Added value of volumetric MRI pulse sequence 3D VISTA (Volume ISotopic Turbo spin echo Acquisition) in perianal fistula depiction and characterization

Abstract

Purpose: Diagnosis of perianal fistula represents a challenge for surgeons. It is well known that magnetic resonance imaging (MRI) plays an important role in that. The new 3D MRI sequence VISTA (Volume ISotopic Turbo spin echo Acquisition) can improve detection and characterization of perianal fistula compared with two-dimensional (2D) sequences. The aim of the study was to compare the diagnostic performance of the new 3D MRI sequence VISTA with the widely routinely used T2 FSE pulse sequence in depiction and characterization of perianal fistula by using the contrast-enhanced (CE) 3D T1 sequence THRIVE (T1-weighted high-resolution isotropic volume examination) as a reference standard.

Material and methods: Forty adult patients were enrolled in this prospective study. They underwent MRI perianal region examination using routine T2 TSE and CE 3D T1 sequence THRIVE with addition of the new 3D MRI sequence VISTA. T2, 3D VISTA and (CE) 3D T1 sequence THRIVE images were evaluated by two radiologists separately for detection and characterization of perianal fistula, then comparison between of T2 and 3D VISTA sequences was done using (CE) 3D T1 sequence THRIVE as a reference. Each sequence sensitivity, specificity and accuracy were calculated by both readers.

Results: For reader 1, the sensitivity, specificity and accuracy were 92.5%, 90.5% and 93.6% for 3D VISTA and 84.1%, 83.7% and 87.3% for T2 FSE. For reader 2, the sensitivity, specificity and accuracy were 91.5%, 92.8% and 94.8% for 3D VISTA and 82.9%, 84.5% and 86.7% for T2 FSE.

Conclusions: Using CE 3D T1 sequence THRIVE as the reference standard, 3D VISTA pulse sequence on the perianal region has better diagnostic performance in the detection and characterization of perianal fistula as compared to the routinely used T2 FSE sequence.

Keywords: T1-weighted high-resolution isotropic volume examination (3D THRIVE); magnetic resonance imaging; perianal fistula; volume isotopic turbo spin echo acquisition (3D VISTA).

Figure 1

38-year-old male patient with severe perianal pain associated with purulent discharge with MRI of the perianal region. Each row represents T2 TSE, 3D VISTA and CE 3D THRIVE respectively, first row axial images and second row coronal images. There is a non-branching fistulous tract seen extending from the posterior subcutaneous soft tissue upward and piercing the posterior aspect of the external anal sphincter to the inter-sphincteric space then abutting the internal anal sphincter at 6 o’clock, with no abscess or collections. This tract is not clearly seen in T2 TSE and well depicted in 3D THRIVE images (open arrow) and in CE 3 D THRIVE images (arrows)

Figure 2

42-year-old female patient with perianal pain with MRI of the perianal region. Images represent axial T2 TSE, 3 D VISTA and CE 3D THRIVE respectively. Narrow, non-branching fistulous tract seen extending from the left perianal subcutaneous tissue and extending, piercing the posterior aspect of the external anal sphincter to end in the inter-sphincteric space at 6 o’clock, with no abscess or collections. This tract is not clearly seen in T2 TSE and well depicted in 3D THRIVE images (open arrow) and in CE 3 D THRIVE images (arrows)

Figure 3

24-year-old male patient with Crohn disease and perianal pain with MRI of the perianal region. Each row represents axial T2 TSE, 3 D VISTA and CE 3D THRIVE respectively, first row axial images at the level of internal anal sphincter and second row just below this level. The right-branching interhemispheric fistulous tract is identified. It has three external opening at the right side, one posterior at 6 and 7 o’clock with multilocular abscess. The fistula then extends anterosuperiorly; it is seen branching in the inter-sphincteric space with an internal opening at 11 o’clock with small abscess collection. These branching fistulous tracts and abscess are not clearly seen in T2 TSE and well depicted in 3D THRIVE images (open arrow) and in CE 3 D THRIVE images (arrows)

Figure 4

Sensitivity, specificity and accuracy of sequences for two readers