Segments of the internal carotid artery during endoscopic transnasal and open cranial approaches: can a uniform nomenclature apply to both?

BACKGROUND

The classic anatomic view of the course of the internal carotid artery (ICA) and its segments familiar to neurosurgeons by a 3-dimensional microscopic cranial view may be challenging to understand when seen in the unique 2-dimensional view of transnasal endoscopic surgery.

OBJECTIVE

We re-examined our 1996 classification of 7 (C1-C7) segments of the ICA, comparing the arterial course in cadaveric dissections for both a transnasal endoscopic transpenoidal approach and frontotemporal craniotomy.

METHODS

Five formalin-fixed cadaveric heads injected with colored silicone underwent thin-cut computed tomographic scanning for bony and vascular analysis. The ICA's intracranial course viewed by transnasal endoscopic dissection was compared with the view of a bilateral frontotemporal crantiotomy, from the petrous (C2) to communicating (C7) segments.

RESULTS

Refinement of our 1996 ICA classification provides an anatomical understanding for endoscopic exposures transnasally along an inferior skull base trajectory. The changing course of the ICA, initially termed loop is now termed bend (i.e., implying a change in direction). Four bends are described as the ICA enters into the skull base as C2, C3-C4, C4, and C4-C5. We discuss delineation of certain problematic ICA segments and identify landmarks for endoscopic endonasal approaches.

CONCLUSIONS

Our classification of the segments of the ICA achieves consistency without sacrificing either clinical or anatomic accuracy for either transcranial or endoscopic approaches. Universal application of this established nomenclature can avoid new and misleading terms, respects anatomical landmarks delineating segments, and provides a universal language for clear communication between disciplines.

Endoscopic, endonasal variability in the anatomy of the internal carotid artery

BACKGROUND

Classic three-dimensional schemas of the internal carotid artery (ICA) for transcranial approaches do not necessarily apply to two-dimensional endoscopic views. Modifying an existing ICA segment classification, we define endoscopic orientation for the lacerum (C3) to clinoid (C5) segments through an endonasal approach.

METHODS

In 20 cadaveric heads, we classified endoscopic appearance based on shape and angulation of C3 to C5 segments. Distances were measured between both arteries, and between the ICA and pituitary gland.

RESULTS

We identified 4 common ICA patterns: types I through III matched side-to-side, whereas type IV was asymmetric. In 80% of specimens, the pituitary gland had direct contact with the ICA. In 20% of specimens, a space existed between the pituitary gland and the cavernous segment. Access to the posterior aspect of the cavernous sinus medial to the cavernous segment was possible without retraction of the artery or pituitary gland. Spaces between the lacerum and cavernous segments were trapezoid (80%) and hourglass (20%).

CONCLUSIONS

Distinguishing which ICA type courses between the lacerum and clinoid segments can help clarify the relationships between the artery and its surrounding structures during endoscopic approaches. Adapting the classic terminology of ICA segments provided consistency of endoscopic relevance, defined potential endoscopic corridors, and highlighted the critical step of arterial contact.

Endoscopic endonasal approach to the maxillary strut: anatomical review and case series

OBJECTIVES/HYPOTHESIS

The maxillary strut is the bone that separates the foramen rotundum and superior orbital fissure. Tumors involving the lateral wall of the sphenoid sinus, posterior ethmoid, or posterior maxillary sinus may invade this region. The authors detail the anatomy of the strut and present a case series that emphasizes the importance and utility of this useful landmark during an endoscopic endonasal approach to lesions in this region.

STUDY DESIGN

Cadaveric dissections and retrospective case series.

METHODS

Endoscopic endonasal dissections were performed on six formalin-fixed cadaver heads. Morphometric analyses of 100 skulls were conducted using CT scans and BrainLab. Four patients underwent procedures that exposed the maxillary strut.

RESULTS

The maxillary strut was trapezoidal shaped with an average cross-sectional area of 15.25 ± 0.48 mm(2) and average thickness of 4.43 ± 0.10 mm. The maxillary strut was present bilaterally in all skulls examined. Anteroposterior length averaged 4.18 ± 0.15 mm on the right and 3.90 ± 0.14 mm on the left. Our patient series illustrated the clinical utility of the maxillary strut as a landmark during endoscopic approaches to the skull base.

