Microsurgical anatomy of the subtentorial supracerebellar and infracerebellar approach to the trigeminal and facial nerves.

The microsurgical anatomy of the subtentorial supracerebellar approach to the trigeminal nerve and the infracerebellar lateral approach to the facial nerve was examined in five formalin-fixed adult cadavers. Particular attention was directed to the arrangement of the blood vessels within the posterior fossa, especially the superior petrosal vein and its tributaries, the superior cerebellar artery (SCA), the anterior inferior cerebellar artery (AICA) and the posterior inferior cerebellar artery (PICA). The subtentorial supracerebellar approach provides satisfactory exposure of both, the lateral segment of the SCA, which is the most common vessel involved in the neurovascular conflict resulting in trigeminal neuralgia and the y-inverted shaped superior petrosal vein. The latter results more often from the convergence of the pontotrigeminal vein and the vein of the cerebellopontine fissure. The relationship between the AICA, the PICA and the vertebral artery to the facial-vestibulocochlear complex was studied by an infracerebellar lateral approach. The subpial course of the facial nerve, where the vascular compression is usually found which results in hemifacial spasm, was also documented. These two approaches, as well as a historical review of the evolution of these surgical techniques, since the first description by Dandy, are discussed. Copyright 1999 Harcourt Publishers Ltd.

Microanatomic and vascular aspects of the temporomesial region.

OBJECTIVE: The aim of this work was to provide a detailed description of the arterial vascularization of the temporomesial region (TMR), correlated with the definitions of the macroscopic and cytoarchitectonic subdivisions of this area. METHODS: Selective colored arterial injections were performed in 16 hemispheres to study their blood supply. Four hemispheres were used to illustrate the macroscopic aspect of the TMR and were then cut into thin sections and stained with Nissl's stain to study the cytoarchitectonic areas. RESULTS: The surface of the TMR is subdivided into several areas: anteriorly, the lateral olfactory gyrus is covered by prepiriform cortex; dorsomedially, the semilunar gyrus and uncus hippocampi consist, respectively, of cortical amygdaloid nucleus and hippocampal cytoarchitectonic fields; and ventrolaterally, the anterior part of the parahippocampal gyrus is covered by periamygdaloid cortex, entorhinal, and transentorhinal areas and its posterior part is covered by Fields TH and TF per Von Economo and subicular complex. Six cortical arterial groups were defined: Group I, anterosuperior parahippocampal arteries (mean, 3.9 arteries) vascularize the ambiens, semilunar, and lateral olfactory gyri (origins: middle cerebral artery, anterior choroidal artery [AChA], posterior cerebral artery [PCA], and internal carotid artery); Group II, anteroinferior parahippocampal arteries (mean, 2.8 arteries) irrigate the anterior ventrolateral region of the parahippocampal gyrus (origins: middle cerebral artery, PCA, and AChA); Group III, medial uncal arteries (mean, 1.9 arteries) supply the medial part of uncus hippocampi (origins: AChA and PCA); Group IV, lateral uncal arteries (mean, 2.9 arteries) vascularize the lateral part of the uncus hippocampi (origins: AChA and PCA); Group V, several small posterior parahippocampal arteries irrigate Fields TF and TH per Von Economo (origins: PCA and AChA); and Group VI, posterior hippocampal arteries (mean, 3.2 arteries) irrigate the posterior part of hippocampal formation (origin: PCA). Many anastomoses are found among these arteries, particularly in the ventrolateral part of the TMR. Three groups of amygdaloid arteries were defined: Group I, the anterolateral group (mean, 5.7 arteries) (origin: middle cerebral artery); Group II, the medial group (mean, 6.4 arteries) (origins: AChA, internal carotid artery, and PCA); and Group III, the posterolateral group (mean, 5 arteries) (origins: AChA and internal carotid artery). CONCLUSION: We hope that this work will be useful for any microneurosurgical procedures on the TMR. We have clarified the macroscopic and histological definitions of the cortical and nuclear areas of the TMR and the arterial groups closely related to them. The systematic analysis of the variability of the arterial vascularization of this area was our second goal; such a goal, however, requires more observations to be exhaustive. The numerous interterritorial anastomoses found inside the TMR imply that a selective presurgical injection of short-acting barbiturates to evaluate its functions (Wada test) may well result in its diffusion to other areas of the TMR.

