Surgical Anatomy of the occipital condyle and its relation to hypoglossal canal

Abstract

Occipital condyles (OC) are two bony structures located laterally to the foramen magnum (FM) on the inferior surface of the occipital bone. It is commonly described as an ovoid structure. Craniovertebral junction (CVJ) is an area that connects the cranium to the upper cervical spine. It is bounded laterally by the jugular foramen (JF), hypoglossal canal (HC), and OC. Lesions at CVJ are difficult to manage because of their location and complex anatomic relations. Stability of CVJ after surgery in depends mainly on the resection of OC. HC has been used as a landmark for the extent of OC resection. It was claimed to locate in the middle part of OC. OC resection should not extend beyond HC to prevent CVJ instability. However, previous study showed that the HC was not always located at the middle part of OC. This study aimed to focus on the measurement of OC and its relation to HC in dry skull collected from Thailand for improving the successful surgical outcome.One hundred dry skulls of equal number of both sex were examined for the shape and dimension of each OC. The location of intra and extra cranial orifice of HC (iHc and eHC) related to OC length and the distance to the posterior edge of OC (OCPE‐iHC, OCPE‐eHC) were determined. The results showed that the most prevalence of OC shape was oval‐like (33%) and the least was ring like (1%). Symmetrical OC shape was found in 46% of cases. The mean OC length was 22.13+2.51mm in male and 20.50+ 2.08 mm in female with a significant difference between sex (p=000). The OC width and height were 10.41+1.48 and 7.45+ 1.14 mm in male, 10.62+ 1.34 and 7.34+ 1.13 mm in female. No statistical significant difference of OC width and OC height between sex was found. The dimension of OC did not show any significant difference between sides. The location of iHC was mostly related to middle 1/3 of OC in 54% on the left side and located at the junction between anterior and middle 1/3 of OC in 36% on the right side. In contrast, eHC was located at anterior 1/3 of OC in 81% and 67% on the left and right side, respectively. None was related to posterior 1/3 of OC. Symmetrical location of iHC and eHC was found in 36% and 64% of cases, respectively. The distance OCPE‐iHC, OCPE‐eHC was 9.16+ 1.56, 14.1.0 + 1.98 mm in male and 8.83+ 1.62, 13.30+ 2.4 mm in female. Statistical significant difference between sex was found in OCPE‐eHC (p=0.011). In conclusion, the OC length is longer in male, the eHC located more anteriorly than iHC, therefore resection of the OC should not beyond posterior 1/3 of the OC length or about 7 mm from the posterior edge of OC. These morphometric data might be a benefit for surgical planning on resection of the occipital condyle to avoid injury to neurovascular structure and reserve the stability of craniovertebral junction.