Jeffrey T. Keller

Connections of the subthalamic nucleus in the monkey

Attempts were made to determine the afferent and efferent connections of the subthalamic nucleus (STN) in the monkey using retrograde and anterograde axoplasmic transport technics. Following HRP injections limited to the STN, label was transported to arrays of cells adjacent, and parallel, to the lateral medullary lamina in the rostral two thirds of the lateral pallidal segment (LPS). Only sparse label was transported to cells of the pedunculopontine nucleus (PPN) and the locus ceruleus (LC). No enzyme was transported across the midline, or to the striatum, medial pallidal segment (MPS), thalamus, substantia nigra (SN) or dorsal nucleus of the raphe (DNR). HRP injected into portions of both the STN and SN produced retrograde transport of the enzyme to cells in parallel arrays in the LPS related rostrocaudally to the injection site. Additional enzyme transport was seen in cells of the striatum, the DNR and the PPN. Only a few isolated cells were labeled in the sensorimotor cortex. Efferent connections of the STN were studied in monkeys in which [3H]amino acids were injected hydraulically or iontophoretically into the STN. Isotope traced in serial autoradiographs was distributed to: (1) both segments of the globus pallidus (GP) in arrays parallel to the medullary laminae, and (2) the pars reticulata of SN (SNpr). The greatest number of terminals was found in the MPS. Fibers from the rostral part of the STN descended along the dorsal border of the SN and projected ventrally to terminations in the SNpr. No isotope was transported across the midline, or to the striatum, thalamus, DNR or PPN. Isotope injected into both the STN and SN produced similar transport to the GP and transport via nigral efferent fibers to: (1) portions of the striatum, (2) specific thalamic nuclei (VAmc, VLm, DMpl), (3) deep and middle gray layers of the superior colliculus and (4) PPN. Control studies indicated that [3H]amino acids injected only into the SN were transported to PPN. HRP injected into PPN produced profuse retrograde transport in cells of the MPS and SNpr and distinct label in a few cells of the zona incerta and STN. These data suggest that the STN receives its major subcortical input from cell of the LPS arranged in arrays which have a rostrocaudal organization. No cells of the MPS or SN project to the STN. The output of the STN is to both segments of the GP and SNpr. Major subcortical projections to PPN arise from the MPS and SNpr, but afferents also arise from other sources. The major projection of PPN is to SN.

Transpetrosal approach : surgical anatomy and technique

Transpetrosal operations have been shown to offer distinct advantages over traditional operations in approaching lesions of the petroclival area. Confusion about these approaches exists due to the variety of names given to these procedures and the lack of detailed descriptions needed to perform them. After extensive review of the literature, we have determined that all transpetrosal techniques fall into one of two categories: anterior petrosectomy or posterior petrosectomy. Combining one of these procedures with existing conventional procedures accurately describes all existing transpetrosal operations and eliminates confusion over nomenclature. In addition, through a series of cadaveric dissections and operative experience, we have detailed each of these procedures as a series of steps that will enable the surgeon to understand the unfamiliar anatomy of the temporal bone and to perform these transpetrosal techniques.

Colored silicone injection for use in neurosurgical dissections: anatomic technical note.

OBJECTIVE The dissection of cadaveric specimens is very important for a more sophisticated understanding of neurosurgical anatomic features and approaches. Teaching known approaches to residents or learning new approaches is best performed in a cadaveric laboratory. The utility of neurosurgical cadaveric dissections can be improved by injecting the intracranial vascular tree with colored silicone. The vascular anatomic features, which are integral to neurosurgical procedures, are much more clearly defined in injected specimens. METHODS Self-curing colored silicone rubber is used to inject the arteries and veins (red and blue, respectively) of the head. This process is described in a step-by-step format. Six steps are required and can be summarized as follows: 1) exposure of the great vessels, 2) cannulation of the great vessels, 3) irrigation of the head, 4) preparation of the colored silicone, 5) injection of the colored silicone, and 6) evaluation of the final specimen. CONCLUSION Injection of colored silicone into the vascular tree can enhance the educational value of cadaveric head dissections. This report describes the technique of vascular injection that is used in the Goodyear Microsurgical Laboratory, the University of Cincinnati, and the Mayfield Clinic.

