Pituitary adenoma with posterior area invasion of cavernous sinus: surgical anatomy, approach, and outcomes.

We found a series of Knosp grade 3A-4 pituitary adenomas in the posterior areas of the cavernous sinus (CS), a triangular-like structure on axial MRI. In this study, we dissected the surrounding neurovascular structure, discussed the surgical approach, and analyzed outcomes for patients with this invasion into this area. Eight embalmed adult cadaveric specimens were prepared for this study to demonstrate in detail the surgical anatomy related to this triangular-like structure. We used the "two points and one line" method to determine the surgical approach, and 35 cases with this area invasion were retrospectively reviewed. According to the endoscopic and microsurgical anatomy, the triangular-like structure appearing on the axial MRI is correlated with a square-based pyramid structure in the CS, and the upper surface is the posterior portion of the oculomotor triangle. A total of 37 posterior areas of the CS were involved in 35 patients. The accuracy of the "two points and one line" method in predicting the surgical approach is 86.5% (32/37). All three patients with Knosp 3A underwent gross total resection (GTR). Twenty (62.5%) patients with Knosp 4 underwent GTR, 9 (28.1%) patients underwent subtotal resection, and 3 (9.4%) patients underwent partial resection. Preoperative symptoms were alleviated to varying degrees, and no worsening occurred. Postoperative complications included two (5.7%) cases of cerebrospinal fluid leakage, one (2.9%) case of meningitis, two (5.7%) cases of permanent diabetes insipidus, and three (8.6%) cases of transient cranial nerve palsy. The "two points and one line" method is of great value in predicting the surgical approach of pituitary adenomas with CS invasion. The anatomic description of this particular square-based pyramid structure in the CS refines the understanding of pituitary adenomas with CS invasion.