**2. Anterior skull base**

### **2.1 Introduction**

The sellar and parasellar skull base contain several critical neurovascular structures. These include cranial nerves II through VI, the internal carotid arteries, the cavernous sinus, and the pituitary gland. Tumors in this area are likely to involve the olfactory nerves and the visual system in its orbital and cisternal course [2, 3]. Good pre-operative cranial nerve function predicts favorable neurologic outcome and pre-operative evaluation of cranial nerve function is essential. Anosmia in particular can herald the presence of a tumor [4]. Similarly, loss of olfactory function can significantly affect a patient's quality of life and should be taken into consideration when planning surgery. Ophthalmologic evaluation of visual function, including acuity, fundoscopy, and visual field testing may be useful in surgical planning. Evaluation by a multi-disciplinary team of neurosurgeons, ophthalmologists, and otolaryngologists is recommended for all anterior skull base tumors. We routinely obtain hi-resolution magnetic resonance imaging (MRI) and computed tomography (CT) during pre-operative evaluation. Constructive interference steady state (CISS) is especially useful in determining the course of cranial nerves involved in the tumor and surgical corridor. Gadolinium enhanced T1 weighted, and T2 weighted images help evaluate the extent of tumor invasion along the cranial nerves (peri-neural spread) as well as the bony skull base. MR or CT angiography is obtained in cases of suspected vascular encasement to determine the safety of surgical access and if bypass should be planned before resection. Formal angiography is performed in cases where bypass is planned. A detailed endocrinologic history and serologic workup should be completed for tumors involving the sellar and parasellar structures.