CONCLUSIONS

An endoscopic endonasal approach can be used to expose the maxillary strut. Improved understanding of this anatomy is important to achieving success when using this approach for the biopsy or resection of lesions in the lateral sellar compartment, pterygopalatine fossa, and aspects of the middle cranial fossa.

Anatomy of the inferior orbital fissure: implications for endoscopic cranial base surgery

Considering many approaches to the skull base confront the inferior orbital fissure (IOF) or sphenomaxillary fissure, the authors examine this anatomy as an important endoscopic surgical landmark. In morphometric analyses of 50 adult human dry skulls from both sexes, we divided the length of the IOF into three segments (anterolateral, middle, posteromedial). Hemotoxylin- and eosin-stained sections were analyzed. Dissections were performed using transnasal endoscopy in four formalin-fixed cadaveric cranial specimens (eight sides); three endoscopic approaches to the IOF were performed. IOF length ranged from 25 to 35 mm (mean 29 mm). Length/width of the individual anterolateral, middle, and posteromedial segments averaged 6.46/5, 4.95/3.2, and 17.6/ 2.4 mm, respectively. Smooth muscle within the IOF had a consistent relationship with several important anatomical landmarks. The maxillary antrostomy, total ethmoidectomy approach allowed access to the posteromedial segment of the fissure. The endoscopic modified, medial maxillectomy approach allowed access to the middle and posterior-medial segment. The Caldwell-Luc approach allowed complete exposure of the IOF. The IOF serves as an important anatomic landmark during endonasal endoscopic approaches to the skull base and orbit. Each of the three segments provides a characteristic endoscopic corridor, unique to the orbit and different fossas surrounding the fissure.

Anatomic variation of the optic strut: classification schema, radiologic evaluation, and surgical relevance

Objective Anatomic variability of the optic strut in location, orientation, and dimensions is relevant in approaching ophthalmic artery aneurysms and tumors of the anterior cavernous sinus, medial sphenoid wing, and optic canal. Methods In 84 dry human skulls, imaging studies were performed (64-slice computed tomography [CT] scanner, axial view, aligned with the zygomatic arch). Optic strut location related to the prechiasmatic sulcus was classified as presulcal, sulcal, postsulcal, and asymmetric. Morphometric analysis was performed. Results The optic strut was presulcal in 11.9% specimens (posteromedial margin bilaterally anterior to limbus sphenoidale), sulcal in 44% (posteromedial part adjacent to the sulcus's anterior two thirds bilaterally), postsulcal in 29.8% (posteromedial margin posterior to the sulcus's anterior two thirds), and asymmetric (left/right) in 14.3%. Optic strut length, width, and thickness measured 6.54 ± 1.69 mm, 4.23 ± 0.69 mm, and 3.01 ± 0.79 mm, respectively. Optic canal diameter was 5.14 ± 0.47 mm anteriorly and 4.79 ± 0.64 mm posteriorly. Angulation was flat (>45 degrees) in 13% or acute (<45 degrees) in 87% specimens. Conclusions Anatomical variations in the optic strut are significant in planning for anterior clinoidectomy and optic-canal decompression. Our optic strut classification considers these variations relative to the prechiasmatic sulcus on preoperative imaging.

Measuring surgical outcomes in neurosurgery: implementation, analysis, and auditing a prospective series of more than 5000 procedures

OBJECT

Health care reform debate includes discussions regarding outcomes of surgical interventions. Yet quality of medical care, when judged as a health outcome, is difficult to define because of impediments affecting accuracy in data collection, analysis, and reporting. In this prospective study, the authors report the outcomes for neurosurgical treatment based on point-of-care interactions recorded in the electronic medical record (EMR).

