Preoperative MR imaging of anal fistulas: Does it really help the surgeon?
OBJECTIVE
To evaluate the accuracy of magnetic resonance (MR) imaging with a quadrature phased-array coil for the detection of anal fistulas and to evaluate the additional clinical value of preoperative MR imaging, as compared with surgery alone.


METHODS
Fifty-six patients with anal fistulas underwent high-spatial-resolution MR imaging. Twenty-four had a primary fistula; 17, a recurrent fistula; and 15, a fistula associated with Crohn disease. MR imaging findings were withheld from the surgeon until surgery ended and verified, and surgery continued when required.


RESULTS
MR imaging provided important additional information in 12 (21%) of 56 patients. In patients with Crohn disease, the benefit was 40% (six of 15); in patients with recurrent fistulas, 24% (four of 17); and in patients with primary fistulas, 8% (two of 24). The difference between patients with or without Crohn disease and between patients with a simple fistula versus the rest was significant (P <.05). The sensitivity and specificity for detecting fistula tracks were 100% and 86%, respectively; abscesses, 96% and 97%, respectively; horseshoe fistulas, 100% and 100%, respectively; and internal openings, 96% and 90%, respectively.


CONCLUSIONS
High-spatial-resolution MR imaging is accurate for detecting anal fistulas. It provides important additional information in patients with Crohn disease-related and recurrent anal fistulas and is recommended in their preoperative work-up.
Beets-Tan
R G
RG
Department of Radiology, University Hospital of Maastricht, P. Debyelaan 25, 6229 HX Maastricht, The Netherlands. rbe@rdia.azm.nl
Beets
G L
GL
van der Hoop
A G
AG
Kessels
A G
AG
Vliegen
R F
RF
Baeten
C G
CG
van Engelshoven
J M
JM
D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011300:Preoperative Care; D011446:Prospective Studies; D012372:ROC Curve; D012003:Rectal Fistula / Q000473:pathology* / Q000601:surgery; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity