Knosp classification of cavernous sinus invasion by pituitary macroadenomas

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The Knosp classification is one of the more commonly used systems to determine the likelihood of cavernous sinus invasion by pituitary macroadenomas. This is important in operative planning, predicting residual tumor post-resection and is useful in everyday clinical practice.

Classification system

Three lines are drawn between the supraclinoid ICA and intracavernous ICA on coronal MRI imaging .

  • medial tangent
  • intercarotid line
  • lateral tangent

    • These lines are used to define 4 grades of tumor invasion:

    • grade 0 = medial to medial tangent
    • grade 1 = tumor extends to space between the medial tangent and the intercarotid line
    • grade 2 = tumor extends to space between the intercarotid line and the lateral tangent
    • grade 3 = tumor extends lateral to the lateral tangent
      • 3A = above the intracavernous ICA into the superior cavernous sinus compartment
      • 3B = below the intracavernous ICA into the inferior cavernous sinus compartment
    • grade 4 = complete encasement of intracavernous ICA

    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 :

    • 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: combined histological invasion: 86%
      • 3A: surgical invasion: 26.5%
      • 3B: surgical invasion: 70.6%
    • grade 4
      • surgical invasion: 100%
      • histological invasion: 100%

    Similarly, these grades are predictive of gross total resection and endocrinological remission .

    • 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%