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[Proposal for the definition of "foramen magnum syndrome"--foramen magnum tumor and abnormalities].

The clinical appearance of foramen magnum tumor is protean and, even at the stage when serious neurological deficits are present, the lesions are often misdiagnosed as another disease, especially cervical spondylosis and multiple sclerosis, and patients may undergo improper concervative or even surgical treatments. The best guarantee against misdiagnosis, we believed, was to establish a definition of "Foramen Magnum Syndrome" to facilitate the recollection of its peculiar clinical findings. "Foramen Magnum Syndrome" is composed of: 1. Cape distribution of sensory loss; 2. Atrophy of the intrinsic muscles of the hands; 3. Neck or suboccipital pain; 4. Dysesthesia of the hands (numbness, tingling, and cold sensation); 5. Eleventh cranial nerve palsy; 6. Stereoanesthesia. (Remember the mnemonic CANDES or DESCAN) Among these, cape distribution of sensory loss, eleventh cranial nerve palsy and cold dysesthesia (not numbness or tingling sensation) are of great importance for topological diagnosis. We also pointed out the similarities between the clinical picture of syringomyelia and that of the advanced stage of foramen magnum tumor. The syringomyelic syndrome, often seen in Arnold-Chiari malformation and basilar impression, has been attributed to the concurrent syrinx of cervical cord. But the clinical analysis of foramen magnum tumors showed that this is not always true and that compressive lesions at the foramen magnum alone can cause syringomyelic syndrome.

Accessory Nerve

Microanatomy of retia mirabilia of bowhead whale foramen magnum and mandibular foramen.

The morphology of vessels of the cervical rete mirabile near the region of the foramen magnum of the bowhead whale, Balaena mysticetus, as well as of retial vessels of the mandibular foramen was studied by light and transmission electron microscopy. A comparison of arterial and venous components of the mandibular rete revealed considerable arterial branching and arteriovenous anastomoses. Although the small arteries of bowhead retia contained the same layers found in nonretial arteries, several distinctive morphologic features were evident. These included wide separation by collagenous connective tissue and small size of individual smooth muscle cells of the tunica media. These myocytes also contained considerable perinuclear glycogen and communicated minimally with adjacent myocytes by small foot-like cytoplasmic appendages as well as branching of basement membranes. Ganglia-like neural plexuses were observed within the tunica media of arterial retia. Endothelial cells lining the intima demonstrated loose peripheral edges which frequently projected into the vessel lumen, and these cells rested upon a subjacent layer of reticular fibers. It is known for some species that the retial supply to the brain in whales largely supplants an internal carotid arterial supply and that the spinal cord is supplied by retia. The physiologic role of the bowhead mandibular retia remains unknown. The retia mirabilia of cetaceans are considered as one of the morphologic adaptations which modulate hemodynamics during diving and resurfacing. The morphologic features of these vessels in the bowhead whale, as revealed by electron microscopy, appear to reflect the capability to respond in a slow but sustained manner to diving, and the large glycogen deposits may help sustain vascular myocyte metabolism during prolonged submersion.

Animals

Hoarseness as the sole presenting symptom of foramen magnum meningioma.

Foramen magnum tumours are rare. They may present with bizarre symptoms and mimic many conditions. We report a presentation with the sole complaint of hoarseness, never previously described in the literature. Voice returned to normal after surgical removal of the foramen magnum meningioma.

Aged

Growth of the foramen magnum in achondroplasia.

Foramen magnum growth curves in achondroplasia and in the general population are presented. The achondroplastic foramen magnum is small at birth, and during the first year it has a severely impaired rate of growth especially in the transverse dimension. This markedly diminished growth results not only from abnormal endochondral bone growth but also because of abnormal placement and premature fusion of the synchondroses. Evaluation of the foramen magnum in achondroplasia should address absolute size of the transverse and sagittal dimensions, shape, and growth centers to determine growth potential of this area.

Achondroplasia

Position and orientation of the foramen magnum in higher primates.

The location of the foramen magnum, with respect to the longitudinal axis of the cranium, and its orientation with respect to the Frankfurt Horizontal, have been studied in a total of 328 modern human and Pan crania. The samples were chosen in order to examine the effect of overall size difference on foramen magnum disposition. Foramen position (expressed as three indices) and inclination are relatively invariant among the modern human samples, but the foramen magnum is consistently, and statistically significantly, more anteriorly located in Pan paniscus than in Pan troglodytes. Sexual dimorphism is virtually non-existent. There is an apparent allometric effect on foramen position, but not on inclination, so that larger crania in the modern human and Pan paniscus samples tend to have more posteriorly situated foramina. The disposition of the foramen is unrelated to cranial base angle or facial prognathism, except that in Pan paniscus its relative anterior location is linked with the more flexed cranial base in that species. These results provide a comparative context for the examination of differences in foramen magnum disposition in fossil hominids. Differences in foramen magnum position and orientation between KNM-ER 1813 and A. africanus are most unlikely to be due to within-taxon variability.

