Microsurgical anatomy of the central core of the brain.

OBJECTIVE The purpose of this study was to describe in detail the cortical and subcortical anatomy of the central core of the brain, defining its limits, with particular attention to the topography and relationships of the thalamus, basal ganglia, and related white matter pathways and vessels. METHODS The authors studied 19 cerebral hemispheres. The vascular systems of all of the specimens were injected with colored silicone, and the specimens were then frozen for at least 1 month to facilitate identification of individual fiber tracts. The dissections were performed in a stepwise manner, locating each gray matter nucleus and white matter pathway at different depths inside the central core. The course of fiber pathways was also noted in relation to the insular limiting sulci. RESULTS The insular surface is the most superficial aspect of the central core and is divided by a central sulcus into an anterior portion, usually containing 3 short gyri, and a posterior portion, with 2 long gyri. It is bounded by the anterior limiting sulcus, the superior limiting sulcus, and the inferior limiting sulcus. The extreme capsule is directly underneath the insular surface and is composed of short association fibers that extend toward all the opercula. The claustrum lies deep to the extreme capsule, and the external capsule is found medial to it. Three fiber pathways contribute to form both the extreme and external capsules, and they lie in a sequential anteroposterior disposition: the uncinate fascicle, the inferior fronto-occipital fascicle, and claustrocortical fibers. The putamen and the globus pallidus are between the external capsule, laterally, and the internal capsule, medially. The internal capsule is present medial to almost all insular limiting sulci and most of the insular surface, but not to their most anteroinferior portions. This anteroinferior portion of the central core has a more complex anatomy and is distinguished in this paper as the "anterior perforated substance region." The caudate nucleus and thalamus lie medial to the internal capsule, as the most medial structures of the central core. While the anterior half of the central core is related to the head of the caudate nucleus, the posterior half is related to the thalamus, and hence to each associated portion of the internal capsule between these structures and the insular surface. The central core stands on top of the brainstem. The brainstem and central core are connected by several white matter pathways and are not separated from each other by any natural division. The authors propose a subdivision of the central core into quadrants and describe each in detail. The functional importance of each structure is highlighted, and surgical approaches are suggested for each quadrant of the central core. CONCLUSIONS As a general rule, the internal capsule and its vascularization should be seen as a parasagittal barrier with great functional importance. This is of particular importance in choosing surgical approaches within this region.

The Superior Thalamic Vein and its Variations: A Proposed Classification.

BACKGROUND: The superior thalamic vein (STV) was first described comprehensively by Ferner in 1958 as the most prominent thalamic vein; it originates from the central superior portion of the thalamus, coursing medially to the third ventricular thalamic surface, where it turns posteriorly to parallel the internal cerebral vein (ICV) before ending into its posterior portion. Since historical anatomic and angiographic studies in the pre-computed tomography (CT)/magnetic resonance imaging era, the STV has not been investigated. OBJECTIVE: To describe the anatomic course of the STV with its variations, and to propose a classification system based on its draining pattern. METHODS: We retrospectively screened our imaging database for 50 patients who had a CT-angiography with predefined parameters. The images were independently reviewed by 3 neurosurgeons and 1 neuroradiologist to classify the STV into 4 types: type 1A-drainage into the anterior portion of the ICV, type 1B-drainage into the posterior portion of the ICV, type 2-drainage into the vein of Rosenthal, type 3-drainage into a medial (3A) or lateral (3B) atrial vein, and type 4-drainage into the vein of Galen. RESULTS: In 50 patients, we could identify 96 STVs. In 2 hemispheres, the STV was doubled. The 92 single STVs were classified as type 1A in 25 hemispheres (27.2%), type 1B in 45 (48.9%), type 2 in 12 (13.0%), type 3A in 8 (8.7%), type 3B in 1 (1.1%), and type 4 in 1 (1.1%). CONCLUSION: The draining pattern of the STV varies widely from the initial description.

Sturge-Weber syndrome with spontaneous intracerebral hemorrhage in childhood.

A girl aged 2 years 10 months suddenly went into a deep coma and demonstrated left hemiplegia. At birth, she had exhibited a left-sided facial port-wine stain typical of Sturge-Weber syndrome (SWS) and involving the V1 and V2 distributions of the trigeminal nerve. Computed tomography showed a right thalamic hemorrhage with acute hydrocephalus. Magnetic resonance imaging with Gd enhancement 8 months before the hemorrhage had shown a patent superior sagittal sinus (SSS) and deep venous system. Magnetic resonance imaging and MR angiography studies 2 months before the hemorrhage had revealed obstruction of the SSS and right internal cerebral vein (ICV). Given that a digital subtraction angiography study obtained after the hemorrhage did not show the SSS or right ICV, the authors assumed that impaired drainage was present in the deep venous system at that stage. The authors speculated that the patient's venous drainage pattern underwent compensatory changes because of the occluded SSS and deep venous collectors, shifting outflow through other cortical venous channels to nonoccluded dural sinuses. Sudden congestion (nearly total to total obstruction) of the ICV may have caused the thalamic hemorrhage in this case, which is the first reported instance of pediatric SWS with intracerebral hemorrhage and no other vascular lesion. Findings suggested that the appearance of major venous sinus occlusion in a child with SWS could be a warning sign of hemorrhage.

An anatomical assessment of the supracerebellar midline and paramedian approaches to the inferior colliculus for auditory midbrain implants using a neuronavigation model on cadaveric specimens.

The inferior colliculus (IC) is an alternative site for electrode placement in neural deafness due to its surgical accessibility and its well-known tonotopic stratification. In patients where tumor surgery has already occurred and the cerebellopontine angle contains scar tissue or tumor-remnants, midline and paramedian supracerebellar approaches are alternative routes. They are often avoided due to concerns regarding the venous drainage of the cerebellum, the electrode trajectory and the course of the electrode cable. We studied these surgical routes in five neuronavigated fixed cadaveric specimens. For paramedian and midline approaches, the transverse sinus was exposed 5.8mm on average. A mean of 1.6 cerebellar veins, with an average diameter of 2.0mm, draining to the tentorium were transected to reach the tentorial notch. Only 0.4 arterial branches were met. We conclude that the supracerebellar midline and paramedian approaches provide a good exposure of the IC and offer safe and viable alternative routes to the IC. Additionally, they provide a wider angle of action for optimal electrode placement.

Alternative uses for the subgaleal shunt in pediatric neurosurgery.

The subgaleal shunt has been used for the temporary bypass of the normal cerebrospinal fluid (CSF) pathways. We retrospectively reviewed all subgaleal shunts placed at the Children's Hospital, Birmingham, Ala., USA, from 1997 to the present and examined all uses (e.g. indication, length of follow-up) of the subgaleal shunt outside its use for temporary CSF diversion in premature infants with intraventricular hemorrhage and subsequent hydrocephalus. The average length of survival of the primary subgaleal shunt in this population was 32.2 days. We have had good success with subgaleal shunts in children with malignant brain tumors, intraventricular abscesses, chronic truncal wounds, chronic subdural hygromas and meningitis. However, the greatest utility has been in those scenarios in which the peritoneal cavities were not currently, but with time would be, candidates for distal shunt implantation. Examples of these instances are patients with hydrocephalus and necrotizing enterocolitis or hydrocephalus and preoperative abdominal wall pathology such as omphalocele.