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Cranial Neuropathies II, III, IV, and VI
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Tanyatuth Padungkiatsagul, Heather E. Moss
The nucleus of the CN VI is located in the dorsal pons (Figures 22.20, 22.21). The genu of the CN VII fascicle wraps around it, corresponding with facial colliculus on external surface of the pons. The CN VI fascicles travel through the body of the pons ventrally, passing through the cortical spinal tracts. In the posterior fossa, the CN VI ascends from the pontomedullary junction along clivus and passed under Gruber's ligament into Dorello's canal and the cavernous sinus. While in the cavernous sinus, the postganglionic sympathetic fibers to the pupil join the CN VI for a short distance. Ultimately, it innervates the ipsilateral lateral rectus muscle in each eye.
The Facial Nerve and its Non-Neoplastic Disorders
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
Christopher Skilbeck, Susan Standring, Michael Gleeson
Special visceral/branchial efferent (SVE) motor axons supply muscles derived from the second branchial arch, namely the mimetic facial muscles, buccinator, stapedius, platysma, the posterior belly of digastric and stylohyoid. The axons arise from neurons in the facial nuclear complex in the lateral part of the central tegmentum of the pons just rostral to the pons-medulla transition5 and run posteromedially through the pons, arching over the abducens nucleus to raise the facial colliculus on the floor of the fourth ventricle (which may be seen in axial MRI sections), before turning anterolaterally to leave the brainstem. Neurons in the face area of the motor cortex (supranuclear neurons) project bilaterally to facial motor neurons that control muscles in the upper face (frontalis, orbicularis oculi) but contralaterally to facial motor neurons that innervate the muscles of the middle and lower face. However, sparing of the forehead in facial paralysis is not necessarily pathognomonic of a central lesion (see ‘Physical examination’ below). Axons supplying orbicularis oculi constitute the efferent limb of the corneal reflex. Detailed information about the spatial organization of human stapedial motor neurons is unavailable, but findings in guinea pigs, cats and rats suggest that nerve to stapedius may arise from motor neurons that lie outside the main facial motor nucleus.6 The stapedial reflex is used to test for topographical assessment of a facial nerve lesion and to assess cochlear function as it is elicited by a sound impulse of threshold + 80 dB.
Anatomy for neurotrauma
Published in Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor, Essentials of Anesthesia for Neurotrauma, 2018
Vasudha Singhal, Sarabpreet Singh
The pons lies caudal to the midbrain, separated ventrally from the clivus by the cisterna pontis, and dorsally from the cerebellum by the upper part of the rhomboid fossa of fourth ventricle. The cerebellopontine angle, which lies lateral in relation to the pons, contains the roots of CN VII, VIII and IX, and the nervus intermedius, overlying the choroid plexus of the fourth ventricle. The ventral surface of the pons is convex and lodges the basilar artery in a vertical median sulcus. On each side, the ventral surface is continuous with the middle cerebellar peduncle. The motor and sensory roots of the CN V emerge at the junction of the pons and the middle cerebellar peduncle. Bundles of transverse cerebellopontine fibers produce faint ridges or grooves on the ventral surface. The dorsal surface of the pons is formed by the rostral part of the floor of the fourth ventricle. A rounded elevation, called the facial colliculus, on the dorsal surface, is produced by the underlying CN VI nucleus and the internal genu of motor fibers of CN VII.
Microsurgical techniques for achieving gross total resection of ependymomas of the fourth ventricle
Published in Acta Chirurgica Belgica, 2020
Marx and colleagues [51] detail a most interesting and unique microsurgical strategy developed to achieve gross total resection of this traditionally operatively challenging tumor (Figures 3 and 4). The microsurgical technique developed by Marx and colleagues [51], adapted from the experience of El Refaee and colleagues [72] in microsurgically resecting spinal cord tumors, has accordingly excellent in achieving complete removal of ependymomas adherent to the floor of the fourth ventricle, generally precipitating fewer neurologic deficits compared with the classic microsurgical technique of blunt and sharp dissection. In their clinical series, patients were most commonly operated upon in the prone position, with a generous and capacious surgical view and facile access provided via the transtelovelar approach. One patient was trephined in the left lateral decubitus position given significant tumoral extension into the left cerebellopontine angle and one patient was trephined in the sitting position, with appropriate measures taken in order to prevent intraoperative venoatrial air embolism. Tumoral adherence localized to the caudal aspects of the rhomboid fossae in all patients, generally below the level of the facial colliculus [51].
Horizontal gaze palsy and progressive scoliosis—a tale of two siblings with ROBO3 mutation
Published in Ophthalmic Genetics, 2020
Poornima Narayanan Nambiar, Santha Kumar S, Ramshekhar Menon, Sruthi S Nair, GK Madhavilatha, Soumya Sundaram
This case illustrates the classical neuro-ophthalmological and radiological features described in HGPPS (2,3). The oculomotor abnormalities in this syndrome are due to the absence of midline decussation of the oculomotor pathways at the level of pons and medulla (1). ROBO3 plays a role in axonal guidance during embryogenesis, is responsible for hindbrain axon crossing (2). Hence, the mutation in ROBO3 leads to maldevelopment of dorsomedial brainstem structures and impaired decussation of the ascending sensory, descending motor, and oculomotor pathways (1,2). The structure of the pons in this condition is similar to the embryonic metencephalon between 5 and 8 weeks, where the fourth ventricle shows a ventral cleft that splits the dorsal metencephalon, before the dorsomedial nuclei and tracts begin to develop (3). The site of involvement hypothesized for the oculomotor abnormalities in HGPPS includes the paramedian pontine reticular formation (PPRF), abducens nucleus, or the medial longitudinal fasciculus (MLF) (1,3). Bilateral horizontal gaze palsy along with absent horizontal VOR argue for a localization at the level of abducens nucleus and the preserved convergence implies a relative sparing of the midbrain (4). The absence of normal contour of the facial colliculus also implies an agenesis or hypoplasia of the abducens nuclei (3).
Horizontal gaze palsy and progressive scoliosis with two novel ROBO3 gene mutations in two Jordanian families
Published in Ophthalmic Genetics, 2019
Liqa A. Rousan, Abu Baker L. Qased, Ziad A Audat, Laila T. Ababneh, Saied A. Jaradat
All patients had a brain CT scan and/or MRI as part of the investigation of the cause of strabismus. All patients showed the same imaging findings: hypoplastic pons (Figure 4) with a dorsal midsagittal cleft giving a split pons sign best seen on axial images (Figure 5). Absence of the facial colliculi resulting in a tented shape of the floor of the fourth ventricle on axial images (Figure 6). The medulla oblongata was hypoplastic with prominent olivary nuclei with respect to the pyramids, and on the posterior aspect the gracile and cuneate nuclei prominence was absent giving the medulla the typical butterfly appearance (Figure 7). The extraocular muscles were normal distinguishing horizontal gaze palsy and progressive scoliosis from other congenital eye movement disorders.