The microsurgical anatomy of Dorello's canal has been studied in 20 specimens obtained from 10 cadaver heads fixed in formalin. The bow-shaped canal through which courses the abducens nerve before reaching the cavernous sinus is located inside a venous confluence which occupies the space between the dural leaves of the petroclival area. The petrosphenoidal ligament (Gruber's ligament), which forms the posteromedial wall of the canal, appears as a fibrous trabecula surrounded by venous blood. Canal measurements were performed and its anatomical relationship with the sixth cranial nerve is described. Angulations of variable degrees were observed in the course of the nerve inside and outside the canal. The influence of this relatively tortuous course of the abducens nerve upon its vulnerability in some pathological conditions is discussed.

The superior wall of the cavernous sinus was studied in 30 specimens obtained from 15 cadaver heads fixed in formalin. Trapezoidal in shape, the superior wall of cavernous sinus is limited laterally by the anterior petroclinoid ligament, medially by the dura of the diaphragma sellae, anteriorly by the endosteal dura of the carotid canal, and posteriorly by the posterior petroclinoid ligament. An interclinoid ligament bisects the wall, dividing it into two triangles: the carotid trigone anteromedially and the oculomotor trigone posterolaterally. Similar to the lateral wall of the cavernous sinus, the superior wall is formed by two layers: a smooth superficial dural layer and a thin, less defined deep layer. In the area of the carotid trigone, both layers separate to wrap the anterior clinoid process. The removal of this process will reveal a "clinoid space" medial to which the internal carotid artery can be identified. This clinoid segment of the artery, still extracavernous, is surrounded by two fibrous rings: a distal ring formed by fibers of the superficial dural layer and a proximal ring related to the deep dural layer. Below the proximal ring, the internal carotid artery becomes intracavernous; above the distal ring, the artery is continuous with its supraclinoid segment. The complex dural anatomy of the superior wall, its fibrous rings, and the clinoid space in relation to a superior surgical approach to the cavernous sinus are discussed.

The microsurgical anatomy of the abducens nerve through its intracranial course was studied in 20 specimens obtained from 10 cadaver heads fixed in formalin. Another 20 specimens were used to study the pattern of branching of the nerve trunk. The following intracranial segments were studied: subarachnoid or intracisternal, petroclival, and intracavernous. Angulations, neurovascular relationships, and branching patterns of the nerve are described. The long intracranial course of the abducens nerve, its tortuosity, and its tight attachment to the skull base at the level of the petrous apex may influence its vulnerability in some pathological conditions.

Thirty-three patients with giant (diameter > or = 4.5 cm) cranial base tumours who underwent surgery at the Hadassah Hospital over the last ten years are described. Twenty-three of the patients had meningiomas, 4 neurinomas, one giant cell tumour, one haemangiopericytoma, and 4 had malignant meningiomas. Four tumours were at the cerebellopontine angle, 9 within the anterior cranial fossa, 8 petroclival, 8 on middle fossa floor, and 4 along the sphenoid ridge. The average pre-operative symptom duration was 31 months, range 3-180 months. Nineteen patients had a radical tumour resection, 10 subtotal, and 4 a partial resection on an average 1.7 operations per patient. The mean follow-up period from the first operation was 39 months (range 2-120). There was no mortality peri-operatively or during the follow-up period. The mean pre-operative Karnofsky score was 68 and at the last follow-up 76. There was no correlation between histology and degree of resection, complications, or status at last follow-up. The best resections (92% radical) and outcome (mean Karnofsky 92) with the least number of operations (mean 1.4) were in the anterior fossa and along the sphenoid wing. The patients requiring the most operations (mean 2.1), having the smallest percentage of radical resections (25%) and the least favourable outcomes (mean Karnofsky 52) were those with petroclival tumours. Patients with giant cranial base tumours have a good overall long-term prognosis, but especially those with petroclival tumours challenge us to improve our techniques.

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