METHODS

The authors' neurosurgery practice collected outcome data for 19 physicians and ancillary personnel using the EMR. Data were analyzed for 5361 consecutive surgical cases, either elective or emergency procedures, performed during 2009 at multiple hospitals, offices, and an ambulatory spine surgery center. Main outcomes included complications, length of stay (LOS), and discharge disposition for all patients and for certain frequently performed procedures. Physicians, nurses, and other medical staff used validated scales to record the hospital LOS, complications, disposition at discharge, and return to work.

RESULTS

Of the 5361 surgical procedures performed, two-thirds were spinal procedures and one-third were cranial procedures. Organization-wide compliance with reporting rates of major complications improved throughout the year, from 80.7% in the first quarter to 90.3% in the fourth quarter. Auditing showed that rates of unreported complications decreased from 11% in the first quarter to 4% in the fourth quarter. Complication data were available for 4593 procedures (85.7%); of these, no complications were reported in 4367 (95.1%). Discharge dispositions reported were home in 86.2%, rehabilitation center in 8.9%, and nursing home in 2.5%. Major complications included culture-proven infection in 0.61%, CSF leak in 0.89%, reoperation within the same hospitalization in 0.38%, and new neurological deficits in 0.77%. For the commonly performed procedures, the median hospital LOS was 3 days for craniotomy for aneurysm or intraaxial tumor and less than 1 day for angiogram, anterior cervical discectomy with fusion, or lumbar discectomy.

CONCLUSIONS

With prospectively collected outcome data for more than 5000 surgeries, the authors achieved their primary end point of institution-wide compliance and data accuracy. Components of this process included staged implementation with physician pilot studies and oversight, nurse participation, point-of-service data capture, EMR form modification, data auditing, and confidential surgeon reports.

Muller's muscle, no longer vestigial in endoscopic surgery

BACKGROUND

As a thin filmy covering overlaying the inferior orbital fissure (IOF), Muller's muscle was considered a vestigial structure in humans, and for this reason, its anatomical significance was neglected. Because of increasing interest in endonasal approaches to the skull base that encompasses this region, we re-examined this structure's role as an anatomical landmark from an endoscopic perspective.

METHODS

In 10 cadaveric specimens, microanatomical dissections were performed (n = 5); endoscopic dissections were performed (n = 5) via approaches of the middle turbinate or inferior turbinate, and via the Caldwell-Luc approach through the maxillary sinus. Histological examinations were performed in 20 human fetuses (Embryology Institute, Universidad Complutense de Madrid, Madrid, Spain).

RESULTS

In cadaveric dissections, Muller's muscle was demonstrated in all specimens, serving as a bridge-like structure that spanned the entire IOF and separated the orbit from the temporal, infratemporal, and pterygopalatine fossas. Depending on which endoscopic corridor was used, a different aspect of the IOF and Muller's muscle was identified. In our endoscopic and microscopic observations, Muller's muscle was extensive, not only spanning the IOF but also extending posteriorly to reach the superior orbital fissure (SOF) and anterior confluence of the cavernous sinus. Histological analysis identified many anastomotic connections between the ophthalmic venous system and pterygoid plexus that may explain how infection or tumor spreads between these regions.

CONCLUSIONS

Muller's muscle serves as an anatomical landmark in the IOF and facilitates anatomical orientation in this region for endoscopic skull base approaches. Its recognition during endoscopic approaches allows for a better three-dimensional understanding of this anterior cranial base region.

Maximizing the extent of tumor resection during transsphenoidal surgery for pituitary macroadenomas: can endoscopy replace intraoperative magnetic resonance imaging?

OBJECT

Endoscopic approaches to pituitary tumors have become an effective alternative to traditional microscopic transsphenoidal approaches. Despite a proven potential to decrease unexpected residual tumor, intraoperative MR (iMR) imaging is infrequently used even in the few operating environments in which such technology is available. Its use is prohibitive because of its cost, increased complexity, and longer operative times. The authors assessed the potential of intrasellar endoscopy to replace the need for iMR imaging without sacrificing the maximum extent of resection.

