The Shape-Classification: A New Grading System for Growth Patterns of Pituitary Adenomas

Object: Tumor size, invasion into the surrounding structures, and extent of growth have been described as factors influencing the outcome of transsphenoidal tumor surgery. The classifications described by Knosp and Hardy have proven helpful in comparing surgical results and predicting the patient’s outcome. While different growth patterns have been advocated as an additional factor, a standardized classification does not exist. The goal of this study is to assess the impact of a new grading system based on tumor shapes.

Methods: Patients suffering from nonfunctioning pituitary adenomas, who underwent transsphenoidal surgery at our institution, were eligible for inclusion. Shape grades resulted from measuring the tumors' maximum diameters as follows:

Shape-I: spherical. In all sections the maximum diameters do not differ > 25%.

Shape-IIA: oval shape, no cavernous sinus invasion (aka Knosp grade 0–2). One of the maximum diameters differs >25% from the others.

Shape-IIB: oval shape as defined for Shape-IIA, but with invasion into the cavernous sinus (aka Knosp grade 3 and 4).

Shape-III: Dumbbell-like appearance, caused by intra- and suprasellar growth with a constriction on the level of the sphenoidal plane. On the level of the constriction, the maximum diameter is at least 25% smaller than the maximum intra- and suprasellar diameters.

Shape-IV: Mushroom-like appearance, caused by a maximum suprasellar diameter >50% larger than the intrasellar diameter

Shape-V: Polylobulated appearance caused by at least three parts of the tumor with maximum diameters >50% of the intrasellar part spreading in the supra/parasellar confines, the sphenoid sinus, and/or the clivus.

Results: A total of 191 patients (Shape-I, n = 28 [15%]; Shape-IIA, n = 66 [35%]; Shape-IIB, n = 25 [13%]; Shape-III, n = 37 [19%]; Shape-IV, n = 12 [6%]; Shape-V, n = 23 [12%]) were included in the study. The gross total resection (GTR) rate varied significantly between the different Shape grades with higher grades being less likely to be totally resected. Invasion into the cavernous sinus only influenced the GTR rate in Shape-II tumors, which justifies subdividing Shape-II tumors into IIA and IIB. The finding of pre- and postoperative optic chiasm and pituitary stalk compression was significantly more frequent in higher Shape grades.

Conclusion: The surgical outcome of nonfunctioning pituitary adenoma is influenced by the tumors' shape. The Shape-classification offers a standardized grading system to describe the different tumor shapes.

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