Noritaka Komune

Auditory brainstem implantation: Anatomy and approaches

BACKGROUND: Auditory brainstem implantation at the cochlear nuclei used mainly for neurofibromatosis type 2 patients with bilateral loss of the cochlear nerves has more recently been extended to the inferior colliculus. OBJECTIVE: To examine the microsurgical and endoscopic anatomy of the cochlear nuclei and inferior colliculus as seen through the translabyrinthine and retrosigmoid approaches used for cochlear nuclei and inferior collicular implantation. METHODS: Ten cerebellopontine angles of formalin-fixed adult cadaveric heads were examined with the aid of the surgical microscope and endoscope. The ascending auditory pathways between the cochlear nuclei and inferior colliculi and above were examined by the fiber dissection technique. RESULTS: Both the translabyrinthine and retrosigmoid routes provide sufficient exposure for concurrent tumor removal and implantation at either the cochlear nuclei or inferior colliculus. The position of the inferior colliculus in the auditory pathways and its accessibility in the infratentorial supracerebellar exposure directed through either the translabyrinthine or retrosigmoid approach makes it an alternative site for electrode placement if the cochlear nuclei are not functionally or structurally suitable for implantation. Endoscopic assistance may aid the exposure and electrode placement at either site. CONCLUSION: The translabyrinthine or retrosigmoid approaches provide access to the cochlear nuclei for implantation and also to the inferior colliculus through the translabyrinthine or retrosigmoid infratentorial supracerebellar route. The endoscope may aid in exposing either site. ABBREVIATIONS: ABI, auditory brainstem implant AMI, auditory midbrain implant CN, cranial nerve NF2, neurofibromatosis type 2 SCA, superior cerebellar artery

Preservation of the nerves to the frontalis muscle during pterional craniotomy.

OBJECT There continues to be confusion over how best to preserve the branches of the facial nerve to the frontalis muscle when elevating a frontotemporal (pterional) scalp flap. The object of this study was to examine the full course of the branches of the facial nerve that must be preserved to maintain innervation of the frontalis muscle during elevation of a frontotemporal scalp flap. METHODS Dissection was performed to follow the temporal branches of facial nerves along their course in 5 adult, cadaveric heads (n = 10 extracranial facial nerves). RESULTS Preserving the nerves to the frontalis muscle requires an understanding of the course of the nerves in 3 areas. The first area is on the outer surface of the temporalis muscle lateral to the superior temporal line (STL) where the interfascial or subfascial approaches are applied, the second is in the area medial to the STL where subpericranial dissection is needed, and the third is along the STL. Preserving the nerves crossing the STL requires an understanding of the complex fascial relationships at this line. It is important to preserve the nerves crossing the lateral and medial parts of the exposure, and the continuity of the nerves as they pass across the STL. Prior descriptions have focused largely on the area superficial to the temporalis muscle lateral to the STL. CONCLUSIONS Using the interfascial-subpericranial flap and the subfascial-subpericranial flap avoids opening the layer of loose areolar tissue between the temporal fascia and galea in the area lateral to the STL and between the galea and frontal pericranium in the area medial to the STL. It also preserves the continuity of the nerve crossing the STL. This technique allows for the preservation of the nerves to the frontalis muscle along their entire trajectory, from the uppermost part of the parotid gland to the frontalis muscle.

