[Paraclinoid region: descriptive anatomy and radiological correlations with MR imaging]. / La région paraclinoïdienne: anatomie descriptive et corrélations radiologiques en imagerie par résonance magnétique.

OBJECTIVE: The paraclinoid region has a complex anatomy. The purpose of this study was to depict in details its anatomical landmarks and their radiological translations with magnetic resonance imaging (MRI). MATERIAL AND METHOD: Ten anatomical specimens (20 paraclinoid regions) were prepared, then dissected and further analyzed with MRI in order to describe their important radio-anatomical structures (dural folds, osseous surfaces, arteries and nerves) along with their course and measurements, and the reference points of the carotid distal dural ring. The paraclinoid MR protocol consisted in a T2 high-resolution sequence with thin and contiguous slices acquired in a coronal (diaphragmatic) and sagittal oblique (carotid) plane. Reproducibility in living subjects was evaluated on 15 patients (30 paraclinoid regions). Statistical comparison was made between laboratory and MR measurements obtained on cadavers. RESULTS: A detailed description of paraclinoid anatomy and structures was provided. Its landmarks were satisfactorily identified with the dedicated MR protocol. Reproducibility in living subjects was obtained. No statistical difference was found between laboratory and MR measurements. CONCLUSION: This study provides a precise description of paraclinoid anatomical structures and their radiological correlations. This paraclinoid MR protocol allows locating paraclinoid lesions in comparison with the cavernous sinus roof, which is of paramount importance for the management of paraclinoid carotid artery aneurysms.

Morphological evidence for direct interaction between gonadotrophin-releasing hormone neurones and astroglial cells in the human hypothalamus.

In rodents, there is compelling evidence indicating that dynamic cell-to-cell communications involving cross talk between astroglial cells (such as astrocytes and specialised ependymoglial cells known as tanycytes) and neurones are important in regulating the secretion of gonadotrophin-releasing hormone (GnRH), the neurohormone that controls both sexual maturation and adult reproductive function. However, whether such astroglial cell-GnRH neurone interactions occur in the human brain is not known. In the present study, we used immunofluorescence to examine the anatomical relationship between GnRH neurones and glial cells within the hypothalamus of five women. Double-staining experiments demonstrated the ensheathment of GnRH neurone perikarya by glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte processes in the periventricular zone of the tuberal region of the hypothalamus. GFAP immunoreactivity did not overlap that of GnRH at the GnRH neurone's projection site (i.e. the median eminence of the hypothalamus). Rather, human GnRH neuroendocrine fibres were found to be closely associated with vimentin or nestin-immunopositive radial glial processes likely belonging to tanycytes. In line with these light microscopy data, ultrastructural examination of GnRH-immunoreactive neurones showed numerous glial cells in direct apposition to pre-embedding-labelled GnRH cell bodies and/or dendrites in the infundibular nucleus, whereas postembedding immunogold-labelled GnRH nerve terminals were often seen to be enwrapped by glial cell processes in the median eminence. GnRH nerve button were sometimes visualised in close proximity to fenestrated pituitary portal blood capillaries and/or evaginations of the basal lamina that delineate the pericapillary space. In summary, these data demonstrate that GnRH neurones morphologically interact with astrocytes and tanycytes in the human brain and provide evidence that glial cells may contribute physiologically to the process by which the neuroendocrine brain controls the function of GnRH neurones in humans.

[MRI localization of paraclinoid carotid aneurysms]. / Localisation en IRM des anevrismes carotidiens paraclinoidiens.

AIM: The distal dural ring plane (DDRP) separates the intracavernous from the supracavernous paraclinoid internal carotid artery. The purpose of this MRI protocol is to evaluate the position of this plane for the characterization of paraclinoid aneurysms. METHOD: The protocol uses a T2 weighted sequence in two orthogonal planes (diaphragmatic and carotid planes) and two correlation lines in each plane. These lines pass through anatomo-radiological reference points correlated with the medio-lateral and antero-posterior margins of the DDRP. We use the intersection angle of these lines as the inferior radiological limit of the DDRP curve. RESULTS: An aneurysm located above this angle is supracavernous; an aneurysm located below this angle is intracavernous; an aneurysm crossing this angle is transitional. CONCLUSION: In difficult cases, this MRI protocol could help better characterize the exact localization of paraclinoid aneurysms on both sides of the cavernous sinus roof.

