebra and thus support the skull on top of the vertebral. The most striking feature of the occipital bone is this large opening, the foramen magnum, through which the spinal cord and its accompanying structures pass. The part of the occipital bone in front of the foramen magnum is called the basilar part, often referred to as the base of the occiput. The two temporal bones converge on it from each side

BIO113-Skulls

Aim: The two bony projections that are present in the inferior surface of the occipital bone in the skull. are called as Occipital condyles. They are pr esent on either side of the foramen magnum. Foramen Magnum is the largesr foramen of skull. It is divided into anterior and posterior parts by Alar ligament. Anterior part structures — 1. Membrana tectoria 2. Upper band of cruciate ligament 3. Apical ligament of Dens Posterior part structur..

disruption of CSF flow through foramen magnum. Compression of cord and medulla may result in myelopathy and lower cranial nerve and nuclear dysfunction. Compression of cerebellum may result in ataxia, dysmetria, nystagmus, and dysequilibrium. Disruption of CSF flow through the foramen magnum probably accounts for the most common symptom, pain. 10.1055/b-0034-84433 Anatomical Basis of Surgical Approaches to the Region of the Foramen MagnumAlbert L. Rhoton, Jr. and Evandro De Oliveira Lesions in the region of the foramen magnum present special problems in operative management because many structures are involved. The structures that must be considered in planning an operative approach to the region include th What does foramen mean? An opening or orifice, as in a bone or in the covering of the ovule of a plant. The large opening in the base of the skull through which the spinal cord passes is called the foramen magnum nəm). &diamf3; The opening in the septum between the right and left atria of the heart, present in the fetus but usually. condylar canals.The foramen magnum lies in an anteromedian position and leads into posterior cranial fossa. Anteriorly, the margin of the foramen magnum is slightly overlapped by the occipital condyles which project down to articulate with the superior articular facets on the lateral masses of the atlas [1].The dimen-sions of the foramen magnum.

Chiari Malformation Fact Sheet National Institute of

Foramen magnum meningiomas are challenging tumors, requiring special considerations because of the vicinity of the medulla oblongata, the lower cranial nerves, and the vertebral artery. After detailing the relevant anatomy of the foramen magnum area, we will explain our classification system based on the compartment of development, the dural insertion, and the relation to the vertebral artery In the present study mean value of foramen magnum index was found to be 1.23.withminimum value of 0.970 and maximum being 1.921 with standard deviation of 0.187 for 40 specimens. Table-4: Frequency and Percentage of Foramen Magnum Index Foramen Magnum Index (FMI) Frequency Percentage (%) <1.20 18 45 ≥1.20 22 55 Total 40 10 In the present study, we determined the use of the foramen magnum as well as the occipital condyles for sex determination on adults from a modern Greek population. Seven parameters were examined (4 obtained from the foramen magnum; 3 obtained from the occipital condyles) and the sample consisted of 154 adult crania (77 males and 77 females) In our patient, the symptom was probably associated with the meningioma that was located at the foramen magnum and C1 level. The involuntarily tilting of her head to the side of the tumor relieved pressure on medulla. This made her involuntarily maintain that position of the head prior to tumor removal

On the other-side some describes it as like, it is the triangular interval between the alar ligaments is another fibrous cord ( a bone of spinal cord), the apical ligament of dens (apical odontoid ligament), which expands from the top of the odontoid procedure to the anterior margin of the foramen magnum, being intimately mixture with the deep. Foramen magnum meningiomas are very rare lesions. They frequently originate from the arachnoid cells at the dura matter of the craniocervical junction. Foramen magnum meningiomas are challenging for neurosurgeons because of the complex anatomy of foramen magnum. We present a rare case of FMM with excessive calcification and without the dura.

external pressure it may cause on vertebral artery as it passes from foramen transversarium of first cervical vertebra to the foramen magnum of the skull. Materials and Methods: The present study was carried out on 200 dried fully ossified adult human atlas vertebrae of unknown sex and age for evaluation of arcuate foramen the normal patients ranged from 8 mm above the foramen magnum (+8 mm) to 5 mm below the foramen magnum (-5 mm) with a mean value of +1 mm and standard deviation of 1.9 mm. In the 25 Chiari I patients, the range was from 29 mm below the foramen magnum (-29 mm) to 3 mm below the foramen magnum (-3 mm) with a mean value of -13 m Magnum between foetal, adolescent & adult age. 3) To study symmetry of the foramen Magnum with respect to midline. Also statistical analysis has been carried out to show the age changes and morphology of foramen magnum from foetal to adult age and in male and female sex and to show the symmetry of foramen magnum

Round shape was found in 5 skulls of males (15.625%), 3 skulls of females Table 1: Showing the gender wise frequency of types of foramen magnum in present study Shape MALE % FEMALE % TOTAL % OVAL 16 50 8 44.44 24 48 ROUND 5 15.625 3 16.666 8 16 TETRAGONAL 9 28.125 6 33.333 15 30 HEXAGONAL 2 6.25 1 5.555 3 6 32 100% 18 100% 50 100% Table 2. Foramen magnum decompression, or posterior fossa craniectomy, is the surgery procedure used to treat Chiari malformation. Chiari malformation is a benign abnormality that results in a part of the brain extending into the upper spinal canal. During the procedure, small sections of bone are removed from the rear of the skull and spine to create.