Microsurgical anatomy of the lateral condylar vein and its clinical significance

BACKGROUND: Although the lateral condylar vein has been encountered in some skull base approaches and used as a route to access the anterior condylar venous confluence, few descriptions can be found in the literature regarding its morphology. OBJECTIVE: To examine the anatomy of the lateral condylar vein and its clinical significance. METHODS: The craniocervical junctions of 3 cadaveric heads, 15 dry bones, and 25 computed tomography venography images were examined. RESULTS: The lateral condylar vein was identified in 88.0% of paracondylar areas, with an average diameter of 3.6 mm. This vein originated near the jugular bulb, descended along the lateral surface of the occipital condyle and medial to the internal jugular vein, cranial nerves IX to XI, and rectus capitis lateralis muscle to drain into the vertebral venous plexus surrounding the vertebral artery. The veins were classified according to their origin from either (1) the anterior condylar confluence or (2) the internal jugular vein. In some specimens, the lateral condylar vein courses within a small osseous canal lateral to the occipital condyle, the paracondylar canal, which was identified in 16.7% of paracondylar areas in the dry bones. CONCLUSION: The lateral condylar vein may be encountered in exposing the jugular bulb, hypoglossal canal, or foramen magnum. This vein has been reported to be a main draining route of dural arteriovenous fistulas, in which case it can be utilized as a transvenous route for endovascular treatment, or obliterated. An understanding of the anatomy of this vein may prove useful in planning skull base and endovascular procedures. ABBREVIATIONS: CN, cranial nerve DAVF, dural arteriovenous fistula

Surgical approaches to jugular foramen schwannomas: An anatomic study.

The variety of surgical approaches to jugular schwannomas makes selection of an approach difficult. The purpose of this study was to define the anatomic elements of these approaches.

The accuracy of an electromagnetic navigation system in lateral skull base approaches

Image‐guided optical tracking systems are being used with increased frequency in lateral skull base surgery. Recently, electromagnetic tracking systems have become available for use in this region. However, the clinical accuracy of the electromagnetic tracking system has not been examined in lateral skull base surgery. This study evaluates the accuracy of electromagnetic navigation in lateral skull base surgery.

Surgical anatomy and utility of pedicled vascularized tissue flaps for multilayered repair of skull base defects.

OBJECT The objective of this study was to describe the surgical anatomy and technical nuances of various vascularized tissue flaps. METHODS The surgical anatomy of various tissue flaps and their vascular pedicles was studied in 5 colored silicone-injected anatomical specimens. Medical records were reviewed of 11 consecutive patients who underwent repair of extensive skull base defects with a combination of various vascularized flaps. RESULTS The supraorbital, supratrochlear, superficial temporal, greater auricular, and occipital arteries contribute to the vascular supply of the pericranium. The pericranial flap can be designed based on an axial blood supply. Laterally, various flaps are supplied by the deep or superficial temporal arteries. The nasoseptal flap is a vascular pedicled flap based on the nasoseptal artery. Patients with extensive skull base defects can undergo effective repair with dual flaps or triple flaps using these pedicled vascularized flaps. CONCLUSIONS Multiple pedicled flaps are available for reconstitution of the skull base. Knowledge of the surgical anatomy of these flaps is crucial for the skull base surgeon. These vascularized tissue flaps can be used effectively as single or combination flaps. Multilayered closure of cranial base defects with vascularized tissue can be used safely and may lead to excellent repair outcomes.

Absence of the superior petrosal veins and sinus: Surgical considerations.

Background: The superior petrosal vein, one of the most constant and largest drainage pathways in the posterior fossa, may result in complications if occluded. This study calls attention to a unique variant in which the superior petrosal veins and sinus were absent unilaterally, and the venous drainage was through the galenic and tentorial drainage groups. Methods: This study examines one venogram and another anatomic specimen in which the superior petrosal vein and sinus were absent. Results: The superior petrosal veins, described as 1–3 bridging veins, emptying into the superior petrosal sinus, are the major drainage pathways of the petrosal group of posterior fossa veins. In the cases presented, the superior petrosal vein and sinus were absent and venous drainage was through the galenic and tentorial groups, including the lateral mesencephalic or bridging vein on the tentorial cerebellar surface. Conclusions: In cases in which the superior petrosal sinus and veins are absent, care should be directed to preserving the collateral drainage through the galenic and tentorial tributaries. Although surgical strategies for intraoperative management and preservation of venous structures are still controversial, knowledge of the possible anatomical variations is considered to be essential to improve surgical outcomes.

