The vestibulocochlear nerve (VIII).

The vestibulocochlear nerve (8th cranial nerve) is a sensory nerve. It is made up of two nerves, the cochlear, which transmits sound and the vestibular which controls balance. It is an intracranial nerve which runs from the sensory receptors in the internal ear to the brain stem nuclei and finally to the auditory areas: the post-central gyrus and superior temporal auditory cortex. The most common lesions responsible for damage to VIII are vestibular Schwannomas. This report reviews the anatomy and various investigations of the nerve.

The lower cranial nerves: IX, X, XI, XII.

The lower cranial nerves innervate the pharynx and larynx by the glossopharyngeal (CN IX) and vagus (CN X) (mixed) nerves, and provide motor innervation of the muscles of the neck by the accessory nerve (CN XI) and the tongue by the hypoglossal nerve (CN XII). The symptomatology provoked by an anomaly is often discrete and rarely in the forefront. As with all cranial nerves, the context and clinical examinations, in case of suspicion of impairment of the lower cranial nerves, are determinant in guiding the imaging. In fact, the impairment may be located in the brain stem, in the peribulbar cisterns, in the foramens or even in the deep spaces of the face. The clinical localization of the probable seat of the lesion helps in choosing the adapted protocol in MRI and eventually completes it with a CT-scan. In the bulb, the intra-axial pathology is dominated by brain ischemia (in particular, with Wallenberg syndrome) and multiple sclerosis. Cisternal pathology is tumoral with two tumors, schwannoma and meningioma. The occurrence is much lower than in the cochleovestibular nerves as well as the leptomeningeal nerves (infectious, inflammatory or tumoral). Finally, foramen pathology is tumoral with, outside of the usual schwannomas and meningiomas, paragangliomas. For radiologists, fairly hesitant to explore these lower cranial pairs, it is necessary to be familiar with (or relearn) the anatomy, master the exploratory technique and be aware of the diagnostic possibilities.

Facial nerve: from anatomy to pathology.

The facial nerve (CN VII) emerges from the facial nerve nucleus in the pons. It is accompanied by CN VIII along its cisternal pathway, as well as at the internal auditory meatus. Its petrous pathway includes a labyrinthine segment, a horizontal tympanic segment and a vertical mastoid segment until the stylomastoid foramen. It then continues to the parotid gland. Pontine impairment is usually associated with other neurological symptoms. Lesions of the cerebellopontine angle (most often meningioma and schwannoma) initially result in impairment of CN VIII. The impairment of CN VII takes second place. Peripheral impairment (outside of a traumatic context) is most often due to Bell's palsy.

Brain infections.

Brain infections are relatively rare, but they are potentially serious and have a poor prognosis. The cornerstone of the diagnosis is cerebrospinal fluid (CSF) analysis. Imaging is not systematic, but the indications of imaging are broad, particularly when faced with suspected focal damage, depending on the characteristics of the patient (child, immunosuppressed patient, geographic origin, etc.). It is based on MRI, which allows for aetiological diagnosis and an extension evaluation. In addition, in a certain number of cases, the type of infection is not known and it is up to the MRI via use of an exhaustive technique to diagnose an infectious origin when faced with a mass syndrome. This technical mastery, associated with knowledge of major brain infections, their method of contamination and their particular appearance on the MRI, should make it possible for the radiologist to fulfill his or her diagnostic role.

[Skull base osteomyelitis]. / Ostéite de la base du crâne.

Skull base osteomyelitis is a rare but serious infection. It typically afflicts immunosuppressed patients and should be suspected in patients with persistent otitis complicated by cranial nerve palsy (VII, IX and XII). The most frequent germ is pseudomonas aeruginosa. Contiguous spread of infection occurs along neurovascular structures and weaker regions of the skull base, then into the soft tissue compartments of the face and nasopharynx. Diagnosis and treatment should be made early for this disease with poor prognosis and high mortality.

[Pathology of the cerebellopontine angle]. / Pathologie de l'angle pontocérébelleux.

The pathology of the cistern of the cerebellopontine angle is primarily that of the nervous and vascular structures that it contains and of the meninges that line it. Knowledge of its anatomy makes it possible to understand and search for a rare pathology, the hemifacial spasm, due to a conflict between the facial nerve and the vertebral artery and the posterior inferior cerbellerar artery. However, the pathology of the cerebellopontine angle remains especially tumoral. Imaging should not only make the diagnosis but also make an exhaustive, pretherapy, and accurate assessment of the three main tumours found in this area: the vestibular schwannoma, the meningioma, and the epidermoid cyst.

[Infra tentorial tumors]. / Tumeurs de la fosse postérieure.

Infra tentorial tumors in adults are half as frequent as supra tentorial tumors. Extra-axial tumours are more frequent, mainly in the cerebellopontine angle cistern: vestibular schwannomas, meningiomas and epidermoid cysts. Tumors of the pons and cerebellum are fewer but medulloblastomas and hemangioblastomas are located primarily in the cerebellum: they are typical tumors of this area. Tumors of the IV ventricle are represented primarily by papilloma and ependymoma. The role of imaging is to ascertain the tumoral nature of the lesion and to determine its location.

