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Errors in development occur in all vertebrates. When severe, these anomalies are lethal and frequently escape attention. In rare cases, animals with profound malformations are born and can provide a glimpse into structures and their respective function that would otherwise go unnoticed. A rare abnormality in a hatchling Alligator mississippiensis is described in which duplication of the skull, face, and brain was incomplete. The rostral skull, face, and associated forebrain, including the olfactory apparatus, were duplicated. However, the caudal skull and brainstem were not. These observations were made with advanced imaging using both computed tomography and magnetic resonance coupled with gross brain dissections. These abnormal features emphasize the complex and intertwined relationship between the development of the brain, face, and skull which are influenced by certain signaling molecules, possible gene mutation(s), and potential environmental factors.

Local circuit neurons are present in the thalamus of all vertebrates where they are considered inhibitory. They play an important role in computation and influence the transmission of information from the thalamus to the telencephalon. In mammals, the percentage of local circuit neurons in the dorsal lateral geniculate nucleus remains relatively constant across a variety of species. In contrast, the numbers of local circuit neurons in the ventral division of the medial geniculate body in mammals varies significantly depending on the species examined. To explain these observations, the numbers of local circuit neurons were investigated by reviewing the literature on this subject in these two nuclei in mammals and their respective homologs in sauropsids and by providing additional data on a crocodilian. Local circuit neurons are present in the dorsal geniculate nucleus of sauropsids just as is the case for this nucleus in mammals. However, sauropsids lack local circuits neurons in the auditory thalamic nuclei homologous to the ventral division of the medial geniculate body. A cladistic analysis of these results suggests that differences in the numbers of local circuit neurons in the dorsal lateral geniculate nucleus of amniotes reflects an elaboration of these local circuit neurons as a result of evolution from a common ancestor. In contrast, the numbers of local circuit neurons in the ventral division of the medial geniculate body changed independently in several mammalian lineages. .

The thalamic reticular nucleus in reptiles, Caiman crocodilus, shares a number of morphological similarities with its counterpart in mammals. In view of the immunohistochemical properties of this nucleus in mammals and the more recently identified complexity of this neuronal aggregate in Caiman, this nucleus was investigated using a number of antibodies. These results were compared with findings described for other amniotes. The following antibodies gave consistent and reproducible results: polyclonal sheep anti-parvalbumin (PV), monoclonal mouse anti-PV, and polyclonal sheep anti-glutamic acid decarboxylase (GAD). In the transverse plane, this nucleus is divided into two. In each part, a compact group of cells sits on top of the fibers of the forebrain bundle with scattered cells among these fibers. In the lateral forebrain bundle, this neuronal aggregate is represented by the dorsal peduncular nucleus and the perireticular nucleus while, in the medial forebrain bundle, these parts are the interstitial nucleus and the scattered cells in this fiber tract. The results of this study are the following. First, the thalamic reticular nucleus of Caiman contains GAD(+) and PV(+) neurons, which is similar to what has been described in other amniotes. Second, the morphology and distribution of many GAD(+) and PV(+) neurons in the dorsal peduncular and perireticular nuclei are similar and suggest that these neurons colocalize these markers. Third, neurons in the interstitial nucleus and in the medial forebrain bundle are GAD(+) and PV(+). At the caudal pole of the thalamic reticular nucleus, PV immunoreactive cells predominated and avoided the central portion of this nucleus where GAD(+) cells were preferentially located. However, GAD(+) cells were sparse when compared with PV(+) cells. This immunohistochemically different area in the caudal pole is considered to be an area separate from the thalamic reticular nucleus.

BACKGROUND AND PURPOSE: Intracranial aneurysms originating at the posterior communicating artery are known to have high rupture risk compared with other locations. We tested the hypothesis that different angioarchitectures (ie, branch point configuration) of posterior communicating artery aneurysms are associated with aneurysm hemodynamics, which in turn predisposes aneurysms to rupture. MATERIALS AND METHODS: A total of 313 posterior communicating artery aneurysms (145 ruptured, 168 unruptured) were studied with image-based computational fluid dynamics. Aneurysms were classified into different angioarchitecture types depending on the location of the aneurysm with respect to parent artery bifurcation. Hemodynamic characteristics were compared between ruptured and unruptured aneurysms, as well as among aneurysms with different angioarchitectures. RESULTS: Angioarchitecture was associated with rupture ( P = .003). Ruptured aneurysms had higher, more concentrated, and more oscillatory wall shear stress distributions (maximum wall shear stress, P P P P = .01; inflow concentration index, P P P P = .02) and minimum wall shear stress ( P = .002) than unruptured aneurysms. CONCLUSIONS: High-flow intrasaccular hemodynamic characteristics, commonly found in bifurcation-type angioarchitectures, are associated with the posterior communicating artery aneurysm rupture status. These characteristics include strong and concentrated inflow jets, concentrated regions of elevated wall shear stress, oscillatory wall shear stress, lower normalized wall shear stress, and complex and unstable flow patterns.

Forebrain connections of the thalamic reticular nucleus associated with the lateral forebrain bundle were analyzed in Caiman crocodilus. Both the compact portion, the dorsal peduncular nucleus, and the diffuse part, the perireticular region, associated with the lateral forebrain bundle, were studied. A small tracer injection into the dorsal peduncular nucleus demonstrated reciprocal connections with a restricted portion of the dorsal thalamus. Tracer placements into this nucleus retrogradely labeled cells in a caudal portion of the ventrolateral area of the telencephalon. These results are compared with similar studies in other amniotes.

