Korean J Radiol.  2014 Dec;15(6):712-723. 10.3348/kjr.2014.15.6.712.

Imaging of Anal Fistulas: Comparison of Computed Tomographic Fistulography and Magnetic Resonance Imaging

Affiliations
  • 1Shandong Medical Imaging Research Institute, Shandong University, Jinan 250021, China.
  • 2Traditional Chinese Medicine Department, Provincial Hospital Affiliated to Shandong University, Jinan 250021, China. yongchaolu123456@163.com
  • 3Shandong Provincial Center for Disease Control and Prevention, Public Health Institute, Jinan 250014, China.
  • 4Department of Radiology, Taishan Medical University, Taian 271000, China.

Abstract

The primary importance of magnetic resonance (MR) imaging in evaluating anal fistulas lies in its ability to demonstrate hidden areas of sepsis and secondary extensions in patients with fistula in ano. MR imaging is relatively expensive, so there are many healthcare systems worldwide where access to MR imaging remains restricted. Until recently, computed tomography (CT) has played a limited role in imaging fistula in ano, largely owing to its poor resolution of soft tissue. In this article, the different imaging features of the CT and MRI are compared to demonstrate the relative accuracy of CT fistulography for the preoperative assessment of fistula in ano. CT fistulography and MR imaging have their own advantages for preoperative evaluation of perianal fistula, and can be applied to complement one another when necessary.

Keyword

CT; MR imaging; Fistulography; Perianal fistula

MeSH Terms

Adult
Anal Canal/anatomy & histology
Female
Humans
*Magnetic Resonance Imaging
Male
Middle Aged
Rectal Fistula/diagnosis/*radiography/surgery
Tomography, X-Ray Computed
Young Adult

Figure

  • Fig. 1 Normal perianal anatomy of 47-year-old female volunteer imaged with CT and MR imaging. Anal sphincter complex is seen as two concentric rings. MR imaging: inner (+) internal sphincter and outer external sphincter (white dovetail arrows) appear relatively hypointense on all T2-weighted images without fat suppression (A-C). Levator ani muscle (B, thick arrows) forms superior boundary of fat-containing ischioanal fossa (*) on either side of anal canal. CT (D-F) of inner internal sphincter (+), outer external sphincter (white dovetail arrows), levator ani muscle (E, thick arrows), and fat-containing ischioanal fossa (*).

  • Fig. 2 Normal perianal anatomy of 45-year-old male volunteer imaged with CT and MR imaging. MR imaging (T2-weighted without fat suppression images; A-C) and CT (D-F): anal sphincter complex is seen as two concentric rings. Inner internal sphincter (+), outer external sphincter (white or black dovetail arrows), levator ani muscle (thick arrows), fat containing ischioanal fossa (*).

  • Fig. 3 21-year-old male with perianal complex fistulas. CT fistulography images clearly show complex perianal fistula tracts in subcutaneous shallow area, in rear of coccyx. Three anomalous fistula tracts with external opening were successfully identified. Extent of disease and complicated spatial information are better seen on volume rendering image. Minute fistula was not clearly seen (white dovetail arrow in D) on MR image. CT fistulography (A-C) and MRI (contrast-enhanced liver acquisition with volume acceleration [LAVA] in D, F; T2-weighted with fat suppression in E): thick fistula (white arrow), minute fistula (white dovetail arrow), and long fistula (black dovetail arrow) are identified.

  • Fig. 4 44-year-old female with recurrent fistulas after two operations. CT fistulography (A, C) and MR imaging (contrast-enhanced T1-weighted with fat suppression in B): reconstructed images clearly show complicated spatial information of two separate fistula tracts (short white arrows) with irregularly shaped abscess (* in C), which closes to mid-anal canal. Internal tiny ramifications (long white arrows in *) are not exactly confirmed at corresponding position on MR image. Fistula cavities are surrounded by inflammatory tissue (fistula wall, + in A, B). Irregular shape of abscess (* in B).

  • Fig. 5 64-year-old male with perianal complex fistulas. CT fistulography (B, C) and MR imaging (contrast-enhanced T1-weighted with fat suppression in A): reconstructed images clearly show complicated spatial information of fistula tract (short white arrows). Latent secondary extensions (long white arrows in B, C) are clearly confirmed on CT but not corresponding MR image (long white arrow in A).

  • Fig. 6 64-year-old male with extrasphincteric fistula. MR imaging (T2-weighted with fat suppression in A) and CT fistulography (B): internal opening (short white arrow in A, B) of fistula (+ in A, B) is well identified in corresponding MR and CT images; confirmation of internal opening is major surgical aim.

  • Fig. 7 64-year-old male with perianal complex fistulas. MR imaging (contrast-enhanced T1-weighted with fat suppression in A) and CT fistulography (B): internal opening (short white arrow in A, B) of fistula (+ in A, B) is well identified in corresponding MR, CT images.

  • Fig. 8 38-year-old male with semi-horseshoe fistula. CT fistulography (D-G) and MR imaging (T2-weighted with fat suppression in A-C): transverse, coronal images clearly show circumferential spread of fistula (short white arrows in A-G). Extent of disease and complicated spatial information are better seen on volume rendering image (short arrows in G). External opening (long white arrow in B, E, G), internal opening (short black arrow in D), and secondary ramification (long black arrow in C, F) are seen.

  • Fig. 9 26-year-old male with fistula. MR imaging (T1-weighted with fat suppression in A, T2-weighted with fat suppression in C) and CT fistulography (B): fistula (short white arrow in A, B) spreads backward to skin's surface with evident external opening. Tenuous internal opening (long white arrow in C) was successfully identified on MR image. Internal opening is confirmed clearly on MR image but not corresponding CT image, owing to lack of contrast agent filling.

  • Fig. 10 25-year-old female with fistula. MR imaging (T2-weighted with fat suppression in A, contrast-enhanced liver acquisition with volume acceleration in C) and CT fistulography (B). Fistula (short white arrows in C) perforating backward toward anal sphincter, spreads (short white arrow in A) backward to skin's surface with evident external opening (long white arrow in A, B). Fistula is confirmed clearly on MR image but not corresponding CT image, owing to lack of contrast agent filling.

  • Fig. 11 54-year-old female with fistula caused by ruptured teratoma in pelvic cavity. MR imaging (contrast enhanced T1-weighted with fat suppression in A, C; T2-weighted without fat suppression image in B), and CT fistulography (D-F): mass (teratoma, short white arrows in A-F) perforates levator ani muscle downward, entering perianal spaces. Images (A-F) provide excellent imaging of fistula (long white arrow in C, F), teratoma, and their relationship to adjacent organ organization. Calcification (short black arrow in F) and gas (long black arrow in F) in teratoma can be seen.


Cited by  2 articles

MRI T2-Weighted Imaging and Fat-Suppressed T2-Weighted Imaging Image Fusion Technology Improves Image Discriminability for the Evaluation of Anal Fistulas
Shi-Ting Feng, Mengqi Huang, Zhi Dong, Ling Xu, Yin Li, Yingmei Jia, Huasong Cai, Bingqi Shen, Zi-Ping Li
Korean J Radiol. 2019;20(3):429-437.    doi: 10.3348/kjr.2018.0260.

Crohn’s disease at radiological imaging: focus on techniques and intestinal tract
Giuseppe Cicero, Silvio Mazziotti
Intest Res. 2021;19(4):365-378.    doi: 10.5217/ir.2020.00097.


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