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Resection of the quadrangular lobule of the cerebellum to increase exposure of the cerebellomesencephalic fissure: an anatomical study with clinical correlation

Juan Leonardo Serrato-Avila, Juan Alberto Paz Archila, Alejandro Monroy-Sosa, Sebastian Aníbal Alejandro, Marcos Devanir Silva da Costa, Sergio Cavalheiro, Kaan Yagmurlu, Michael T. Lawton, and Feres Chaddad-Neto

OBJECTIVE

The lateral aspect of the cerebellomesencephalic fissure frequently harbors vascular pathology and is a common surgical corridor used to access the pons tegmentum, as well as the cerebellum and its superior and middle peduncles. The quadrangular lobule of the cerebellum (QLC) represents an obstacle to reach these structures. The authors sought to analyze and compare exposure of the cerebellar interpeduncular region (CIPR) before and after QLC resection and provide a case series to evaluate its clinical applicability.

METHODS

Forty-two sides of human brainstems were prepared with Klingler’s method and dissected. The exposure area before and after resection of the QLC was measured and statistically studied. A case series of 59 patients who underwent QLC resection for the treatment of CIPR lesions was presented and clinical outcomes were evaluated at 1-year follow-up.

RESULTS

The anteroposterior surgical corridor of the CIPR increased by 10.3 mm after resection of the QLC. The mean exposure areas were 42 mm2 before resection of the QLC and 159.6 mm2 after resection. In this series, ataxia, extrapyramidal syndrome, and akinetic mutism were found after surgery. However, all these cases resolved within 1 year of follow-up. Modified Rankin Scale score improved by 1 grade, on average.

CONCLUSIONS

QLC resection significantly increased the exposure area, mainly in the anteroposterior axis. This surgical strategy appears to be safe and may help the neurosurgeon when operating on the lateral aspect of the cerebellomesencephalic fissure.

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A new classification of parasagittal bridging veins based on their configurations and drainage routes pertinent to interhemispheric approaches: a surgical anatomical study

Derya Karatas, Jaime L. Martínez Santos, Saygı Uygur, Ahmet Dagtekin, Zeliha Kurtoglu Olgunus, Emel Avci, and Mustafa K. Baskaya

OBJECTIVE

Opening the roof of the interhemispheric microsurgical corridor to access various neurooncological or neurovascular lesions can be demanding because of the multiple bridging veins that drain into the sinus with their highly variable, location-specific anatomy. The objective of this study was to propose a new classification system for these parasagittal bridging veins, which are herein described as being arranged in 3 configurations with 4 drainage routes.

METHODS

Twenty adult cadaveric heads (40 hemispheres) were examined. From this examination, the authors describe 3 types of configurations of the parasagittal bridging veins relative to specific anatomical landmarks (coronal suture, postcentral sulcus) and their drainage routes into the superior sagittal sinus, convexity dura, lacunae, and falx. They also quantify the relative incidence and extension of these anatomical variations and provide several preoperative, postoperative, and microneurosurgical clinical case study examples.

RESULTS

The authors describe 3 anatomical configurations for venous drainage, which improves on the 2 types that have been previously described. In type 1, a single vein joins; in type 2, 2 or more contiguous veins join; and in type 3, a venous complex joins at the same point. Anterior to the coronal suture, the most common configuration was type 1 dural drainage, occurring in 57% of hemispheres. Between the coronal suture and the postcentral sulcus, most veins (including 73% of superior anastomotic veins of Trolard) drain first into a venous lacuna, which are larger and more numerous in this region. Posterior to the postcentral sulcus, the most common drainage route was through the falx.

CONCLUSIONS

The authors propose a systematic classification for the parasagittal venous network. Using anatomical landmarks, they define 3 venous configurations and 4 drainage routes. Analysis of these configurations with respect to surgical routes indicates 2 highly risky interhemispheric surgical fissure routes. The risks are attributable to the presence of large lacunae that receive multiple veins (type 2) or venous complex (type 3) configurations that negatively impact a surgeon’s working space and degree of movement and thus are predisposed to inadvertent avulsions, bleeding, and venous thrombosis.

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Microsurgical and fiber tract anatomy of the interthalamic adhesion

Mehmet Hakan Şahin, Abuzer Güngör, Oğuz Kağan Demirtaş, Çağrı Postuk, Zeynep Fırat, Gazanfer Ekinci, Hakan Hadi Kadıoğlu, and Uğur Türe

OBJECTIVE

The authors of this study aimed to define the microanatomy of the interthalamic adhesion (ITA) using microfiber dissection, magnetic resonance (MR) tractography, and histological analysis.

