Distinct rhythm generators for inspiration and expiration in the juvenile rat

Inspiration and active expiration are commonly viewed as antagonistic phases of a unitary oscillator that generates respiratory rhythm. This view conflicts with observations we report here in juvenile rats, where by administration of fentanyl, a selective mu-opiate agonist, and induction of lung reflexes, we separately manipulated the frequency of inspirations and expirations. Moreover, completely transecting the brainstem at the caudal end of the facial nucleus abolished active expirations, while rhythmic inspirations continued. We hypothesize that inspiration and expiration are generated by coupled, anatomically separate rhythm generators, one generating active expiration located close to the facial nucleus in the region of the retrotrapezoid nucleus/parafacial respiratory group, the other generating inspiration located more caudally in the preBötzinger Complex.

Brainstem gliomas

INTRODUCTION

Brainstem gliomas have historically been one of the most difficult pediatric cancers to treat. Tumors arising in the brainstem were once uniformly discounted as surgically unresectable lesions. Early neurosurgeons thought this location to be inoperable and fraught with disaster. The advent of computed tomography (CT), magnetic resonance imaging (MRI), and sophisticated neurophysiological monitoring techniques have significantly advanced the surgical treatment of these precarious lesions.

REVIEW

Brainstem gliomas are now recognized as a heterogenous group of tumors. They have been broadly classified into several categories depending upon the classification scheme. All these classification systems provide a framework to predict growth patterns, surgical resectability, and overall prognosis of these tumors. These systems allow the surgeon to obtain a better understanding of the distinction between low-grade tumors and diffuse inoperable tumor types. The authors review the current literature and management of brainstem tumors.

Magnetic resonance image-directed stereotactic neurosurgery: use of image fusion with computerized tomography to enhance spatial accuracy

Distortions of the magnetic field, such as those caused by susceptibility artifacts and peripheral magnetic field warping, can limit geometric precision in the use of magnetic resonance (MR) imaging in stereotactic procedures. The authors have routinely found systematic error in MR stereotactic coordinates with a median of 4 mm compared to computerized tomography (CT) coordinates. This error may place critical neural structures in jeopardy in sme procedures. A description is given of an image fusion technique that uses a chamfer matching algorithm; the advantages of MR imaging in anatomical definition are combined with the geometric precision of CT, while eliminating most of the anatomical spatial distortion of stereotactic MR imaging. A stereotactic radiosurgical case is presented in which the use of MR localization alone would have led to both irradiation of vital neural structures outside the desired target volume and underdose of the intended target volume. The image fusion approach allows for the use of MR imaging, combined with stereotactic CT, as a reliable localizing technique for stereotactic neurosurgery and radiosurgery.

[Hypersomnia by isthmic lesion in cat. II. Neurophysiological and pharmacological study]

(1) The bilateral destruction of the region of the dorsal norepinephrine bundle in the isthmus or in the mesencephalon induces a significant increase of both paradoxical sleep (PS) (up to 400%) and of slow-wave sleep (SWS). The increase of PS lasts for 4-5 days while the increase of SWS lasts at least 8-10 days. The same phenomenon is observed after total hypophysectomy. (2) control lesions effectuated in the isthmus outside the area of the dorsal norepinephrine bundle do not affect significantly the slee-walking cycle. (3) pretreatment with p-chlorophenylalanine suppresses the increase of sleep if the lesion is effectuated at the time of maximum insomnia, while a significant increase of PS is still observed if the lesion is made at the time of the recovery of sleep. (4) the mechanisms of this hypersomnia are discussed in light of the biochemical results showing an increase of the biosynthesis of serotonin in the rostral raphe system. It is postulated that some neurons of the dorsal norepinephrine bundle might tonically control the activity of the raphe system.

Diffusion tensor imaging and white matter tractography in patients with brainstem lesions

BACKGROUND

Diffusion tensor imaging (DTI) and white matter tractography (WMT) are promising techniques for estimating the course, extent, and connectivity patterns of the white matter (WM) structures in the human brain. In this study, we investigated the ability of DTI and WMT to visualize white matter tract involvement for the preoperative surgical planning and postoperative assessment of brainstem lesions.