Observations on surgical anatomy for rectal cancer surgery.

BACKGROUND/AIMS: The investigators studied the surgical anatomy of the main structures involved in the mobilization of the rectum (Denonvilliers' fascia, mesorectum, middle rectal artery, superior and inferior hypogastric plexuses). METHODOLOGY: The study was carried out on 20 cadavers (17 unembalmed and 3 embalmed). To study Denonvilliers' fascia, ten embryos and fetuses (11 mm to 80 mm CRL) were also examined. RESULTS: Denonvilliers' fascia originates from the fusion of the primary pouch of Douglas. The two leaves making up this structure are easily separated. The mesorectum surrounds the rectum on three sides; it is easily separated from the presacral fascia and its connective tissue is bordered by a thin membrane. The middle rectal artery varies in appearance rate, origin, size, distribution and anastomosis. It runs under the lateral ligament and also sends branches to the genital apparatus. Of the two hypogastric plexuses, the inferior is the most difficult one to identify. Its superior branches extend to the rectum, and the inferior ones to the genital apparatus. Because the anterior part contains the parasympathetic nerves and the middle rectal artery, this region is at major risk during surgical dissection. CONCLUSIONS: A sound understanding of the surgical anatomy of the rectum enables the surgeon to perform a more correct and reasonable procedure in terms of both the extent of surgical treatment and the preservation of important anatomical structures.

The anatomy of the inferior laryngeal nerve.

Contradictory opinions are found in the literature concerning the precise anatomy and role of the inferior laryngeal nerve, the terminal portion of the recurrent laryngeal nerve. Moreover, operative damage to this nerve beyond the thyroid area is seldom described. Twenty-one human larynges were dissected to give a precise description of the inferior laryngeal nerve and to draw attention to the risks of injury to the nerve during specific laryngological operations. In contrast with the varied descriptions found in the literature, only small variations in the terminal branching of the nerve were found. The nerve divides generally extralaryngeally into two branches: a motor, anterior one, innervating the intrinsic laryngeal musculature (except the cricothyroid muscle), and a sensory, posterior one, forming Galen's anastomosis. The anterior branch of the nerve is particularly susceptible to damage just behind the cricothyroid joint; two of its terminal rami, supplying respectively the interarytenoid and thyro-arytenoid muscles, incur potential risks of injury during endoscopic CO2 laser surgery.

Tibial component positioning in total knee arthroplasty: bone coverage and extensor apparatus alignment.

Correct positioning of the tibial component in total knee arthroplasty (TKA) must take into account both an optimal bone coverage (defined by a maximal cortical bearing with posteromedial and anterolateral support) and satisfactory patellofemoral tracking. Consequently, a compromise position must be found by the surgeon during the operation to simultaneously meet these two requirements. Moreover, tibial tray positioning depends upon the tibial torsion, which has been shown to act mainly in the proximal quarter of the tibia. Therefore, the correct application of the tibial tray is also theoretically related to the level of bone resection. In this study, we first quantified the torsional profile given by an optimal bone coverage for a symmetrical tibial tray design and for an asymmetrical one. Then, for the two types of tibial trays, we measured the angle difference between optimal bone coverage and an alignment on the middle of the tibial tubercule. Results showed that the values of the torsional profile given by the symmetrical tray were more scattered than those from the asymmetrical one. However, determination of the mean differential angle between the position providing optimal bone coverage and the one providing the best patellofemoral tracking indicated that the symmetrical prosthetic tray offered the best compromise between these two requirements. Although the tibiofemoral joint is known to be asymmetric in both shape and dimension, the asymmetrical tray chosen in this study was found to fulfill this compromise with more difficulty.

Maturation of the neuronal metabolic response to vibrissa stimulation in the developing whisker-to-barrel pathway of the mouse.