Microsurgical Anatomic Features and Nomenclature of the Paraclinoid Region

OBJECTIVE We describe the detailed microsurgical anatomic features of the clinoid (C5) segment of the internal carotid artery (ICA) and surrounding structures, clarify the anatomic relationships of structures in this region, and emphasize the clinical relevance of these observations. Furthermore, because the nomenclature of the paraclinoid region is confusing and lacks standardization, this report provides a glossary of terms that are commonly used to descibe the anatomic features of the paraclinoid region. METHODS The region surrounding the anterior clinoid process was observed in 70 specimens from 35 formalin-fixed cadaveric heads. Detailed microanatomic dissections were performed in 10 specimens. Histological sections of this region were obtained from the formalin-fixed cadaveric specimens. RESULTS The clinoid segment of the ICA is the portion that abuts the clinoid process. This portion of the ICA can be directly observed only after removal of the clinoid process. The dura of the cavernous sinus roof separates to enclose the clinoid process. The clinoid segment of the ICA exists only where this separation of dural layers is present. Because the clinoid process does not completely enclose the ICA in most cases, the clinoid segment is shaped more like a wedge than a cylinder. The outer layer of the dura (dura propria) is a thick membrane that fuses with the adventitia of the ICA to form a competent ring that separates the intradural ICA from the extradural ICA. The thin inner membranous layer of the dura loosely surrounds the ICA throughout the entire length of its clinoid segment. The most proximal aspect of this membrane defines the proximal dural ring. The proximal ring is incompetent and admits a variable number of veins from the cavernous plexus that accompany the ICA throughout its clinoid segment. CONCLUSION The narrow space between the inner dural layer and the clinoid ICA is continuous with the cavernous sinus via an incompetent proximal dural ring. This space between the clinoid ICA and the inner dural layer contains a variable number of veins that directly communicate with the cavernous plexus. Given the inconstancy of the venous plexus surrounding the clinoid ICA, we think that categorical labeling of the clinoid ICA as intracavernous or extracavernous cannot be justified.

Synovial cyst of the cervical spine

A case of acute posttraumatic myelopathy resulting from hemorrhage into synovial cysts bilaterally at the C-6, C-7 facet joints is presented. The pathogenesis of synovial cysts remains unclear, although reports in the literature have implicated trauma leading to cyst enlargement. Hemorrhage into the cavity of the synovial cysts resulted in epidural compression of the spinal cord in this patient. Because spinal synovial cysts cannot be unequivocally diagnosed preoperatively, other more common conditions must be considered in the differential diagnosis. Radiographic analysis including plain films, computed axial tomography, and metrizamide myelography are of value in establishing a neurological diagnosis. Surgical decompression and excision of the lesion may result in significant neurological improvement.

Linear arrays of homogenous mast cells in the dura mater of the rat

SummaryUsing fluorescence histochemistry, 5-HT, histamine and heparin were colocalized in a large population of cells in the dura mater thereby identifying them as mast cells. In addition, because these cells were highly sensitive to compound 48/80 and were densely packed with granules of a consistent density, they were identified specifically as ‘connective tissue’ mast cells. Other types of mast cells, i.e. ‘mucosal’ or ‘neurolipomastocytes’, were not present in the rat dura mater. 5-HT immunohistochemistry was the best technique for demonstrating that there were two populations of mast cells, one associated with each of the two layers of dura. Although shaped differently the type of mast cell in each layer was the same. It was observed that mast cell shape is dependent on the contiguity, density and orientation of its surrounding elements, not its type. In general, mast cells in the outer layer were aligned parallel to the middle meningeal artery and those in the inner layer were parallel to trigeminal nerve branches that coursed obliquely across the middle meningeal artery. Examination of cross-sections of dura revealed that most mast cells also were aligned at the interface between the two dural layers. The linear orientation of mast cells in two planes of each layer suggests a programmed lamellar seeding of these cells during development of the dura. This study also demonstrated that the majority of dural mast cells were more closely related to other connective tissue elements than to blood vessels and nerves. These results (1) are compatible with the suggestion that dural mast cells play a non-obligatory role in the neuroinflammatory response, (2) leave open to question the role of the dural mast cell in headache or the regulation of blood flow, and (3) support evidence that dural mast cells play an important role in connective tissue related functions, e.g. development, inflammatory response to injury and wound repair.

Innervation of the posterior fossa dura of the cat

This study was designed to identify the location of neurons giving rise to fibers innervating the posterior fossa dura in the cat using horseradish peroxidase (HRP, Sigma, Type VI). Investigations since the 19th century have implicated innervation by cranial nerves V, VII, IX, X and XII and the upper cervical nerves, C1-3. The meninges of the posterior fossa of 14 cats was exposed using one of three surgical approaches: (1) a suboccipital craniectomy and C1 laminectomy, (2) a parieto-occipital craniectomy with removal of the occipital lobe and bony tentorium exposing the meninges over the cerebellum, or (3) an anterior approach through the upper neck, exposing the dura of the ventral surface of the caudal brainstem. A unilateral, curvilinear incision was made in the dura and HRP was applied to the exposed dural edges. Following 48 hours the animals were sacrificed and fixed by perfusion. Cranial nerve ganglia of V, VII, IX, X, dorsal root ganglia (DRG) of C1-3, and superior cervical ganglia (SCG) were removed bilaterally, sectioned and processed with tetramethylbenzidine (TMB). HRP labeled cells were located bilaterally, always more ipsilaterally, in DRG of C1, C2, C3, and SCG with application of HRP to all three regions of the dura. Labeled cells were also located in trigeminal ganglia and superior ganglia of CN X, occasionally bilaterally, depending on the site of application. No HRP was ever identified in neurons of the geniculate ganglion, inferior ganglion of CN X or superior or inferior ganglia of CN IX. This information is valuable to an understanding of the innervation of intracranial structures and the problems of head pain.

