Ken Matsushima

Classification of the Superior Petrosal Veins and Sinus Based on Drainage Pattern

BACKGROUND: The increasing number of reports of complications after sacrificing the superior petrosal veins, the largest veins in the posterior fossa, has led to a need for an increased understanding of the anatomy of these veins and the superior petrosal sinus into which they empty. OBJECTIVE: To examine the anatomy of the superior petrosal veins and their size, draining area, and tributaries, as well as the anatomic variations of the superior petrosal sinus. METHOD: Injected cadaveric cerebellopontine angles and 3-dimensional multifusion angiography images were examined. RESULTS: The 4 groups of the superior petrosal veins based on their tributaries, course, and draining areas are the petrosal, posterior mesencephalic, anterior pontomesencephalic, and tentorial groups. The largest group was the petrosal group. Its largest tributary, the vein of the cerebellopontine fissure, was usually identifiable in the suprafloccular cistern located above the flocculus on the lateral surface of the middle cerebellar peduncle. The medial or lateral segment of the superior petrosal sinus was absent in 40% of cerebellopontine angles studied with venography. CONCLUSION: The superior petrosal veins and their largest tributaries, especially the vein of the cerebellopontine fissure, should be preserved if possible. Obliteration of superior petrosal sinuses in which either the lateral or medial portion is absent may result in loss of the drainage pathway of the superior petrosal veins. Preoperative assessment of the superior petrosal sinus should be considered before transpetrosal surgery in which the superior petrosal sinus may be obliterated. ABBREVIATION: CPA, cerebellopontine angle

Exposure of Wide Cerebellomedullary Cisterns for Vascular Lesion Surgeries in Cerebellomedullary Cisterns: Opening of Unilateral Cerebellomedullary Fissures Combined with Lateral Foramen Magnum Approach

OBJECTIVE To clarify microsurgical anatomic features of the cerebellomedullary fissure (CMF), the natural cleavage plane between the cerebellum and the medulla, and its relationship to the cerebellomedullary cistern (CMC) and to describe a surgical technique that uses the unilateral trans-CMF approach for CMC surgeries. METHODS In the anatomic study, 2 formalin-fixed cadaver heads were used. In the clinical study, 3 patients with vertebral artery-posterior inferior cerebellar artery aneurysms and 3 patients with glossopharyngeal neuralgia were surgically treated through the unilateral trans-CMF approach combined with the transcondylar fossa approach, which is a lateral foramen magnum approach. RESULTS The CMC was present at the lateral end of the CMF. The CMF was closed by arachnoidal adhesion, and the cerebellar hemisphere was superiorly attached to the cerebellar peduncle. After the unilateral CMF was completely opened, the cerebellar hemisphere was easily retracted rostrodorsally. Clinically, almost completely opening the unilateral CMF markedly enabled the retraction of the biventral lobule to obtain a wide surgical field safely for vascular CMC lesions. We present 2 representative cases. CONCLUSION Combined unilateral trans-CMF/lateral foramen magnum approaches provide a wide and close surgical field in the CMC, allowing easy and safe CMC surgery.

Anatomy and approaches along the cerebellar-brainstem fissures.

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.

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.

Anatomy of the superior petrosal veins and their exposure and management during petrous apex meningioma surgery using the lateral suboccipital retrosigmoid approach

During surgeries in the upper cerebellopontine angle (CPA), the superior petrosal veins (SPVs) often act as obstacles; and their sectioning sometimes causes serious complications. In this study, we introduced a classification system for the SPVs wherein their tributaries were classified into four groups on the basis of their courses and draining areas. We furthermore explained the detailed anatomy of the vein of the cerebellopontine fissure, which is the largest tributary. In surgeries of petrous apex meningioma, the knowledge of the displacement pattern of the vein is very helpful for avoiding major venous complications. Therefore, we elucidated its anatomical situation in relation to the original portion of the meningioma and the natural draining point of the vein into the superior petrosal sinus (SPS) in each patient. In addition, we described the methods and techniques used to expose and manage the vein of the cerebellopontine fissure during surgery using the lateral suboccipital retrosigmoid approach. Presenting two illustrative cases, we recommend that the initial exposure of the tumor should be performed through the infratentorial lateral supracerebellar route and that the suprafloccular cistern is the best area to find the vein of the cerebellopontine fissure. We emphasized the importance of the preservation of the vein of the cerebellopontine fissure and also proposed the order for exposure of SPV tributaries during upper CPA surgery using the retrosigmoid approach.

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.

Thrombosed giant aneurysm of the distal anterior cerebral artery treated with aneurysm resection and proximal pericallosal artery-callosomarginal artery end-to-end anastomosis: Case report and review of the literature.

Background: Giant distal anterior cerebral artery (DACA) aneurysms are extremely rare, with only 32 cases reported in the literature. Most giant DACA aneurysms have features that make standard neck clipping difficult, and bypass surgery is sometimes required, although this surgery was performed in only three reported cases. This report presents the fourth case treated with bypass surgery. Case Description: A 69-year-old female presented with an unruptured thrombosed giant DACA aneurysm. She underwent wrapping operation 7 years before, but radiological imaging revealed enlargement of the aneurysm at the left pericallosal artery (PerA)–callosomarginal artery (CMA) junction. Before operation, three different strategies were considered for bypass surgery in case the neck could not be clipped. Aneurysm resection and left proximal PerA–CMA end-to-end anastomosis were successfully performed under intraoperative digital subtraction angiography (DSA) and motor-evoked potential (MEP) monitoring. Conclusion: Most DACA aneurysms are located at the PerA–CMA junction. In some cases, adequate retrograde flow to the distal PerA from the posterior or middle cerebral artery can be expected, making distal PerA reconstruction unnecessary. Moreover, when the distal PerA is cut, proximal PerA–CMA end-to-end anastomosis can be easily performed because of reduced tension in both vessels. We therefore conclude that this strategy should be utilized for treating such patients. We also presented here the effectiveness of intraoperative modalities, such as intraoperative DSA and MEP monitoring, for performing a safe operation.

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.