METHODS

Preoperative and postoperative DTI data (echo-planar, 1.5T) were retrospectively analyzed in 10 patients with brainstem lesions (3 diffuse, 7 focal). WMT applying a tensor deflection algorithm was used to reconstruct WM tracts adjacent to the lesions. Reconstructed tracts included corticospinal tracts and medial lemnisci. The clinical and imaging follow-up data were also compared and analyzed.

FINDINGS

WMT revealed a series of tract alteration patterns including deviation, deformation, infiltration, and apparent tract interruption. WMT reconstructions showed that the major WM tracts were preserved during surgery and improved in position and appearance postoperatively. These findings correlated with the improvement or preservation of neurological function as determined by clinical assessment.

CONCLUSIONS

Compared with the information provided by conventional MR imaging, DTI and WMT provided superior quantification and visualization of lesion involvement in eloquent fibre tracts of the brainstem. Moreover, DTI and WMT were found to be beneficial for white matter recognition in the neurosurgical planning and postoperative assessment of brainstem lesions.

Real-time image-guided direct convective perfusion of intrinsic brainstem lesions. Technical note

Recent preclinical studies have demonstrated that convection-enhanced delivery (CED) can be used to perfuse the brain and brainstem with therapeutic agents while simultaneously tracking their distribution using coinfusion of a surrogate magnetic resonance (MR) imaging tracer. The authors describe a technique for the successful clinical application of this drug delivery and monitoring paradigm to the brainstem. Two patients with progressive intrinsic brainstem lesions (one with Type 2 Gaucher disease and one with a diffuse pontine glioma) were treated with CED of putative therapeutic agents mixed with Gd-diethylenetriamene pentaacetic acid (DTPA). Both patients underwent frameless stereotactic placement of MR imaging-compatible outer guide-inner infusion cannulae. Using intraoperative MR imaging, accurate cannula placement was confirmed and real-time imaging during infusion clearly demonstrated progressive filling of the targeted region with the drug and Gd-DTPA infusate. Neither patient had clinical or imaging evidence of short- or long-term infusate-related toxicity. Using this technique, CED can be used to safely perfuse targeted regions of diseased brainstem with therapeutic agents. Coinfused imaging surrogate tracers can be used to monitor and control the distribution of therapeutic agents in vivo. Patients with a variety of intrinsic brainstem and other central nervous system disorders may benefit from a similar treatment paradigm.

Stereotactic surgery for mass lesions of the midbrain and pons

Appropriate treatment for intracranial mass lesions depends upon accurate histological diagnosis. Although both advanced generation computed tomographic and magnetic resonance scanners can detect small lesions within the brain stem, only the combination of these advanced imaging tools with stereotactic instrumentation permits safe and accurate pathological diagnosis of such lesions. We present the results of 13 operations performed on 12 patients with mass lesions of the pons and mesencephalon. A definitive diagnosis was obtained in all patients. Aspiration of necrotic tumors (3 patients), neoplastic or benign cysts (2 patients), and chronic hematomas (2 patients) resulted in immediate neurological improvement in 7 of these 12 patients. No morbidity or mortality related to surgery occurred in this series. Both the preoperative clinical and radiographic diagnoses were erroneous in 6 patients so that accurate histological diagnosis indeed altered subsequent therapy. A transfrontal approach to the midbrain and a transcerebellar approach to the lateral pons are described. The importance of accurate diagnosis, the possibility of definitive therapy in selected patients, and the encouraging benefits and safety of stereotactic surgery indicate that empiric treatment of mass lesions of the midbrain and pons is no longer justified.

