Tag: anatomy

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Dorsal location of the cochlear nerve on vestibular schwannoma: preoperative evaluation, frequency, and functional outcome

Dorsal location of the cochlear nerve on vestibular schwannoma

Neurosurg Rev (2013) 36:39–44

The cochlear nerve is most commonly located on the caudoventral portion of the capsule of vestibular schwannomas and rarely on the dorsal portion. In such a condition, total removal of the tumor without cochlear nerve dysfunction is extremely difficult.

The purpose of our study was to identify the frequency of this anatomical condition and the status of postoperative cochlear nerve function; we also discuss the preoperative radiological findings.

The study involved 114 patients with unilateral vestibular schwannomas operated on via a retrosigmoid (lateral suboccipital) approach. Locations of the cochlear nerve on the tumor capsule were ventral, dorsal, caudal, and rostral. Ventral and dorsal locations were further subdivided into rostral, middle, and caudal third of the tumor capsule. The postoperative cochlear nerve function and preoperative magnetic resonance (MR) findings were reviewed retrospectively.

In 56 patients that had useful preoperative hearing, useful hearing was retained in 50.0 % (28 of 56) of patients after surgery. The cochlear nerve was located on the dorsal portion of the tumor capsule in four patients (3.5 %), and useful hearing was preserved in only one of these patients (25 %) in whom the tumor had been partially resected.

This tumor-nerve anatomical relationship was identified in all tumors of <2 cm at preoperative MR cisternography. MR cisternography has the potential to identify the tumor–nerve anatomical relationship, especially in small-sized tumors that usually require therapeutic intervention that ensures hearing preservation. Hence, careful evaluation of the preoperative MR cisternography is important in deciding the therapeutic indications.

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Frontal cortico-subcortical functional anatomy

Subcortical surgical anatomy of the lateral frontal region

J Neurosurg 117:1053–1069, 2012

Recent neuroimaging and surgical results support the crucial role of white matter in mediating motor and higher-level processing within the frontal lobe, while suggesting the limited compensatory capacity after damage to subcortical structures. Consequently, an accurate knowledge of the anatomofunctional organization of the pathways running within this region is mandatory for planning safe and effective surgical approaches to different diseases. The aim of this dissection study was to improve the neurosurgeon’s awareness of the subcortical anatomofunctional architecture for a lateral approach to the frontal region, to optimize both resection and postoperative outcome.

Methods. Ten human hemispheres (5 left, 5 right) were dissected according to the Klingler technique. Proceeding lateromedially, the main association and projection tracts as well as the deeper basal structures were identified. The authors describe the anatomy and the relationships among the exposed structures in both a systematic and topographical surgical perspective. Structural results were also correlated to the functional responses obtained during resections of infiltrative frontal tumors guided by direct cortico-subcortical electrostimulation with patients in the awake condition.

Results. The eloquent boundaries crucial for a safe frontal lobectomy or an extensive lesionectomy are as follows: 1) the motor cortex; 2) the pyramidal tract and premotor fibers in the posterior and posteromedial part of the surgical field; 3) the inferior frontooccipital fascicle and the superior longitudinal fascicle posterolaterally; and 4) underneath the inferior frontal gyrus, the head of the caudate nucleus, and the tip of the frontal horn of the lateral ventricle in the depth.

Conclusions. Optimization of results following brain surgery, especially within the frontal lobe, requires a perfect knowledge of functional anatomy, not only at the cortical level but also with regard to subcortical white matter connectivity.

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Anatomy and Pathology of the Cranial Emissary Veins: A Review With Surgical Implications

Neurosurgery 70:1312–1319, 2012 DOI: 10.1227/NEU.0b013e31824388f8

Emissary veins connect the extracranial venous system with the intracranial venous sinuses. These include, but are not limited to, the posterior condyloid, mastoid, occipital, and parietal emissary veins.

A review of the literature for the anatomy, embryology, pathology, and surgery of the intracranial emissary veins was performed.

Detailed descriptions of these venous structures are lacking in the literature, and, to the authors’, knowledge, this is the first detailed review to discuss the anatomy, pathology, anomalies, and clinical effects of the cranial emissary veins.

Our hope is that such data will be useful to the neurosurgeon during surgery in the vicinity of the emissary veins.