A technique of measuring the precision of an MR-guided stereotaxic installation using anatomic specimens.

PURPOSE: To develop a method for direct measurement, using anatomic specimens, of the precision of MR-guided stereotaxic location and to describe its application to a 1.5-T MR unit with a Leksell stereotaxic frame. METHODS: Small pieces of gelfoam (1 X 1 X 1 mm), soaked in gadopentetate dimeglumine, were stereotaxically introduced into formalin-fixed human heads using a Leksell D (three experiments) or G (nine experiments) stereotaxic frame. The head and the frame were then introduced into a 1.5-T MR unit. The target coordinates (as set on the stereotaxic frame by one investigator) were then compared with the MR-determined stereotaxic coordinates (calculated independently by another investigator). The imprecisions Ex, Ey, and Ez in each direction were defined as the differences between the calculated and the chosen coordinates. RESULTS: Regarding the three targets studied with the D frame, mean imprecision Ex was 1.08 +/- 0.50 mm (mean +/- SEM), Ey 0.83 +/- 0.58 mm, and Ez 0.75 +/- 0.25 mm. For the nine targets studied with the G frame, Ex was 0.48 +/- 0.17 mm, Ey 0.69 +/- 0.14 mm, and Ez 0.82 +/- 0.13 mm. Statistical analysis of the results showed no significant difference between Ex or Ey and half the size of a pixel, indicating that, in the axial plane, stereotaxic MR precision is limited only by pixel size. A statistically significant difference was observed in the coronal plane between Ez and half the size of a pixel, but it must be stressed that Ez remained smaller than 1 mm. CONCLUSION: MR-guided stereotaxic location can be used with confidence for most diagnostic, functional, and therapeutic procedures.

High resolution T1 weighted magnetic resonance imaging of the deep brain structures using a reduced bandwidth.

High spatial resolution T1 weighted images of the brain were acquired in 5-13 min on a whole-body magnetic resonance imager operating at 1.5 T. In order to obtain 5-8 cm field of view images, the receiver bandwidth (Bw) was lowered to 2 kHz. The use of a 2 kHz Bw, instead of the standard 16 kHz Bw, partially compensated the signal loss due to the small pixel size by increasing the signal-to-noise ratio, without scan time penalty. The chemical shift artifact associated with reduced Bw was not observed because fat signal is negligible in the brain.

Anatomic study of arcus tendineus fasciae pelvis.

OBJECTIVE: To describe the anatomy of the arcus tendineus fasciae pelvis. MATERIAL AND METHODS: Two fixed female cadaver pelvises (88 and 66 years old) were dissected. RESULTS: The arcus tendineus fasciae pelvis is a 10-cm-long fibrous thickening of the pelvic fascia which is medial to the obturator internus muscle and lateral to the peritoneum. It is inserted on the ischiatic spine and courses downward and anteriorly to the pubovesical ligament. The posterior third of the arcus tendineus fasciae pelvis is fused with the posterior third of the arcus tendineus musculus levatoris ani, forming a curve with upward and anterior concavity. This portion of the arcus tendineus is thick and easy to recognise upon palpation. It is located 1cm slightly above and anterior to the ischiatic spine and 2 cm from of the pudendal vessels, which course around the posterior inferior margin of the ischiatic spine. The superior margin of the median part of the arcus tendineus fasciae pelvis is crossed laterally by vessels for the obturator internus muscle arising from the internal iliac vessels. CONCLUSION: In genital prolapse cure, sutures must be placed through the anterior or median parts of the arcus tendineus fasciae pelvis. In any case, they must remain anterior to the posterior part of the arcus tendineus fasciae pelvis to avoid injury to the pudendal vessels.

[Unilateral paralysis of the glossopharyngeal, vagus and hypoglossal nerves]. / Paralysie unilatérale des nerfs glossopharyngien, vague et grand hypoglosse.

A 32-year-old woman complained of swallowing difficulty after a general seizure. Neurological examination revealed unilateral palsies of the 9th, 10th, and 12th cranial nerves. CT, MRI and internal carotid artery angiogram were normal. Selective catheterization of the external carotid artery and ascending pharyngeal system suggested a cranial nerve ischaemic arterial syndrome. The apparent sparing of the eleventh nerve may be explained by the double vascularization of this nerve. This may also be related to the double innervation of the trapezius and sterno-cleido-mastoid muscles by the 11th nerve and cervical spinal nerves.