Knowledge of brain circuitry is critical for understanding the organization, function, and evolution of central nervous systems. Most commonly, brain connections have been elucidated using histological and experimental methods that require animal sacrifice. On the other hand, magnetic resonance diffusion tensor imaging and associated tractography have emerged as a preferred method to noninvasively visualize brain white matter tracts. However, existing studies have primarily examined large, heavily myelinated fiber tracts. Whether tractography can visualize fiber bundles that contain thin and poorly myelinated axons is uncertain. To address this question, the midbrain auditory pathway to the thalamus was investigated in Alligator. This species was chosen because of its evolutionary importance as it is the reptilian group most closely related to birds and because its brain contains many thin and poorly myelinated tracts. Furthermore, this auditory pathway is well documented in other reptiles, including a related crocodilian. Histological observations and experimental determination of anterograde connections confirmed this path in Alligator. Tractography identified these tracts in Alligator and provided a 3-dimensional picture that accurately identified the neural elements of this circuit. In addition, tractography identified one possible unrecognized pathway. These results demonstrate that tractography can visualize circuits containing thin, poorly myelinated fibers. These findings open the door for future studies to examine these types of pathways in other vertebrates.

The thalamic reticular nucleus in reptiles, Caiman crocodilus, shares a number of morphological similarities with its counterpart in mammals. In view of the immunohistochemical properties of this nucleus in mammals and the more recently identified complexity of this neuronal aggregate in Caiman, this nucleus was investigated using a number of antibodies. These results were compared with findings described for other amniotes. The following antibodies gave consistent and reproducible results: polyclonal sheep anti-parvalbumin (PV), monoclonal mouse anti-PV, and polyclonal sheep anti-glutamic acid decarboxylase (GAD). In the transverse plane, this nucleus is divided into two. In each part, a compact group of cells sits on top of the fibers of the forebrain bundle with scattered cells among these fibers. In the lateral forebrain bundle, this neuronal aggregate is represented by the dorsal peduncular nucleus and the perireticular nucleus while, in the medial forebrain bundle, these parts are the interstitial nucleus and the scattered cells in this fiber tract. The results of this study are the following. First, the thalamic reticular nucleus of Caiman contains GAD(+) and PV(+) neurons, which is similar to what has been described in other amniotes. Second, the morphology and distribution of many GAD(+) and PV(+) neurons in the dorsal peduncular and perireticular nuclei are similar and suggest that these neurons colocalize these markers. Third, neurons in the interstitial nucleus and in the medial forebrain bundle are GAD(+) and PV(+). At the caudal pole of the thalamic reticular nucleus, PV immunoreactive cells predominated and avoided the central portion of this nucleus where GAD(+) cells were preferentially located. However, GAD(+) cells were sparse when compared with PV(+) cells. This immunohistochemically different area in the caudal pole is considered to be an area separate from the thalamic reticular nucleus.

BACKGROUND: Intracranial aneurysms at the posterior communicating artery (PCOM) are known to have high rupture rates compared to other locations. We developed and internally validated a statistical model discriminating between ruptured and unruptured PCOM aneurysms based on hemodynamic and geometric parameters, angio-architectures, and patient age with the objective of its future use for aneurysm risk assessment. METHODS: A total of 289 PCOM aneurysms in 272 patients modeled with image-based computational fluid dynamics (CFD) were used to construct statistical models using logistic group lasso regression. These models were evaluated with respect to discrimination power and goodness of fit using ten-fold nested cross-validation and a split-sample approach to mimic external validation. RESULTS: The final model retained maximum and minimum wall shear stress (WSS), mean parent artery WSS, maximum and minimum oscillatory shear index, shear concentration index, and aneurysm peak flow velocity; along with aneurysm height and width, bulge location, non-sphericity index, mean Gaussian curvature, angio-architecture type, and patient age. The corresponding area under the curve (AUC) was 0.8359. When omitting data from each of the three largest contributing hospitals in turn, and applying the corresponding model on the left-out data, the AUCs were 0.7507, 0.7081 and 0.5842, respectively. CONCLUSIONS: Statistical models based on a combination of patient age, angio-architecture, hemodynamics and geometric characteristics can discriminate between ruptured and unruptured PCOM aneurysms with an AUC of 84%. It is important to include data from different hospitals to create models of aneurysm rupture that are valid across hospital populations.

Objective Perforator and secondary branch origin in relation to the neck of cerebral, saccular bifurcation aneurysms were analyzed. These two features were considered important for treatment. Methods From a series of microsurgically clipped saccular cerebral aneurysms, 142 bifurcation aneurysms had detailed imaging studies and operative records that could be analyzed. Results The incidence of perforator origin from the aneurysm neck was as follows: basilar, 1/15 (7%); internal carotid artery bifurcation, 4/23 (17%); main stem of the middle cerebral artery/secondary branch of the middle cerebral artery, 6/52 (12%); anterior communicating artery region, 5/46 (11%); and distal bifurcation vessels, 0/6 (0%). Aneurysms arising from the anterior communicating artery between the anterior cerebral arteries had a high incidence of perforator origin from the aneurysm neck. The location of secondary branch origin from the aneurysm neck varied depending on the aneurysm group. Conclusion Perforator origin from the aneurysm neck was infrequent. A subgroup of anterior communicating artery region aneurysms had a high incidence of perforator origin from the aneurysm neck. Although protection of these neck perforators will be difficult, their identification may be even more challenging. Secondary branch origin from the aneurysm neck varied depending on the aneurysm group. Advanced endovascular techniques are needed to obliterate aneurysms in which the secondary branch(es) arise from the aneurysm neck. If this is not possible, craniotomy and clip ligation will be required if complete aneurysm obliteration is the goal.

