The importance of platybasia and the palatine line in patient selection for endonasal surgery of the craniocervical junction: a radiographic study of 12 patients

Abstract

Objective: Ventral decompressive surgery of the craniocervical junction is performed to manage a variety of conditions, including basilar invagination, which can be associated with platybasia. We have noted that the anatomic changes of platybasia could affect the height of the odontoid over a line drawn along the nasal cavity floor, the palatine line (PL). This anatomic change may influence the use of nasal endoscopic surgery for patients with platybasia who also have basilar invagination. We investigated whether the height of the craniocervical junction is elevated over the PL in patients with and without platybasia.

Methods: We conducted a retrospective review of consecutive craniovertebral junction surgical cases during a 14-month period. During that time we treated 12 patients, including 4 with platybasia and 8 without. The average age was 50 years (range, 18-64 years). Preoperative and postoperative radiographic images were evaluated and charts reviewed.

Results: The mean height of the odontoid over the PL without platybasia was 3.5 mm (range, 0-19.0 mm). In those with platybasia, it was 15.5 mm (range, 7-26.0 mm; P=.021). There was a statistically significant increase in the height of the clival tip and C1 ring in patient with platybasia as well.

Conclusions: Platybasia is associated with an increase in the odontoid and craniocervical junction over the PL. This increase in height has implications for endoscopic approach selection in patients with platybasia. Platybasia patients with basilar invagination may be better suited to a transnasal approach.

Figure 1. Relations of the Palatine Line

PL: Palatine line, CL: clival tip, C1R: ring of C1 spine, Od: odontoid tip. The PL is a line drawn parallel along the superior edge of the palatine process starting posterior to the anterior nasal spine. Platybasia is defined as abnormal flattening of the skull base, and occasionally is combined with basilar invagination. Basilar invagination, the upward displacement of the basilar and condylar portions of the occipital bone, causes impression of the foramen magnum, reduction of the posterior fossa, and consequent protrusion of the upper cervical spine into the anterior brain stem. Measurements are made of the distance above or below the PL to Cl, C1R, and Od.

Figure 2. Distributions of Approaches in the Series

Total 12 patients were categorized by endoscopic versus open, transnasal versus transoral, and presence of platybasia. Basilar invaginations with the coexistence of platybasia were never approached via the transoral-only approach.

Figure 3. Varying Height of Odontoid to PL

A) Preoperative saggital computed tomography imaging demonstrates elevation of the odontoid over the PL as part of the disease process of pure basilar invagination (white arrow). The tip of the clivus serves as a second reference point for the true craniocervical junction (black arrow) in relation to the PL. B) Demonstrates an extreme increase in the height of the odontoid tip to the PL in patient with platybasia.

Figure 4. Decompression via Combined Endoscopic Transnasal and Transoral Approaches

Pre- and post-operative sagittal reformatted CT images demonstrating the result of decompression from a combined endoscopic transnasal and transoral approachin for basilar invagination with platybasia.

Figure 5. Intraoperative photographs of Combined Endo nasal/Endo oral Approach

A) Start of incision, scope in the oral corridor B) Continued dissection, scope in the nasal corridor C) Begin of drilling in the midline, scope in the oral corridor D) Extension of drilling for decompression, scope in the oral corridor E) Reach of the upper extent, scope in the nasal corridor F) Stitch closure of the mucosa, scope in the oral corridor