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Supracerebellar transtentorial approach—resection of the tentorium instead of an opening—to provide broad exposure of the mediobasal temporal lobe: anatomical aspects and surgical applications

J Neurosurg 116:764–772, 2012.  http://thejns.org/doi/abs/10.3171/2011.12.JNS111256

The aim of this study was to describe the surgical anatomy of the mediobasal aspect of the temporal lobe and the supracerebellar transtentorial (SCTT) approach performed not with an opening, but with the resection of the tentorium, as an alternative route for the neurosurgical management of vascular and tumoral lesions arising from this region.

Methods. Cadaveric specimens were used to illustrate the surgical anatomy of the mediobasal region of the temporal lobe. Demographic aspects, characteristics of lesions, clinical presentation, surgical results, follow-up findings, and outcomes were retrospectively reviewed for patients referred to receive the SCTT approach with tentorial resection.

Results. Ten patients (83%) were female and 2 (17%) were male. Their ages ranged from 6 to 59 years (mean 34.5 ± 15.8 years). All lesions (3 posterior cerebral artery aneurysms, 3 arteriovenous malformations, 3 cavernous malformations, and 3 tumors) were completely excluded or resected. After a mean follow-up period of 143 months (range 10–240 months), the mean postoperative Glasgow Outcome Scale score was 4.9.

Conclusions. Knowledge of the surgical anatomy provides improvement for microsurgical approaches. The evolution from a small opening to a resection of the tentorium absolutely changed the exposure of the mediobasal aspect of the temporal lobe. The SCTT approach with tentorial resection is an excellent alternative route to the posterior part of mediobasal aspect of the temporal lobe, and it was enough to achieve the best neurosurgical management of tumoral and vascular lesions located in this area.

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Analysis of the uncinate processes of the cervical spine

J Neurosurg Spine 16:402–407, 2012. http://thejns.org/doi/abs/10.3171/2011.12.SPINE11541

Although the uncovertebral region is neurosurgically relevant, relatively little is reported in the literature, specifically the neurosurgical literature, regarding its anatomy. Therefore, the present study aimed at further elucidation of this region’s morphological features.

Methods. Morphometry was performed on the uncinate processes of 40 adult human skeletons. Additionally, range of motion testing was performed, with special attention given to the uncinate processes. Finally, these excrescences were classified based on their encroachment on the adjacent intervertebral foramen.

Results. The height of these processes was on average 4.8 mm, and there was an inverse relationship between height of the uncinate process and the size of the intervertebral foramen. Degeneration of the vertebral body (VB) did not correlate with whether the uncinate process effaced the intervertebral foramen. The taller uncinate processes tended to be located below C-3 vertebral levels, and their average anteroposterior length was 8 mm. The average thickness was found to be 4.9 mm for the base and 1.8 mm for the apex. There were no significant differences found between vertebral level and thickness of the uncinate process. Arthritic changes of the cervical VBs did not necessarily deform the uncinate processes. With axial rotation, the intervertebral discs were noted to be driven into the ipsilateral uncinate process. With lateral flexion, the ipsilateral uncinate processes aided the ipsilateral facet joints in maintaining the integrity of the ipsilateral intervertebral foramen.

Conclusions. A good appreciation for the anatomy of the uncinate processes is important to the neurosurgeon who operates on the spine. It is hoped that the data presented herein will decrease complications during surgical approaches to the cervical spine.

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Dural Landmark to Locate the Internal Auditory Canal in Large and Giant Vestibular Schwannomas: The Tübingen Line

Neurosurgery 69[ONS Suppl 1]:ons99–ons102, 2011.  DOI: 10.1227/NEU.0b013e31821664c6

In cases of large and giant vestibular schwannomas (VS), the visualization of the internal auditory canal (IAC) opening is difficult or impossible.

OBJECTIVE: To describe the Tübingen line and explore its relationships with the IAC as a landmark to help locate the IAC.

METHODS: Ten cadaveric heads were used in this study. Between 2004 and 2009, the senior author (M.T.) used the Tübingen line as a landmark to recognize the IAC in 300 consecutive patients with VS. To locate the Tübingen  line, the initial step was to identify several vertical foldings of dura located around the area of the vestibular aqueduct. After this, foldings upward consistently reached a linear level where all of the foldings ended and the dura tightly adhered to the bony surface in a smooth, foldless shape.

