犬寰樞椎之放射線學表現

Abstract

寰樞椎不穩定（atlantoaxial instability）會造成樞椎（axis）相對於寰椎（atlas）往背側移位，進而造成脊髓的壓迫。診斷寰樞椎不穩定的方式主要依據臨床症狀、基本資料、病史以及影像學上的判讀。確診的方式主要是看到寰樞椎不穩定的證據，如：於X光片側照下明顯看到寰樞椎之間距離增加或是於脊髓造影（myelography）、磁振造影（magnetic resonance imaging, MRI）下看到頸部脊髓的壓迫，或是於電腦斷層（computed tomography, CT）下看到寰椎和樞椎相對位置齒突的改變。 由於X光片下不一定可以觀察到寰樞不穩定的證據、而拍攝脊髓造影、磁振造影以及電腦斷層需要負擔較高的費用以及承擔麻醉風險；此外，於過去文獻中，僅有數篇研究指出寰樞椎之間可能具有可動性。因此本研究的目的在於建立單純放射線學拍攝之下，好發品種的無臨床症狀犬其寰樞椎關節活動在三個姿勢下（頸部伸展、自然、屈曲等三種姿勢）的參考值、好發品種及非好發品種其寰樞椎關節之可動性以及比較有症狀犬與無症狀犬其寰樞關節活動範圍之間的差異。並希望以這些數據建立出價格較低廉之診斷流程。 共46隻狗參與本研究之實驗一，包括26隻無臨床症狀犬之好發品種犬（六隻約克夏、七隻博美、七隻吉娃娃以及六隻馬爾濟斯）（組一）、14隻無臨床症狀犬之非好發品種犬（七隻迷你臘腸及七隻米格魯）（組二）以及六隻寰樞椎不穩定之好發品種犬（一隻約克夏、一隻博美、兩隻吉娃娃以及兩隻馬爾濟斯）（組三）參與本研究。所有動物皆拍攝二到三張頸部側照X光片（包括伸展姿、自然姿以及屈曲姿）以及一張腹背照X光片。並於三種側照下，以五種測量方法包括：The distance of atlantoaxial joint（AAD）、horizontal movement（HM）、vertical movement（VM）、cranial to cranial（Cr’-Cr’）以及caudal to cranial（Cd’-Cr’）計算寰樞椎之間的距離。於腹背照下，計算並紀錄齒突以及樞椎的長度。收集上列數據後，進行統計分析。 實驗一結果顯示：比較在同一組的三種不同的側照姿勢之間，組一的寰樞椎椎間距離會有顯著的改變（p<0.05）；組二的寰樞椎之間距離則沒有改變。三種側照下，組一的VM及Cd’-Cr’顯著的小於組二（p<0.05）。於自然姿及屈曲姿下，組一之AAD以及Cr’-Cr’顯著小於組三（p<0.05）。 實驗二是利用實驗一所得結果，包括測量方法及寰樞椎間距之參考值，建立一問卷診斷法。再請12位臨床獸醫師（六位具三年以上臨床經驗，六位具三年以下臨床經驗）判讀12個臨床病例（組一隨機挑選六隻病例以及組三全部病例）之X光片。判讀共分為兩階段，第一階段為目測加上既有經驗判斷這12個病例是否為寰樞椎不穩定（目測檢出率），第二階段則以問卷診斷法判斷這些病例是否為寰樞椎不穩定（問卷檢出率）。 實驗二之結果顯示問卷檢出率顯著高於目測檢出率。 由實驗一可知，好發品種犬之寰樞椎關節確實存在可動性，並明顯大於好發品種犬。同時本研究也建立了三種姿勢的角度定義、測量寰樞椎之間距離的三種較為方便的方法（問卷診斷法）以及齒突佔樞椎椎體之比值。而實驗二則證實此方法能提高好發品種之寰樞椎不穩定的檢出率，並且是一種容易使用的診斷方式。

英文摘要 Atlantoaxial instability (AAI) refers to the instability of the atlantoaxial joint (AAJ) that leads to dorsal displacement of the axis relative to the atlas, causing spinal cord compression. Diagnosis is based on clinical signs, signalment, history and imaging findings. Definitive diagnosis is made by demonstrating the consequence of atlantoaxial instability, such as the apparent increase in space between the dorsal spinous process of the axis and the dorsal arch of the atlas in the survey lateral radiographs, atlantoaxial misalignment causing spinal cord compression in myelography or magnetic resonance imaging (MRI), and the abnormal position of atlantoaxial joint in computed tomography (CT). In some patients, the radiographic findings are not obvious and further investigations with advanced imaging would be required to achieve the diagnosis. However, the availability of the advanced imaging facilities, higher expense for the owner and the risk of general anesthesia would all potentially be the owner’s concern regarding the further investigations. To our knowledge, there are only few studies describing the motility of the atlantoaxial joint in dogs. The objective of this study include: 1) to establish the reference of the distance of the AAJ of predisposed breed dogs in three lateral projections (extended, neutral and flexed), 2) to demonstrate the motility of the AAJ of predisposed breed dogs and non-predisposed breed dogs, 3) to compare radiographic findings in dogs without AAI and clinically affected dogs, and 4) to establish a diagnostic criteria of AAI based on radiographic findings. In total, 46 dogs were included in study one and were divided into three groups. Group one included 26 AAI-predisposed breed dogs which were not affected by AAI (six Yorkshire terriers, seven Pomeranian dogs, seven Chihuahua dogs and six Maltese terriers). Group two included 14 AAI-non-predisposed breed dogs which were not affected by AAI (seven miniature Dachshunds and seven beagles). Six AAI clinically affected dogs of predisposed breed were included in Group three (one Yorkshire terrier, one Pomeranian dog, two Chihuahua dogs and two Maltese dogs). Cervical spine radiographs were obtained in neutral, extended and flexed lateral projections and ventrodorsal projection. Five methods including the distance of atlantoaxial joint (AAD), horizontal movement (HM), vertical movement (VM), cranial to cranial (Cr’-Cr’) and caudal to cranial (Cd’-Cr’) were used to measure the distance between the atlas and the axis in three lateral views. The length of dens and axis were measured in the ventrodorsal view. In Group one, the distance of the atlantoaxial joint significantly changed between three lateral projections (p<0.05), and no significant changes were found in Group two. In all three lateral projections, VM and Cd’-Cr’ of the atlantoaxial joint in Group two was significantly increased compared to that in Group one (p<0.05). In neutral and flexed lateral projections, AAD and Cr’-Cr’ of the atlantaoxial joint in Group three were significantly increased compared to that in Group one (p<0.05). In study two, based on the data analysis of study one, a diagnostic criteria of AAI was generated. Twelve veterinarians were asked to interpret radiographs of 12 dogs (six dogs in Group one and six dogs in Group three) based on their own experience (first stage) and based on the AAI diagnostic criteria (second stage). The diagnostic rate based on the AAI diagnostic criteria was significantly higher. In conclusion, the study demonstrated that the motility of the AAJ exists in several AAI-predisposed breed dogs. The reference range of the distance between atlas and axis in several breed dogs were also established. The AAI diagnostic criteria generated from the study is user friendly, and its application would increase the diagnostic rate of AAI.