cryptoglandular origin are often the result of iatrogenic opening into the rectum by vigorous probing while attempting to find the internal opening of a trans-sphincteric fistula.
Horseshoe extension (arrows) arising from intersphincteric fistula in a male patient. Transverse STIR MR image (same parameters as for Fig 14) shows that, in this case, the horseshoe practically encircles the anal canal. Bilateral supralevator extensions (long arrows) in a female patient. Coronal STIR MR image (same parameters as for Fig 14) clearly show levator plates (short arrows) bilaterally, so that it is easy for the radiologist to be confident that infection extends above them.
Left-sided transsphincteric tract (short arrow) in a female patient. Coronal STIR MR image (same parameters as for Fig 14) shows large extension (long arrow) from apex of tract into roof of ipsilateralischioanalfossa. Transsphincteric fistula in a male patient. Transverse STIR MR image (same parameters as for Fig 14) at level of the internal opening shows primary tract (vertical arrow) at 4–5 o'clock. Unlike Figure 17, the tract cannot be traced right to the anal mucosa, and the adjacent internal sphincter (horizontal arrow) appears intact. However, an internal opening at 4–5 o'clock was reported because this position indicated site of maximal infection in the intersphincteric plane. The internal opening was confirmed at this site during subsequent EUA. Intersphincteric plane is well seen in this patient between hyperintense internal sphincter and the external sphincter.
Coronal (a) T2-weighted fast spin-echo (2500/70; echo train length, 16; field of view, 300 mm; matrix, 256 × 512; section thickness, 4 mm; gap, 0.4 mm) and (b) coronal STIR (4000/42, inversion time of 150 msec; echo train length, 16; matrix, 224 × 256; section thickness, 4 mm; gap 0.4 mm; two signals acquired) MR images acquired with external phased-array coil show complex transsphincteric fistula with tract (short straight arrows) in left ischioanalfossa that extends below ischial bone (I) toward the upper leg (not shown). At the ischialtuberosity, bone marrow edema (long straight arrow) is visible on b. Arrowhead = external opening, curved arrow = small abscess, AS = anal sphincter.
fistulography has two major drawbacks. First, extensions from the primary tract may fail to fill with contrast material if they are plugged with debris, are very remote, or there is excessive contrast material reflux from either the internal or external opening. Second, the sphincter muscles themselves are not directly imaged, which means that the relationship between any tract and the sphincter must be guessed. Furthermore, an inability to visualize the levator plate means that it can be difficult to decide whether an extension has a supra- or an infralevator location. Similarly, the exact level of the internal opening in the anal canal is often impossible to determine with sufficient accuracy to help the surgeon. The net result is that fistulographic findings are both difficult to interpret and unreliable.
fistulography has two major drawbacks. First, extensions from the primary tract may fail to fill with contrast material if they are plugged with debris, are very remote, or there is excessive contrast material reflux from either the internal or external opening. Second, the sphincter muscles themselves are not directly imaged, which means that the relationship between any tract and the sphincter must be guessed. Furthermore, an inability to visualize the levator plate means that it can be difficult to decide whether an extension has a supra- or an infralevator location. Similarly, the exact level of the internal opening in the anal canal is often impossible to determine with sufficient accuracy to help the surgeon. The net result is that fistulographic findings are both difficult to interpret and unreliable.