METHODS

Sagittal, coronal, and axial MR images from 160 healthy individuals 2–82 years of age were examined. The relationships between age range and ITA morphology as well as between gender and ITA morphology were evaluated statistically. Among these 160 individuals, 100 who had undergone MR tractography were examined. In this group, the presence of fiber tracts in the ITA and the relationship with ITA morphological types were examined. Thirty formalin-fixed human cadaveric brains were also examined endoscopically, and 6 hemispheres were dissected from the medial to lateral and superior to inferior directions under the microscope. Sections taken from one of the brains with an ITA type 2 with both thalami were examined histologically. Anti-neurofilament antibody was used in the histological examination.

RESULTS

Four morphological types of ITA were observed. Type 1 had an adhesion/adherent appearance, type 2 had a bridge/commissure appearance, type 3 showed no adhesion, and type 4 had a double bridge. Tractographic examination revealed that 28% had no fiber tract transition in the ITA, 21% had a significant transition, and 51% had an indistinct transition. Statistically, the presence of the ITA was significantly higher in the pediatric (age) and female (gender) groups. In specimens with ITAs of a bridge/commissure appearance (type 2), fiber tracts showed clear transitions between thalami. In type 1 (adherent/adhesive appearance), fiber tracts were observed within the ITA, but a reciprocal transition was unclear. Dissection showed that these fiber tracts in the ITA reach the nucleus accumbens, caudate nucleus, and frontoorbital region anteriorly and the lateral habenula and posterior commissure posteriorly. Some fibers also joined the ansa peduncularis. In histological studies, axonal fibers moving in the ITA were observed with anti-neurofilament antibody staining.

CONCLUSIONS

This is the first study to demonstrate fiber tracts of the ITA through fiber dissection and transillumination techniques as well as radiological and histological study. Statistical data were obtained by comparing the morphological group with age and gender groups. The anatomy of this structure, which has been neglected for many years, was reexamined. This study showed that the ITA has fibers connecting different parts of the brain, in contrast to previous studies suggesting that it was a simple massa.

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Reappraisal of the anatomy of the frontotemporal branches of the facial nerve

Maximiliano Alberto Nunez, Ahmed Mohyeldin, Dario A. Marotta, Vera Vigo, Karam Asmaro, Yuanzhi Xu, Aaron A. Cohen-Gadol, and Juan C. Fernandez-Miranda

OBJECTIVE

The anatomy of the temporal branches of the facial nerve (FN) has been widely described in the neurosurgical literature because of its relevance in anterolateral approaches to the skull base and implication in frontalis palsies from these approaches. In this study, the authors attempted to describe the anatomy of the temporal branches of the FN and identify whether there are any FN branches that cross the interfascial space of the superficial and deep leaflets of the temporalis fascia.

METHODS

The surgical anatomy of the temporal branches of the FN was studied bilaterally in 5 embalmed heads (n = 10 extracranial FNs). Exquisite dissections were performed to preserve the relationships of the branches of the FN and their relationship to the surrounding fascia of the temporalis muscle, the interfascial fat pad, the surrounding nerve branches, and their final terminal endpoints near the frontalis and temporalis muscles. The authors correlated their findings intraoperatively with 6 consecutive patients with interfascial dissection in which neuromonitoring was performed to stimulate the FN and associated twigs that were observed to be interfascial in 2 of them.

RESULTS

The temporal branches of the FN stay predominantly superficial to the superficial leaflet of the temporal fascia in the loose areolar tissue near the superficial fat pad. As they course over the frontotemporal region, they give off a twig that anastomoses with the zygomaticotemporal branch of the trigeminal nerve, which crosses the superficial layer of the temporalis muscle, spanning the interfascial fat pad, and then pierces the deep temporalis fascial layer. This anatomy was observed in 10 of the 10 FNs dissected. Intraoperatively, stimulation of this interfascial segment yielded no facial muscle response up to 1 mA in any of the patients.

CONCLUSIONS

The temporal branch of the FN gives off a twig that anastomoses with the zygomaticotemporal nerve, which crosses the superficial and deep leaflets of the temporal fascia. Interfascial surgical techniques aimed at protecting the frontalis branch of the FN are safe in their efforts to protect against frontalis palsy with no clinical sequelae when executed properly.