METHODS

In this retrospective study, 27 consecutive patients underwent fully endoscopic resection of pituitary macroadenomas. Intrasellar endoscopy was used to determine the presence of residual tumor within the sella turcica and tumor cavity. Intraoperative MR imaging was used to identify rates of unexpected residual tumor and the need for further tumor resection.

RESULTS

Intraoperative estimates of the extent of tumor resection were correct in 23 patients (85%). Of 4 patients with unacceptable tumor residuals, 3 underwent further tumor resection. After iMR imaging, the rate of successful completion of the planned extent of resection increased to 26 patients (96%). Rates of both endocrinopathy reversal and postoperative complications were consistent with previously published results for microscopic and endoscopic resection techniques.

CONCLUSIONS

The findings in this study provided quantitative evidence that intrasellar endoscopy has significant promise for maximizing the extent of tumor resection and is a useful adjunct to surgical approaches to pituitary tumors, particularly when iMR imaging is unavailable. A larger prospective study on the extent of resection following endoscopic transsphenoidal surgery would strengthen these findings.

Delayed Facial Palsy After the Anterior Petrosal Approach

OBJECTIVE

In this case report, delayed facial palsy developed in a patient without any direct manipulation of the main part of the facial nerve during an anterior petrosal approach. We discuss putative etiologies and management techniques that may help avoid this problem.

CLINICAL PRESENTATION

A 21-year-old woman underwent anterior petrosectomy for gross total resection of a low-grade chondrosarcoma. Six days later, the patient presented with left-sided facial weakness in the emergency department.

RESULTS

Examination revealed evidence of House-Brackmann grade V/VI left-sided facial palsy, and repeat magnetic resonance imaging revealed diffuse enhancement of the contents of the internal auditory canal that was not present immediately after surgery. After a 10-day course of acyclovir and a tapering dose of methylprednisolone, the facial palsy slowly diminished and resolved 2 months after the onset.

CONCLUSION

This unique development of delayed facial palsy after an isolated anterior petrosal approach is evidence that this complication should be considered when dissecting along the floor of the middle fossa. Exposure of the intracranial or intracanalicular segment of the facial nerve is not necessary for delayed facial palsy to develop. Proposed mechanisms (ie, viral reactivation, vasospasm, neural edema) of this condition remain unproven. Prognosis for recovery has been reported to be excellent, with or without treatment.

Endoscopic transnasal approach to the clivus: a radiographic anatomical study

OBJECTIVES/HYPOTHESIS

Operative intervention of anterior skull base lesions is challenging. Various endoscopic surgical approaches have been described. The goal of the present study is to perform a radiographic analysis of the endoscopic transnasal approach to the clivus.

STUDY DESIGN

Anatomic study utilizing computed tomography (CT).

METHODS

High-resolution surgical-guidance CT images of the sinuses from 97 patients at a tertiary care medical center between 2002 and 2007 were evaluated. Axial and sagittal images were used to evaluate surgical access to the clivus. Multiple anatomical measurements were obtained and analyzed with imaging and statistical software.

RESULTS

Of the 97 imaging studies, there were 39 males and 58 females. The width of exposure of the clivus without removal of the septum was 2.7 cm (1.9-3.4 cm) and with removal of the bony septum was 3.6 cm (2.6-4.8 cm) (P < .001). No patients had complete exposure of the width of the clivus without the septum removed compared to 56 (58%) patients with the septum removed. Endoscopic exposure of the inferior and superior limits of the clivus was not limited in any images studied.

CONCLUSIONS

The endoscopic transnasal approach to the clivus is a viable option in the treatment of anterior skull base lesions with the preservation of functional anatomy in select patients. A large portion of the population has limited lateral exposure secondary to the eustachian tube and the medial pterygoid plate with an endoscopic transnasal approach. Vertically, this approach allows complete access to the clivus in all patients studied.

Endoscopic Approach to the Infratemporal Fossa

OBJECTIVE

Classic 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.

METHODS

Endoscopic 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.

RESULTS

The 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.

CONCLUSION

Endoscopic 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.

