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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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Kaan Yağmurlu, Jennifer Sokolowski, Sauson Soldozy, Pedro Norat, Musa Çırak, Petr Tvrdik, Mark E. Shaffrey, and M. Yashar S. Kalani

OBJECTIVE

The discovery of dural lymphatics has spurred interest in the mechanisms of drainage of interstitial fluid from the CNS, the anatomical components involved in clearance of macromolecules from the brain, mechanisms of entry and exit of immune components, and how these pathways may be involved in neurodegenerative diseases and cancer metastasis. In this study the authors describe connections between a subset of arachnoid granulations (AGs) and the venous circulation via intradural vascular channels (IVCs), which stain positively with established lymphatic markers. The authors postulate that the AGs may serve as a component of the human brain’s lymphatic system.

METHODS

AGs and IVCs were examined by high-resolution dissection under stereoscope bilaterally in 8 fresh and formalin-fixed human cadaveric heads. The superior sagittal sinus (SSS) and adjacent dura mater were immunostained with antibodies against Lyve-1 (lymphatic marker), podoplanin (lymphatic marker), CD45 (panhematopoietic marker), and DAPI (nuclear marker).

RESULTS

AGs can be classified as intradural or interdural, depending on their location and site of drainage. Interdural AGs are distinct from the dura, adhere to arachnoid membranes, and occasionally open directly in the inferolateral wall or floor of the SSS, although some cross the infradural folds of the dura’s inner layer to meet with intradural AGs and IVCs. Intradural AGs are located within the leaflets of the dura. The total number of openings from the AGs, lateral lacunae, and cortical veins into the SSS was 45 ± 5.62 per head. On average each cadaveric head contained 6 ± 1.30 intradural AGs. Some intradural AGs do not directly open into the SSS and use IVCs to connect to the venous circulation. Using immunostaining methods, the authors demonstrate that these tubular channels stain positively with vascular and lymphatic markers (Lyve-1, podoplanin).

CONCLUSIONS

AGs consist of two subtypes with differing modes of drainage into the SSS. A subset of AGs located intradurally use tubular channels, which stain positively with vascular and lymphatic markers to connect to the venous lacunae and ultimately to the SSS. The present study suggests that AGs may function as a component of brain lymphatics. This finding has important clinical implications for cancer metastasis to and from the CNS and may shed light on mechanisms of altered clearance of macromolecules in the setting of neurodegenerative diseases.

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Eduardo Carvalhal Ribas, Kaan Yağmurlu, Evandro de Oliveira, Guilherme Carvalhal Ribas, and Albert Rhoton Jr.

OBJECTIVE

The purpose of this study was to describe in detail the cortical and subcortical anatomy of the central core of the brain, defining its limits, with particular attention to the topography and relationships of the thalamus, basal ganglia, and related white matter pathways and vessels.

METHODS

The authors studied 19 cerebral hemispheres. The vascular systems of all of the specimens were injected with colored silicone, and the specimens were then frozen for at least 1 month to facilitate identification of individual fiber tracts. The dissections were performed in a stepwise manner, locating each gray matter nucleus and white matter pathway at different depths inside the central core. The course of fiber pathways was also noted in relation to the insular limiting sulci.

RESULTS

The insular surface is the most superficial aspect of the central core and is divided by a central sulcus into an anterior portion, usually containing 3 short gyri, and a posterior portion, with 2 long gyri. It is bounded by the anterior limiting sulcus, the superior limiting sulcus, and the inferior limiting sulcus. The extreme capsule is directly underneath the insular surface and is composed of short association fibers that extend toward all the opercula. The claustrum lies deep to the extreme capsule, and the external capsule is found medial to it. Three fiber pathways contribute to form both the extreme and external capsules, and they lie in a sequential anteroposterior disposition: the uncinate fascicle, the inferior fronto-occipital fascicle, and claustrocortical fibers. The putamen and the globus pallidus are between the external capsule, laterally, and the internal capsule, medially. The internal capsule is present medial to almost all insular limiting sulci and most of the insular surface, but not to their most anteroinferior portions. This anteroinferior portion of the central core has a more complex anatomy and is distinguished in this paper as the “anterior perforated substance region.” The caudate nucleus and thalamus lie medial to the internal capsule, as the most medial structures of the central core. While the anterior half of the central core is related to the head of the caudate nucleus, the posterior half is related to the thalamus, and hence to each associated portion of the internal capsule between these structures and the insular surface. The central core stands on top of the brainstem. The brainstem and central core are connected by several white matter pathways and are not separated from each other by any natural division. The authors propose a subdivision of the central core into quadrants and describe each in detail. The functional importance of each structure is highlighted, and surgical approaches are suggested for each quadrant of the central core.

