The basic principles of nuclear magnetic resonance (NMR) are reviewed and the appearances of some lesions of the skull base are discussed. NMR is a valuable diagnostic study for skull base lesions and it provides information that is not shown on the CT scan. The modern investigation of unusual skull base lesions should include both CT and NMR.

Early detection of visual loss caused by tumours of the base of the skull is accomplished by systematic tests of the pregeniculate optic pathway. Even when central acuity is relatively preserved, a relative afferent pupillary defect and reduced color perception yield evidence of impaired optic nerve conduction. Although confrontation tests of the visual fields are useful screening techniques, unexplained symptoms should be pursued with static and kinetic perimetry. Patterns of optic nerve and chiasmal field loss and atrophy of the disc or retinal nerve fibers are imprecise guides to the location of basal skull tumours. Regardless of the pattern of visual field defect, unexplained progressive loss of vision demands intensive neuroradiologic study of the basal cisterns and skull.

Despite advances in instrumentation and the use of microsurgical techniques, neurosurgical procedures involving extensive areas of skull base or other critical areas of brain still carry significant risk for neurological injury. The use of intraoperative recording of sensory evoked potentials (SEP) has been advocated to monitor neurologic function during these major neurosurgical procedures to reduce the risk of injury to neural structures.

This report summarizes our experience with intraoperative monitoring of SEP in over 200 patients, and details our findings in a group of 12 patients with skull base and posterior fossa tumours. Somatosensory evoked potentials (SSEP) were monitored in all patients, and brain stem auditory evoked potentials (BAEP) in five. While minor changes in BAEP and SSEP parameters were noted in most patients, significant changes occurred in five. Irreversible loss of BAEP in one patient was associated with complete hearing loss postoperatively. Marked, persistent alteration of both BAEP and SSEP was associated with postoperative brainstem dysfunction. No patient with stable BAEP and SSEP at the end of the procedure suffered additional neurological deficit.

We conclude that intraoperative SEP monitoring may be valuable in minimizing neural injury during major neurosurgical procedures.

Treatment planning for patients with tumours of the skull requires a true multidisciplinary approach. Super-selective angiography, using a protocol approach, is necessary in building a proper strategy plan for treatment of these lesions. Embolization done by a well trained team has proven to be a valuable adjunct to the various treatment methods and it may eliminate the need for radiation of benign lesions of the base of the skull.

The author describes four different approaches to clival tumours, and reviews his experience with 33 chordomas of the clivus. He also reviews his large experience with tumours invading the floor of the anterior and middle cranial fossae, and describes various surgical approaches for the removal of these tumours, followed by reconstruction of the bony floor with bone grafts, and dural reconstruction.

A review has been carried out of those patients with a craniopharyngioma who were treated initially in our institution and had a microsurgical excision of their tumour during the period of time when newer and sophisticated modalities of investigation and treatment were available. Twenty-nine patients with craniopharyngioma were treated initially by microsurgical excision of their tumour at the Hospital for Sick Children from January 1976 to June 1985. In 21 a total removal of the tumour was performed, and there has been no clinical evidence of recurrence. No deaths were recorded in any of the 29 patients. The principal morbidity has resulted from endocrine deficits that these patients exhibit.

This paper reviews the author's personal experience with the management of 204 patients with the clinical diagnosis of acoustic neuroma. Craniotomy was performed in 181 of these cases, all of whom were proven to have acoustic neuromas. The remaining 23 cases with the clinical diagnosis of acoustic neuroma did not have tumour surgery, mainly because of advanced age or concurrent disease, although some required shunts for hydrocephalus. The management of acoustic neuromas including the selection of surgical approach depends upon the patient's age and general health, the size and growth direction of the tumour, previous surgical attempts at removal, and the presence of hydrocephalus, a contralateral tumour, and serviceable hearing. Twenty-nine other cases with the clinical diagnosis of acoustic neuroma underwent craniotomy: 20 had petrous or tentorial meningiomas encroaching on the porus acousticus or growing in the internal auditory canal, six had neuromas of the seventh cranial nerve and three had arachnoiditis occluding the internal auditory canal.

Thorough pathological examination disclosed considerable diversity of abnormal cell types and correspondingly different surgical correction rates among patients with apparently similar syndromes of pituitary hypersecretion.The surgical correction of acromegaly in patients with densely granulated growth hormone tumours was threefold that in patients whose tumours showed sparse granulation. Two non-prolactinoma tumour types associated with hyperprolactinemia have aggressive growth patterns; their special therapeutic management is discussed. Of 33 patients with Cushing's disease solitary adenomas were found in only 14, while six patients had proven corticotroph cell hyperplasia. Elective hypophysectomy should replace selective adenomectomy in selected cases of Cushing's disease.

The author reviews the Princess Margaret Hospital (Ontario Cancer Institute) experience with radiation therapy in certain tumours involving the skull base including meningiomas, chordomas, craniopharyngiomas and other less common tumours. Radiation therapy offers an effective supplementary or alternative treatment for such lesions.

The rationale for interstitial irradiation of tumours in and around the skull base is reviewed, and the experience accumulated with pituitary adenomas, meningiomas, and chordomas is summarized. Intracystic irradiation for craniopharyngiomas is also reviewed.

Interest in photodynamic therapy of malignant brain tumours has been growing in recent years as intra-operative laser applications become more available.

We have developed an inflatable balloon which can be coupled to an argon dye pump laser in order to deliver light to a brain tumour cavity created by the subtotal resection of tumour. Eight patients with primary malignant brain tumours have been treated with photodynamic therapy (PDT) using this device. The 8 patients tolerated the treatment well; morbidity attributable to the PDT was acceptably low.