In Caiman crocodilus, identification of nuclei that comprise the dorsal thalamus was determined by: injections of retrograde tracers into cortex/pallium; injections of retrograde tracers into the noncortical telencephalon; and injections of anterograde tracers into thalamic nuclei. With the exception of nucleus dorsolateralis anterior, which has bilateral projections, all other dorsal thalamic nuclei send axons to terminate in the ipsilateral telencephalon. Nuclei that only projected to cortex/pallium were: dorsolateralis anterior; diagonalis; and dorsal geniculate. Neuronal aggregates that send axons that terminated in the dorsolateral area (dorsal ventricular ridge) included: rotundus; reuniens pars centralis and pars diffusa; medialis complex posterior; posterocentralis; and area ventrolateralis. Medialis complex anterior axons ended in the ventrolateral area (basal ganglia). Nucleus dorsomedialis projected to both cortex/pallium and the dorsolateral area. Based on the locus of telencephalic termination and fiber trajectory from the dorsal thalamus, nuclei of the dorsal thalamus were divided into several groups.

Background Saccular, side-branch aneurysms are cerebral aneurysms that occur at the junction between a major intracranial artery and a smaller vessel that originates from this parent artery. The geometry of this group of aneurysms was investigated to determine the location of the side branch in relation to the parent vessel or aneurysm neck. Methods From a series of microsurgically clipped cerebral aneurysms, 121 side-branch aneurysms had detailed imaging studies and operative records that could be analyzed to determine side-branch vessel origin in relation to the aneurysm neck. Results The distribution of aneurysms (N) and the number in which the side-branch originated from the parent artery (PA) were: internal carotid ophthalmic (N = 37; PA = 11); internal carotid-superior hypophyseal (N = 2; PA = 2); internal carotid-posterior communicating (N = 28; PA = 11); internal carotid-anterior choroidal (N = 5; PA = 1); main stem of the middle cerebral artery (N = 13; PA = 6); main stem of the anterior cerebral artery (N = 7; PA = 6); secondary branch of the middle cerebral artery (N = 8; PA = 7); secondary branch of the anterior cerebral artery (N = 1; PA = 0); vertebral-posterior inferior cerebellar artery (N = 11; PA = 5); basilar-anterior inferior cerebellar artery (N = 2; PA = 1); and basilar-superior cerebellar artery (N = 7; PA = 5). Conclusions Regardless of whether these observations reflect the universe of cerebral aneurysms, a certain percentage of this group of aneurysms will have the side-branch vessel originate from the aneurysm neck. This incidence will likely be influenced by aneurysm location and other factors. Protection of these important vessels from occlusion during endovascular management will require sophisticated endovascular techniques. If these measures are either unavailable or prove unsuccessful, then clipping will be needed if the side-branch vessel originates from the aneurysm neck and its preservation is critical.

Interconnections between the dorsal column nucleus and the cerebellum were examined in one group of reptiles, Caiman crocodilus. After anterograde tracer injections into the dorsal column nucleus, efferents terminated nearly exclusively in the white matter and ventral portion of the granule cell layer of the ipsilateral cerebellum. Subsequent to deposition of a retrograde tracer into the cerebellum, neurons in the central and ventral half of the dorsal column nucleus were labeled. When compared with the origin of midbrain and spinal cord projecting cells in Caiman, cerebellar projecting neurons arose from a more rostral location in the dorsal column nucleus than did neurons that terminated in either of these two other targets. The results of the present and previous experiments suggest that the dorsal column nucleus in this reptilian group is organized into sectors based on efferent target in a fashion similar to what has been described in certain mammals. Furthermore, the presence of this circuit in crocodilians and turtles suggests that his pathway from the dorsal column nucleus to the cerebellum arose early in amniote evolution.

Cerebral aneurysms are commonly named based on their relationship with adjacent vessels in either the anterior or posterior circulation. Although such an approach has long proved useful, this terminology does not take into account potential hemodynamic forces or aneurysm wall properties that are likely to be important for cerebral aneurysm formation, growth, rupture, and treatment. Dissecting, traumatic, false, infectious, and tumorous aneurysms were excluded from review. Only aneurysms in which preoperative imaging studies and operative findings were sufficient for classification were included. All 329 reviewed aneurysms could be divided into 2 groups: fusiform (n=16) and saccular (n=313). Fusiform aneurysms could be subdivided into 2 types: simple (no branch vessel; n=10) and complex (one or more side branches; n=6). Saccular aneurysms could be subdivided into 3 groups: those not associated with a branch vessel (n=31), those associated with a side-branch vessel (n=125), and those located at a bifurcation (n=157). Each of these categories of aneurysms could be classified further based on its association with a conducting, primary, secondary, tertiary, or side-branch vessel. Classification of cerebral aneurysms according to this scheme adequately described all reviewed aneurysms. Grouping aneurysms according to this approach focuses on similarities in angioarchitecture and potential rheologic properties that should prove useful for evaluation of aneurysm growth, rupture, and treatment.