Comparison of lateral microsurgical preauricular and anterior endoscopic approaches to the jugular foramen.

INTRODUCTION This project compares access to the anterolateral part of the jugular foramen provided by the lateral microsurgical preauricular and the anterior endoscopic approaches, and defines the important landmarks involved in each approach. STUDY DESIGN Cadaveric study. RESULTS The endoscopic transnasal/transmaxillary transpterygoid corridor provides a less invasive route for selected lesions in the jugular foramen than the traditional open route through the preauricular subtemporal infratemporal fossa approach. However, the anterior endoscopic approach provides a smaller channel to the jugular foramen than the preauricular approach. CONCLUSIONS The anterior endoscopic approach to the anterolateral part of the jugular foramen is a useful alternative to the lateral microsurgical preauricular approach in carefully selected cases. The vaginal process of the tympanic part of the temporal bone provides a valuable landmark to aid in accessing the jugular foramen in both procedures and can be drilled to open the foramen in the preauricular approach.

Microsurgical Anatomy of Subtotal Temporal Bone Resection En Bloc With the Parotid Gland and Temporomandibular Joint

BACKGROUND: Subtotal temporal bone resection (STBR) has been used for half a century to remove temporal bone malignancies. However, there are few reports on the detailed anatomy involved in the resection. OBJECTIVE: To describe the microsurgical anatomy of STBR combined en bloc with the resection of the parotid gland and temporomandibular joint (TMJ). METHODS: Cadaveric specimens were dissected in a stepwise manner using 3× to 40× magnification. RESULTS: STBR can be combined with the total parotidectomy and the resection of the TMJ if the tumor extends into the parotid gland, TMJ, or facial nerve. In this study, we describe the step-by-step microsurgical anatomy of STBR en bloc with the parotid gland and TMJ. The surgical technique described combines 3 approaches: the high cervical, subtemporal-infratemporal fossa, and retromastoid-paracondylar approaches. Combining these 3 approaches aided in efficiently completing this modified approach. CONCLUSION: STBR is a complicated and technically challenging procedure. This study highlights the importance of understanding the surgical anatomy of STBR and will serve as a catalyst for improvement of the surgical technique for temporal bone resection. ABBREVIATIONS: CN, cranial nerve JF, jugular foramen ICA, internal carotid artery STBR, subtotal temporal bone resection TMJ, temporomandibular joint

Variations of Occipital Artery-Posterior Inferior Cerebellar Artery Bypass: Anatomic Consideration

BACKGROUND Advances in diagnosis of posterior inferior cerebellar artery (PICA) aneurysms have revealed the high frequency of distal and/or dissecting PICA aneurysms. Surgical treatment of such aneurysms often requires revascularization of the PICA including but not limited to its caudal loop. OBJECTIVE To examine the microsurgical anatomy involved in occipital artery (OA)-PICA anastomosis at various anatomic segments of the PICA. METHODS Twenty-eight PICAs in 15 cadaveric heads were examined with the operating microscope to take morphometric measurements and explore the specific anatomy of bypass procedures. RESULTS OA bypass to the p2, p3, p4, or p5 segment was feasible with a recipient vessel of sufficient diameter. The loop wandering near the jugular foramen in the p2 segment provided sufficient length without requiring cauterization of any perforating arteries to the brainstem. Wide dissection of the cerebellomedullary fissure provided sufficient exposure for the examination of some p3 segments and all p4 segments hidden by the tonsil. OA-p5 bypass was placed at the main trunk before the bifurcation in 5 hemispheres and at the larger hemispheric trunk in others. CONCLUSION Understanding the possible variations of OA-PICA bypass may enable revascularization of the appropriate portion of the PICA when the parent artery must be occluded. A detailed anatomic understanding of each segment clarifies important technical nuances for the bypass on each segment. Dissection of the cerebellomedullary fissure helps to achieve sufficient exposure for the bypass procedures on most of the segments.