We examined functional maturation in the mouse whisker-to-barrel pathway from P2 (P0 is the day of birth) to adulthood using the autoradiographic deoxyglucose (DG) method. After intraperitoneal DG injection, left whiskers C1-3 and E1 were stimulated. Sections were cut transversely through the brainstem, and coronally or tangentially through the parietal cortex. After autoradiography, the sections were stained for Nissl or for cytochrome oxidase (CO) activity. In subnuclei caudalis and interpolaris of the spinal trigeminal nucleus ipsilateral to stimulation, DG uptake evoked by the deflection of whiskers C1-3 was present at P2; in subnucleus oralis, nucleus principalis and the contralateral nucleus ventrobasalis of the thalamus, at P4; and in the contralateral barrel cortex, at P7. The first stimulus-dependent DG uptake appeared a few days after the appearance of whisker-related patterns seen in the CO- or Nissl-stained sections. In subnuclei caudalis and interpolaris, areas of stimulus-dependent DG uptake were initially larger than the CO segments representing the stimulated whiskers. Later, areas of stimulus-dependent DG uptake and CO segments matched well. DG uptake evoked by the stimulation of whisker E1 appeared 2-3 days later than that evoked by stimulation of whiskers C1-3. In nucleus principalis, one large area of stimulus-dependent DG uptake covered the representations of the caudal whiskers of all five rows--an observation made at all ages studied. In thalamus, stimulus-dependent DG uptake was found laterally in nucleus ventrobasalis. In barrel cortex, at P7, stimulus-dependent DG uptake was restricted to layers III and IV, but covered more barrels than whiskers stimulated. At P9, a second spot of high DG uptake was seen in deep layer V in register with that in layers III and IV. From P10 onwards, stimulus-dependent DG uptake stretched from layer II to layer VI, and in layer IV, in which it was highest, it was restricted to the barrels C1-3 and E1. In all stations, stimulus-dependent DG uptake decreased in magnitude after P10. While the onset of stimulus-dependent DG uptake is the result of the establishment of functional projections up to that station, the subsequent changes in size of the responding areas may well be due to the partial elimination of terminals, the maturation of local inhibitory circuits, and/or the development of cortical projections to the nuclei of termination and to the thalamic relay.

Plasticity in the barrel cortex of the adult mouse: effects of chronic stimulation upon deoxyglucose uptake in the behaving animal.

We investigated experience-dependent regulation of neuronal activity in the whisker-to-barrel pathway of the adult mouse using the autoradiographic deoxyglucose (DG) method. Animals were placed in the Lausanne whisker stimulator, and three of their whisker follicles were passively stimulated for a period of 1, 2, or 4 d. After this period, mice received a dose of DG and were placed in a cage containing a pile of wooden sticks. Mice that underwent the same procedure except the passive stimulation served as controls. Patterns of stimulus-dependent DG uptake were studied in the somatosensory cortex and in the trigeminal sensory brainstem complex. DG uptake in the barrels corresponding to the passively stimulated whiskers was lower than in controls. This decrease was present throughout the radial extent of a barrel column and was observed in all passively stimulated animals. Quantitative analysis confirmed these observations and, furthermore, showed a statistically significant decrease in DG uptake in barrels neighboring the passively stimulated ones. In half of the animals, the brainstem nuclei showed a decreased DG uptake in the representation of the passively stimulated whiskers, whereas in the other animals the pattern of DG uptake was as in controls. We propose that the signs of cortical plasticity are due to a mechanism that operates in layer IV and functions as a gate for peripheral sensory activity to enter cortical circuitry.

Plasticity in the barrel cortex of the adult mouse: transient increase of GAD-immunoreactivity following sensory stimulation.

Sensory experience during perinatal life and adulthood modifies physiological and anatomical characteristics of the central nervous system. So far, this phenomenon has been studied in situations of complete or partial sensory deprivation. We here report that increased sensory stimulation, during four days, of a number of whisker follicles on the face of the adult mouse results in an increased immunoreactivity of glutamic acid decarboxylase (the biosynthetic enzyme of the inhibitory neurotransmitter GABA) in the somatosensory cortex of the adult mouse. Effects were limited to a column of tissue corresponding to the representation of the stimulated follicles and lasted two days beyond stimulation. These findings suggest that sensory stimulation transiently modifies local cortical processing.