PAX6 expression was examined during early development of the diencephalon and midbrain of Alligator using an immunocytochemical methodology. These observations focused on the basal plate to determine whether diencephalic prosomere organization in this region followed a pattern previously identified for alar plate areas. PAX6 expression was also described in alar diencephalic regions and the adjacent midbrain. PAX6 (+) cells in the basal plate were first seen in prosomere 1 at stage 7, in the midbrain at stage 10, and lastly in prosomeres 2 and 3 at stage 11. By stage 12, a nearly continuous column of PAX6 (+) cells extended from the midbrain basal plate through the entire diencephalon. In the diencephalon, PAX6 (+) cells in the basal plate were of greatest number in prosomere 1, least in prosomere 2, and intermediate in prosomere 3. This pattern of PAX6 expression distinguished these individual basal plate prosomeres. These results indicate that basal plate prosomeres follow a pattern similar to alar plate prosomereric organization during the later stages of early diencephalon development. Over a comparable time period of early diencephalon development, similar observations have been made in chick basal plate. In Alligator and chick, PAX6 expression in the basal plate is similar in the midbrain and prosomere 1 but different in prosomeres 2 and 3: present in Alligator and absent in chick. In alar plate areas of the Alligator diencephalon, PAX6 expression follows a similar pattern to that described for chick and mouse. These similarities in PAX6 expression in alar diencephalic prosomeres suggest that this is a common feature of amniotes. Differential PAX6 expression in alar prosomere 1 and the midbrain in Alligator is similar to that described for a wide range of species which suggests that these features are common to all vertebrates.

Organization and development of the forebrain in crocodilians are reviewed. In juvenile Caiman crocodilus, the following features were examined: identification and classification of dorsal thalamic nuclei and their respective connections with the telencephalon, presence of local circuit neurons in the dorsal thalamic nuclei, telencephalic projections to the dorsal thalamus, and organization of the thalamic reticular nucleus. These results document many similarities between crocodilians and other reptiles and birds. While crocodilians, as well as other sauropsids, demonstrate several features of neural circuitry in common with mammals, certain striking differences in organization of the forebrain are present. These differences are the result of evolution. To explore a basis for these differences, embryos of Alligator misissippiensis were examined to address the following. First, very early development of the brain in Alligator is similar to that of other amniotes. Second, the developmental program for individual vesicles of the brain differs between the secondary prosencephalon, diencephalon, midbrain, and hindbrain in Alligator. This is likely to be the case for other amniotes. Third, initial development of the diencephalon in Alligator is similar to that in other amniotes. In Alligator, alar and basal parts likely follow a different developmental scheme.

A technique using vascularized pericranium to close dural defects after anterior clinoid and/or optic canal roof removal is described. This approach is simple, inexpensive, and uses autologous tissue. This method has provided satisfactory dural closure and has avoided cerebrospinal fluid leaks or extradural accumulation of cerebrospinal fluid.

Cell proliferation, as determined by immunoreactivity to proliferating cell nuclear antigen (PCNA) was investigated during early hindbrain development in Alligator. At the earliest stage examined, stage 3, when five rhombomeres are present, PCNA immunoreactivity is more robust laterally towards the pial margin and interrhombomeric boundaries are clearly seen. Subsequently, PCNA immunoreactivity fills each respective rhombomere and increases in intensity but respects the boundaries between segments until stage 7. At this time, borders between rhombomeres become less distinct. At stage 8, when the full compliment of rhombomeres is present, two longitudinal columns of PCNA immunoreactivity are seen rostrally which coalesce into a single column caudally. Interrhombomeric borders are indistinct. Later, at stage 9/10, two longitudinal columns span the entire length of the hindbrain and interrhombomeric boundaries remain less clear. The more lateral column fades whereas the medial stripe persists through stage 12. Thereafter, immunoreactivity fades. These observations confirm the findings in other species that rhombomeres are centers of cell proliferation. This feature is most likely common to hindbrain development in all gnathostomes. It is hypothesized that these two longitudinal columns of cell proliferation might be important for future patterning of the hindbrain.

A pathologically confirmed angiographically visible and invisible arteriovenous malformation in the same patient is described. The potential clinical significance of these observations is detailed and discussed.

The origin of midbrain projecting cells in the dorsal column nucleus (DCN) was investigated in reptiles, Caiman crocodilus, using a retrograde tracer. Labeled neurons were confined to a caudal-central portion of the DCN. Midbrain projecting DCN neurons had round, oval, or triangular soma and were small. While neurons that project to the spinal cord in Caiman are also located in the caudal half of the DCN, midbrain projecting cells are located more dorsally and are smaller than those whose axons terminate in the spinal cord. Taken together, these observations suggest that the DCN in Caiman is subdivided, at least in part, according to target location. In view of similar findings in certain birds and mammals, subdivisions of the DCN into sectors is likely a phylogenetically ancient feature of amniote sensory systems transmitting somatosensory information from the body surface.

Quantitative data from a recent human cadaveric study suggested that removal of the lateral orbital rim alone may be sufficient to reach many targets for which the orbitozygomatic craniotomy has been used. Consequently, a lateral orbital rim osteotomy was substituted for an orbitozygomatic craniotomy in seven patients with a variety of pathologies located in the anterior, middle, and interpeduncular fossae. In each case, lateral orbitotomy provided a satisfactory surgical corridor for diagnosis and treatment. Compared with the orbitozygomatic craniotomy, the lateral orbital rim osteotomy offers several advantages: technical simplicity, shorter operating time, and a low risk of postoperative malocclusion. If, however, prolonged access to a wide expanse of the anterior portion of the middle fossa and inferotemporal area is needed, an orbitozygomatic approach is a better choice.