Visibility of cranial nerves at MRI.

In order to assess the value of MRI in the depiction of intracranial nerves, we retrospectively reviewed 60 patients investigated over a 2-year period. The purposes of this study were: 1) to determine the score of MRI in detecting cranial nerves III to XII, and 2) to establish accurate landmarks for easy detection of these nerves. Cranial nerves III, V, VII and VIII are well seen (70 to 100%), very often on axial, sagittal and coronal sections. Nerves IX to XII are correctly studied only on axial planes (81 and 83%), but it is difficult to distinguish between the vagus nerve and the glossopharyngeal and spinal nerves. Due to their oblique direction and small size, nerves IV and VI are seldom visualized. The most important landmarks are the chiasma, the colliculi, Meckel's cavity, the internal auditory canal, the jugular foramen, the hypoglossal canal and the brainstem structures. We suggest the following scanning technique: short spin-echo sequences (TR 600 ms, TE 20 ms), 3 to 5 mm thick contiguous sections, 16 to 20 cm field of view with 4 or 2 excitations respectively, 256 x 256 matrix, and at least one acquisition plane (axial plane), but preferably two or three planes. MRI is a sensitive examination in the recognition of cranial nerves. It should be the first-step exploratory procedure in patients with cranial nerve pathology.

[Identification of the central sulcus using the scanner and MRI]. / Repérage du sillon central en scanner et en IRM.

Methods to directly and indirectly identify the central sulcus are presented. In the axial plan, direct method is remarkable but obviously requires good visualization of the sulci in the central region. Sulci are readily visible in 90% of the cases on CT scans and in 50% of the cases on MRI. The method can also be applied when tumoral development erases the cerebral sulci by direct lecture of the controlateral rolandic region and right-left transfer. Within the precision limits of the method, it can be considered that the central sulci are symmetrical. The main signs are: the relative morphologies of the superior frontal sulcus and the precentral sulcus, the hook-shaped aspect of the middle part of the central sulcus, the internal end of the central sulcus projection anteriorly to the pars marginalis, the bifid nature of the internal end of the posterior central sulcus contouring the pars marginalis, and the lesser thickness of the posterior central gyrus compared with the precentral gyrus. The indirect method is less precise and is used when the direct method is unsuccessful. The central sulcus is identified on the sagittal images and, using the lateral view of the skull as a reference image, the topographic information is transferred to the axial images.

[Anatomic variants of Meckel's cave on MRI]. / Variantes anatomiques du cavum de Meckel en IRM.

Magnetic resonance imaging (MRI) gives an accurate analysis of Meckel's cave variability. Images were acquired in 50 patients with several sections for anatomical comparison. Using several sections, MRI is a suitable method for better analysis of the trigeminal cistern. The most frequent findings are symmetrical trigeminal cisterns. Expansion of Meckel's cave or its disappearance has pathological significance.

[MRI of normal spinal epidural fat]. / IRM de la graisse épidurale rachidienne normale.

The authors perform a retrospective study of 65 spines examined with MRI. They specify the distribution of normal posterior epidural fat and establish the relationship between the anteroposterior thickness of epidural fat and the sagittal diameter of the spine on axial sections. On sagittal sections, the fat has a variable appearance, but a constant location along the spinal canal.

[The normal cranial nerves in MRI. Description and visualization frequency]. / Les nerfs crâniens normaux en IRM. Description et fréquence de visualisation.

In order to assess the value of MR in the depiction of intracranial nerves, we retrospectively reviewed 60 patients investigated over a period of 2 years. The aim of this study was: 1) to assess the score of MR in the detection of cranial nerves III to XII; 2) to determine accurate landmarks allowing for easy detection of those cranial nerves. Cranial nerves III, V, VII, VIII are well seen (70 to 100%), very often in both axial, sagittal and coronal sections. Nerves IX to XII are correctly studied only on axial planes [81 and 83%), but it is difficult to distinguish between the vagal nerve and the glossopharyngeal and spinal nerves. Due to their oblique direction and small size, fourth and sixth nerves are rarely visualized. The more important landmarks are the chiasma, the colliculi, the Meckel's cave, the internal auditory canal, the jugular foramen, the hypoglossal canal and the different brainstem structures. We suggest the following scanning protocol: short spin echo sequences (TR = 600 ms, TE = 20 msec), 3 to 5 continuous sections, 16 to 20 cm field of vue with respectively 4 or 2 excitations, 256 x 256 matrix, with at least one acquisition plane (axial), but preferably two or three planes. Thus MR is sensitive exam in the recognition of cranial nerves, and it must be the first step exam in patients presenting with cranial nerve disease.

