Introduction: The difference between endoscopic visualization and working space together with the complexity and functional importance of nasal anatomy, which require to balance invasiveness and adequacy of pituitary tumors exposure, has led to the recent description of multiple variations of endoscopic endonasal transsphenoidal approaches. Currently clinical data on these variations are limited and, therefore, the choice of the approach is often entirely left to the individual surgeon. Aim of this study was to quantitatively compare endoscopic endonasal transsphenoidal approaches the sella and parasellar region, using a novel, neuronavigation-based research method, which allows the quantification and comparison of the "surgical pyramid" that anatomically defines a neurosurgical approach.

Methods: Eleven anatomical specimens underwent computed tomography scan and were registered in a dedicated optical neuronavigation system. Endoscopic dissections were performed bilaterally on each specimen. Quantified approaches included: 1. paraseptal; 2. transrostral; 3. extended transrostral (after superior turbinectomy); 4. transethmoidal (after posterior ethmoidectomy). GTxEyesII - ApproachViewer software was used for the quantifications and post-dissection analyses. It allows the real-time, 3D visualization of the surgical pyramid on CT scans during dissections; afterwards, areas of interest can be defined and matched with each surgical pyramid, defining the percentage of exposure achieved by each approach.

Results: The paraseptal approach has a limited role in transsphenoidal surgery due to the reduced exposure of areas of interest and the small working volume. At least a transrostral approach is necessary to expose the sella bilaterally, but the adequate exposure of lateral structures (i.e. cavernous sinus, optic nerve) requires the extended transrostral or transethmoidal approaches.

Conclusions: These results support a modular, evidence-based, classification of endoscopic endonasal transsphenoidal approaches, which can guide the choice of the approach for sellar tumors. The study validates our present clinical practice, in which approaches of increasing nasal morbidity are used according to tumor extension.

Patient Care: This preclinical, anatomical study provides evidence for a modular classification of endoscopic endonasal transsphenoidal approaches. The classification represents a guide for a tailored endoscopic endonasal transsphenoidal approach based on the extension of the patient's sellar tumor.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the modular classification of endoscopic endonasal transsphenoidal approaches; 2) Discuss, in small groups, the indications for each of the transsphenoidal approaches; 3) Identify an effective treatment for pituitary adenomas, according to their extension.

References: 1. Doglietto et al. Quantification and comparison of neurosurgical approaches in the anatomy laboratory: a novel, neuronavigation-based, research method. to be submitted 2. Doglietto F, Radovanovic I, Ravichandiran M, Agur A, Zadeh G, Qiu J, Kucharczyk W, Fernandez E, Fontanella MM, Gentili F. Quantification and comparison of neurosurgical approaches in the preclinical setting: literature review. Neurosurg Rev. 2016 Jan 19.