The significance of Knosp classification and cavernous sinus division in endoscopic transnasal surgery for invasive pituitary adenomas

Objective To evaluate the value of Knosp classification and cavernous sinus zoning in the diagnosis of pituitary adenoma invasiveness and the significance of endoscopic transnasal surgery for pituitary adenomas. Methods There were 75 cases with pituitary adenomas of Knosp grade 3-4 (44 cases of Knosp grade 3 and 31 cases of Knosp grade 4) who were performed endoscopic transnasal surgery from July 2015 to June 2017 in our hospital. Based on coronal MRI of sellar region in patients with Knosp 3 pituitary adenomas, the ratio R of distance from the middle point of internal carotid artery (ICA) cavernous sinus segment to the upper part of anterior clinoid process segment and vertical distance from the furthest point of tumor invasion to the line was calculated and analyzed statistically. According to cavernous sinus zoning under endoscope and involvement of medial wall of cavernous sinus, patients with Knosp grade 3 pituitary adenomas were further divided into Knosp grade 3A (invasive and non-invasive) and 3B by invading different cavernous spaces. The total removal rate of tumor was reviewed by MRI in sellar region after operation. Results Among 75 cases, 36 were classified as Knosp grade 3A in 44 cases of Knosp grade 3 pituitary adenomas, including 12 cases of invasive pituitary adenomas (mainly involving posterior superior space of cavernous sinus and affecting oculomotor nerve) and 24 cases of non-invasive pituitary adenomas (the tumor pushed against the medial wall of cavernous sinus, presenting "pseudoinvasion"). The ratio R of invasive pituitary adenomas was significantly smaller than non-invasive pituitary adenomas (1.28 ± 0.18 vs. 1.74 ± 0.27; t = 5.275, P = 0.000). The Knosp grade 3A was divided into 2 groups according to the median value of ratio R: ≤ 1.59 group (17 cases) and > 1.59 group (19 cases). The invasion rate of ratio R ≤ 1.59 group was higher than that of > 1.59 group (12/17 vs. 0/19; Fisher's exact probability, P = 0.000). The total resection rate of 75 cases was 72% (54/75), among which the total resection rate of Knosp grade 3 was 84.09% (37/44), and rate of Knosp grade 4 was 54.84% (17/31). The average follow-up period was (14.84 ± 5.66) months, and no one case relapsed. Conclusions The calculation of ratio R in preoperative coronal MRI helps to evaluate the invasion degree of Knosp grade 3A pituitary adenomas. Combined with artificial division of cavernous sinus, it has guiding significance in endoscopic transnasal surgery for pituitary adenoma removal. DOI: 10.3969/j.issn.1672-6731.2019.03.00