BACKGROUND Although subarachnoid hemorrhage (SAH) is often associated with electrocardiographic abnormalities, profound effects on cardiac performance are rare. CASE DESCRIPTION A 57-year-old woman who developed loss of consciousness, respiratory distress, severe hypotension, and left ventricular hypokinesis with minimal coronary artery disease is described. Despite normal appearance of the coronary arteries on angiography, left ventricle function was so severely depressed that she required intra-aortic balloon pump support for 24 hours. Mental status changes prompted a head computed tomographic (CT) scan, which showed severe SAH and an intraventricular hemorrhage (IVH). Cerebral angiography demonstrated a basilar apex aneurysm. An echocardiogram done on hospital day 6 was normal. A left frontal ventriculostomy catheter was placed. This was later changed to a lumbar subarachnoid (SA) drain. The patient underwent an orbito-zygomatic craniotomy and aneurysm clipping. Although several serious medical problems occurred during her hospitalization, at follow-up, her sole neurological impairment was a minimal and resolving oculomotor paresis. CONCLUSION This patient's respiratory failure and severe hypotension were initially thought to be due to a chemical pneumonitis or a cardiomyopathy. However, her symptoms ultimately proved to be secondary to a ruptured basilar apex aneurysm. The complex relationship of SAH to myocardial stunning, as illustrated by this patient, is discussed.

Caiman crocodilus, as a representative of the order Crocodilia, was used in immunohistochemical studies. Immunohistochemical procedures were performed on free-floating sections using a monoclonal antibody against porcine glial fibrillary acidic protein (GFAP) and employing standard avidin-biotin complex methodology. The astroglia of Caiman exhibited robust immunoreactivity to the antibodies raised against mammalian GFAP. In Caiman, the predominant GFAP-immunopositive elements are the radial ependymoglia, similar to other reptiles. The regional variability of glial architecture in Caiman, however, seems greater than in other reptiles so far examined, although it is less compared with chickens. We suggest that this finding corresponds to a more advanced “regional adaptation” of the glial structure in Caiman compared with other reptiles. The main feature that distinguishes the astroglia of Caiman from those of other reptiles is the widespread occurrence of GFAP-immunopositive astrocytes. These cells are limited in lizards and snakes, are not present in turtles, but are found in every major brain area in Caiman. However, even in Caiman, astrocytes are only intermingled with radial glia and are not the predominant glial element of any brain area. The occurrence of astrocytes does not correlate with brain wall thickness. Despite their origin from different ancestral groups of stem reptiles (synapsid or diapsid), mammals and birds exhibit some common general features in their glial architecture and GFAP distribution: 1) predominance of astrocytes and 2) absent or limited GFAP immunopositivity of several brain areas. The present study demonstrates that, even in Caiman, a representative of the reptilian group most closely related to birds, these features are present only in part, suggesting that, in mammals and birds, they have evolved independently. J. Comp. Neurol. 431:460–480, 2001. © 2001 Wiley-Liss, Inc.

STUDY DESIGN A technique for posterior cervical hemilaminectomy reconstruction is described. OBJECTIVE To describe a technique for reconstruction of cervical hemilaminae in an adult that resulted in osseous fusion and to suggest modifications for use in children. SUMMARY OF BACKGROUND DATA Although uncommon, cervical hemilaminectomy can result in spine deformity. Re-establishment of the osseous and ligamentous structures should minimize this problem. METHOD After excision of an intraspinal neurenteric cyst, removed cervical hemilaminae at C2 and C3 were reconstructed with metal plates, and posterior ligaments were reapproximated with suture. RESULTS Radiologic evidence of osseous fusion was present at 1 year after surgery. CONCLUSIONS The advantages of this technique are restoration of normal anatomy, technical ease, and simplicity. A modification of this technique in children by using absorbable rather than metal plates should allow for normal spine growth.

Rhombomere development was investigated in a reptile, Alligator mississippiensis, using a variety of methodologies: cytoarchitecture (cresyl violet), histochemistry (peanut agglutinin), immunocytochemistry (antibodies to acetylated tubulin, vimentin, calretinin, and acetylcholinesterase), and external and internal morphology of wholemount embryos. Rhombomere boundaries form sequentially until 8 rhombomeres are present at stage 8. From stage 11 onwards, rhombomere borders fade. When present, boundaries of rhombomeres 2 through 5 were distinct. In all embryos, except the earliest stages, neural tissue was divided between the caudal end of the mesencephalon and the rostral end of the rhombencephalon. This area of transection was designated as the isthmus. For these technical reasons, a distinct border between the midbrain and the first rhombomere was not seen and the isthmic rhombomere could not be identified. The interrhombomeric boundary between rhombomere 7 and rhombomere 8 and between the most caudal rhombomere and the spinal cord was not nearly as clear as were the boundaries of rhombomeres 2 through 5. Development of rhombomeres 2 through 5 was investigated in wholemount preparations between stages 5/6 and 11. Qualitative and quantitative observations were made. In these rhombomeres, r2 through r5, rostrocaudal caudal expansion occurs at a slower rate than mediolateral development. This differential growth sculpts the morphology of rhombomeres 2 through 5. Rhombomere development in Alligator shares several features in common with hindbrain segmentation in chick. The identification of rhombomeres in a multitude of vertebrates from a variety of classes suggests that segmentation is a feature common to hindbrain development in all vertebrates.