Animals

Effects of age and gender on the location and orientation of the foramen magnum in rhesus macaques (Macaca mulatta).

Endocasts from 378 rhesus macaque skulls from the Cayo Santiago skeletal collection were measured to determine the effects of age and gender on the position and orientation of the foramen magnum. The foramen magnum migrates from a rostral to a caudal position and its angle changes during postnatal development. The angles and relative positions of the foramen magnum are similar for both genders of infants and for both genders of adults. However, analyses of linear response and plateau (LRP) functions reveal significant differences between males and females in the timing of reorientation of the angle and migration of the foramen magnum. The mean adult angle and relative position of the foramen magnum are reached by 4.7 years in females, but they do not achieve their adult values until 7.1 years in males. A similar pattern is observed for the brainstem region of the basicranium. Mean adult lengths of the brainstem region are reached at 5.2 years in females and 7.1 years in males. The relationships between cranial capacity, the growth pattern of the brainstem, and the pattern of change for the angle and the relative position of the foramen magnum are examined. Quantification of the effects of age and gender on the location of the foramen magnum in a large sample of endocasts from one species of higher primate has potential implications for research on human development, and for interpretation of juvenile specimens in the hominid fossil record.

Age Factors

Variations in the shape of foramen magnum in Indian skulls.

200 skulls from anthropology museum of GSVM Medical College, Kanpur, U.P., India, were studied to note the variations in the shape of foramen magnum. Foramen magnum was found to be variable in shape: Shapes noted were oval (64%), hexagonal (24.5%), pentagonal (7.5%), irregular (3.5%) and round (0.5%). The findings are hitherto not reported.

Foramen Magnum

Morphometric analysis of the foramen magnum in Pekingese dogs.

The size and shape of the foramen magnum were studied in skulls from 75 adult and 5 juvenile Pekingese dogs. After maceration of the skulls, the height, width, and area of each foramen magnum were measured, and various skull indices were determined. The shape of the foramen varied from ovoid to rectangular and had a dorsal notch in all but 2 skulls. Prolapse of cerebellum or brain stem through the enlarged opening was prevented by a fibrous membrane covering the dorsal notch. Mean +/- SD area of the foramen was 138.1 +/- 26.1 mm2; its mean total height was 15.0 +/- 2.9 mm, and its mean maximal width was 13.3 +/- 1.1 mm. Statistically, variability in the area of the foramen was mainly correlated with total height of the foramen, including the dorsal notch. Total height of the foramen was not correlated with age or gender. The degree of dysplasia, notch index, and occipital index of each foramen magnum were determined. To allow a more accurate evaluation of the morphology of the foramen, the foramen magnum index, defined as the ratio between the maximal width and the total height of the foramen, was also computed. Mean +/- SD foramen magnum index was 91.8 +/- 17.1 in the adult Pekingese dogs. Foramen magnum index was not significantly correlated with age, but was significantly larger in male than in female dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging

Surgical approaches to foramen magnum meningioma--report of three cases.

Although foramen magnum meningiomas are usually removable, their location poses considerable surgical risk. The authors present three cases of foramen magnum meningioma. The first involved a ventral type tumor extending to the second cervical body. Following bilateral mandibulotomy, surgery was performed via the anterior transoral approach and the tumor was totally removed. Nine days postoperatively, she developed meningitis, which was successfully treated with antibiotics. The second patient's tumor was dorsal type and was deeply embedded in the lateral part of the vermis. The tumor was totally removed via the midline suboccipital approach and she recovered uneventfully, with only slight upper-extremity paresthesia. In the third case, the tumor was ventral type and situated mainly in the clivus. Craniotomy was performed by the bilateral suboccipital approach and extended nearly to the jugular tubercle. The tumor, which severely displaced the lower cranial and upper cervical nerves, was totally removed. The postoperative course was lengthy and complicated. Artificial ventilation was required for 2 months, and difficulty in swallowing persisted during long-term follow-up. As illustrated by the second case, dorsal and lateral type foramen magnum meningiomas can usually be removed via the lateral suboccipital approach. In the case of ventral type tumors, the anterior transoral approach entails the risk of infection, as occurred in the first case. The authors conclude that the lateral suboccipital approach is preferable; craniotomy extending to the jugular tubercle lowers the risk of brainstem damage.