[Imaging of postoperative lumbar spine]. / Imagerie du rachis lombaire opéré

Complications following lumbar spine surgery are reported to occur in 15 to 30% of cases. Acute postsurgical complications (hematoma, infection.) require urgent imaging. Imaging of recurrent pain following lumbar surgery, often with a clinical presentation that is poorly specific in nature, is sometimes difficult. Selection of the initial imaging technique must simplify the diagnostic work-up. Because of its high contrast resolution, pre- and postcontrast MRI is the most effective imaging technique. Noncontrast CT may be added to facilitate detection of bony abnormalities. Diskography with post-diskogram CT can be added as well in patients with discordant results at clinical and imaging work up. The main causes of failed back syndrome are recurrent disk herniation (usually easily diagnosed), postsurgical granulation tissue/epidural fibrosis (diagnosed based on imaging) and central or lateral bony spinal stenosis. Spondylodiskitis, arachnoiditis and pseudomeningocele are other less frequent etiologies.

Functional MR imaging in assessment of language dominance in epileptic patients.

The value of functional MR Imaging (fMRI) in assessing language lateralization in epileptic patients candidate for surgical treatment is increasingly recognized. However few data are available for left-handed patients. Moreover determining factors for atypical dominance in patients investigated with contemporary imaging have not been reported. We studied 20 patients (14 males, 6 females; 9 right handed, 11 left handed) aged from 9 to 48 years, investigated for intractable partial epilepsy. Epileptic focus location was temporal in 14 cases, extratemporal in 6, and lateralized in the left hemisphere in 11/20. Hemispheric dominance for language was evaluated by both Wada test and fMRI using a silent word generation paradigm in all patients. Furthermore, a postictal speech test was performed in 15 patients. An fMRI language lateralization index was calculated from the number of activated pixels (Student's t test, P < 0.0001) in the right and left hemispheres. The Wada test showed a right hemispheric dominance in 8 patients (6 were left handed and 2 right handed) and a left hemispheric dominance in 12 patients (5 were left handed and 7 right handed). These results were concordant with clinical postictal examination in 11/15 patients (73%). Clinical status did not allow a conclusion about hemispheric dominance for the remaining 4 patients. FMRI was concordant with the Wada test in 19/20 cases. For one left-handed patient, fMRI showed bilateral activation, whereas the Wada test demonstrated a right hemispheric dominance. Right language lateralization was significantly correlated with left lateralized epilepsy (P < 0.05) but was not correlated with age at epilepsy onset, early brain injury (before 6 years), and lobar localization of epileptogenic focus. However the lack of a significant relationship between these factors and atypical language lateralization may be related to the small sample size.

Sensorimotor cortical activity in patients with complete spinal cord injury: a functional magnetic resonance imaging study.

Residual activation of the cortex was investigated in nine patients with complete spinal cord injury between T6 and L1 by functional magnetic resonance imaging (fMRI). Brain activations were recorded under four conditions: (1) a patient attempting to move his toes with flexion-extension, (2) a patient imagining the same movement, (3) passive proprio-somesthesic stimulation of the big toes without visual control, and (4) passive proprio-somesthesic stimulation of the big toes with visual control by the patient. Passive proprio-somesthesic stimulation of the toes generated activation posterior to the central sulcus in the three patients who also showed a somesthesic evoked potential response to somesthesic stimulation. When performed under visual control, activations were observed in two more patients. In all patients, activations were found in the cortical areas involved in motor control (i.e., primary sensorimotor cortex, premotor regions and supplementary motor area [SMA]) during attempts to move or mental imagery of these tasks. It is concluded that even several years after injury with some local cortical reorganization, activation of lower limb cortical networks can be generated either by the attempt to move, the mental evocation of the action, or the visual feedback of a passive proprio-somesthesic stimulation.

Unusual lesions of the cerebellopontine angle: a segmental approach.

Tumors of the cerebellopontine angle (CPA) are frequent; acoustic neuromas and meningiomas represent the great majority of such tumors. However, a large variety of unusual lesions can also be encountered in the CPA. The site of origin is the main factor in making a preoperative diagnosis for an unusual lesion of the CPA. In addition, it is essential to analyze attenuation at computed tomography (CT), signal intensity at magnetic resonance (MR) imaging, enhancement, shape and margins, extent, mass effect, and adjacent bone reaction. CPA masses can primarily arise from the cerebellopontine cistern and other CPA structures (arachnoid cyst, nonacoustic schwannoma, aneurysm, melanoma, miscellaneous meningeal lesions) or from embryologic remnants (epidermoid cyst, dermoid cyst, lipoma). Tumors can also invade the CPA by extension from the petrous bone or skull base (cholesterol granuloma, paraganglioma, chondromatous tumors, chordoma, endolymphatic sac tumor, pituitary adenoma, apex petrositis). Finally, CPA lesions can be secondary to an exophytic brainstem or ventricular tumor (glioma, choroid plexus papilloma, lymphoma, hemangioblastoma, ependymoma, medulloblastoma, dysembryoplastic neuroepithelial tumor). A close association between CT and MR imaging findings is very helpful in establishing the preoperative diagnosis for unusual lesions of the CPA.