BACKGROUND Many reports indicate that acoustic neuromas greater than 2.0 cm should be removed without hearing preservation attempted, even if hearing is present preoperatively. These studies advocate a translabyrinthine approach because the likelihood of hearing preservation is low. Medial acoustic neuromas, unlike the more common lateral tumors that involve the internal auditory canal, originate medial to that portion of the eighth nerve complex where the cochlear and vestibular nerves are fused. This anatomical feature suggests that these tumors may be amenable to resection with hearing preservation. METHODS A patient with a 3.5 cm medial acoustic neuroma and useful preoperative hearing is presented. RESULTS Gross total tumor removal with functional hearing was achieved after a two-stage procedure using a suboccipital approach. CONCLUSION Based on the anatomico-pathologic features in this case, we believe that, if a patient has reasonable preoperative hearing (speech discrimination score > 70%) and a medial acoustic neuroma, an approach to preserve hearing should be considered regardless of tumor size.

We describe a retroauricular approach, adjacent to the mastoid tip, in two patients that allowed successful biopsy of posterior skull base lesions. Diagnoses were central giant cell granuloma, an unusual tumor rarely reported in the skull base, and meningioma. In both patients, the needle biopsy accurately identified the pathology found at surgery. The described approach may allow biopsy of posterior lesions that are inaccessible with other methods.

Nucleus rotundus is a prominent nucleus in the dorsal thalamus of nonmammalian amniotes. In one group of reptiles, Caiman crocodilus, previous studies have identified three parts of this neuronal aggregate. The central portion, the rotundal core, which receives visual input from the midbrain and projects to a restricted portion of the telencephalon, contains relay cells only. Previous examinations using Nissl morphology indicated that neurons of the rotundal core were not a homogeneous population of cells. The present investigation utilized another methodology to examine cell populations within the rotundal core, immunoreactivity to the calcium binding proteins, calbindin/calretinin and parvalbumin. Light microscopic observations revealed the following features. First, calbindin/calretinin immunoreactive neurons and parvalbumin immunoreactive neurons were present in the rotundal core. Of these two antibodies, immunoreactivity to calbindin/calretinin was much more robust and calbindin/calretinin immunoreactive neurons were more numerous than parvalbumin cells. Second, neurons immunoreactive to either calbindin/calretinin or parvalbumin were not homogeneous but comprised several populations based on perikaryal shape and size and neuronal process morphology. These results are compared with similar data in other amniotes.

Granuloma formation is a known complication after microvascular decompression using Teflon fibers. Such granulomas commonly present with recurrent neuralgia whereas other symptoms are exceedingly rare. We report the first case of a multicystic lesion due to a Teflon granuloma that is also uncommon for the lack of recurrent neuralgia.

Background Timing of carotid endarterectomy after stroke in a patient with a fixed neurological deficit remains an important but unresolved question. Early surgery has been associated with cerebral hemorrhage and infarct extension. Delayed endarterectomy exposes the patient to recurrent stroke and carotid occlusion. This review investigates the hypothesis that timing of surgery after stroke influences outcome and complications. Summary of Review This analysis critically evaluates peer-reviewed reports that retrospectively examined outcome after surgery performed “early” and “late” after stroke. The basis for intracerebral hemorrhage after endarterectomy is discussed. Clinical features that influence outcome are investigated. Conclusions Patients undergoing carotid endarterectomy are considered a heterogeneous group based on the following features: presence of low density on cranial CT, vascular territory of the infarct, brain shift, and level of consciousness. While critical review of these retrospective studies suggests that some patients with an acute stroke can safely undergo endarterectomy shortly after the diagnosis is made, direct answers to these questions of timing of endarterectomy after stroke are best addressed by prospective studies. Nevertheless, the present review provides a basis for decision making in certain patients and for the design of future investigations.

The morphology of nucleus rotundus, a visual thalamic nucleus, was investigated in one species of reptiles. Caiman crocodilus, using Nisst stained material in transverse, sagittal, and horizontal planes. The topographical location of nucleus rotundus and its relationship to surrounding thalamic nuclear groups are described. Nucleus rotundus in Caiman can be subdivided into three areas: (1) an outer shell; (2) an inner core; and (3) a cell poor zone located between the shell and core. Most rotundal core neurons were round, fusiform, triangular, pear-shaped, or elliptical. Core neurons were not distributed evenly throughout the nucleus but, in many instances, were arranged in clusters composed of two to ten neurons. Quantitative measurements of area, perimeter, and eccentricity (greatest width/greatest length), which served as an index of cell roundness, were made on rotundal core neuron profiles in transverse, sagittal, and horizontal planes of section. Qualitative and quantitative observations were not appreciably different regardless of the plane of orientation. Both qualitative and quantitative data suggest that relay cells located in the core of nucleus rotundus are not a homogeneous population of neurons but comprise several subtypes.

