Maysam Alimohamadi and Madjid Samii
Ken Matsushima, Kaan Yagmurlu, Michihiro Kohno and Albert L. Rhoton Jr.
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.
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.
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.
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.
Charles Kulwin, Ken Matsushima, Mahdi Malekpour and Aaron A. Cohen-Gadol
Pineal region tumors pose certain challenges in regard to their resection: a deep surgical field, associated critical surrounding neurovascular structures, and narrow operative working corridor due to obstruction by the apex of the culmen. The authors describe a lateral supracerebellar infratentorial approach that was successfully used in the treatment of 10 large (> 3 cm) midline pineal region tumors. The patients were placed in a modified lateral decubitus position. A small lateral suboccipital craniotomy exposed the transverse sinus. Tentorial retraction sutures were used to gently rotate and elevate the transverse sinus to expand the lateral supracerebellar operative corridor. This approach placed only unilateral normal structures at risk and minimized vermian venous sacrifice. The surgeon achieved generous exposure of the caudal midline mesencephalon through a “cross-court” oblique trajectory, while avoiding excessive retraction on the culmen. All patients underwent the lateral approach with no approach-related complication. The final pathological diagnoses were consistent with meningioma in 3 cases, pilocytic astrocytoma in 3 cases, intermediate grade pineal region tumor in 2 cases, and pineoblastoma in 2 cases. The entire extent of these tumors was readily reachable through the lateral supracerebellar route. Gross-total resection was achieved in 8 (80%) of the 10 cases; in 2 cases (20%) near-total resection was performed due to adherence of these tumors to deep diencephalic veins.
Large midline pineal region tumors can be removed through a unilateral paramedian suboccipital craniotomy. This approach is simple, may spare some of the midline vermian bridging veins, and may be potentially less invasive and more efficient.
Ken Matsushima, Michihiro Kohno, Noritaka Komune, Koichi Miki, Toshio Matsushima and Albert L. Rhoton Jr.
Jugular foramen tumors often extend intra- and extracranially. The gross-total removal of tumors located both intracranially and intraforaminally is technically challenging and often requires a combined skull base approach. This study presents a suprajugular extension of the retrosigmoid approach directed through the osseous roof of the jugular foramen that allows the removal of tumors located in the cerebellopontine angle with extension into the upper part of the foramen, with demonstration of an illustrative case.
The cerebellopontine angles and jugular foramina were examined in dry skulls and cadaveric heads to clarify the microsurgical anatomy around the jugular foramen and to define the steps of the suprajugular exposure.
The area drilled in the suprajugular approach is inferior to the acoustic meatus, medial to the endolymphatic depression and surrounding the superior half of the glossopharyngeal dural fold. Opening this area exposed the upper part of the jugular foramen and extended the exposure along the glossopharyngeal nerve below the roof of the jugular foramen. In the illustrative case, a schwannoma originating from the glossopharyngeal nerve in the cerebellopontine angle and extending below the roof of the jugular foramen and above the jugular bulb was totally removed without any postoperative complications.
The suprajugular extension of the retrosigmoid approach will permit removal of tumors located predominantly in the cerebellopontine angle but also extending into the upper part of the jugular foramen without any additional skull base approaches.