Comparative Anatomy: Skull of Fish, Frog, Lizard, Bird and

Foramen magnum (FM) meningiomas are challenging lesions because of the vicinity of the medulla oblongata, the lower cranial nerve s, and the vertebral artery . The surgical treatment of FMMs has evolved considerably due to the progress in microsurgical techniques and development of a multitude of skull base approaches foramen meaning: 1. a natural passage in the body, especially into a bone 2. a natural passage in the body. Learn more spinal cord. Furthermore, intrajugular tumors typically present with otologic symptoms and jugular foramen syndrome, characterized by symptoms of tin-nitus, hearing impairment, dysphagia, and hoarseness [8]. Intracisternal [3] schwannomas generally present with symptoms accessory nerve palsy, cof e-rebellar signs and myelopathy [3] Other articles where Foramen magnum is discussed: skull: has a central opening (foramen magnum) to admit the spinal cord. The parietal and temporal bones form the sides and uppermost portion of the dome of the cranium, and the frontal bone forms the forehead; the cranial floor consists of the sphenoid and ethmoid bones. The facial area include A large opening, the foramen magnum, lies centrally in the floor of the posterior cranial fossa. It is the largest foramen in the skull. It is the largest foramen in the skull. It transmits the medulla of the brain, meninges, vertebral arteries, spinal accessory nerve (ascending), dural veins and anterior and posterior spinal arteries

Lab: Axial Skeleton Flashcards Quizle

Foramen Spinosum was first identified and described by Danish anatomist Jakob Benignus Winslow in 18th century. To lean about the other foramina present in the skull, check Foramen Magnum, Foramen Lacerum, Foramen Ovale, Infraorbital foramen and supraorbital foramen The foramen magnum functions as a passage of the central nervous system through the skull connecting the brain with the spinal cord. On either side of the foramen magnum is an occipital condyle. These condyles form joints with the first cervical vertebra The image shows the sella tursica projected in the foramen magnum. The entire occipital bone, the posterior portion of the parietal bone, and the lambdoid suture should be clearly demonstrated. The petrous pyramids are symmetric and the distance between the lateral skull margin and lateral border of the foramen magnum is equal on either side

Skull Flashcards Quizle

  1. oval processes with convex surfaces on either side of the foramen magnum. Articulate with depressions on the first cervical vertebrae (atlas) to form the atlanto-occipital joint. Term. Atlanto-occipital joint: Definition. Joint found where the occipital condyles articulate with the atlas; allows the head to nod yes or no
  2. Each condyle is located to either side of the foramen magnum, the hole in the skull base through which the spinal cord enters the cranium. Found at the base of the occipital bone on the lower back portion of the skull, the occipital condyle is one of two kidney-shaped convex surfaces that articulate with the superior facets of the atlas bone
  3. a. The fora
  4. Foramen magnum definition is - the opening in the skull through which the spinal cord passes to become the medulla oblongata
  5. The squamous part of the largest part of the occipital bone. It is situated above and behind the foramen magnum and curved downward on each side. There are two curved lines on each side: the highest nuchal line and the superior nuchal line. There is also a middle line running through the nuchal plane called the inferior nuchal line

A suboccipital craniectomy with removal of the foramen magnum rim was performed on the side of the tumor. In addition a C 1 - C 2 hemilaminectomy was done on the same side. In both patients the C 1 arch was thinned out by the tumor. A limited (less than one-third) C 1-C 2 facet joint removal was done o If MRI is contraindicated or cannot be performed, high-resolution sagittal computed tomography (CT) of the brain may also be used. CM-1 can be diagnosed if the tonsils are displaced > 5 mm through the foramen magnum, or if they are > 3 mm past the foramen magnum in the presence of other characteristics of the disease (e.g. syringomyelia) Foramen magnum meningiomas are rare tumors, accounting for only 0.5 percent to 3 percent of all meningiomas, and usually appearing in men and women ages 40 through 70. With our experienced fellowship-trained skull base surgeons, Mount Sinai serves as a major center in the New York City and the tri-state area for foramen magnum meningioma. A cervicomedullary kink is present (arrowhead), and a peglike appearance of the tonsils is noted. The lower border of the pons lies at the level of the foramen magnum (arrow), indicating that the medulla lies beneath the foramen magnum. This case meets the criteria for a Chiari 1.5 malformation. Complication