Objective Saccular cerebral aneurysms located at nonbranching sites are uncommon. Their distribution, morphological features, and presence of a branch vessel or a tiny perforator(s) separate from the aneurysm neck were investigated. Methods From a series of 303 microsurgically clipped saccular cerebral aneurysms, 40 aneurysms were identified at sites not related to a branch vessel. Results The distribution of aneurysms at nonbranching sites was internal carotid: 21 of 40 (52.5%); main stem of the middle cerebral artery/secondary branch of the middle cerebral artery: 6 of 40 (15%); anterior cerebral artery: 1 of 40 (2.5%); pericallosal artery: 1 of 40 (2.5%); pericallosal/callosal marginal: 3 of 40 (7.5%); vertebral artery: 1 of 40 (2.5%); posterior cerebral artery: 1 of 40 (2.5%); posterior cerebral artery/secondary branch of the posterior cerebral artery: 1 of 40 (2.5%); anterior inferior cerebellar artery: 1 of 40 (2.5%); and distal posterior inferior cerebellar artery: 1 of 40 (2.5%). Branch vessels were seen in 5 cases, and small perforating vessels were observed in 2 instances. Conclusions Saccular aneurysms occurring at nonbranching sites are uncommon. Their geometry is particularly favorable for flow directed stents and is most amenable to aneurysms located on large-diameter conducting vessels such as the internal carotid, vertebral, and vertebrobasilar vessels. Smaller parent arteries harboring this type of aneurysm will require new technology to maintain patency of these more distal vessels. If endovascular techniques cannot achieve aneurysm sac obliteration, then open craniotomy and aneurysm clipping will provide a satisfactory alternative.

Subarachnoid hemorrhage affects more than 25,000 Americans yearly and is most commonly caused by a ruptured, saccular, cerebral aneurysm. Current measures to evaluate and manage patients with nontraumatic subarachnoid hemorrhage are detailed. Areas of future progress are presented. The diagnosis and treatment of intracranial subarachnoid hemorrhage represent a medical and surgical emergency.

Interconnections between the dorsal column nucleus and the spinal cord were investigated in a reptile, Caiman crocodilus. After placement of an anterograde tracer into the dorsal column nucleus, descending fibers are seen to leave this nucleus to enter the dorsal funiculus where they course ventrally to terminate in lamina V of the spinal cord as far caudally as C2. Placement of a retrograde tracer into cut fibers of the cervical spinal cord identified the relay cells of the dorsal column nucleus that project to the spinal cord. These neurons were mainly clustered in a caudal and ventral part of this nucleus. The soma of these spinally projecting cells were small and were generally round or oval in shape. A number of these neurons had the long axis of their soma oriented dorsoventrally, with a primary dendrite extending dorsally. Fibers in the dorsal funiculus that originated from the spinal cord enter the caudal part of the dorsal column nucleus and turn ventral. In the dorsal column nucleus, these axons run parallel to the vertically oriented dendrites of these spinally projecting cells before termination in close relation to the cell bodies of these neurons. Quantitative observations (mean +/- standard error) were made on well labeled neurons and included several measurements: area, perimeter, and degree of eccentricity (greatest width/greatest length) in both the transverse as well as the sagittal plane. These spinally projecting neurons in Caiman are located in the dorsal column nucleus in a position similar to that of spinally projecting cells in cats.

Vertebrate brains share many features in common. Early in development, both the hindbrain and diencephalon are built similarly. Only later in time do differences in morphology occur. Factors that could potentially influence such changes include certain physiological properties of neurons. As an initial step to investigate this problem, embryonic Alligator brain neurons were cultured and calcium responses were characterized. The present report is the first to document culture of Alligator brain neurons in artificial cerebrospinal fluid (ACSF) as well as in standard mammalian tissue culture medium supplemented with growth factors. Alligator brain neuron cultures were viable for at least 1 week with unipolar neurites emerging by 24 hours. Employing Fura-2 AM, robust depolarizationinduced calcium influx, was observed in these neurons. Using selective blockers of the voltage-gated calcium channels, the contributions of N-, P/Q-, R-, T-, and L-type channels in these neurons were assessed and their presence documented. Lastly, Alligator brain neurons were challenged with an excitotoxic stimulus (glutamate + glycine) where delayed calcium deregulation could be prevented by a classical NMDA receptor antagonist.

Certain aspects of thalamic organization in reptiles and mammals are reviewed. Features shared by the dorsal thalamus of reptiles and that of mammals include projection to the telencephalon, specific and non-specific non-telencephalic afferents, and input from the thalamic reticular nucleus. Differences between the dorsal thalamus of reptiles and that of mammals are the absence of reciprocal telencephalic efferents to the dorsal thalamus and lack of local circuit neurons in reptiles (with the exception of the dorsal geniculate complex in turtles) and their presence in mammals. A thalamic reticular nucleus is present in both reptiles and mammals. In both of these classes of vertebrates, this neuronal aggregate surrounds the dorsal thalamus along its lateral surface, projects to the dorsal thalamus, and is organized into sectors. In one group of reptiles, Caiman crocodilus, the sole reptilian group in which immunocytochemical features have been investigated in detail, the reticular nucleus contains at least three neuronal subpopulations: neurons immunoreactive for glutamic acid decarboxylase (GAD); neurons immunoreactive for parvalbumin; and cells that are not immunoreactive for parvalbumin or, probably, GAD. On the other hand, the reticular nucleus of mammals contains a single population of neurons immunoreactive for GAD, gamma amino butyric acid, and parvalbumin.