Generation of auditory brain stem responses (ABRs). II. Effects of surgical section of the trapezoid body on the ABR in guinea pigs and cat

Auditory brain stem potentials were recorded between the skull and a non-cephalic reference electrode in guinea pig and cat before and after midline section of the trapezoid body from a ventral approach. The ABR after complete section was altered: N2 was delayed, P3 and N3 were lost, P4 and N4 were shortened in latency but only N4 was attenuated in amplitude. With partial section of the trapezoid body the amplitude of P3 was linearly related to the extent of the section. Recordings from the surface of the trapezoid body before and after section revealed a loss of activity contralateral to the ear stimulated and a preservation of activity ipsilateral to the section. Binaural interaction in P4 and N4 was attenuated in a linear manner as a function of the extent of trapezoid body section. This study suggests that auditory brain stem structures contralateral to the midline of the trapezoid body generate components N2, P3, N3, N4, whereas auditory structures ipsilateral to the midline generate components P1, N1, P2 and P4.

The anterior subtemporal, medial transpetrosal approach to the upper basilar artery and ponto-mesencephalic junction

OBJECTIVE

To describe and anatomically analyze the amount of exposure provided by an anterior subtemporal, medial transpetrosal approach to access the upper third of the basilar artery, ventral mesencephalon, pons, and posterior cavernous sinus.

PATIENTS AND METHODS

The outcomes of six patients who underwent surgical treatment via the anterior subtemporal, medial transpetrosal approach at our institution during the past 2 years were reviewed. The series included three patients with subarachnoid hemorrhage from low-lying basilar apex aneurysms, one patient with intraparenchymal hemorrhage from a pontine cavernous malformation, and two patients with slowly progressive cranial neuropathies secondary to petroclival tumors. Thirty dry temporal bone specimens were also measured to quantify the height of petrous bone resection and added proximal basilar artery exposure.

RESULTS

The surgical exposure was greatly enhanced in each instance, allowing each lesion to be treated in a straightforward manner with minimal added morbidity (one trochlear nerve palsy, one worsening of a preexistent oculomotor nerve palsy). Our subsequent morphometric analysis indicates that an additional 1 to 1.5 cm of basilar artery, clivus, and pons exposure over that of a standard anterior subtemporal approach is provided by this technique.

CONCLUSION

This approach combines the wide view of the subtemporal approach with the more proximal exposure afforded by a medial petrosectomy. The widened visualization of the ventral pons and mesencephalon minimizes cranial nerve morbidity, greatly facilitates dissection of low-lying aneurysms, and provides proximal basilar artery control that would otherwise be obscured by the petrous ridge.

Trigeminal Neuralgia Caused by Venous Compression

OBJECTIVE:

The purpose of this study is to clarify whether venous compression on the trigeminal nerve really causes trigeminal neuralgia or not, and to identify which veins are the offending veins.

METHODS:

We used microvascular decompression in operations on 121 patients with typical trigeminal neuralgia. We analyzed the intraoperative findings and surgical results in these 121 cases.

RESULTS:

In 7 of the 121 cases, only the vein was identified as a compressive factor on the trigeminal nerve. In 6 of these 7 cases, single venous compression was found, whereas the remaining case had two offending veins. The transverse pontine vein was most frequently found as the offending vein near Meckel's cave. All patients showed complete relief of trigeminal pain after decompression of the veins, but four of them developed facial numbness after surgery, which tended to be slight and did not require any treatment.

CONCLUSION:

Our surgical experiences showed that venous compression could cause trigeminal neuralgia by itself and that the transverse pontine vein should be carefully observed because it is most frequently the offending vein.

Pontomedullary transection attenuates central respiratory modulation of sympathetic discharge, heart rate and the baroreceptor reflex in the in situ rat preparation

Previous studies have indicated a major role for the pons in the genesis of the respiratory pattern. The respiratory rhythm is coupled to the cardiovascular system to ensure optimal matching of minute ventilation and cardiac output. Since much of this coupling results from cross-talk between brainstem circuits, we have assessed the role of the pons in both the co-ordination of respiratory and cardiovascular efferent activities and the baroreceptor reflex efficacy. Using the arterially perfused in situ rat preparation, we recorded neural activities from the left phrenic nerve, central end of the vagus nerve, thoracic sympathetic chain (T8-T10) and heart rate. Respiratory sinus arrhythmia, respiratory modulation of sympathetic nerve activity (and Traube-Hering waves in arterial pressure) and postinspiratory discharges recorded from vagal efferents were eliminated after pontine transection. We also found that although the sympathetic arterial baroreflex remained intact, respiratory gating of the baroreceptor reflex (i.e. both bradycardia and sympathoinhibition) was abolished after pontine removal. We propose that neural activity of the pons is essential for physiological coupling of centrally generated respiratory and cardiovascular efferent activities.