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Microsurgical anatomy and insular connectivity of the cerebral opercula

Oğuz Kağan Demirtaş, Abuzer Güngör, Pınar Çeltikçi, Emrah Çeltikçi, Alberth Patricio Munoz-Gualan, Fikret Hüseyin Doğulu, and Uğur Türe

OBJECTIVE

Radiological, anatomical, and electrophysiological studies have shown the insula and cerebral opercula to have extremely high functionality. Because of this complexity, interventions in this region cause higher morbidity compared to those in other areas of the brain. In most early studies of the insula and white matter pathways, insular dissection was begun after the opercula were removed. In this study, the authors examined the insula and deep white matter pathways to evaluate the insula as a whole with the surrounding opercula.

METHODS

Twenty formalin-fixed adult cerebral hemispheres were studied using fiber microdissection techniques and examination of sectional anatomy. Dissections were performed from lateral to medial, medial to lateral, inferior to superior, and superior to inferior. A silicone brain model was used to show the normal gyral anatomy. Sections and fibers found at every stage of dissection were photographed with a professional camera. MRI tractography studies were used to aid understanding of the dissections.

RESULTS

The relationships between the insula and cerebral opercula were investigated in detail through multiple dissections and sections. The relationship of the extreme and external capsules with the surrounding opercula and the fronto-occipital fasciculus with the fronto-orbital operculum was demonstrated. These findings were correlated with the tractography studies. Fibers of the extreme capsule connect the medial aspect of the opercula with the insula through the peri-insular sulcus. Medial to lateral dissections were followed with the removal of the central core structures, and in the last step, the medial surface of the cerebral opercula was evaluated in detail.

CONCLUSIONS

This anatomical study clarifies our understanding of the insula and cerebral opercula, which have complex anatomical and functional networks. This study also brings a new perspective to the connection of the insula and cerebral opercula via the extreme and external capsules.

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Microsurgical anatomy and the importance of the petrosal process of the sphenoid bone in endonasal surgery

Ayoze Doniz-Gonzalez, Vera Vigo, Maximiliano Alberto Nunez, Yuanzhi Xu, Ahmed Mohyeldin, Aaron A. Cohen-Gadol, and Juan C. Fernandez-Miranda

OBJECTIVE

The petrosal process of the sphenoid bone (PPsb) is a relevant skull base osseous prominence present bilaterally that can be used as a key surgical landmark, especially for identifying the abducens nerve. The authors investigated the surgical anatomy of the PPsb, its relationship with adjacent neurovascular structures, and its practical application in endoscopic endonasal surgery.

METHODS

Twenty-one dried skulls were used to analyze the osseous anatomy of the PPsb. A total of 16 fixed silicone-injected postmortem heads were used to expose the PPsb through both endonasal and transcranial approaches. Dimensions and distances of the PPsb from the foramen lacerum (inferiorly) and top of the posterior clinoid process (PCP; superiorly) were measured. Moreover, anatomical variations and the relationship of the PPsb with the surrounding crucial structures were recorded. Three representative cases were selected to illustrate the clinical applications of the findings.

RESULTS

The PPsb presented as a triangular bony prominence, with its base medially adjacent to the dorsum sellae and its apex pointing posterolaterally toward the petrous apex. The mean width of the PPsb was 3.5 ± 1 mm, and the mean distances from the PPsb to the foramen lacerum and the PCP were 5 ± 1 and 11 ± 2.5 mm, respectively. The PPsb is anterior to the petroclival venous confluence, superomedial to the inferior petrosal sinus, and inferomedial to the superior petrosal sinus; constitutes the inferomedial limit of the cavernous sinus; and delimits the upper limit of the paraclival internal carotid artery (ICA) before the artery enters the cavernous sinus. The PPsb is anterior and medial to and below the sixth cranial nerve, forming the floor of Dorello’s canal. During surgery, gentle mobilization of the paraclival ICA reveals the petrosal process, serving as an accurate landmark for the location of the abducens nerve.

CONCLUSIONS

This investigation revealed details of the microsurgical anatomy of the PPsb, its anatomical relationships, and its application as a surgical landmark for identifying the abducens nerve. This novel landmark may help in minimizing the risk of abducens nerve injury during transclival approaches, which extend laterally toward the petrous apex and cavernous sinus region.

