A Teaching Atlas of the Ultrasound Anatomy of The Skull Base: Implications for Future Applications of Intraoperative Ultrasound in Endoscopic Endonasal Skull Base Surgery

Introduction: Intraoperative real-time imaging and visualization techniques have the potential to optimize the safety and efficacy of endoscopic endonasal skull base surgery. The potential of intraoperative ultrasound has not been evaluated in this setting. Barriers to adoption include characterization of ultrasound skull base anatomy and establishing best use cases for the technology. Here, we describe the creation of an anatomical ultrasound teaching atlas of the skull base which details critical neurovascular structures, tumor anatomy, arachnoid membrane anatomy, and blood flow in a series of endoscopic endonasal surgery cases using a novel minimally invasive ultrasound probe.

Methods: During endoscopic endonasal surgical cases for pituitary and other parasellar pathology, ultrasound images and video were captured through the endonasal corridor and interpreted in real-time by the surgical team. Postoperatively, the images were compared to intraoperative videos and brain MRI and CT imaging by the skull base surgery team to create a practical teaching atlas of ultrasound anatomy. Ultrasound footage was obtained at key stages of the operation, including the sphenoidotomy to assess the location of the nasoseptal artery, after sellar and skull base bone removal to define tumor, pituitary gland, cavernous sinus, brainstem, and arachnoidal membrane anatomy, and after tumor removal to evaluate extent of resection. A minimally invasive ultrasound probe (6 × 7 mm tip diameter and 150-mm shaft length, BK Medical) was incorporated into normal surgical workflow and used by the surgical team without a technician.

Results: Skull base ultrasound anatomy was studied in 23 patients undergoing endoscopic endonasal surgery for nonfunctioning adenoma, Cushing's disease, acromegaly, craniopharyngioma, and meningioma over a three-month period. The ultrasound generator/monitor was placed between the two surgical monitors for ease of viewing. We characterized skull base ultrasound impressions of the pituitary gland and tumor, pituitary stalk, bony sella and posterior clinoid processes, diaphragma dura, carotid arteries and anterior cerebral arteries, and basal cisterns and Lilliquist's membrane. We also were able to evaluate tumor characteristics, such as internal hemorrhage, cysts, and calcifications. Blood flow was measured in the parasellar carotid arteries, anterior cerebral and basilar arteries, and posterior nasal septal arteries.

Conclusion: We constructed a teaching library of ultrasound skull base anatomy from a series of endoscopic endonasal surgical cases. This work may help aid surgeons interested in applying ultrasound to their practice. Based on our experience, possible use cases include identification of critical neurovascular structures to improve surgical safety, evaluating extent of tumor resection, and assessing blood flow through nasoseptal flaps. Anatomical figures and ultrasound videos from the teaching library will be presented at the upcoming annual meeting.

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No conflict of interest has been declared by the author(s).

Publication History

Article published online:
15 February 2022