Habituation and desensitization of the Hering-Breuer reflex in rat

1. Many processes in mammalian and invertebrate central nervous systems exhibit habituation and/or sensitization of their responses to repetitive stimuli. Here, we studied the adaptive behaviours of the respiratory pattern generator in rat on repetitive vagal-afferent stimulation and compared these behaviours obtained in vivo with the reported effects of such stimuli on synaptic transmission in the corresponding signal pathway in vitro. 2. Sustained (1 min) electrical pulsed stimulation of the vagus nerve elicited the classic Hering-Breuer (HB) reflex slowing of the respiratory rhythm followed by a bi-exponential recovery, and a post-stimulus rebound (PR). The recovery from the HB reflex satisfied the classic criteria of habituation. 3. The fast component of the recovery and the PR were abolished by systemic administration of an NMDA receptor antagonist or electrolytic lesioning of the pontine Kolliker-Fuse nucleus. The characteristics of the fast recovery and PR suggest a vagally induced desensitization of the NMDA receptor-dependent pontine input to the respiratory pattern generator. 4. The slow component of recovery persist after both experimental interventions and accounted for the habituation to the vagal input. The characteristics of the slow recovery in vivo were reminiscent of the reported synaptic accommodation in vitro in the medullary region where vagal afferents terminate. 5. The habituation of vagal input and desensitization of pontine input act in concert to offset the HB reflex. Such simultaneous habituation-desensitization in parallel neural pathways with differing sensitivities to NMDA receptor activation represent a hitherto unknown pairing of dual non-associative learning processes in the mammalian brain.

Characterization of REM-sleep associated ponto-geniculo-occipital waves in the human pons

STUDY OBJECTIVES

Ponto-geniculo-occipital (PGO) waves are phasic pontine, lateral geniculate, and cortical field potentials occurring during and before REM sleep that are proposed to mediate a wide variety of sleep related neural processes. We sought to identify and characterize human PGO waves.

DESIGN

We recorded simultaneously from intrapontine depth electrodes and scalp electrodes in a human subject across sleep states.

SETTING

Tertiary care neurological and neurosurgical referral center.

PATIENTS OR PARTICIPANTS

We studied a patient involved in a study of the clinical effects of unilateral pedunculopontine nucleus (PPN) stimulation on Parkinson disease (PD).

INTERVENTIONS

No interventions.

MEASUREMENTS AND RESULTS

We recorded phasic potentials from the human pons occurring during and before REM sleep with a morphology, temporal distribution, and localization similar to those of PGO waves in other mammals. The source of these potentials was localized to a circumscribed region of the pontomesencephalic tegmentum. These potentials were only incompletely associated with eye movements. They were followed by characteristic cortical potentials with a latency of 20-140 msec.

CONCLUSIONS

We conclude that PGO waves are a feature of human REM sleep, that they are generated or propagated in the pontomesencephalic tegmentum, that they are only partially associated with eye movements, and that they are associated with characteristic changes in cortical activity.

Role of the pons in hypoxic respiratory depression in the neonatal rat

The main purpose of this study was to evaluate the role of the pons in hypoxic respiratory depression (HRD) of the neonatal rat. Experiments were conducted using the isolated brainstem-spinal cord preparation of the neonatal rat (1-3 days old). The brainstem was transected at various levels. We found that ablation of the diencephalon decreased respiratory frequency (fR), and conversely, that ablation of the midbrain or pons increased fR. In the preparation with the pons intact (without the midbrain), hypoxia (superfusate PO2 = 56 mmHg) caused strong depression of respiratory activity, which was characterized by a steady decrease in fR and in integrated inspiratory burst amplitude (integral of Phr). In the preparation with the intact ventral pons (without midbrain and dorsal pons) we observed similar, though weaker, HRD. When the entire pons was ablated, integral of Phr was little depressed by hypoxia and thus, HRD was further attenuated. We conclude that the pons contributes importantly to the induction of hypoxic respiratory depression in the neonatal rat. Both the ventral and dorsal portions of the pons are involved in the control of hypoxic respiratory depression. In addition, we show that the respiratory modulatory functions of the diencephalon (facilitating) and midbrain (inhibitory) are already expressed at the time of birth.