Telencephalic projections of a thalamic somatosensory area were investigated in a reptilian species, Caiman crocodilus, by means of horseradish peroxidase (HRP) neurohistochemistry. Injections of HRP into the medialis complex labeled axons that leave the ventral aspect of this nucleus to enter the dorsal peduncle of the lateral forebrain bundle where they ascend. These fibers course rostrally to enter the central portion of the lateral forebrain bundle. Here, axons turn dorsally, pass through, and probably synapse on, interposed neurons of the ventrolateral area, to end in a central portion of the dorsal ventricular ridge (DVR). These findings were confirmed by HRP injections into this somatosensory area of the DVR that retrogradely labeled neurons in the medialis complex. This telencephalic somatosensory area identified in transverse sections was then reconstructed onto a surface view of the DVR. The locus of this forebrain somesthetic region was then compared with the location of the DVR projection areas of auditory (nucleus reuniens) and visual (nucleus rotundus) thalamic nuclei. This analysis suggested two features. First, telencephalic terminal zones of dorsal thalamic nuclei were largely separate and non-overlapping. Second, the locus of termination in the DVR of each thalamic nucleus reflected each nucleus's topography in the dorsal thalamus. Additional parallels in the neural circuitry of auditory, visual, and somatosensory systems that synapse in the midbrain and project to the DVR are documented.

The presence of a postsynaptic dorsal column system was investigated in reptiles, Caiman crocodilus . Several experiments were undertaken. First, a cytoarchitectonic analysis of the

Telencephalic projections of a thalamic somatosensory area were investigated in a reptilian species, Caiman crocodilus, by means of horseradish peroxidase (HRP) neurohistochemistry.

Gene expression was investigated in the major brain subdivisions (telencephalon, diencephalon, midbrain and hindbrain) in a representative reptile, Alligator mississipiensis, during the later stages of embryonic development. The following genes were examined: voltage-gated sodium channel isoforms: NaV1.1 and NaV1.2; synaptic vesicle 2a (SV2a); synaptophysin; and calbindin 2. With the exception of synaptophysin, which was only expressed in the telencephalon, all genes were expressed in all brain regions sampled at the time periods examined. For NaV1.1, gene expression varied according to brain area sampled. When compared with NaV1.1, the pattern of NaV1.2 gene expression differed appreciably. The gene expression of SV2a was the most robust of any of the genes examined. Of the other genes examined, although differences were noted, no statistically significant changes were found either between brain part or time interval. Although limited, the present analysis is the first quantitative mRNA gene expression study in any reptile during development. Together with future experiments of a similar nature, the present gene expression results should determine which genes are expressed in major brain areas at which times during development in Alligator. When compared with other amniotes, these results will prove useful for determining how gene expression during development influences adult brain structure.

BACKGROUND While rupture of a cerebral aneurysm into the subdural space is rare, aneurysmal subarachnoid hemorrhage in the presence of subdural hematoma(s) is much more uncommon. Such a patient requires changes in routine perioperative management. CASE DESCRIPTION A patient with a ruptured middle cerebral artery bifurcation aneurysm and bilateral subdural hematomas is presented. He underwent successful aneurysm clipping and subdural hematoma evacuations. At the time of surgery, measures commonly used to obtain brain relaxation were avoided. The patient was kept normovolemic, normocarbic, and normotensive. He recovered completely and resumed his prior occupation. CONCLUSIONS Changes in standard techniques for a patient undergoing a pterional craniotomy for a ruptured cerebral aneurysm are required when bilateral extra-axial mass lesions are present.

Injections of horseradish peroxidase (HRP) into a caudocentral portion of the non-cortical telencephalon of Caiman known as the dorsolateral area (dorsal ventricular ridge) resulted in retrogradely labeled neurons throughout the entire extent of the ipsilateral nucleus reuniens. HRP-positive cells were most numerous in nucleus reuniens pars diffusa with only sparse labeling of neurons in nucleus reuniens pars centralis. The results of the present experiment, when compared with those of a prior study that determined the telencephalic connections of nucleus reuniens pars centralis, suggested that those two forebrain areas are separate. Staining with succinate dehydrogenase and acetylcholinesterase revealed that nucleus reuniens pars centralis and pars diffusa and their respective telencephalic projection areas can be differentiated on the basis of histochemical features. These findings in Caiman suggest that certain thalamic and telencephalic auditory areas in birds and crocodilians are most likely the result of common ancestry rather than examples of parallel evolution.

The relationship between fiber tract formation and transverse and longitudinal borders of the diencephalon was investigated in Alligator embryos beginning when this structure was a single unit and continuing until internal subgroups were present within individual segments. At all stages of development, distinct bundles of fibers were not restricted to borders between morphological segments nor were they located at the alar/basal plate boundary. With the exception of a few fine fibers that occupied only a part of certain inter-diencephalic boundaries, fiber tracts were present within the parenchyma of respective subdivisions. In the process of this analysis, fiber tract formation was also documented in the telencephalon, secondary prosencephalon, and midbrain during this period of early development. Fiber tracts were classified into three groups based on orientation: transverse; longitudinal; and commissural. At early stages of development, similarities between Alligator and other species suggest that these bundles represent a primary scaffold for all vertebrates with two exceptions. One was the presence of the descending tract of the mesencephalic trigeminal nucleus in Alligator and other jawed animals but not in jawless vertebrates. The other was the absence of the dorsoventral diencephalic tract in Alligator which lacks a pineal gland.