Demographic Analysis:
The study included 38 patients,
35 were males and 3 were females.
Mean age was 37 ± 8.9 years old with a range of 24 – 60 years of age.
The total number of perianal fistulas and abscess was 45.
These included 30 fistulas and 15 abscesses.
The sites of these fistulas/abscesses were inter-sphincteric (n = 25,
55.6%),
trans-sphincteric (n = 11,
24.4%) and extra-sphincteric (n = 9,
20%).
According to St.
James’s University Hospital classification,
there were 21 grade 1 fistulas,
4 grade 2 abscesses,
4 grade 3 fistulas,
5 grade 4 abscesses and 6 grade 5 fistulas and abscesses.
Five extra-sphincteric fistulas/abscesses were recorded.
Extra-sphincteric fistulas that reached to the level of the levator ani muscle were considered grade 5 fistulas (n = 4).
DWI and T2 visibility of perianal fistulas:
In perianal fistulas (n = 30),
15 fistulas (50%) were well visualized (Score 2) on DWI,
in comparison to 20 fistulas (66.7%) well visualized on T2W.
Fifteen fistulas were wither not visualized (Score 0,
n = 5) or poorly visualized (Score 1,
n = 10) on DWI.
In comparison,
9 fistulas were poorly visualized (Score 1) on T2W and only 1 was not visualized (Score 0).
The visibility scores on T2W were not significantly different from that of DWI (p = 0.14) and both of them were less than the visibility scores of the combined DWI and T2W evaluation,
although not significant.
This is shown in table.
Visibility Score for Perianal Fistulas |
T2W |
DWI |
Combined T2W & DWI |
Significance level |
Score 2 |
20 |
15 |
29 |
0.08-0.26
|
Score 1 |
9 |
10 |
1 |
Score 0 |
1 |
5 |
0 |
All perianal abscesses were well visualized on both sequences.
The visibility scores of perianal fistulas on DWI were not significantly different between PIA and NIA groups (p = 0.78).
Similarly,
these scores on T2W didn’t show any significant variation between PIA and NIA groups (p = 0.49).
ADC values and activity:
The ADC values for perianal fistulas was 1.39 ± 0.4 x 10-3 mm2/sec,
while for abscesses,
it was 0.8 ± 0.66 x 10-3 mm2/sec,
with significant difference between both entities (p = 0.001).
This is displayed in figure 1.
There was no significant difference between PIA and NIA groups regarding the ADC value of perianal fistulas (PIA: 1.3 ± 0.5 x 10-3 mm2/sec and NIA: 1.43 ± 0.4 x 10-3 mm2/sec,
p = 0.45).
This is displayed in figure 2.
ADC values didn’t reveal any significant correlation to the CRP level (p = 0.38) or leucocytic counts (p = 0.59).
Grading of perianal fistulas:
Using the St.
James’s University Hospital classification,
38 fistulas and abscesses were correctly classified by DWI alone (84.4%),
whereas 6 cases (13.3%) could not be classified due to poor or non-visualization and 1 case (2.2%) was misclassified.
Two of these cases belonged to the PIA group (28.6% of the PIA group and 4.4% of the entire sample) and 5 cases belonged to the NIA group.
The DWI based grading was significantly less than the combined T2W & post-contrast images in the classification of perianal fistulas and abscesses (p = 0.023) when testing the entire sample.
However,
for the PIA group only,
DWI was not significantly different from combined T2W & post-contrast images (p = 0.66).
On the other hand,
44 perianal fistulas and abscesses were correctly classified using combined T2W & DWI evaluation (97.8%).
The only case,
which could not be well visualized on both sequences,
belonged to the NIA group.
The grading of perianal fistula/abscess using combined T2W & DWI evaluation was not significantly different from that using combined T2W & postcontrast images when testing the entire sample (p = 0.32) or when testing the PIA group separately (p = 1).