[Imaging cranial nerves with inframillimetric T2-weighted MRI]. / Etude des nerfs crâniens en IRM en coupes inframillimétriques T2.

Fifty files were evaluated to determine the normal anatomy of the cranial nerves. All the cranial nerves were studied including the labyrinth, in different planes with a 3DFT-CISS imaging technique. The 3DFT-CISS is especially interesting to study cranial nerves because of the excellent contrast with CSF-fluid and the possibility of thin sections. It might be essential for the diagnosis of neuralgia and cranial nerves paralysis.

[MRI of the spinal epidural fat in pathology]. / IRM de la graisse épidurale rachidienne en pathologie.

The authors report about their experience with the merits of the normal systematization of epidural fat with MRI. On sagittal sections, this fat has a variable appearance, but its location along the spinal canal is constant. On axial sections, its morphology is suggestive of the level of section: cervical, upper or lower thoracic, lumbar. Some changes in this fat are precious data to explain local hypertrophy (scoliosis) or to locate an intra- or extradural process.

[Arcus tendineus fascia pelvis: anatomical study]. / L'arc tendineux du fascia pelvien: étude anatomique.

OBJECTIVE: To reveal the anatomy of arcus tendineus fascia pelvis. MATERIAL: and methods. 2 fixed female cadaver pelvises (88 and 66 years old) were dissected. RESULTS: The arcus tendineus fascia pelvis is a fibrous recess of the pelvic fascia which is 10 cm long, laterally to the obturator internus muscle and medially to the peritoneum. It reaches the ischial spine lower and anteriorly to the pubo-vesical ligament. The third posterior part of the arcus tendineus of the pelvic fascia is commun with the posterior part of the arcus tendineus of the levator ani. This third posterior part is like a curve concave anteriorly. This curve is thick and easy to recognize by the palpation. This third posterior curve is 1cm in front of the ischial spine and 2cm in front of the pudendal vessel which took place behind the ischial spine. The vessels of the obturator internus muscle originated from the internal iliac vessel and crossed laterally the median part of the arcus tendineus of the pelvic fascia. CONCLUSION: Sutures must be placed through the anterior and median part of the arcus tendineus fascia pelvis, in front of the posterior part of the arcus tendineus fascia pelvis to avoid any injury to the pudendal vessels.

[Choice of a technic of stabilization in surgical treatment of recent fractures of the odontoid process. 90 cases]. / Choix d'une technique de stabilisation lors du traitement chirurgical des fractures récentes de l'odontoïde. 90 observations.

The objective of this study is to analyse the advantages and disadvantages of different surgical technics of odontoid process fracture stabilization. We try to find the best indications for each of them. We won't consider stable odontoid fractures which haven't treated by surgical therapy. A review of ninety acute dens fractures since 1979 has been analysed before 1985, the most of our injured person had a surgical stabilization by posterior approach. The analysis of our results had incited us, since that date, to vary our indications, by taking possibilities of anterior approach into consideration. So, have been realized 55 C1-C2 lacings, 20 of which with bone graft, 12 occipito-cervical arthrodesis, 10 screw fixations of odontoid process, 9 atlanto-axial arthrodesis by screw fixations, 2 posterior fixations by CD pediatric instrumentation, 1 Knodt instrumentation, 1 osteosynthesis by trans-oral exposure. Patients have been seen again, 1 month, 3 month, 6 month, 1 year later. Results have been estimated: Clinically by cervical mobility study in rotation and by local pain (16 excellent results, 24 good results, 27 middle results, and 23 bad results); Radiologically by analysis of specific complications of each technic (8 secondary removing, 6 incomplete deplacement corrections, 4 excessive corrections, 3 pseudarthrosis). We have regrouped global results technic by technic. We propose a therapeutic planning in which each technic can find the best result. The objective is to assure an effective retention by preserving movings of superior cervical spine.