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  • Author or Editor: Kaan Yağmurlu x
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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 Yagmurlu, Erik H. Middlebrooks, Necmettin Tanriover and Albert L. Rhoton Jr.

OBJECT

The aim of this study was to examine the arcuate (AF) and superior longitudinal fasciculi (SLF), which together form the dorsal language stream, using fiber dissection and diffusion imaging techniques in the human brain.

METHODS

Twenty-five formalin-fixed brains (50 hemispheres) and 3 adult cadaveric heads, prepared according to the Klingler method, were examined by the fiber dissection technique. The authors’ findings were supported with MR tractography provided by the Human Connectome Project, WU-Minn Consortium. The frequencies of gyral distributions were calculated in segments of the AF and SLF in the cadaveric specimens.

RESULTS

The AF has ventral and dorsal segments, and the SLF has 3 segments: SLF I (dorsal pathway), II (middle pathway), and III (ventral pathway). The AF ventral segment connects the middle (88%; all percentages represent the area of the named structure that is connected to the tract) and posterior (100%) parts of the superior temporal gyri and the middle part (92%) of the middle temporal gyrus to the posterior part of the inferior frontal gyrus (96% in pars opercularis, 40% in pars triangularis) and the ventral premotor cortex (84%) by passing deep to the lower part of the supramarginal gyrus (100%). The AF dorsal segment connects the posterior part of the middle (100%) and inferior temporal gyri (76%) to the posterior part of the inferior frontal gyrus (96% in pars opercularis), ventral premotor cortex (72%), and posterior part of the middle frontal gyrus (56%) by passing deep to the lower part of the angular gyrus (100%).

CONCLUSIONS

This study depicts the distinct subdivision of the AF and SLF, based on cadaveric fiber dissection and diffusion imaging techniques, to clarify the complicated language processing pathways.

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Kaan Yagmurlu, M. Yashar S. Kalani, Mark C. Preul and Robert F. Spetzler

The authors describe a safe entry zone, the superior fovea triangle, on the floor of the fourth ventricle for resection of deep dorsal pontine lesions at the level of the facial colliculus. Clinical data from a patient undergoing a suboccipital telovelar transsuperior fovea triangle approach to a deep pontine cavernous malformation were reviewed and supplemented with 6 formalin-fixed adult human brainstem and 2 silicone-injected adult human cadaveric heads using the fiber dissection technique to illustrate the utility of this novel safe entry zone. The superior fovea has a triangular shape that is an important landmark for the motor nucleus of the trigeminal, abducens, and facial nerves. The inferior half of the superior fovea triangle may be incised to remove deep dorsal pontine lesions through the floor of the fourth ventricle. The superior fovea triangle may be used as a safe entry zone for dorsally located lesions at the level of the facial colliculus.

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Ken Matsushima, Kaan Yagmurlu, Michihiro Kohno and Albert L. Rhoton Jr.

OBJECT

Fissure dissection is routinely used in the supratentorial region to access deeply situated pathology while minimizing division of neural tissue. Use of fissure dissection is also practical in the posterior fossa. In this study, the microsurgical anatomy of the 3 cerebellar-brainstem fissures (cerebellomesencephalic, cerebellopontine, and cerebellomedullary) and the various procedures exposing these fissures in brainstem surgery were examined.

METHODS

Seven cadaveric heads were examined with a microsurgical technique and 3 with fiber dissection to clarify the anatomy of the cerebellar-brainstem and adjacent cerebellar fissures, in which the major vessels and neural structures are located. Several approaches directed along the cerebellar surfaces and fissures, including the supracerebellar infratentorial, occipital transtentorial, retrosigmoid, and midline suboccipital approaches, were examined. The 3 heads examined using fiber dissection defined the anatomy of the cerebellar peduncles coursing in the depths of these fissures.

RESULTS

Dissections directed along the cerebellar-brainstem and cerebellar fissures provided access to the posterior and posterolateral midbrain and upper pons, lateral pons, floor and lateral wall of the fourth ventricle, and dorsal and lateral medulla.

CONCLUSIONS

Opening the cerebellar-brainstem and adjacent cerebellar fissures provided access to the brainstem surface hidden by the cerebellum, while minimizing division of neural tissue. Most of the major cerebellar arteries, veins, and vital neural structures are located in or near these fissures and can be accessed through them.

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

Dorsal pons lesions at the facial colliculus level can be accessed with a suboccipital telovelar (SOTV) approach using the superior fovea safe entry zone. Opening the telovelar junction allows visualization of the dorsal pons and lateral entry at the level of the fourth ventricle floor. Typically, a lateral entry into the floor of the fourth ventricle is better tolerated than a midline opening. This video demonstrates the use of the SOTV approach to remove a cavernous malformation at the level of the facial colliculus. This case is particularly interesting because of a large venous anomaly and several telangiectasias in the pons. Dissections in the video are reproduced with permission from the Rhoton Collection (http://rhoton.ineurodb.org).

The video can be found here: https://youtu.be/LqzCfN2J3lY.

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M. Yashar S. Kalani, Kaan Yagmurlu, Nikolay L. Martirosyan, Daniel D. Cavalcanti and Robert F. Spetzler

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Eberval G. Figueiredo, Manoel J. Teixeira and Leonardo C. Welling

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Eduardo Carvalhal Ribas, Kaan Yagmurlu, Hung Tzu Wen and Albert L. Rhoton Jr.

