Outcomes of Intraoperative Ultrasound for Endoscopic Endonasal Transsphenoidal Pituitary Surgery

Introduction: Pituitary tumors with parasellar extension into the cavernous sinus present a technical challenge for adequate visualization and gross total resection (GTR). The introduction of endoscopes into common use for transsphenoidal pituitary surgery has augmented the ability for intraoperative identification of parasellar extension with wider views and an enhanced ability to inspect the medial wall of the cavernous sinus. GTR and endocrinological remission in the case of pituitary adenomas are impacted by parasellar extension, significantly decreasing reported cure rates. Intraoperative MRI has been shown in some studies to increase the likelihood of GTR, guiding further tumor removal in a variable number of cases depending on the strength of magnet utilized. However, this comes with a significant increase in operative time and implementation costs secondary to the required infrastructure and equipment. Therefore, there remains interest in the development and validation of more time- and cost-effective intraoperative imaging techniques to aid in tumor resection. Intraoperative ultrasound may provide an effective and inexpensive solution.

Methods: A series of 20 consecutive patients, who underwent endoscopic endonasal transsphenoidal surgery for pituitary tumors with the assistance of intraoperative ultrasound, were prospectively collected. The intraoperative ultrasound findings were prospectively recorded at the time of each case. The 3-month postoperative MRI studies were obtained and independently reviewed to assess for residual tumor. The findings from the postoperative MRI were then compared with the intraoperative findings based on ultrasound.

Results: Median preoperative Knosp grade was 2. Cavernous sinus invasion was encountered intraoperatively in three patients, all of whom were Knosp grade 3 preoperatively. Three patients had undergone previous resection. Median operative time was 152 minutes. Based on intraoperative ultrasound findings, 17 patients (85%) were expected to have a GTR while three patients (15%) underwent subtotal resection and residual tumor was expected. Eighteen patients completed a 3-month postoperative MRI. The intraoperative ultrasound and MRI findings were concordant in 17 cases (94.4%) with only one instance of discordance where GTR was expected, but a small amount of residual tumor was noted on the postoperative MRI. No intraoperative complications were observed.

Conclusion: Intraoperative ultrasound can reliably predict tumor resection as assessed by 3-month postoperative MRI in pituitary adenomas with parasellar extension. Image capture and interpretation may vary based on operator experience with a learning curve likely present. However, once proficiency is gained, ultrasound provides immediate assessment of extent of resection and can assist in identification of tumor remnant, normal pituitary gland, and other important structures in the sellar region without significantly increasing operative time.