Meningioma: Surgery, Treatment & Symptoms Skull Base

  1. Foramen magnum is a Latin word meaning the largest aperture in skull. The foramen magnum is an important landmark for surgeries as it lies at the transition zone between spine and skull. The foramen magnum is a fun-damental component in the complex interaction of bony
  2. The optic foramen, the opening through which the optic nerve runs back into the brain and the large ophthalmic artery enters the orbit, is at the nasal side of the apex; the superior orbital fissure is a larger hole through which pass large veins and nerves.. Click to see full answer
  3. 2. Observe each skull from the side, recording your observations about the following features (use the table below to record your observations): 3. Observe each skull from the bottom view and locate the foramen magnum. This is the hole that connects the brain stem to the spinal cord
  4. Illustration of the foramen magnum anatomy through a postero-lateral approach. The skin incision (dotted line) extends on the midline just upper to the occipital protuberance and curves laterally toward the pathological side.The right vertebral artery has been elevated from the C1 posterior arch

Chiari I malformation & syringomyelia Mayfield Brain & Spin

Keywords: Occipital condyle, hypoglossal canal, foramen magnum, transcondylar approach. Introduction The condylar parts of the occipital bone flank the foramen magnum. The inferior surface of the occipital condyles present for articulation with the superior atlantal facets present on the lateral mass of the atlas. Thi Because the most complete fossil is a skull, the foramen magnum is one of the best pieces of evidence linking Sahelanthropus to the human lineage. The conversation over the foramen magnum's importance is far from over. The authors present interesting results that raise many questions, said Russo of Ruth's paper The foramen magnum receives special attention, as it is located in a region together with many strong muscles and ligaments. The measures were taken with a sliding digital caliper. Our results showed that the foramen magnum had a mean anteroposterior diameter of 34.23±2.54 mm, and the mean transverse diameter was 28.62±2.83 mm. The most.

Foramen - The Definitive Guide Biology Dictionar

The foramen magnum is an oval-shaped opening in the occipital bone, surrounded anteriorly by the clivus, laterally by the occipital condyles, and posteriorly by the squamous portion of the occipital bone. Normally, only the medulla traverses through the foramen magnum and merges seamlessly with the cervical cord If you have a patent foramen ovale, a color flow Doppler echocardiogram could detect the flow of blood between the right atrium and left atrium. Saline contrast study (bubble study). With this approach, a sterile salt solution is shaken until tiny bubbles form and then is injected into a vein. The bubbles travel to the right side of your heart.

Foramen magnum | definition of foramen magnum by MedicalSphenoidDr Balaji Anvekar FRCR: HemangioblastomaOccipitalArnold Chiari malformation and Chiropractic - BlairComparative study of skull of camel, ox

foramen [fo-ra´men] (pl. fora´mina) (L.) a natural opening or passage, especially one into or through a bone. aortic foramen aortic hiatus. apical foramen an opening at or near the apex of the root of a tooth. auditory foramen, external the external acoustic meatus. auditory foramen, internal the passage for the auditory (vestibulocochlear) and facial. Lesions of the ventral foramen magnum and craniovertebral junction present a difficult challenge. This complex region can harbor neoplastic, degenerative, or inflammatory lesions that can cause compression of the cervicomedullary junction and craniocervical instability. Treatment may require surgical decompression and subsequen We present a case of a 42-year-old male patient suffering from a foramen magnum choroid plexus papilloma, which resembled meningioma in an initial evaluation, who developed dizziness, hearing loss, and gait disturbance. The patient was treated with suboccipital craniotomy and the tumor was partially removal 3. Foramen magnum meningiomas are challenging tumors, requiring special considerations because of the vicinity of the medulla oblongata, the lower cranial nerves, and the vertebral artery. Meningiomas represent 25 - 30 % of all hospital-based primary intracranial neoplasms. The foramen magnum meningiomas constitutes 1 - 3 % of all cranial. History. A foramen magnum tumor was first described by Hallopeau in 1874 10 in a case report of a 50-year-old woman who presented with spastic upper extremity weakness that progressed to quadriparesis with brainstem signs. The patient eventually died of respiratory failure. Autopsy revealed a foramen magnum tumor, the size of a small chestnut, that caused compression of the lateral. We present a personal series of 44 patients harboring Chiari type I malformation (CM-I) operated with a suboccipital craniectomy and a C1 (or C1/C2) laminectomy, plus an extreme lateral Foramen Magnum opening, a Y shaped dural incision with preservation of the arachnoid membrane, and an expansile duraplasty employing autogenous periosteum