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Microvascular anatomy of the medial temporal region

Yuanzhi Xu, Ahmed Mohyeldin, Maximiliano Alberto Nunez, Ayoze Doniz-Gonzalez, Vera Vigo, Aaron A. Cohen-Gadol, and Juan C. Fernandez-Miranda

OBJECTIVE

The authors investigated the microvascular anatomy of the hippocampus and its implications for medial temporal tumor surgery. They aimed to reveal the anatomical variability of the arterial supply and venous drainage of the hippocampus, emphasizing its clinical implications for the removal of associated tumors.

METHODS

Forty-seven silicon-injected cerebral hemispheres were examined using microscopy. The origin, course, irrigation territory, spatial relationships, and anastomosis of the hippocampal arteries and veins were investigated. Illustrative cases of hippocampectomy for medial temporal tumor surgery are also provided.

RESULTS

The hippocampal arteries can be divided into 3 segments, the anterior (AHA), middle (MHA), and posterior (PHA) hippocampal artery complexes, which correspond to irrigation of the hippocampal head, body, and tail, respectively. The uncal hippocampal and anterior hippocampal-parahippocampal arteries contribute to the AHA complex, the posterior hippocampal-parahippocampal arteries serve as the MHA complex, and the PHA and splenial artery compose the PHA complex. Rich anastomoses between hippocampal arteries were observed, and in 11 (23%) hemispheres, anastomoses between each segment formed a complete vascular arcade at the hippocampal sulcus. Three veins were involved in hippocampal drainage—the anterior hippocampal, anterior longitudinal hippocampal, and posterior longitudinal hippocampal veins—which drain the hippocampal head, body, and tail, respectively, into the basal and internal cerebral veins.

CONCLUSIONS

An understanding of the vascular variability and network of the hippocampus is essential for medial temporal tumor surgery via anterior temporal lobectomy with amygdalohippocampectomy and transsylvian selective amygdalohippocampectomy. Stereotactic procedures in this region should also consider the anatomy of the vascular arcade at the hippocampal sulcus.

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Microsurgical approaches to the cerebellar interpeduncular region: qualitative and quantitative analysis

Juan Leonardo Serrato-Avila, Juan Alberto Paz Archila, Marcos Devanir Silva da Costa, Paulo Ricardo Rocha, Sergio Ricardo Marques, Luis Otavio Carvalho de Moraes, Sergio Cavalheiro, Kaan Yağmurlu, Michael T. Lawton, and Feres Chaddad-Neto

OBJECTIVE

The cerebellar interpeduncular region (CIPR) is a gate for dorsolateral pontine and cerebellar lesions accessed through the supracerebellar infratentorial approach (SCITa), the occipital transtentorial approach (OTa), or the subtemporal transtentorial approach (STa). The authors sought to compare the exposures of the CIPR region that each of these approaches provided.

METHODS

Three approaches were performed bilaterally in eight silicone-injected cadaveric heads. The working area, area of exposure, depth of the surgical corridor, length of the interpeduncular sulcus (IPS) exposed, and bridging veins were statistically studied and compared based on each approach.

RESULTS

The OTa provided the largest working area (1421 mm2; p < 0.0001) and the longest surgical corridor (6.75 cm; p = 0.0006). Compared with the SCITa, the STa provided a larger exposure area (249.3 mm2; p = 0.0148) and exposed more of the length of the IPS (1.15 cm; p = 0.0484). The most bridging veins were encountered with the SCITa; however, no significant differences were found between this approach and the other approaches (p > 0.05).

CONCLUSIONS

To reach the CIPR, the STa provided a more extensive exposure area and more linear exposure than did the SCITa. The OTa offered a larger working area than the SCIT and the STa; however, the OTa had the most extensive surgical corridor. These data may help neurosurgeons select the most appropriate approach for lesions of the CIPR.

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Lack of somatotopy among corticospinal tract fibers passing through the primate craniovertebral junction and cervical spinal cord: pathoanatomical substrate of central cord syndrome and cruciate paralysis

Robert J. Morecraft, Kimberly S. Stilwell-Morecraft, Jizhi Ge, Alexander Kraskov, and Roger N. Lemon

OBJECTIVE

In some cases of incomplete cervical spinal cord injury (iSCI) there is marked paresis and dysfunction of upper-extremity movement but not lower-extremity movement. A continued explanation of such symptoms is a somatotopic organization of corticospinal tract (CST) fibers passing through the decussation at the craniovertebral junction (CVJ) and lateral CST (LCST). In central cord syndrome, it has been suggested that injury to the core of the cervical cord may include selective damage to medially located arm/hand LCST fibers, without compromising laterally located leg fibers. Because such somatotopic organization in the primate CST might contribute to the disproportionate motor deficits after some forms of iSCI, the authors made a systematic investigation of CST organization in the CVJ and LCST using modern neuroanatomical techniques.

