BASILAR INVAGINATION: IMPORTANCE OF CRANIOMETRIC MEASUREMENT

Abstract

<h3>BACKGROUND</h3> Basilar invagination (BI) is a congenital or degenerative craniovertebral junction abnormality that results from the odontoid process prolapsing into the foramen magnum. Even though the acquired form is frequently seen with rheumatoid arthritis, BI commonly presents in many congenital conditions such as in people with Chiari malformation. In another type, it has been classified as those in which the odontoid process invaginates into the foramen magnum, resulting in cranio-cervical instability (Type 1) and those with flattened base of cranium that is not associated with instability (Type 2). Clinical presentations include chronic headaches, limited neck motion, and acute neurologic deterioration. <h3>CASE REPORT</h3> A 31-year-old male patient presented for treatment of a sleep-related breathing disorder. Cone beam computed tomography (CBCT) was completed for airway evaluation. Standard radiographic parameters described by Chamberlain were used to assess the craniovertebral junction. Osseous fusion of the C1/C2 joint and extension of the odontoid process approximately 10.5 mm above the Chamberlain line were noted. BI is diagnosed once the tip of the odontoid is 5 mm or more above this line. <h3>DISCUSSION/CONCLUSIONS</h3> The diagnosis of BI relies on radiographic evaluation and various radiographic reference lines such as the Chamberlain line, McGregor line, or McRae line. However, the radiographic interpretation of the cervical vertebrae is often challenging and results in missing important findings. This case report aimed to demonstrate the characteristic radiographic features of BI as seen on CBCT and the use of craniometric measurements to assist health care providers in diagnosing and managing this condition. It is important for oral and maxillofacial radiologists to pay attention to this anatomically critical junction on every study that captures it and perform an assessment so they do not miss BI-related anomalies in asymptomatic patients.