OBJECT

The purpose of this study was to describe the location of each white matter pathway in the area between the inferior limiting insular sulcus (ILS) and temporal horn that may be crossed in approaches through the temporal stem to the medial temporal lobe.

METHODS

The fiber tracts in 14 adult cadaveric cerebral hemispheres were examined using the Klingler technique. The fiber dissections were completed in a stepwise manner, identifying each white matter pathway in different planes and describing its position in relation to the anterior end of the ILS.

RESULTS

The short-association fibers from the extreme capsule, which continue toward the operculae, are the most superficial subcortical layer deep to the ILS. The external capsule fibers are found deeper at an intermediate layer and are formed by the uncinate fasciculus, inferior frontooccipital fasciculus, and claustrocortical fibers in a sequential anteroposterior disposition. The anterior commissure forms the next deeper layer, and the optic radiations in the sublenticular part of the internal capsule represent the deepest layer. The uncinate fasciculus is found deep to the anterior third of the ILS, whereas the inferior frontooccipital fasciculus and optic radiations are found superficial and deep, respectively, at the posterior two-thirds of this length.

CONCLUSIONS

The authors' findings suggest that in the transsylvian approach, a 6-mm incision beginning just posterior to the limen insula through the ILS will cross the uncinate fasciculus but not the inferior frontooccipital fasciculus or optic radiations, but that longer incisions carry a risk to language and visual functions.

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Ali M. Elhadi, Hasan A. Zaidi, Kaan Yagmurlu, Shah Ahmed, Albert L. Rhoton Jr., Peter Nakaji, Mark C. Preul and Andrew S. Little

OBJECTIVE

Endoscopic transmaxillary approaches (ETMAs) address pathology of the anterolateral skull base, including the cavernous sinus, pterygopalatine fossa, and infratemporal fossa. This anatomically complex region contains branches of the trigeminal nerve and external carotid artery and is in proximity to the internal carotid artery. The authors postulated, on the basis of intraoperative observations, that the infraorbital nerve (ION) is a useful surgical landmark for navigating this region; therefore, they studied the anatomy of the ION and its relationships to critical neurovascular structures and the maxillary nerve (V2) encountered in ETMAs.

METHODS

Endoscopic anatomical dissections were performed bilaterally in 5 silicone-injected, formalin-fixed cadaveric heads (10 sides). Endonasal transmaxillary and direct transmaxillary (Caldwell-Luc) approaches were performed, and anatomical correlations were analyzed and documented. Stereotactic imaging of each specimen was performed to correlate landmarks and enable precise measurement of each segment.

RESULTS

The ION was readily identified in the roof of the maxillary sinus at the beginning of the surgical procedure in all specimens. Anatomical dissections of the ION and the maxillary branch of the trigeminal nerve (V2) to the cavernous sinus suggested that the ION/V2 complex has 4 distinct segments that may have implications in endoscopic approaches: 1) Segment I, the cutaneous segment of the ION and its terminal branches (5–11 branches) to the face, distal to the infraorbital foramen; 2) Segment II, the orbitomaxillary segment of the ION within the infraorbital canal from the infraorbital foramen along the infraorbital groove (length 12 ± 3.2 mm); 3) Segment III, the pterygopalatine segment within the pterygopalatine fossa, which starts at the infraorbital groove to the foramen rotundum (13 ± 2.5 mm); and 4) Segment IV, the cavernous segment from the foramen rotundum to the trigeminal ganglion (15 ± 4.1 mm), which passes in the lateral wall of the cavernous sinus. The relationship of the ION/V2 complex to the contents of the cavernous sinus, carotid artery, and pterygopalatine fossa is described in the text.

CONCLUSIONS

The ION/V2 complex is an easily identifiable and potentially useful surgical landmark to the foramen rotundum, cavernous sinus, carotid artery, pterygopalatine fossa, and anterolateral skull base during ETMAs.

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Ting Lei, Evgenii Belykh, Alexander B. Dru, Kaan Yagmurlu, Ali M. Elhadi, Peter Nakaji and Mark C. Preul

Chen Jingrun (1933–1996), perhaps the most prodigious mathematician of his time, focused on the field of analytical number theory. His work on Waring's problem, Legendre's conjecture, and Goldbach's conjecture led to progress in analytical number theory in the form of “Chen's Theorem,” which he published in 1966 and 1973. His early life was ravaged by the Second Sino-Japanese War and the Chinese Cultural Revolution. On the verge of solving Goldbach's conjecture in 1984, Chen was struck by a bicyclist while also bicycling and suffered severe brain trauma. During his hospitalization, he was also found to have Parkinson's disease. Chen suffered another serious brain concussion after a fall only a few months after recovering from the bicycle crash. With significant deficits, he remained hospitalized for several years without making progress while receiving modern Western medical therapies. In 1988 traditional Chinese medicine experts were called in to assist with his treatment. After a year of acupuncture and oxygen therapy, Chen could control his basic bowel and bladder functions, he could walk slowly, and his swallowing and speech improved. When Chen was unable to produce complex work or finish his final work on Goldbach's conjecture, his mathematical pursuits were taken up vigorously by his dedicated students. He was able to publish Youth Math, a mathematics book that became an inspiration in Chinese education. Although he died in 1996 at the age of 63 after surviving brutal political repression, being deprived of neurological function at the very peak of his genius, and having to be supported by his wife, Chen ironically became a symbol of dedication, perseverance, and motivation to his students and associates, to Chinese youth, to a nation, and to mathematicians and scientists worldwide.