Anatomical Analysis and Proposed Design of an Angled Drill for Endoscopic Endonasal Petrosectomy

Background: Endonasal endoscopic surgery actively and continuously evolves with the trend to expand the targeted anatomical areas laterally, dragging along with it is the development of finer and more specialized instruments. One of the major obstacles for the lateral expansion of endonasal endoscopic approach (EEA) is the internal carotid artery. Although detailed techniques for endoscopic anterior petrosectomy have been described by several authors, including our group, the extent of the surgery is limited mainly by the degree of ICA mobilization and its configuration. As angled visualization is available, a well-fit designed angled drill may be the game-changer in targeting petrous apex lesions. In this abstract, we present our anatomical analysis and propose a dimension-wise concept design of such drill.

Materials and Methods: This study was performed at the Surgical Neuroanatomy Laboratory of the Department of Neurological Surgery, University of Pittsburgh School of Medicineon 68 anatomical specimens. All specimens were injected with colored latex in neurovascular system and scanned with thin sliced CT, ranging from 0.625 to 1.2 mm for navigation purpose. We defined three key anatomical landmarks for petrosectomy: (A) most anterior part of the nasal septum, (B) posteromedial border of lacerum ICA, and (C) the projection of medial rim of internal acoustic meatus on the axis of petrous apex. The AB, BC distances, and ABC angle were measured radiographically ([Fig. 1]). Means, standard deviations, and box-plot graphs were performed in SPSS Statistics Base 22.0 (SPSS, Inc., Chicago, Illinois).

Results: Detailed findings are presented on [Table 1]. From the results, we propose the dimensions for the angled drill to be at 135 degree and the distal arm of hand piece to be 20 mm long, the nasal portion of proximal arm to be 90-mm long. Concept was tested and demonstrated on two dissected anatomical specimens ([Fig. 1]).

Conclusion: We present our anatomical analysis and proposed dimension for an ideal angled drill for the purpose of endoscopic petrosectomy. We strongly believe the availability of such drill will improve the safety and extent of tumor resection during endoscopic surgery to the petrous apex.

Table 1 Detailed findings of this study

	Right side (mean ± SD)	Left side (mean ± SD)	Both side (mean ± SD)
AB distance (mm)	81.1 ± 5.7	81.8 ± 5.9	81.1 ± 5.7
BC distance (mm)	20.4 ± 2.8	19.2 ± 2.4	19.8 ± 2.7
ABC angle	137.4 ± 4.5	136.1 ± 5.5	136.7 ± 4.5

Fig. 1 (A): Screenshot of CT scan image demonstrating landmarks and methods for measurements; (B) Endoscopic view of an anterior petrosectomy performed on an anatomical specimen with straight drill and mobilization of ICA. (C and D) Illustration of angled drill in surgical perspective using bent instrument with proposed dimensions.

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