Endoscopic anatomy of the petrous segment of the internal carotid artery

BACKGROUND

Exposure of the petrous (C2) segment of the internal carotid artery (ICA; petrous carotid) is necessary to treat lesions that have spread from the intracranial space or adjacent sinonasal region. Recent advancements in endonasal-endoscopic approaches to the anterior skull base raise the possibility of extending these approaches beyond the sinonasal cavity. In this cadaveric study, we evaluate the feasibility and extent of exposure of the petrous carotid artery via a combined endoscopic endonasal approach.

METHODS

Endoscopic dissection was performed in four formalin-fixed cadaver heads (eight sides). An endoscopic, endonasal, transmaxillary approach was used to identify the cervical and petrous carotid artery.

RESULTS

With the endoscopic endonasal, Caldwell-Luc approach, we could visualize the ventral petrous bone after dissecting the contents of the pterygopalatine fossa and infratemporal fossa. Careful dissection allowed exposure of the petrous carotid artery from the upper cervical carotid to the foramen lacerum.

CONCLUSION

In this cadaveric study using an endoscopic endonasal approach for exposure of the petrous carotid artery, combination with the transmaxillary-transpterygopalatine-transinfratemporal approaches permitted exposure of the ventral portion of the artery. The anatomy presented will assist experienced endoscopic skull base surgeons in the removal of lesions involving the ventral skull base.

DELAYED EXTRUSION OF HYDROXYAPATITE CEMENT AFTER TRANSPETROSAL RECONSTRUCTION

OBJECTIVE

Use of hydroxyapatite cement has been advocated for closure of transpetrosal defects to decrease the incidence of cerebrospinal fluid leaks. We previously identified delayed extrusion of this cement as a significant complication associated with this closure technique and now update our long-term experience.

METHODS

In our retrospective review, we identified 1231 patients who underwent transpetrosal procedures by our multidisciplinary cranial base team between 1984 and 2005. Of the subgroup of 177 patients who had hydroxyapatite cement used during the closure of the procedure, 13 patients (7.3%) experienced delayed extrusion of hydroxyapatite cement.

RESULTS

Extrusion occurred in 3 patients within 12 months and in 10 patients within 68 to 140 months. Twelve patients presented with draining fistulae and concomitant Staphylococcus aureus infection; 1 patient presented asymptomatically with a large temporal lobe abscess identified on surveillance magnetic resonance imaging. All 13 patients underwent reoperation, including 1 who underwent a second procedure.

CONCLUSION

Delayed extrusion of hydroxyapatite cement resulted in significant morbidity to our patients and often presented in an indolent manner. We recommend serial examination and imaging studies in patients who have had transpetrosal closures with hydroxyapatite cement. Because of the complication rates associated with hydroxyapatite cement, we have discontinued its use.

Extension of the one-piece orbitozygomatic frontotemporal approach to the glenoid fossa: cadaveric study

OBJECTIVE

Resection of the glenoid fossa has been described as part of cranial approaches to the clivus and subtemporal approaches. However, radical resection carries a significant risk of postoperative temporomandibular joint dysfunction. We examine a simple variation of our previously described one-piece frontotemporal orbitozygomatic (FTOZ) osteotomy that adds en bloc resection of the root of the zygomatic arch and a portion of the glenoid fossa.

METHODS

Five cadaveric fixed heads injected with colored silicone underwent an FTOZ osteotomy that extended to the root of the zygomatic arch and glenoid fossa.

RESULTS

A step-by-step guide to the surgical technique is described, with illustrations to depict the glenoid fossa keyhole and bony cuts that free the zygomatic arch and portions of glenoid fossa. The first cut was made through the posterior root, and the second cut was made through the anterior root of the zygomatic arch.

CONCLUSION

In this cadaveric study, extension of the one-piece FTOZ approach included the posterior root of the zygoma and the lateral part of the glenoid fossa. En bloc resection of the glenoid fossa and root of the zygomatic arch, together with the FTOZ osteotomy, facilitated reconstruction of the temporomandibular joint and increased the amount of exposure obtained with this FTOZ osteotomy. Comprehensive understanding of functional outcomes awaits further clinical study.

