Petroclival meningiomas: predictive parameters for transpetrosal approaches.

OBJECTIVE: To determine parameters that influence the selection of the proper petrosal approach or combined approaches for the excision of petroclival meningiomas. METHODS: We dissected 15 cadaver heads, inspected the petroclival region in 50 dry human skulls, and performed a retrospective analysis of the cases of 35 patients with petroclival meningiomas who underwent surgery via transpetrosal approaches. RESULTS: The petroclival region was divided into three "zones" based on the extent of surgical exposure achieved via the petrosal approaches with microscopic dissection of 15 preserved and silicone-injected cadaveric heads and with the measurements of 50 dry skulls. Zone I, defined as the area from the dorsum sellae to the internal auditory canal, is accessible via the anterior petrosal approach. Zone II, defined as the area from the internal auditory canal to the upper border of the jugular tubercle, is easily accessible in its lateral portion via the posterior petrosal approach. The medial portion of Zone II, the "central clival depression," is accessible only with cochlear resection and posterior facial nerve transposition. Zone III, defined as the area from the upper border of the jugular tubercle to the lower edge of the foramen magnum, is accessible via a suboccipital/transcondylar approach. The retrospective analysis of the cases of 35 patients who underwent transpetrosal resection of petroclival meningiomas between 1991 and 1998 was used to determine the predictive value of these anatomic parameters. The degree of tumor resection was analyzed with a novel grading scale combining the percentage of resection and the percentage of brainstem reexpansion. Total excision was achieved in 37% of the patients and complete brainstem reexpansion was achieved in an additional 40%. Residual tumor was concentrated in the central clival depression in Zone II, as predicted by anatomic parameters, and around infiltrated neurovascular structures. New cranial nerve deficit occurred in 31% of the patients in the early postoperative period and improved to 17% at 6 months. Major morbidity occurred in 9% of the patients, and mortality was 0%. Early Karnofsky scores were reduced in 37% of the patients, but 6-month Karnofsky scores were equal to preoperative baseline scores or improved in 91%. CONCLUSION: Anatomic parameters can predict the resectability of petroclival meningiomas. Judicious application of cytoreductive surgery in selected patients maintains an acceptable morbidity and achieves adequate brainstem reexpansion.

Colored silicone injection for use in neurosurgical dissections: anatomic technical note.

OBJECTIVE: The dissection of cadaveric specimens is very important for a more sophisticated understanding of neurosurgical anatomic features and approaches. Teaching known approaches to residents or learning new approaches is best performed in a cadaveric laboratory. The utility of neurosurgical cadaveric dissections can be improved by injecting the intracranial vascular tree with colored silicone. The vascular anatomic features, which are integral to neurosurgical procedures, are much more clearly defined in injected specimens. METHODS: Self-curing colored silicone rubber is used to inject the arteries and veins (red and blue, respectively) of the head. This process is described in a step-by-step format. Six steps are required and can be summarized as follows: 1) exposure of the great vessels, 2) cannulation of the great vessels, 3) irrigation of the head, 4) preparation of the colored silicone, 5) injection of the colored silicone, and 6) evaluation of the final specimen. CONCLUSION: Injection of colored silicone into the vascular tree can enhance the educational value of cadaveric head dissections. This report describes the technique of vascular injection that is used in the Goodyear Microsurgical Laboratory, the University of Cincinnati, and the Mayfield Clinic.

Primary lymphoma of Meckel's cave mimicking trigeminal schwannoma: case report.

OBJECTIVE AND IMPORTANCE: We report the first case of primary lymphoma of Meckel's cave. The ability of a lymphoma to mimic a trigeminal schwannoma, both clinically and radiographically, resulted in misdiagnosis and flawed surgical strategy. We discuss the characteristics of a Meckel's cave lymphoma on magnetic resonance images, the predisposing medical conditions that should cause the neurosurgeon to add lymphoma to the normal differential diagnosis, and appropriate management strategies. CLINICAL PRESENTATION: A 40-year-old African-American woman presented with a 5-month history of progressive facial numbness and pain in all three divisions of the left trigeminal nerve. Magnetic resonance imaging revealed a mass in the left side of Meckel's cave, with extension into the lateral compartment of the cavernous sinus, without encasement of the internal carotid artery, through the foramen rotundum into the posterior aspect of the maxillary sinus, and through the foramen ovale into the pterygopalatine fossa. The diagnosis, based on clinical history and radiographic imaging, was schwannoma of Meckel's cave. The patient had a history of systemic lupus erythematosus that had been treated with intermittent steroid therapy. INTERVENTION: The surgical approach selected was a frontotemporal craniotomy with orbitozygomatic osteotomy and anterior petrosectomy. The lesion was totally excised, although the gross intraoperative appearance of the lesion was inconsistent with the preoperative diagnosis, and the pathological examination was unable to establish a histological diagnosis on the basis of frozen sections. Histological diagnosis was confirmed on permanent section after surgery as B-cell lymphoma. Evaluation for other primary sites produced negative results. The patient was then treated with cyclophosphamide (Cytotoxan; Bristol-Myers Oncology, Princeton, NJ), doxorubicin (Adriamycin; Pharmacia & Upjohn, Kalamazoo, MI), vincristine, and prednisone chemotherapy every 3 weeks for six cycles and then by radiation therapy to the affected area. CONCLUSION: The diagnosis of lymphoma should be considered for lesions affecting Meckel's cave in high-risk immunocompromised patients. The presence of an apparent dural tail in an otherwise typical schwannoma is the distinguishing characteristic of a lymphoma. The absence of hyperostosis helps differentiate it from a meningioma. At this point, the preferred surgical strategy is biopsy for diagnosis and then radiotherapy and chemotherapy rather than major cranial base surgery for total resection.