Transorbital Neuroendoscopic Surgery (Tones) Trajectory Planning

Objective Transorbital neuroendoscopic surgery (TONES) is a relatively new technique that offers surgical access and management of complications involving the frontal sinus, orbit, and anterior skull base. Accessing these areas through a transorbital approach, versus a transnasal approach, can be difficult and poses a challenge to the surgeon. The purpose of this study is to examine four TONES patients’ computed tomography (CT) scans to create three-dimensional (3D) trajectory planning for surgical operations.

Methods A retrospective review of all TONES patients at a tertiary referral center was performed in 2017. Deidentified preoperative CT scans were collected and utilized for analysis. All sinus CT scans were imported into MimicsTM 18.0 (Materialise, Inc.) imaging software. 3D reconstructions were created for each scan. Various anatomical landmarks were marked for trajectory planning. Superior, inferior, medial, and lateral portions of the pathology of interest were marked. A line was created between the zygomaticofrontal suture and nasofrontal sutures on the ipsilateral side of the pathology. Angle measurements from zygomaticofrontal and nasofrontal sutures to four areas of the pathology of interest were computed for each CT scan.

Results A total of four patients with TONES CT scans were analyzed. [Table 1] summarizes the data obtained. Subject 4 was only marked on the medial and lateral parts of the pathology of interest due to pathology location. Subject 2 required a craniotomy due to inadequate access with a TONES approach. Fig. 1A represents a coronal view of a sinus CT of Subject 1 and Fig. 1B represents a 3D skull reconstruction of Subject 1 with angle measurements from the zygomaticofrontal suture to the lateral and inferior tumors.

Table 1 TONES angle measurements

Subject	Pathology	ZF to lateral	ZF to medial	ZF to superior	ZF to inferior	NF to lateral	NF to medial	NF to superior	NF to inferior
1	Ossifying fibroma	41.97	29.98	41.01	33.04	29.95	74.03	63.33	51.97
2	Intracranial abscess	26.60	27.73	27.22	28.68	22.09	73.74	74.75	65.84
3	Encephalocele	37.59	29.98	34.72	31.93	37.49	49.02	49.75	33.34
4	Encephalocele	31.17	26.68	N/A	N/A	37.74	48.58	N/A	N/A

Abbreviations: N/A, not available; NF, nasofrontal suture; TONES, transorbital neuroendoscopic surgery; ZF, zygomaticofrontal suture.

Conclusion TONES approach to surgical resection of skull base pathology is technically challenging. Our study highlights that preoperative planning for TONES is feasible by utilizing imaging software. Implementing methodology from such preoperative planning will give the surgeon the foresight in the operating room optimizing maneuverability for complex approaches while effectively minimizing morbidity.

Fig. 1 (A) CT sinus coronal view with superior, inferior, medial, and lateral tumor markings. (B) 3D skull reconstruction with angles from zygomaticofrontal suture to lateral and inferior tumors.