CONCLUSIONS

As a general rule, the internal capsule and its vascularization should be seen as a parasagittal barrier with great functional importance. This is of particular importance in choosing surgical approaches within this region.

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Feres Chaddad-Neto, Marcos Devanir Silva da Costa, Baran Bozkurt, Hugo Leonardo Doria-Netto, Daniel de Araujo Paz, Ricardo da Silva Centeno, Andrew W. Grande, Sergio Cavalheiro, Kaan Yağmurlu, Robert F. Spetzler, and Mark C. Preul

OBJECTIVE

The authors report a novel surgical route from a superior anatomical aspect—the contralateral anterior interhemispheric-transcallosal-transrostral approach—to a lesion located in the subcallosal region. The neurosurgical approach to the subcallosal region is challenging due to its deep location and close relationship with important vascular structures. Anterior and inferior routes to the subcallosal region have been described but risk damaging the branches of the anterior cerebral artery.

METHODS

Three formalin-fixed and silicone-injected adult cadaveric heads were studied to demonstrate the relationships between the transventricular surgical approach and the subcallosal region. The surgical, clinical, and radiological history of a 39-year-old man with a subcallosal cavernous malformation was retrospectively used to document the neurological examination and radiographic parameters of such a case.

RESULTS

The contralateral anterior interhemispheric-transcallosal-transrostral approach provides access to the subcallosal area that also includes the inferior portion of the pericallosal cistern, lamina terminalis cistern, the paraterminal and paraolfactory gyri, and the anterior surface of the optic chiasm. The approach avoids the neurocritical perforating branches of the anterior communicating artery.

CONCLUSIONS

The contralateral anterior interhemispheric-transcallosal-transrostral approach may be an alternative route to subcallosal area lesions, with less risk to the branches of the anterior cerebral artery, particularly the anterior communicating artery perforators.

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M. Yashar S. Kalani, Kaan Yağmurlu, and Robert F. Spetzler

The authors describe the interpeduncular fossa safe entry zone as a route for resection of ventromedial midbrain lesions. To illustrate the utility of this novel safe entry zone, the authors provide clinical data from 2 patients who underwent contralateral orbitozygomatic transinterpeduncular fossa approaches to deep cavernous malformations located medial to the oculomotor nerve (cranial nerve [CN] III). These cases are supplemented by anatomical information from 6 formalin-fixed adult human brainstems and 4 silicone-injected adult human cadaveric heads on which the fiber dissection technique was used.

The interpeduncular fossa may be incised to resect anteriorly located lesions that are medial to the oculomotor nerve and can serve as an alternative to the anterior mesencephalic safe entry zone (i.e., perioculomotor safe entry zone) for resection of ventromedial midbrain lesions. The interpeduncular fossa safe entry zone is best approached using a modified orbitozygomatic craniotomy and uses the space between the mammillary bodies and the top of the basilar artery to gain access to ventromedial lesions located in the ventral mesencephalon and medial to the oculomotor nerve.

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Kaan Yağmurlu, Hasan A. Zaidi, M. Yashar S. Kalani, Albert L. Rhoton Jr., Mark C. Preul, and Robert F. Spetzler

Pineal region tumors are challenging to access because they are centrally located within the calvaria and surrounded by critical neurovascular structures. The goal of this work is to describe a new surgical trajectory, the anterior interhemispheric transsplenial approach, to the pineal region and falcotentorial junction area. To demonstrate this approach, the authors examined 7 adult formalin-fixed silicone-injected cadaveric heads and 2 fresh human brain specimens. One representative case of falcotentorial meningioma treated through an anterior interhemispheric transsplenial approach is also described. Among the interhemispheric approaches to the pineal region, the anterior interhemispheric transsplenial approach has several advantages. 1) There are few or no bridging veins at the level of the pericoronal suture. 2) The parietal and occipital lobes are not retracted, which reduces the chances of approach-related morbidity, especially in the dominant hemisphere. 3) The risk of damage to the deep venous structures is low because the tumor surface reached first is relatively vein free. 4) The internal cerebral veins can be manipulated and dissected away laterally through the anterior interhemispheric route but not via the posterior interhemispheric route. 5) Early control of medial posterior choroidal arteries is obtained. The anterior interhemispheric transsplenial approach provides a safe and effective surgical corridor for patients with supratentorial pineal region tumors that 1) extend superiorly, involve the splenium of the corpus callosum, and push the deep venous system in a posterosuperior or an anteroinferior direction; 2) are tentorial and displace the deep venous system inferiorly; or 3) originate from the splenium of the corpus callosum.