Anatomic and clinical study of the orbitopterional approach to anterior communicating artery aneurysms

OBJECTIVE To evaluate the orbitopterional approach to anterior communicating artery (AComA) aneurysms, on the basis of the quantification of this surgical exposure, compared with the pterional approach, in a cadaveric study and a retrospective review of data for 40 patients who underwent clipping of AComA aneurysms via the orbitopterional approach. METHODS In an anatomic study, four cadaveric heads underwent pterional craniotomies on the left side and orbitopterional craniotomies on the right side. A fifth head was initially subjected to bilateral pterional craniotomies and then underwent bilateral orbital osteotomies, for direct comparison of these approaches. Using frameless stereotaxy, we quantified the angles of exposure and surgical field depths provided by the pterional and orbitopterional craniotomies. In a clinical study, 40 patients who underwent clipping of AComA aneurysms via orbitopterional approaches were evaluated for basal brain injury, the need for resection of the gyrus rectus, dissection of the sylvian fissure, and approach-related complications. The incidence of postoperative hydrocephalus among patients with subarachnoid hemorrhage who underwent lamina terminalis fenestration was also reviewed. RESULTS The angles of observation were increased 46% in the axial plane (orbitopterional, 72.92 +/- 6.57 degrees; pterional, 49.75 +/- 2.27 degrees; P < 0.01) and 137.5% in the projection plane (orbitopterional, 8 +/- 2.19 degrees; pterional, 19 +/- 1.78 degrees; P < 0.01). The surgical window depth was decreased 13% with the orbitopterional approach (P < 0.05). Clinically, there was no incidence of frontobasal hypodensities on postoperative computed tomographic scans. Three patients (7.5%) required resection of the gyrus rectus. No patient required sylvian fissure dissection for aneurysm exposure. Two of 29 patients (6.9%) who survived subarachnoid hemorrhage required ventriculoperitoneal shunts despite lamina terminalis fenestration. No approach-related complications were recognized. CONCLUSION The orbitopterional approach improved the observation of the AComA complex and seemed to decrease the risk of intraoperative brain damage.

Endoscopic approach to the infratemporal fossa: anatomic study.

OBJECTIVEClassic surgical exposures of the infratemporal fossa region, including the adjacent intracranial space, temporal bone, and sinonasal region, require the extensive exposure associated with the transcranial, transfacial, and transmandibular approaches with their inherent neurological and cosmetic morbidities. In this study, we evaluated the feasibility and exposure afforded by combining 2 endoscopic transmaxillary approaches, endonasal and Caldwell-Luc supplement, to the infratemporal fossa. METHODSEndoscopic transmaxillary dissection was performed in 4 formalin-fixed cadaver heads (8 sides). We quantified the extent of exposure achieved within the pterygopalatine and infratemporal fossae after our initial dissection, which was endonasal with a medial antrostomy, and after addition of a Caldwell-Luc incision with an anterior antrostomy. Complementing this anatomic study, we report on a patient in whom this endoscopic transmaxillary approach combining the endonasal and Caldwell-Luc approaches was used for resection of a trigeminal schwannoma in the infratemporal fossa. RESULTSThe combination of these 2 endoscopic transmaxillary approaches enabled visualization of the entire region of the pterygopalatine fossa and anteromedial aspect of the infratemporal fossa. Additional posterolateral exposure of the infratemporal fossa requires significant traumatic traction on the nose. Addition of the Caldwell-Luc transmaxillary approach exposed the remainder of the infratemporal fossa, including the mandibular nerve and branches, middle meningeal artery, and even the distal cervical portion of the internal carotid artery. CONCLUSIONEndoscopic exposure of the infratemporal fossa is feasible. Using the combination of the endonasal and Caldwell-Luc approaches for direct transmaxillary access significantly extended exposure, allowing safe and effective resection of infratemporal fossa lesions.

The One-Piece Orbitozygomatic Approach: The MacCarty Burr Hole and the Inferior Orbital Fissure as Keys to Technique and Application

Summary Objective. Use of the MacCarty keyhole burr hole and the inferior orbital fissure provides simplicity and safety to perform the one-piece frontotemporal orbitozygomatic (FTOZ1) approach. Methods. We performed the FTOZ1 approach with its three subtypes (i.e., total, temporal, and frontal) in cadaveric head specimens in the Goodyear Laboratory and subsequently in surgical cases. Results. The orbitozygomatic osteotomy, when added to a frontotemporal craniotomy, comprises the frontotemporal orbitozygomatic (FTOZ) approach, provides an expanded exposure to the anterior and middle cranial fossae, and enables the surgeon to create a window to the posterior cranial fossa. The MacCarty burr hole is used to facilitate orbital cuts, and the anterolateral portion of the inferior orbital fissure connects the orbital cuts to the zygomatic cuts. This allows the FTOZ1 craniotomy flap to be “out-fractured” with ease. The three types of FTOZ1 approach, i.e., the total, the temporal, and the frontal, are described step by step. Conclusions. Understanding the MacCarty keyhole burr hole and the microsurgical anatomy of the inferior orbital fissure is essential to performing the FTOZ1 approach. The three types of FTOZ1 approach enable the surgeon to tailor the approach according to the surgical exposure needed for each lesion.