Fibrous pseudotumor of the epididymis: imaging and pathologic correlation.

We report the case of a 25-year-old man who presented a fibrous pseudotumor of the epididymis, a rare focal location of nodular and diffuse fibrous proliferation. We provide the ultrasonographic and MRI findings with pathologic correlation.

[The foramen rotundum. Anatomy and radiological explorations. Pathology]. / Le foramen rond. Anatomie et exploration radilogiques. Patholgie.

The foramen rotundum is a small canal deeply situated in the base of the skull which represents the way of exit of the maxillary nerve, second branch of the trigeminal nerve. Its precise individualization and analyse is difficult and necessitates a precise and adapted technique as well as a precise knowledge of its anatomical relationships. Its represents a frontier area between the endo- and exocranial spaces. Its involvement which is preferentially related with tumoral pathologies (and particularly with retrograde perineural invasion) profoundly modifies the prognosis of the disease and so should allow soon a multidisciplinary therapeutic discussion.

[Agenesis of the internal carotid artery: two cases report]. / Agénésie de l'artère carotide interne: à propos de deux cas.

The authors report two cases of agenesis of the internal carotid artery evaluated with MR angiography allows the diagnosis of the internal carotid artery agenesis and appreciates both the supply post.

[Clinical application of functional MRI: a strategic tool for neurosurgery]. / Application clinique de l'IRM fonctionnelle: aide à la stratégie neurochirurgicale.

The purpose was to incorporate preoperative functional imaging data into anatomic data of operative microscope for neurosurgical procedures of patients suffering from lesions contiguous to eloquent brain areas. The day before surgery, patients bearing scalp markers underwent fMRI, just before anatomical contrast-enhanced MR images. FMRI data analysis were realised using a t test (p<0.0001). The resulting functional-anatomical images were downloaded onto a surgical neuronavigation computer in order to outline tumoral target and functional areas. At surgery, cortical stimulation has been used to confirm functional data. Functional image-guided surgery of lesions abutting functional cortex can be safely performed.

Functional MR imaging and traumatic paraplegia: preliminary report.

PURPOSE: To evaluate residual activity in the sensorimotor cortex of the lower limbs in paraplegia. METHODS: 5 patients suffering from a complete paralysis after traumatic medullar lesion (ASIA=A). Clinical evaluation of motility and sensitivity. 1. Control functional MR study of the sensorimotor cortex during simultaneous movements of hands, imaginary motor task and passive hands stimulation. 2. Concerning the lower limbs, 3 fMRI conditions: 1-patient attempts to move his toes with flexion-extension, 2-mental imagery task of the same movement, 3-peripheral passive proprio-somesthesic stimulation (squeezing) of the big toes. RESULTS: Activations were observed in the primary sensorimotor cortex (M1), premotor regions and in the supplementary motor area (SMA) during movement and mental imaginary tasks in the control study and during attempt to move and mental imaginary tasks in the study concerning the lower limbs. Passive somesthesic stimulation generated activation posterior to the central sulcus for 2 patients. CONCLUSION: Activations in the sensorimotor cortex of the lower limbs can be generated either by attempting to move or mental evocation. In spite of a clinical evaluation of complete paraplegia, fMRI can show a persistence of sensitive anatomic conduction, confirmed by Somesthesic Evoked Potentials.

[Contribution of MRI in the dynamic study of the lacrimal outflow system]. / Apport de l'IRM dans l'étude dynamique des voies lacrymales d'excrétion.

PURPOSE: To evaluate a new magnetic resonance imaging protocol for dynamic study of the lacrimal outflow system and to use this protocol to search for problems in patients with an assumed permeable outflow system who develop epiphora. PATIENTS AND METHODS: A prospective study of nine patients, including 2 asymptomatic controls was conducted. The magnetic resonance protocol included, gadolinium instillation into the conjunctival cul-de-sac, 3D gradient-echo T1-weighted acquisition, 2 mm thick images passing through the nasolacrimal duct, dynamic acquisition after gadolinium instillation for timing dye progression through the outflow system. RESULTS: Similar results were obtained for the two control subjects with lacrimal transit time of a median 100 seconds. Three distinct events were individualized gadolinium arrival in the lacrimal sac (t1), at the extremity of the bony portion of the lacrimal duct (té), and the extremity of the mucosal portion of the duct (t3). Patients with an assumed permeable outflow system who had epiphora show results intermediary between passed dye and total blockage of the dye within the lacrimal sac. CONCLUSION: The study of the lacrimal outflow system using this new magnetic resonance imaging protocol contributes to the physiological study of tear evacuation and could be useful for quantitative assessment of lacrimal stenosis, particularly interesting for therapeutic guidance.