Cuenod C A, de Parades V, Siauve N, Marteau P, Grataloup C, Hernigou A, Berger A, Cugnenc P H, Frija G
Service de Radiologie, Hôpital Européen Georges Pompidou, 20 rue Leblanc, 75015 Paris.
J Radiol. 2003 Apr;84(4 Pt 2):516-28.
A good digital examination is usually sufficient for the diagnosis and the treatment planning of anal fistulae. Cross-sectional imaging techniques, however, can accurately identify deep abscesses and characterize complex fistulae. MRI is well suited for this examination, with almost no motion artifact, excellent contrast between muscles and fatty spaces, and multiplanar acquisition. A fistula starts from an internal opening in the digestive tube and can end in an abscess cavity or open at the skin at an external opening. The cryptoglandular anal fistulae (fistula-in-ano) are non-specific in origin and are usually simple, whereas specific fistulae are due to many diseases such as Crohn's disease, tuberculosis, trauma, radiation, colloid carcinoma, hidradenitis suppurative, actinomycosis or lymphoma and are often complex. MRI appears useful in the cases with recurrent fistulae, Crohn's disease, when the secondary orifice is atypically placed, during a multistep treatment for complex fistulae, or when an anal stenosis forbids a clinical or ultrasound examination. A good knowledge of the perineum anatomy is required for analysing the fistula tracts. The muscle planes separate fatty spaces which have an important role in the spread of the disease: sub-mucosal space, marginal space, intersphincteric space, postanal space of Courtney, supralevator space, and the two ischioanal spaces on both sides of the anal canal. The anal canal is surrounded by the ring-like internal sphincter, which continues the internal muscularis propria of the rectum, and the external sphincter, which is intermingled with the puborectalis muscle. We perform our MRI examination with an external phased array coil, and we place a cannula to identify the anal canal. The T2W sequences give the more interesting information, but the sequences with fat-suppression and gadolinium chelate injection are also very useful. The MRI examination allows the analysis of: 1) the location of the fistula tracts according to Park's classification, 2) the location of the internal opening, 3) the locations of the external opening(s), 4) the location of deep abscesses, 5) the long distance extensions, 6) the state of the ano-rectal wall and the perirectal spaces, 6) the damages of the anal sphincter.
一次良好的指诊通常足以用于肛瘘的诊断和治疗规划。然而，横断面成像技术能够准确识别深部脓肿并对复杂肛瘘进行特征描述。MRI非常适合此项检查，几乎不存在运动伪影，肌肉与脂肪间隙之间的对比度极佳，且能够进行多平面采集。肛瘘始于消化道内口，可终止于脓肿腔或在皮肤表面形成外口。隐窝腺源性肛瘘（肛管肛瘘）病因不明，通常较为简单，而特异性肛瘘则由多种疾病引起，如克罗恩病、结核病、创伤、放疗、黏液癌、化脓性汗腺炎、放线菌病或淋巴瘤，且往往较为复杂。在复发性肛瘘、克罗恩病、外口位置不典型、复杂肛瘘的多步骤治疗过程中，或肛门狭窄禁止进行临床或超声检查的情况下，MRI似乎很有用。分析瘘管时需要对会阴解剖结构有充分了解。肌肉平面分隔脂肪间隙，这些脂肪间隙在疾病传播中起重要作用：黏膜下间隙、边缘间隙、括约肌间间隙、考特尼肛后间隙、提肌上间隙以及肛管两侧的两个坐骨直肠间隙。肛管被环状的内括约肌环绕，内括约肌延续直肠的固有肌层，外括约肌与耻骨直肠肌相互交织。我们使用外部相控阵线圈进行MRI检查，并放置一根插管以识别肛管。T2加权序列提供的信息更有价值，但脂肪抑制和钆螯合物注射序列也非常有用。MRI检查能够分析：1）根据帕克分类法确定瘘管的位置，2）内口的位置，3）外口的位置，4）深部脓肿 的位置，5）远距离延伸情况，6）肛管直肠壁和直肠周间隙的状态，6）肛门括约肌的损伤情况。