Successful evacuation of a pontine hematoma secondary to rupture of a pathologically diagnosed "cryptic" vascular malformation. Case report

✓ A posterior fossa exploration was performed on a child thought initially to have an inoperable brain stem lesion. A pontine hematoma was discovered and evacuated. The pathological specimen was designated as a “cryptic” arteriovenous malformation. All preoperative neurological deficits disappeared except for a minimal left seventh nerve palsy.

Transorbital penetrating injury by a chopstick--case report

A one-year-old boy presented with orbitocranial penetrating injury by a chopstick. Neurological examination did not reveal abnormal findings. Skull radiography did not reveal any sign of fracture and there were no abnormal findings. Initially, computed tomography (CT) of the head did not reveal any intracranial lesions. However, bone window CT showed a well-defined low-density abnormality measuring 2.5 cm in length in the right orbit and parasellar region. Magnetic resonance imaging clearly revealed a low-intensity structure extending from the orbit to the prepontine area. Surgical exploration was emergently performed and the wooden fragment was removed. The postoperative course was uneventful. Transorbital penetrating injury by a wooden foreign body is relatively rare. The wound may be superficial and trivial. Major neurological deficit does not usually manifest immediately, so the penetrating injury may be overlooked. If the foreign body is retained in the orbit and cranium, severe infectious complications may occur later.

Partial sensory trigeminal rhizotomy at the pons for trigeminal neuralgia

Microvascular decompression is preferred among open procedures for the treatment of trigeminal neuralgia. However, in some cases the decompression cannot be performed, either because no significant vascular compression of the trigeminal nerve is found at surgery or because a patient's vascular anatomy makes it unsafe. Partial sensory rhizotomy is a commonly used alternative in these instances. The outcome after partial sensory rhizotomy was reviewed retrospectively in 83 patients with an average follow-up period of 72 months. Sixty-four (77%) of these patients had no evidence of vascular contact at operation. The remaining 19 patients (23%) had vascular structures in proximity to the trigeminal nerve but still underwent partial sensory rhizotomy in place of or in addition to microvascular decompression either because the offending vessel could not be moved adequately (11 cases) or because the vascular contact was considered insignificant (eight cases). Outcome was classified as: excellent if there was no trigeminal neuralgia postoperatively; good if pain persisted or recurred but was less severe than preoperatively; and poor if persistent or recurrent pain was equal to or greater than the preoperative pain in severity and was refractory to medication, or was severe enough to require additional surgery. The outcome was excellent in 40 patients (48%), good in 18 (22%), and poor in 25 (30%); follow-up durations were similar for the three outcome categories. The failure rate was 17% for the 1st year and averaged 2.6% each year thereafter. Two variables were predictive of a poor outcome: prior surgery and lack of preoperative involvement of the third trigeminal division. Major complications occurred in 4% of cases and minor complications in 11%. The authors conclude that partial sensory rhizotomy is a safe and effective alternative to microvascular decompression when neurovascular compression is not identified at operation or when microvascular decompression cannot be performed for technical reasons.

Pericollicular surgical approaches to the rhomboid fossa. Part I. Anatomical basis