Selective breeding for variations in patterns of mystacial vibrissae of mice. Bilaterally symmetrical strains derived from ICR stock.

The establishment of certain patterns of mystacial vibrissae in mice has been the aim of an extensive breeding program carried on in this laboratory since 1977. In a companion paper we have reported on variations in this pattern in an outbred population of ICR mice. Starting with 21 ICR animals we bred, mostly by brother-sister mating, for 13 bilaterally symmetric patterns of mystacial vibrissae characterized by the presence (or absence) of supernumerary whiskers (SWs). The strains are classified as follows: I, a mouse strain with the standard pattern; II, eight strains bred for the occurrence of SWs at a given site or sites; and III, four mouse strains bred for a maximal number of SWs in different regions of the whiskerpad. Commonly, SWs occur in regions that coincide with the zones of mergence between the three facial processes except for two class II strains in which we bred for SWs in the "straddler" row of vibrissae, and for one class III strain, in which we cultivated the tendency (that appeared late in our program) to have SWs at the crest of a facial process. For classes I and II we analyzed the results for about 18 generations in terms of "improvement," meaning an increase in the percentages of animals with the desired phenotype together with a decreased frequency of undesired SWs. For class III, success in breeding meant the increase of the mean number of the desired SWs. All results led to the same conclusion: there is a genetic basis for the occurrence of SWs. The side preference of a particular SW is not strain dependent. It disappears in those class I and II strains in which almost 100% of animals obtained the desired phenotype. The increase in number of SWs in one zone of mergence does not depend on the presence of SWs in the other. Where tested, we almost always found a representation of an SW in a topologically equivalent location within the "barrelfield" area of the somatosensory cerebral cortex. Except for some diseases early in the breeding program, and some side effects of inbreeding that were eliminated, the population was without obvious defects. Where tested, there was no correlation between the occurrence of SWs and sex. The observed variations in pattern of mystacial vibrissae and their genetic background led us to propose a morphogenetic model for the formation of the pattern of mystacial vibrissae.

A magnetic device to stimulate selected whiskers of freely moving or restrained small rodents: its application in a deoxyglucose study.

After receiving an intraperitoneal injection of [14C]2-deoxy-D-glucose (2-DG), a total of 28 mice which had pieces of metal wire glued to certain whiskers (all others were clipped) were exposed to magnetic field bursts. The stimulated whiskers were B1 (freely moving mice, set I) or whiskers C1-3 and E1 (restrained mice, set II) on the left side. In set I, stimulated mice were compared with animals of various control groups. Autoradiography demonstrated an activation of columnar shape overlying the presumed corresponding barrel contralateral to stimulation; in a part of the ipsilateral barrelfield, 2-DG uptake was depressed significantly. In the subnuclei caudalis and interpolaris of the trigeminal brainstem complex a spot of activation was observed ipsilaterally but there was no depression contralaterally. Whereas several animals of the control groups showed some aspects of these responses, they were consistent only in stimulated mice. In set II, animals received stimulation with different intensities. 2-DG uptake was higher in barrels C1-3 than in E1. It increased with increasing intensity. The same observations were made in two nuclei of termination. The device we describe here can be used to study stimulus-specific responses at various levels of the somatosensory pathway.

Variation in pattern of mystacial vibrissae in mice. A quantitative study of ICR stock and several inbred strains.

We report on the variation in the pattern of mystacial vibrissae in ICR mice, of which one-half of the about 600 animals investigated showed one or more supernumerary whiskers (SWs). The SWs and their follicles--in all respects identical to the units of the standard pattern except for their smaller size--occurred at a restricted number of sites. In addition, a limited number of mice from two BALB/c strains were analyzed. Half of them also had one or more SWs, but mainly at one site. Mice of the C3H/HeJ and DBA/2J(a) strains were virtually without SWs, whereas animals from the NMRI strain were standard without exception. Nearly all animals of the C57BL/6J strain lacked between 1 and 4 vibrissae, always from one or two of the same adjacent sites. There was a slight overall predominance for the left side of the face to bear SWs and there was no clear-cut association with sex; the entire population was without obvious defects. The sites where extra or lacking whiskers occur are associated with the lines of fusion between the medial and the lateral nasal fold, and between the latter and the maxillary arch. Where tested, we always found a topologic equivalency between the pattern of the whisker follicles and the contralateral pattern of the "barrels"--multineuronal units in layer IV of the parietal cerebral cortex--whether the pattern was standard, "enriched," or lacking in elements. The data presented in this paper provided a basis for several studies carried out subsequently on animals that are the offspring of those characterized here, studies suggesting that the occurrence of supernumerary and of lacking whiskers has a genetic basis.