RESULTS: The Tübingen line was identified in all temporal bones studied and in all 300 patients operated on, with the exception of 2 cases (,1%). Removal of the bone just above the Tübingen line located the IAC in all temporal bone specimens studied. Similarly, the surgical cases showed that the Tübingen line helped locate the IAC in all patients.

CONCLUSION: The Tübingen line is an easy, consistent, and safe method to locate the projection of the IAC along the posterior surface of the temporal bone.

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Preoperative Evaluation of Unruptured Cerebral Aneurysms by Fast Imaging Employing Steady- State Acquisition Image

Neurosurgery 69:412–420, 2011 DOI: 10.1227/NEU.0b013e318213431e

In aneurysm surgery, understanding the microanatomy around the aneurysm such as perforating arteries and cranial nerves is mandatory.

OBJECTIVE: To assess the usefulness in determining the microanatomy around the cerebral aneurysms by the use of fast imaging employing steady-state acquisition (FIESTA) images of magnetic resonance imaging preoperatively, in addition to computed tomography and digital subtraction angiography.

METHODS: Between October 2006 and June 2009, 123 patients with 140 unruptured cerebral aneurysms were treated in our institution. Eighty-two patients were assessed with FIESTA by the operators on the workstation of the magnetic resonance image before surgical clipping of the aneurysms. The small vessels and cranial nerves were confirmed intraoperatively before or after obliteration of the aneurysms.

RESULTS: Sensitivities and specificities of FIESTA imaging were 100% in detecting hypothalamic artery around anterior communicating artery aneurysms, oculomotor nerve attachment to the posterior communicating artery aneurysm domes, and anterior choroidal artery adhesion to the posterior communicating artery aneurysms. This technique was also useful for predicting adhesion between the aneurysm and adjacent main trunks or perforators. Although the specificity was 100%, sensitivity was 56% in detecting vessel adhesion around the middle cerebral aneurysms. This technique can provide limited information in large aneurysms or aneurysms located in minimal cerebrospinal fluid space. The overall outcomes of the patients included 120 excellent recoveries, 1 moderate deficit, 1 severe deficit, and 1 persistent vegetative state according to the Glasgow Outcome Scale.

CONCLUSION: By giving information on the minute anatomical structure around the aneurysm, FIESTA can contribute to thorough preoperative evaluations of cerebral aneurysms.

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Trigeminal schwannomas: experience with 57 cases and a review of the literature

Neurosurg Rev (2011) 34:159–171. DOI 10.1007/s10143-010-0289-y

Trigeminal schwannoma is a mostly benign tumor that can be cured by complete resection. Over the last few decades, several pioneers have developed surgical approaches enabling the total removal of such tumors.

We analyzed 57 patients who underwent radical surgery, including 45 patients who underwent skull base surgery as their initial treatment, for removal of trigeminal schwannomas. Here, we report the surgical management of these cases. Since 1990, all such patients have been treated using three main types of middle fossa skull base approaches, which minimize the exposure of the brain: the anterior transpetrosal approach, subtemporal interdural approach (Dolenc), or a combination of these approaches.

Before 1990, total tumor removal was achieved in only three of eight patients (38%). After 1990, the tumors were totally removed in 43 patients (90%) and were nearly completely removed in an additional three patients (6%). Among the patients who underwent skull base surgery as their initial treatment, a complete resection was achieved in 93% (42/45 patients) of the cases. However, total surgical removal after surgery and Gamma knife surgery was very difficult because of dense adhesions to the brain stem and cranial nerves. No surgery-related mortalities occurred in this series, and the individual KPS scores were more than 90% among the patients who underwent skull base surgery. No recurrences requiring additional surgery have occurred after an average follow-up period of 4.9 years.

Most of the trigeminal schwannomas could be removed totally and safely during a single operation after the introduction of skull base surgery. Therefore, radiosurgery should not be applied as the treatment of first choice for younger patients. A correct anatomical knowledge is critical for minimizing brain exposure and avoiding surgical complications.