Adult

Morphometric analysis of the foramen magnum in German shepherd dogs (Alsatians).

In this study, a total of 32 skulls from German Shepherd (Alsatian) puppies were used. These animals were divided into two groups and examined individually. Group 1 included the puppies of between 43-60 days old. Group 2 included the puppies of between 61-107 days old. We based our study on the changes in shape and size of the foramen magnum and the correlation of normal craniometric measurements in the German Shepherd puppies. In group 1, a maximum width of the foramen magnum of 15.55 mm, a height of the foramen magnum of 14.38 mm and a foramen magnum index of 92.67 were observed. In group 2, a maximum width of the foramen magnum of 17.49 mm, a height of the foramen magnum of 16.34 mm and a foramen magnum index of 93.51 were measured. A high positive correlation was found between the maximum width and height of the foramen magnum, the maximum width of the occipital condyles, the maximum width of the bases of the jugular processes, the skull height, the height of the occipital triangle, the skull length from prosthion to basion and the skull length from prosthion to the caudal borders of the occipital condyles. A negative correlation was observed between the width and height of the foramen magnum and indices. Although there was no relation between the foramen magnum index and the age of the animals, an important difference was found between groups 1 and 2. A negative correlation was observed between the foramen magnum index and the rate of increase in the cranial volume. In all the animals examined, the dorsal bone of the foramen magnum was closed, therefore any extension or dorsal notch was not seen. Such an extension or dorsal notch of the foramen magnum in the German Shepherd puppies may therefore be the result of a pathological condition.

Aging

[An operated case of foramen magnum neurinoma (author's transl)].

A 36-year-old male with craniospinal type of foramen magnum neurinoma removed totally was reported. Foramen magnum neurinoma shows various clinical symptoms called foramen magnum syndrome but none of them is specific. Therefore almost all the cases in the literature have been misdiagnosed as degenerative or demyelinating diseases. The best way for correct diagnosis is to suspect the existence of the tumor. Conventional suboccipital craniectomy has been adopted to remove the tumors. But craniospinal type of this tumor usually develops in the anterior part of the foramen magnum. Therefore we approached to the tumor from aside in the lateral position. In this approach, we can avoid tissue damage of cerebellum and medulla due to retraction and can reach near the midportion of the posterior fossa. The importance of checking respiration during surgery is also emphasized, because surgical intervention is carried out around the medulla oblongata.

Adult

Multiplanar metrizamide-enhanced CT imaging of the foramen magnum.

Definition of masses and malformations at the foramen magnum has been less than optimal with traditional radiographic techniques. The use of intrathecal metrizamide with computed tomographic (CT) scanning improves contrast resolution and facilitates detection of abnormalities that may not be apparent on Pantopaque cisternography, plain films, or conventional axial CT alone. Fifty patients with clinically suspected foramen-magnum lesions were evaluated with this technique. Forty were abnormal with the following findings: 14 cases of the Chiari malformation (five cases had associated syringomyelia), five meningiomas, three neuromas, a chondrosarcoma, a chordoma, and five cervical and three brainstem gliomas. Six cases of syringomyelia, a large posterior-fossa subarachnoid cyst, and an anomaly of the cisterna magna were also diagnosed. Sagittal and coronal images were beneficial in defining tonsillar position, configuration of the fourth ventricle, and the relations of mass lesions to the spinal canal and subarachnoid space. Metrizamide CT cisternography provides superior spatial and contrast resolution of lesions at the foramen magnum not obtainable with other radiographic techniques. Morbidity is minimal because of the low dose of metrizamide used. Multiplanar reformations are particularly helpful in assessing anatomic detail not readily recognized on axial scans alone.

Adolescent

Foramen magnum decompression for cervicomedullary encroachment in craniometaphyseal dysplasia: case report.

OBJECTIVE AND IMPORTANCE: Foramen magnum encroachment has been cited as a potential cause for the premature demise of patients afflicted with craniometaphyseal dysplasia (CMD). To our knowledge, the association of Chiari malformation and syringomyelia with CMD has not been previously reported. We describe our evaluation and surgical treatment of a patient presenting with CMD, foramen magnum stenosis, Chiari I malformation, and syringomyelia. CLINICAL PRESENTATION: A 15-year-old female patient with CMD presented with severe headaches and progressive myelopathy. Evaluation by computed tomography and magnetic resonance imaging revealed mild ventriculomegaly, cervicomedullary compression secondary to Chiari I malformation and foramen magnum stenosis, and C3-T10 syringomyelia. INTERVENTION: Foramen magnum decompression was performed via suboccipital craniectomy, C1-C2 laminectomy, and dural augmentation. Dysplastic bone was revealed to be extremely thick and mineralized. Removal required lengthy and extensive drilling. The postoperative course was complicated by prolonged intubation secondary to airway obstruction and a perforated duodenal ulcer. Airway obstruction was attributed to severe nasopharyngeal bony dysplasia and soft tissue edema. The use of steroids in the treatment of airway edema and delayed enteral feeding was thought to contribute to ulcer development. Nevertheless, neurological symptoms improved dramatically. CONCLUSION: Foramen magnum decompression can be used to treat life-threatening cervicomedullary compression in patients with CMD. However, caution should be used because surgical intervention may be associated with a higher incidence of complications because of lengthy procedures and the spectrum of craniofacial impairments in patients with CMD.