METHODS

High-resolution anterograde tracers were used in 11 rhesus macaque monkeys to define the course of the corticospinal projection (CSP) through the CVJ and LCST from the arm/hand, shoulder, and leg areas of the primary motor cortex (M1). This approach labels CST fibers of all sizes, large and small, arising in these areas. The CSP from the dorsolateral and ventrolateral premotor cortex and supplementary motor area were also studied. A stereological approach was adapted to quantify labeled fiber distribution in 8 cases.

RESULTS

There was no evidence for somatotopic organization of CST fibers passing through the CVJ or contralateral LCST. Fiber labeling from each cortical representation was widespread throughout the CST at the CVJ and LCST and overlapped extensively with fibers from other representations. This study demonstrated no significant difference between medial versus lateral subsectors of the LCST in terms of number of fibers labeled from the M1 arm/hand area.

CONCLUSIONS

This investigation firmly rejects the concept of somatotopy among CST fibers passing through the CVJ and LCST, in contrast with the somatotopy in the cortex, corona radiata, and internal capsule. All CST fibers in the CVJ and LCST would thus appear to be equally susceptible to focal or diffuse injury, regardless of their cortical origin. The disproportionate impairment of arm/hand movement after iSCI must therefore be due to other factors, including greater dependence of hand/arm movements on the CST compared with the lower limb. The dispersed and intermingled nature of frontomotor fibers may be important in motor recovery after cervical iSCI.

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Comparative analysis of the combined petrosal and the pretemporal transcavernous anterior petrosal approach to the petroclival region

Mohamed A. Labib, Xiaochun Zhao, Lena Mary Houlihan, Irakliy Abramov, Joshua S. Catapano, Komal Naeem, Mark C. Preul, A. Samy Youssef, and Michael T. Lawton

OBJECTIVE

The combined petrosal (CP) approach has been traditionally used to resect petroclival meningioma (PCM). The pretemporal transcavernous anterior petrosal (PTAP) approach has emerged as an alternative. A quantitative comparison of both approaches has not been made. This anatomical study compared the surgical corridors afforded by both approaches and identified key elements of the approach selection process.

METHODS

Twelve cadaveric specimens were dissected, and 10 were used for morphometric analysis. Groups A and B (n = 5 in each) underwent the CP and PTAP approaches, respectively. The area of drilled clivus, lengths of cranial nerves (CNs) II–X, length of posterior circulation vessels, surgical area of exposure of the brainstem, and angles of attack anterior and posterior to a common target were measured and compared.

RESULTS

The area of drilled clivus was significantly greater in group A than group B (mean ± SD 88.7 ± 17.1 mm2 vs 48.4 ± 17.9 mm2, p < 0.01). Longer segments of ipsilateral CN IV (52.4 ± 2.33 mm vs 46.5 ± 3.71 mm, p < 0.02), CN IX, and CN X (9.91 ± 3.21 mm vs 0.00 ± 0.00 mm, p < 0.01) were exposed in group A than group B. Shorter portions of CN II (9.31 ± 1.28 mm vs 17.6 ± 6.89 mm, p < 0.02) and V1 (26.9 ± 4.62 mm vs 32.4 ± 1.93 mm, p < 0.03) were exposed in group A than group B. Longer segments of ipsilateral superior cerebellar artery (SCA) were exposed in group A than group B (36.0 ± 4.91 mm vs 25.8 ± 3.55 mm, p < 0.02), but there was less exposure of contralateral SCA (0.00 ± 0.00 mm vs 7.95 ± 3.33 mm, p < 0.01). There was no statistically significant difference between groups with regard to the combined area of the exposed cerebral peduncles and pons (p = 0.75). Although exposure of the medulla was limited, group A had significantly greater exposure of the medulla than group B (p < 0.01). Finally, group A had a smaller anterior angle of attack than group B (24.1° ± 5.62° vs 34.8° ± 7.51°, p < 0.03).

CONCLUSIONS

This is the first study to quantitatively identify the advantages and limitations of the CP and PTAP approaches from an anatomical perspective. Understanding these data will aid in designing maximally effective yet minimally invasive approaches to PCM.