The musculature of the mystacial vibrissae of the white mouse.

Striated muscles of the mystacial region of the common albino mouse have been described. They were divided into two categories: extrinsic and intrinsic. The four extrinsic muscles (m. levator labii superioris, m. maxillolabialis, m. transversus nasi, m. nasalis) belong to the facial muscles. They originate on the skull and insert into the corium between the mystacial vibrissae. Their contraction moves the whole mystacial region in directions dependent on their origins. Intrinsic (follicular) muscles are associated solely with the vibrissal follicles and have no bony attachment. They were found around follicles alpha, beta, gamma, delta, around all follicles of rows A and B, and around the first six follicles of rows C, D and E. The form of the follicular muscle is a sling connecting two adjacent follicles of the same row. The arc of the sling surrounds the inferior part of the rostral follicle and the two extremities insert to the conical body of the caudal follicle and to the neighbouring corium. They are the protractors of the vibrissae. The inferior parts of the vibrissal follicles of a given row are fixed in a fibrous band which inserts in the anterior part of the muzzle. It is proposed that these bands become stretched during the protraction of vibrissae and contract, by their elasticity, immediately upon the end of the follicular muscles' contraction, executing the fast return of vibrissae to their resting, retracted position.

Migration of tendinous insertions. II. Experimental modifications.

The relationship between the migration of tendinous insertions, periosteal growth and muscular traction was studied in young rabbits. Normal growth was modified in two ways: (i) the growth of the proximal and distal epiphyseal plates of the tibia was arrested by staples. as a consequence, the neighbouring periosteum, no longer stretched, stopped growing in length; insertions were thus no longer dragged by the periosteum and ceased to migrate. (ii) The nature of the insertion of the anterior annular ligament of the tibia was changed by sectioning the tendon of the tibialis anterior muscle near its insertion and reflecting it proximally in a loop around the ligament. In this case the ligament migrated normally in spite of the muscular traction in a direction opposite to the direction of migration. It is concluded that the direct cause of the migration of muscular and ligamentous insertions is periosteal growth.

Migration of tendinous insertions. I. Cause and mechanism.

The cause and mechanisms of the migration of tendons and ligaments were studied in young rabbits. Three techniques were used: (1) Marking of insertions, the neighbouring periosteum and the diaphysis with metallic markers. (2) Marking of insertion sites by tetracycline as an indicator of osteogenesis. (3) Histological examination. The insertions used in the study were of three different characters: (1) Insertions subject to muscular traction (patellar ligament, quadratus femoris muscle, tibialis anterior muscle). (2) The distal insertions of the medial collateral ligament of the knee, stretched by the activity of the proximal epiphyseal cartilage of the tibia. (3) The proximal and distal insertions of the anterior annular ligament of the tibia, inserted solely in bone and periosteum. The cause of migration is the growth of periosteum dragging the insertions during its stretching, caused itself by the activity of the epiphyseal plates. The local mechanism governing migration while ensuring a continuous connexion with the bone is not the same in all sites. It depends upon the character of the bony surface at the insertion and of the function of the insertion zone, which can be osteogenic, resorptive or both. A plexus of precollagenous fibres is present at all resorptive insertion sites, and at some of the osteogenic sites.

Does the skin tell the somatosensory cortex how to construct a map of the periphery?

When the muzzle of a mouse bears an occasional extra whisker, the corresponding barrelfield (in the contralateral somatosensory cortex) contains an extra barrel in a topologically equivalent place and vice versa. Since the pattern of vibrissal follicles is laid down 7 days before birth and that of the barrels 3 days after birth, the former pattern appears to be responsible for the establishment of the latter. We propose that the answer to the title's question is yes.