Objective: Cavernous sinus (CS) invasion is of paramount importance in the surgical planning
of pituitary adenomas. The most widely used classification (Knosp grading) has several
limitations, such as its evaluation of only superior and inferior compartments, and
variability in the position of the lines, leading to variable incidences of true invasion
and low interobserver agreement. Therefore, we set out to develop a new classification
to address these shortcomings.
Methods: A classification was developed based on the evaluation of each CS compartment (superior,
inferior, lateral, and posterior) and clinoidal space. For each compartment, a line
bisecting the carotid artery, following anatomical planes, was used to grade the lateral
extension of the adenoma. Tumors medial to these lines were graded as 0, and those
lateral to it were graded as 1. The classification was used to evaluate MRIs of 255
patients (510 CS) that underwent endoscopic endonasal approach (EEA), either with
transcavernous extension (139 CS) or without it (371 CS). Invasion of each CS compartment
was evaluated by intraoperative assessment in transcavernous cases, and by postoperative
MRI in the rest. Results were compared with the Knosp classification, stratified by
the presence of apoplexy, carotid tortuosity, and previous surgery, and interobserver
agreement (IOA) was calculated.
Results: Cavernous sinus invasion was present in 19.4% of CS, with superior compartment invasion
in 13.3%, posterior compartment in 12%, inferior compartment in 11.2%, lateral compartment
in 4.5%, and clinoidal space in 10.2%. Our classification yielded an overall sensitivity
of 90.8% (95% CI: 86.6–94%), specificity of 98.4% (95% CI: 97.8–98.9%), PPV of 86.5%
(95% CI: 82.3–89.8%), NPV of 99% (95% CI: 98.5–99.3%), and accuracy of 97.6% (95%
CI: 96.9–98.2%), with comparable results in all compartments. Previous surgery increased
the rate of invasion of grade 0 in superior and posterior compartments, as well as
in Knosp grade 2 cases. IOA was rated as almost perfect for superior and inferior
compartments, and substantial for lateral, posterior, and clinoidal space. Knosp classification
achieved only moderate agreement.
Conclusion: Our classification provided a reliable and accurate tool to evaluate CS compartment
invasion, outperforming Knosp classification.
Fig. 1 Classification of superior (A, B) and inferior (C, D) compartments in coronal MR. A vertical line bisects the horizontal carotid artery,
with adenomas staying medial to this line graded as 0, and those with extension lateral
to this line as 1.
Fig. 2 Classification of lateral compartment in coronal MR. The line bisects the carotid
on the horizontal plane. Adenomas crossing this line on the lateral aspect of the
carotid, either from the superior (A, B) or inferior (C, D) compartment are graded as 1, while adenomas not crossing this line are graded as
0.
Fig. 3 (A, B) Posterior compartment classification: The line bisects the short vertical segment
of the carotid artery parallel to the midline. Adenomas staying medial are graded
as 0, and those lateral as 1. (C, D) Clinoidal space classification. The line bisects the clinoid segment of the carotid
artery. Adenomas staying medial, behind the clinoid carotid, are graded as 0, and
those lateral as 1.