A safe paramedian approach to the rhomboid fossa for surgical treatment of intrinsic brainstem lesions is based on detailed knowledge of the morphometric anatomy of superficially located motor structures. The morphometry of the rhomboid fossa is described in this report on the basis of histological studies conducted in six human brainstem specimens, with special emphasis on the colliculus facialis and the trigona nervi hypoglossi and vagi. Morphometric data include analysis of shrinkage factors in each specimen. The colliculus is a landmark for the nervus facialis, oculomotor nuclei, and the paramedian pontine reticular formation. In the surgeon's view from the posterior approach, the colliculus covers an area of 5.7 mm in the mediolateral and 6.8 mm in the craniocaudal direction and is located 0.6 mm lateral to the median sulcus. The fibers of the nervus facialis come as close as 0.2 mm to the surface of the fourth ventricle. The colliculus is located 15.7 mm above the obex. The trigona nervi hypoglossi and vagi cover a rectangular area measuring 3.1 by 6.5 mm and serve as a landmark for lower cranial nerve nuclei. These nuclei are located 0.3 mm lateral to the midline. An area with a maximum extension of 0.9 cm between the colliculus and trigona can be used for an infracollicular paramedian approach. The same applies to a supracollicular approach cranial to the colliculus and caudal to the fibers of the nervus trochlearis within the medullary velum, with a craniocaudal extension of 4 mm. Superficial motor nuclei and fibers can be identified by neurophysiological mapping, which helps to define safe surgical corridors into the rhomboid fossa, thus reducing functional morbidity caused by the operative approach in intrinsic pontine and pontomedullary lesions.

Successful evacuation of a pontine hematoma secondary to rupture of a venous angioma

A middle-aged woman presented with progressive brainstem neurological deficits. Clinical manifestations and preoperative radiological examination were indicative of an expanding intrapontine mass. At operation, an intrapontine hematoma and a venous angioma adherent to the floor of the fourth ventricle were discovered. Successful evacuation of the hematoma was followed by an excellent recovery. Postoperative angiography demonstrated the venous angioma. To our knowledge, this is the first case of angiographically proved ruptured venous angioma of the pons treated successfully by an operation.

Mesopontine contribution to the expression of active 'twitch' sleep in decerebrate week-old rats

Myoclonic twitching is a ubiquitous feature of infant behavior that has been used as an index of active sleep. Although the active sleep of infants differs in some ways from the REM sleep of adults, their marked similarities have led many to view them them as homologous behavioral states. Recently, however, this view has been challenged. One avenue for resolving this issue entails examination of the neural substrates of active sleep. If the neural substrates of active sleep were found to be similar to those of REM sleep, then this would support the view that the two states are homologous. Therefore, in the present study, decerebrations were performed in the pons and midbrain to determine whether the mesopontine region is important for the expression of active sleep in infants, just as it is for the expression of REM sleep in adults. It was found that, in comparison to controls, caudal pontine decerebrations reduced myoclonic twitching by 76%, rostral pontine decerebrations reduced twitching by 40%, and midbrain transections had no significant effect on twitching. Moreover, analysis of the temporal organization of twitching indicated that pontine decerebrations predominantly affected high-frequency twitching while leaving unaffected the low-frequency twitching that is thought to be contributed by local spinal circuits at this age. These results indicate that the mesopontine region plays a central role in the expression of active sleep in infant rats.

Pontine-mesencephalic cavernomas: indications for surgery and operative results

Cavernous haemangiomas cavernomas of the brainstem can be diagnosed by MRI and safely removed when elective surgery is performed in the subacute stage after haemorrhage. Recurrent haemorrhage and/or neurological deterioration are indications for surgery. In cases with additional venous malformation the cavernoma should be selectively removed. The experiences with our own series of 18 cases are presented.

Status dissociatus after surgery for tegmental ponto-mesencephalic cavernoma: A state-dependent disorder of motor control during sleep

After surgery for a tegmental ponto-mesencephalic cavernoma, a patient developed sleep-related excessive fragmentary myoclonus, diffuse myoclonic jerks, simple quasipurposeful movements of the limbs, and rapid eye movement (REM) sleep behaviour disorder as motor features of status dissociatus, a condition in which elements of one state of being (wake, NREM and REM sleep) pathologically intrude into another.

Spontaneous intracerebral haemorrhage in patients suspected of multiple sclerosis

Two cases of spontaneous intracerebral haemorrhage in adolescent girls suspected of having multiple sclerosis are reported. Surgical evacuation of haematomas in the left thalamus and left side of the pons, respectively, was performed with excellent recovery in both cases. Some clinical and pathological aspects of small arteriovenous malformations are discussed and the pertinent literature reviewed.