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Letter to the Editor: “Clivopalate angle: a new diagnostic method for basilar invagination at magnetic resonance imaging”

by Liwei Peng, Chao Cheng, Wei Zuo, Peng Wang, Zilong Mao, Weixin Li (tangdunaowai@163.com)

Clivopalate angle: a new diagnostic method for basilar invagination at magnetic resonance imaging

Dear Editor in Chief,

We read with great interest the article of Ma et al [1], in which they conducted a retrospective case-control study that enrolled 112 patients who were diagnosed as basilar invagination (BI), to illuminate the diagnostic value of a new angle: clivopalate angle (CPA). They demonstrated that the diagnostic performance of CPA was similar to other previously used angles. However, it was more reliable in the evaluation of BI. Considering diagnosis value of this new parameter for BI, the novelty of this paper should be highlighted. We would, however, like to raise the following concerns.

First, as shown in Figure 2 in the article, the CPA was formed at the intersection of the Wackenheim line and a line along the hard palate plane. However, in accordance with our clinical experience, we found that CPA cannot be adjusted during the operation. If a parameter does not change before or after surgery, its diagnostic significance is questionable. Besides, our viewpoint is confirmed by the anatomic structure of this angle. Both these two lines consisting CPA came from the skull, how can we change the relevant position of them? We can’t create angles simply for the sake of their iconography significance. It is not appropriate to create CPA for simplicity to simplify CXA and clivodens angle (CDA) [2]. Furthermore, the clinical significance should be taken into consideration. CPA does not reflect the compression of the odontoid process on the ventral medulla oblongata. Therefore, we suggested that some corrections be made here. The defining imaging parameter of basilar invagination is Chamerlain Line Violation (CLV), and we believe that all parameters should be diagnosed with CLV as the gold standard.

Fig.1 Clivopalate angle (CPA) and Clivus slope

Second, another study conducted by Baysal B et al [3] showed that the diagnostic accuracy of CPA was the lowest (0.438) compared with other angles. They thought that CPA was inadequate for the diagnosis of BI. According to Ma et al, the diagnostic accuracy of CPA, CXA or CDA (0.973, 0.964) were higher than that of CXA and CDA alone (0.957). But the increased diagnostic ability was probably due to the combination of angles and the added value was quietly limited. We boldly assume that the diagnostic efficacy of CPA is not as good as that of clivus slope, which is formed at the intersection of the Wackenheim line and a horizonal line. Clivus slope is simpler and easier to measure than CPA, and can be adjusted during surgery.

In summary, this study by Ma et al was a great work focusing on a new diagnostic method for BI at MRI. However, due to its small flaws and limited clinical significance, it is vital to make revision based on CPA or design other angles which can be adjusted during the operation. A new invented angle should serve as a basis for the clinic.