Exposure of the Distal Cervical Segment of the Internal Carotid Artery Using the Trans-spinosum Corridor: Cadaveric Study of Surgical Anatomy

Background:

Exposure of the most distal portion of the cervical segment of the internal carotid artery (ICA) is technically challenging. Previous descriptions of cranial base approaches to expose this segment noted facial nerve manipulation, resection of the glenoid fossa, and significant retraction or resection of the condyle. We propose a new approach using the frontotemporal orbitozygomatic approach to expose the distal portion of the cervical segment of the ICA via the trans-spinosum corridor.

Methods:

Six formalin-fixed injected heads were used for cadaveric dissection. Two blocs containing the carotid canal and surrounding region were used for histological examination.

Results:

The ICA lies immediately medial to the vaginal process. The carotid sheath attaches laterally to the vaginal process. With use of the trans-spinosum corridor, the surgeon's line of sight courses in front of the temporomandibular joint, through the foramen spinosum, spine of the sphenoid, and vaginal process. Removal of the vaginal process exposes the vertical portion of the petrous segment of the ICA. The loose connective tissue space between the adventitia and the carotid sheath is easily entered from above. Incision of the carotid sheath exposes the ICA without disruption of the temporomandibular joint.

Conclusion:

Control of the cervical segment of the ICA can be critical when dealing with cranial base tumors that invade or surround the petrous segment of the ICA. This novel technique through the trans-spinosum corridor can effectively expose the distal portion of the cervical segment of the ICA without causing manipulation of the facial nerve and while maintaining the integrity of the temporomandibular joint.

Refinement of the extradural anterior clinoidectomy: surgical anatomy of the orbitotemporal periosteal fold

OBJECTIVE

Extradural removal of the anterior clinoid process is technically challenging because of the limited exposure. In our study of the extradural anterior clinoidectomy, we describe anatomic details and landmarks to facilitate sectioning of the orbitotemporal periosteal fold and elevation of the temporal fossa dura from the superior orbital fissure. We assess the morbidity associated with these procedures as well as compare the indications, advantages, and disadvantages of intra-versus extradural clinoidectomy.

METHODS

Of five formalin-fixed cadaveric heads, four were used for cadaveric dissections and one was used for histological examination.

RESULTS

Sectioning of the orbitotemporal periosteal fold revealed a cleavage plane between the temporal fossa dura and a thin layer of connective tissue that covers the superior orbital fissure. The lacrimal nerve coursed immediately medial to this surgically created cleavage plane. The superior orbital vein crossed laterally under the cranial nerves, which pass through the superior orbital fissure. This vein is particularly vulnerable as it is composed only of endothelium and a basal membrane.

CONCLUSION

Both intra- and extradural techniques for anterior clinoidectomy are important parts of the neurosurgical armamentarium. Sharp incision of the orbitotemporal periosteal fold to increase the extradural exposure of the anterior clinoid process should be made at the level of the sphenoid ridge and restricted to the periosteal bridge. Subsequent blunt elevation of the temporal fossa dura should be performed; however, peeling of the temporal fossa dura should be limited to avoid cranial nerve morbidity.

Surgery of the subthalamic nucleus: use of movement-related neuronal activity for surgical navigation

THE BASAL GANGLIA have important roles in somatic motor, oculomotor, limbic, and associative functions. These functions are represented in anatomically distinct territories in each basal ganglion nucleus. During surgery of the subthalamic nucleus for Parkinson's disease, the primary goal is to influence the physiology of the motor territory without affecting nonmotor areas. This article describes the use of movement-related cellular activity during single-unit microelectrode mapping to identify and to navigate within the motor territory of the subthalamic nucleus.

