Prediction of Intraoperative Pituitary Adenoma Consistency by Preoperative MRI Evaluation

Objective An endoscopic endonasal approach to the skull base has many surgical advantages due to the minimally invasive and direct access it provides to intracranial lesions with little to no brain or neurovascular manipulation. The majority of pituitary adenomas are of soft consistency and can be effectively resected via the endonasal transsphenoidal approach. However, it has been estimated that up to 10% may be fibrous and require more complex operative methods for maximum resection. The ability to predict the consistency of a pituitary adenoma on preoperative MRI imaging will allow the surgical team to better guide the patient about the risks and benefits of surgery, and also allow the surgical team to better prepare for the operation. We propose that adenoma consistency can be predicted based on T2-weighted and fluid attenuated inversion recovery (FLAIR) MRI sequences. In T2-weighted images and FLAIR sequence images, fluid appears hyperintense or bright and should reflect a soft consistency of a tumor that would usually allow an easier resection.

Methods We retrospectively reviewed the T2-weighted and FLAIR MRI images of 50 consecutive patients who underwent pituitary adenoma resection via an endoscopic endonasal transsphenoidal approach for nonfunctional adenomas with the same neurosurgeon and otolaryngologist team. Using MRI T2-weighted and FLAIR sequences, we quantitatively sampled the signal intensity of the adenoma and signal intensity of the pons and calculated an intensity ratio. The ratios were calculated independently of intraoperative tumor consistency. A high ratio indicates that the adenoma is more intense than the region of interest (ROI) of the pons, while a low ratio indicates that the adenoma is less intense. The operating neurosurgeon prospectively graded the adenoma consistency based on the surgical instruments used. A Kruskal–Wallis test was performed to determine if there is a significant correlation between the calculated intensity ratio based on preoperative MRI imaging and intraoperative adenoma consistency.

Results A nonparametric Kruskal–Wallis test was used to test for associations. The area under the curve (AUC) estimates were 0.77 (95 CI: 0.59–0.96) indicating patients' adenoma/pons ratio scores using a T2-weighted coronal view discriminates reasonably well between patients who have fibrous adenomas and those who have adenomas of softer consistency. An adenoma/pons ratio cut point of 1.49 maximizes sensitivity (100%) and specificity (68%) in this patient sample, meaning adenomas with a ratio < 1.49 are more likely to be fibrotic and more difficult to resect. However, we did not detect any meaningful association between patient's adenoma/pons ratio scores and adenoma consistency with FLAIR sequences or T2-weighted sequences in the axial view.

Conclusion Fibrous adenomas can be difficult to resect and can have a higher rate of residual tumor and increased complications due to their hard consistency. Having the ability to predict consistency preoperatively may improve surgical outcomes, especially in more fibrous adenomas. Preoperative MRI analysis of T2-weighted images can be useful to help predict the intraoperative consistency of the adenoma, and can help identify more challenging cases, allowing the surgeon to better guide the patient and prepare for the operation.