Posted on

Trigeminal schwannomas: experience with 57 cases and a review of the literature

Neurosurg Rev. DOI 10.1007/s10143-010-0289-y

Trigeminal schwannoma is a mostly benign tumor that can be cured by complete resection. Over the last few decades, several pioneers have developed surgical approaches enabling the total removal of such tumors.

We analyzed 57 patients who underwent radical surgery, including 45 patients who underwent skull base surgery as their initial treatment, for removal of trigeminal schwannomas. Here, we report the surgical management of these cases. Since 1990, all such patients have been treated using three main types of middle fossa skull base approaches, which minimize the exposure of the brain: the anterior transpetrosal approach, subtemporal interdural approach (Dolenc), or a combination of these approaches.

Before 1990, total tumor removal was achieved in only three of eight patients (38%). After 1990, the tumors were totally removed in 43 patients (90%) and were nearly completely removed in an additional three patients (6%). Among the patients who underwent skull base surgery as their initial treatment, a complete resection was achieved in 93% (42/45 patients) of the cases. However, total surgical removal after surgery and Gamma knife surgery was very difficult because of dense adhesions to the brain stem and cranial nerves. No surgery-related mortalities occurred in this series, and the individual KPS scores were more than 90% among the patients who underwent skull base surgery. No recurrences requiring additional surgery have occurred after an average follow-up period of 4.9 years.

Most of the trigeminal schwannomas could be removed totally and safely during a single operation after the introduction of skull base surgery. Therefore, radiosurgery should not be applied as the treatment of first choice for younger patients. A correct anatomical knowledge is critical for minimizing brain exposure and avoiding surgical complications.

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Variations of endonasal anatomy: relevance for the endoscopic endonasal transsphenoidal approach

Acta Neurochir (2010) 152:1015–1020. DOI 10.1007/s00701-010-0629-2

The endoscopic endonasal transsphenoidal approach (EETA) to the pituitary is performed by ear, nose, and throat (ENT) surgeons in collaboration with neurosurgeons but also by neurosurgeons alone even though neurosurgeons have not been trained in rhinological surgery.

Purpose To register the frequency of endonasal anatomical variations and to evaluate whether these variations hinder the progress of EETA and require extra rhinological surgical skills.

Methods A prospective cohort study of 185 consecutive patients receiving an EETA through a binostril approach was performed. All anatomical endonasal variations were noted and the relevance for the progress of surgery evaluated.

Results In 48% of patients, anatomical variations were recognized, the majority of which were spinae septi and septum deviations. In 5% of patients, the planned binostril approach had to be converted into a mononostril approach; whereas in 18% of patients with an anatomical variation, a correction had to be performed. There was no difference between the ENT surgeon and the neurosurgeon performing the approach. Complications related to the endonasal phase of the surgery occurred in 3.8%. Fluoroscopy or electromagnetic navigation has been used during 6.5% of the surgeries.

Conclusion Although endonasal anatomical variations are frequent, they do not pose a relevant obstacle for EETA.

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Microsurgical anatomy of the ventral callosal radiations: new destination, correlations with diffusion tensor imaging fiber-tracking, and clinical relevance

J Neurosurg 112:512–519, 2010.DOI: 10.3171/2009.6.JNS081712

In the current literature, there is a lack of a detailed map of the origin, course, and connections of the ventral callosal radiations of the human brain.

Methods. The authors used an older dissection technique based on a freezing process as well as diffusion tensor imaging to investigate this area of the human brain.

Results. The authors demonstrated interconnections between areas 11, 12, and 25 for the callosal radiations of the trunk and rostrum of the corpus callosum; between areas 9, 10, and 32 for the genu; and between areas 6, 8, and 9 for the ventral third of the body. The authors identified new ventral callosal connections crossing the rostrum between both temporal poles and coursing within the temporal stem, and they named these connections the “callosal radiations of Peltier.” They found that the breadth of the callosal radiations slightly increases along their course from the rostrum to the first third of the body of the corpus callosum.

Conclusions. The fiber dissection and diffusion tensor imaging techniques are complementary not only in their application to the study of the commissural system in the human brain, but also in their practical use for diagnosis and surgical planning. Further investigations, neurocognitive tests, and other contributions will permit elucidation of the functional relevance of the newly identified callosal radiations in patients with disease involving the ventral corpus callosum.

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