Adolescent

Clinical utility of magnetic corticospinal tract stimulation at the foramen magnum level.

We applied magnetic stimulation of the corticospinal tract at the foramen magnum level to 19 patients with various neurological disorders. Results were consistent with our previous speculation that activation occurs at the foramen magnum level. This method was clinically useful for the following conditions. (1) Detection of subclinical lesion: one patient who had transient ischemic attack that caused no clinical symptoms at examination was shown to have dysfunction of the corticospinal tract. (2) Multiple lesions: our method disclosed at least one lesion above and below the foramen magnum in two patients with multiple sclerosis. (3) Unmasking of dysfunction of the corticospinal tract masked by peripheral neuropathy: magnetic stimulation showed conduction delay in the corticospinal tract in two patients in whom no pyramidal signs were evident because of muscular atrophy due to neuropathy. One patient had multiple sclerosis and chronic inflammatory demyelinating polyradiculoneuropathy, the other had degenerative ataxia and neuropathy. (4) Association of disorders: conduction delay rostral to the foramen magnum, which should not occur in patients with only cervical myelopathy, was shown in a patient with cervical myeloradiculopathy and amyotrophic lateral sclerosis. We conclude that this magnetic stimulation method which is less painful than electrical stimulation has extensive clinical usefulness.

Adult

[Case report of tumors in the area of the foramen magnum].

This case study describes a spindle cell glioblastoma of the medulla oblongata (foramen magnum region) in a decreased patient aged 35 years. At the beginning of the illness which lasted about 7 months, the symptoms were quite uncharacteristic, and major neurological failure accompanied by tetraparesis and bulbar symptoms appeared only during the terminal phase, which was of several weeks duration. The specific clinical and diagnostic features of tumours at the magnum foramen, which account for only about 1% of all tumours of the CNS, and the difficulties they entail are described.

Adult

[Foramen magnum tumor--the diagnosis and surgical approach].

The seven cases of the foramen magnum tumors were presented with the clinical manifestations and surgical consideration. Early clinical symptoms of the cases with extramedullary lesions were suboccipital neck pain followed by dysesthesia, clumsiness of hand and weakness. On the other hand, early symptoms of the cases with intramedullary lesions were dysesthesia, often followed by swallowing difficulty or hoarsness, which may have some difference from the clinical course of the extramedullary tumor cases. CT scan was remarkably useful in the diagnosis of the foramen magnum tumor. Surgical treatment was done to 6 cases: Five of these cases were operated by suboccipital craniectomy, and one case with an anteriorly located meningioma in the foramen magnum region was operated by transoral approach. Total removal could be performed in the case without damage to the medulla or spinal cord. The surgical treatment was reviewed, and the approach appropriate to tumor location around the foramen magnum should be selected.

Adolescent

Radiological diagnosis of mass lesions within and adjacent to the foramen magnum.

Masses within or adjacent to the foramen magnum may present difficult clinical problems. They may sometimes be misdiagnosed as degenerative disease of the central nervous system, cervical spondylosis, or even cervical disk disease. In most cases, roentgenographyis necessary for proper diagnosis. The anatomy of the region of the foramen magnum is reviewed and 13 cases representing various diseases are presented. Alterations in the regional arterial and venous anatomy are emphasized.

Adult

A morphological comparison of the foramen magnum of the male Middle Kyushuites with that of other ethnological groups.

The foramen magnum of the male Middle Kyushuites was examined by both osteoscopic and osteometric methods. In the osteoscopic study, the two-semicircular shape was the most numerous as in the case of the adult Germans. The breadth and the index of the foramen magnum did not show any significant differences between the male Middle Kyushuites and the other ethnological groups, while the length of the foramen magnum was shorter than that of the others with a statistical significance. The mean length of the foramen magnum of the Kikai-islanders was the longest among the Japanese.

Adult