This is a retrospective study on 187 patients with PitNET operations between 2016 and 2020. The Knosp classification system is a scale used to assess the degree of cavernous sinus invasion in PitNETs. It is based on radiological criteria, such as contact with the internal carotid artery and lateral extension of the tumor. It is divided into five grades (0–4) and categorized in 3 CSI risk groups: low risk (0 to 1), medium risk (2 to 3A), and high risk (3B to 4) [3]. (Fig 1)

Fig 1: shows the 3 lines of Knosp grading system: A) Medial tangent line; B) Intercarotid line; C) Lateral tangent line

This classification is useful for estimating surgical difficulty and the risk of recurrence [4,5]. Three virtual lines are drawn to define tumor extension:

1. Medial tangent: a line tangent to the medial aspects of the intra- and supra cavernous internal carotid artery (ICA);
2. Inter-carotid line: a line drawn between the cross-sectional centers of the intra- and supra- cavernous ICA;
3. Lateral tangent: a line tangent to the lateral aspects of the intra- and supra- cavernous ICA

KNOSP GRADING SYSTEM

• Grade 0: Tumor remains medial to the medial tangent
• Grade 1: Tumor extends between the medial tangent and the inter-carotid line
• Grade 2: Tumor extends between the inter-carotid line and the lateral tangent
• Grade 3: Tumor extends lateral to the lateral tangent
• 3A: Above the intra-cavernous internal carotid artery into the superior cavernous sinus compartment
• 3B: Below the intra-cavernous internal carotid artery into the inferior cavernous sinus compartment
• Grade 4: Complete encasement of the intra- cavernous internal carotid artery

(Fig 2)

Fig 2: shows the Knosp grading system

Inclusion Criteria:

• Patients with PitNET at medium (Knosp 2 and 3A) and high risk (Knosp 3B and 4) of MWCS invasiveness
• Endoscopic evaluation and transsphenoidal surgery
• Histological confirmation of PitNET
• Postoperative follow-up of at least three years

Radiological Evaluation:

Preoperative MRI images were obtained using a 1.5T scanner within six months prior to the surgery. The scans included axial, sagittal, and coronal T2w, and T1-weighted sequences both without and with Gadolinium (Gd) contrast. Imaging analysis was carried out on the 3D-Slicer software, to detect:

• Tumor morphology and volume
• T2 signal intensity
• Knosp grade

Surgical Technique and Endoscopic Inspection:

During surgery, tumor invasiveness was examined, including invasion of the dura mater and cavernous sinus walls, and samples were collected for histopathological analysis.

Histopathological Examination:

Tumors were classified into five histotypes, and tumor proliferation was assessed using Ki-67, mitotic count, and p53 criteria.

Endocrinological Status:

All patients underwent preoperative hormonal evaluation and post operative stimulation tests to assess endocrine function [6].

FINAL CLASSIFICATION SYSTEM (TROUILLAS GRADING)

All collected data were used to categorize tumors into five grades according to the final Trouillas classification system, which combines histotype, proliferation, invasiveness, and metastasis (if present):

• 1a: Non-invasive and non-proliferative tumor
• 1b: Non-invasive but proliferative tumor
• 2a: Invasive but non-proliferative tumor
• 2b: Invasive and proliferative tumor
• 3: Tumor metastases

This system was used to analyze the relationship between radiological, histopathological features, and clinical outcomes [7].

The data were interpreted through statistical analysis to determine the concordance between surgical and radiological assessments and identify predictive variables for tumor residuals and recurrence.