Alireza Shoakazemi, Alexander I. Evins, Justin C. Burrell, Philip E. Stieg and Antonio Bernardo
Surgical approaches to deep-seated brain pathologies, specifically lesions of the third ventricle, have always been a challenge for neurosurgeons. In certain cases, the transcallosal approach remains the most suitable option for targeting lesions of the third ventricle, although retraction of the fornices and wall of the third ventricle have been associated with neuropsychological and hypothalamic deficits. The authors investigated the feasibility of an interhemispheric 3D endoscopic transcallosal approach through a minimally invasive tubular retractor system for the management of third ventricular lesions.
Three-dimensional endoscopic transtubular transcallosal approaches were performed on 5 preserved cadaveric heads (10 sides). A parasagittal bur hole was placed using neuronavigation, and a tubular retractor was inserted under direct endoscopic visualization. Following observation of the vascular structures, fenestration of the corpus callosum was performed and the retractor was advanced through the opening. Transforaminal, interforniceal, and transchoroidal modifications were all performed and evaluated by 3 surgeons.
This approach provided enhanced visualization of the third ventricle and more stable retraction of corpus callosum and fornices. Bayonetted instruments were used through the retractor without difficulty, and the retractor applied rigid, constant, and equally distributed pressure on the corpus callosum.
A transtubular approach to the third ventricle is feasible and facilitates blunt dissection of the corpus callosum that may minimize retraction injury. This technique also provides an added degree of safety by limiting the free range of instrumental movement. The combination of 3D endoscopic visualization with a clear plastic retractor facilitates safe and direct monitoring of the surgical corridor.
Michael A. Cohen, Alexander I. Evins, Gennaro Lapadula, Leopold Arko, Philip E. Stieg and Antonio Bernardo
The rectus capitis lateralis (RCL) is a small posterior cervical muscle that originates from the transverse process of C-1 and inserts onto the jugular process of the occipital bone. The authors describe the RCL and its anatomical relationships, and discuss its utility as a surgical landmark for safe exposure of the jugular foramen in extended or combined skull base approaches. In addition, the condylar triangle is defined as a landmark for localizing the vertebral artery (VA) and occipital condyle.
Four cadaveric heads (8 sides) were used to perform far-lateral, extended far-lateral, combined transmastoid infralabyrinthine transcervical, and combined far-lateral transmastoid infralabyrinthine transcervical approaches to the jugular foramen. On each side, the RCL was dissected, and its musculoskeletal, vascular, and neural relationships were examined.
The RCL lies directly posterior to the internal jugular vein—only separated by the carotid sheath and in some cases cranial nerve (CN) XI. The occipital artery travels between the RCL and the posterior belly of the digastric muscle, and the VA passes medially to the RCL as it exits the C-1 foramen transversarium and courses posteriorly toward its dural entrance. CNs IX–XI exit the jugular foramen directly anterior to the RCL. To provide a landmark for identification of the occipital condyle and the extradural VA without exposure of the suboccipital triangle, the authors propose and define a condylar triangle that is formed by the RCL anteriorly, the superior oblique posteriorly, and the occipital bone superiorly.
The RCL is an important surgical landmark that allows for early identification of the critical neurovascular structures when approaching the jugular foramen, especially in the presence of anatomically displacing tumors. The condylar triangle is a novel and useful landmark for identifying the terminal segment of the hypoglossal canal as well as the superior aspect of the VA at its exit from the C-1 foramen transversarium, without performing a far-lateral exposure.
Hitoshi Fukuda, Alexander I. Evins, Koichi Iwasaki, Itaro Hattori, Kenichi Murao, Yoshitaka Kurosaki, Masaki Chin, Philip E. Stieg, Sen Yamagata and Antonio Bernardo
Occipital artery–posterior inferior cerebellar artery (OA-PICA) bypass is a technically challenging procedure for posterior fossa revascularization. The caudal loop of the PICA is considered the optimal site for OA-PICA anastomosis, however its absence can increase the technical difficulty associated with this procedure. The use of the far-lateral approach for accessing alternative anastomosis sites in OA-PICA bypass in patients with absent or unavailable caudal loops of PICA is evaluated.
A morphometric analysis of OA-PICA bypass with anastomosis on each segment of the PICA was performed on 5 cadaveric specimens through the conventional midline foramen magnum and far-lateral approaches. The difficulty level associated with anastomoses at each segment was qualitatively assessed in each approach for exposure and maneuverability by multiple surgeons. A series of 8 patients who underwent OA-PICA bypass for hemodynamic ischemia or ruptured dissecting posterior fossa aneurysms are additionally reviewed and described, and the clinical significance of the caudal loop of PICA is discussed.
Anastomosis on the caudal loop could be performed more superficially than on any other segment (p < 0.001). A far-lateral approach up to the medial border of the posterior condylar canal provided a 13.5 ± 2.2–mm wider corridor than the conventional midline foramen magnum approach, facilitating access to alternative anastomosis sites. The far-lateral approach was successfully used for OA-PICA bypass in 3 clinical cases whose caudal loops were absent, whereas the midline foramen magnum approach provided sufficient exposure for caudal loop bypass in the remaining 5 cases.
The absence of the caudal loop of the PICA is a major contributing factor to the technical difficulty of OA-PICA bypass. The far-lateral approach is a useful surgical option for OA-PICA bypass when the caudal loop of the PICA is unavailable.
Sukhdeep S. Jhawar, Maximiliano Nunez, Paolo Pacca, Daniel Seclen Voscoboinik and Huy Q. Truong