The Knosp classification is one of the more commonly used systems to determine the likelihood of cavernous sinus invasion by pituitary macroadenomas.
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Usage
By stratifying the likelihood of cavernous sinus invasion, the Knosp classification is important in operative planning, and predicting residual tumor post-resection. Low Knosp grades are associated with a significantly greater chance of surgical remission after resection 3.
Some concerns have been raised over its interobserver reliability 4,5, leading to the development of alternative classification systems (e.g. Zurich pituitary score) 6.
Classification system
Three lines are drawn between the supraclinoid internal carotid artery and intracavernous internal carotid artery on coronal MR images 1,2.
medial tangent
intercarotid line
lateral tangent
These lines are used to define 4 grades of tumor invasion:
grade 0: tumor remains medial to the medial tangent
grade 1: tumor extends to between the medial tangent and the intercarotid line
grade 2: tumor extends to between the intercarotid line and the lateral tangent
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grade 3: tumor extends lateral to the lateral tangent
3A: above the intracavernous internal carotid artery into the superior cavernous sinus compartment
3B: below the intracavernous internal carotid artery into the inferior cavernous sinus compartment
grade 4: complete encasement of intracavernous internal carotid artery
Interpretation
The likelihood of invasion varies across various studies. Generally, the following can be used pragmatically:
grade 0 and 1: no invasion
grade 2: possible invasion
grade 3: probable invasion
grade 4: definite invasion
More specifically 1,2:
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grade 0
surgical invasion: 0%
histological invasion: 0%
-
grade 1
surgical invasion: 1.5%
histological invasion: 0%
-
grade 2
surgical invasion: 9.9%
histological invasion: 88%
-
grade 3
3A: surgical invasion: 26.5%
3B: surgical invasion: 70.6%
combined histological invasion: 86%
-
grade 4
surgical invasion: 100%
histological invasion: 100%
Similarly, these grades are predictive of gross total resection and endocrinological remission 2.
-
grade 1
gross total resection: 83%
endocrinological remission: 88%
-
grade 2
gross total resection: 71%
endocrinological remission: 60%
-
grade 3A
gross total resection: 85%
endocrinological remission: 67%
-
grade 3B
gross total resection: 64%
endocrinological remission: 0%
-
grade 4
gross total resection: 0%
endocrinological remission: 0%
History and etymology
The classification system was originally published by Engelbert Knosp (an Austrian neurosurgeon) in 1993, as grades 1-4 1. The division of grade 3 into grade 3A and grade 3B was added in 2016, in a paper also by Knosp and colleagues 2, and can be referred to as the modified Knosp classification.