Locations of movement-related cells in the human subthalamic nucleus in Parkinson's disease

The subthalamic nucleus (STN) is an emerging target for deep brain stimulator (DBS) implantation for the treatment of advanced Parkinson's disease (PD). Understanding the somatotopic organization of the STN is important for surgical navigation within the nucleus. We analyzed intraoperative data obtained during 54 procedures for the implantation of STN stimulators to assess the locations of movement-related cells. Cells were considered movement-related if they exhibited modulation of the cell discharge during passive movement of the contralateral upper or lower extremity. Microelectrode track reconstructions were plotted on a human brain atlas, using the location of the DBS electrode from postoperative magnetic resonance images as a registration mark in reconstructing microelectrode track locations. Movement-related cells were predominantly located in the dorsal part of the nucleus. The majority of the cells were related to proximal joint manipulation. Arm-related cells were located laterally and at the rostral and caudal poles, whereas leg-related cells were located medially and centrally. The finding of three or more leg-related cells on a given microelectrode track was predictive of a medial localization within the motor area. Our findings are consistent with the small number of published studies on STN somatopy in the human and the nonhuman primate.

Implantation of deep brain stimulators into the subthalamic nucleus: technical approach and magnetic resonance imaging-verified lead locations

OBJECT

Chronic deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a procedure that is rapidly gaining acceptance for the treatment of symptoms in patients with Parkinson disease (PD), but there are few detailed descriptions of the surgical procedure itself. The authors present the technical approach used to implant 76 stimulators into the STNs of patients with PD and the lead locations, which were verified on postoperative magnetic resonance (MR) images.

METHODS

Implantation procedures were performed with the aid of stereotactic MR imaging, microelectrode recording (MER) in the region of the stereotactic target to define the motor area of the STN, and intraoperative test stimulation to assess the thresholds for stimulation-induced adverse effects. All patients underwent postoperative MR imaging, which was performed using volumetric gradient-echo and T2-weighted fast-spin echo techniques, computational reformatting of the MR image into standard anatomical planes, and quantitative measurements of lead location with respect to the midcommissural point and the red nucleus. Lead locations were statistically correlated with physiological data obtained during MER and intraoperative test stimulation.

CONCLUSIONS

The authors' approach to implantation of DBS leads into the STN was associated with consistent lead placement in the dorsolateral STN, a low rate of morbidity, efficient use of operating room time, and robust improvement in motor function. The mean coordinates of the middle of the electrode array, measured on postoperative MR images, were 11.6 mm lateral, 2.9 mm posterior, and 4.7 mm inferior to the midcommissural point, and 6.5 mm lateral and 3.5 mm anterior to the center of the red nucleus. Voltage thresholds for several types of stimulation-induced adverse effects were predictive of lead location. Technical nuances of the surgery are described in detail.

Predictive model for pain recurrence after posterior fossa surgery for trigeminal neuralgia

BACKGROUND

Surgical exploration of the posterior fossa is the definitive treatment for trigeminal neuralgia refractory to medication, but predictors of its success in effecting long-term pain relief have not been established.

OBJECTIVE

To develop a model that allows stratification of patients' risk of postoperative recurrence of pain based on pretreatment factors.

METHODS

We reviewed the records of 420 consecutive patients who underwent posterior fossa exploration by one of us (C.B.W.) for the treatment of idiopathic trigeminal neuralgia. The primary outcome measure was recurrence of trigeminal pain. The predictive value of preoperative and intraoperative factors was evaluated. Multivariate analysis revealed the statistically significant predictors of pain recurrence, permitting creation of a risk model for recurrence of pain.

RESULTS

After surgery, trigeminal pain had lessened in 98% of patients and completely resolved in 87%. There were no perioperative deaths. After a mean follow-up of 56.3 months, 93% of patients reported significant pain improvement and 72% continued to have no pain. The estimated likelihood of pain recurrence at 8 years was 34%. Significant predictors of eventual recurrence of pain were age younger than 53 years at the time of surgery, symptoms lasting longer than 11(1/2) years, female sex, and pain on the left side in men. These factors were weighted and incorporated into a risk model that revealed 4-year pain-free survival of 89% +/- 4% for the low-risk group, 80% +/- 4% for the moderate-risk group, and 58% +/- 6% for the high-risk group (data are mean +/- SD).

CONCLUSIONS

We developed a predictive model that stratifies the risk for eventual recurrence of pain after posterior fossa exploration for trigeminal neuralgia. This information may be useful in counseling patients regarding treatment.