DOI:10.2214/AJR.05.0011
AJR 2006; 187:517-521
© American Roentgen Ray Society
Mucinous Adenocarcinoma Arising from Fistula in Ano: MRI Findings
Yukihiro Hama1,
Kohzoh Makita2,
Tetsuo Yamana3 and
Keiichi Dodanuki4
1 Department of Radiology, National Defense Medical College, 3-2 Namiki,
Tokorozawa, Saitama, 359-0042, Japan.
2 Department of Radiology, Tokyo-kita Social Insurance Hospital, Tokyo,
Japan.
3 Coloproctology Center, Social Insurance Chuo General Hospital, Tokyo,
Japan.
4 Department of Radiology, Social Insurance Chuo General Hospital, Tokyo,
Japan.
Received January 4, 2005;
accepted after revision April 6, 2005.
This work was partially supported by a grant from the Japan-U.S.
Radiological Exchange Association.
Address correspondence to Y. Hama
(yjhama{at}me.ndmc.ac.jp).
Abstract
OBJECTIVE. The purpose of this study was to describe MRI findings in
11 patients with mucinous adenocarcinomas arising from fistula in ano.
CONCLUSION. More than half of patients had a mass filled with
markedly hyperintense content on T2-weighted fast spin-echo images, enhancing
solid components within the mass, mesh-like internal enhancement, fluid
collections without a thick fibrous capsule, contrast enhancement of
peritumoral areas, and a fistula between the mass and the anus. Regional areas
of lymph node enlargement were considered indirect findings of locally
advanced mucinous adenocarcinoma. These MRI findings may help diagnose
mucinous adenocarcinomas arising from fistula in ano.
Keywords: fistula in ano • gastrointestinal radiology • MRI • mucinous adenocarcinoma • oncologic imaging
Introduction
Mucinous adenocarcinoma associated with chronic fistula in ano is rare, and
diagnosis is often difficult
[1]. The absence of a tumor
within the lumen of the bowel and the slow growth of a lesion hidden within
the ischioanal fossa and perineum make early diagnosis difficult
[2]. The patients with a
mucinous adenocarcinoma complicating a chronic fistula in ano usually do not
present with complaints referable to diarrhea or obstruction
[1]. Digital examination may
reveal only an area of induration on the side where the fistula is situated,
and it does not establish a conclusive diagnosis. Biopsy of the external
openings of the fistulous tracts is not conclusive and very often is
misleading because the tissue taken is very superficial and only reveals an
inflammatory reaction, especially when scarring and fibrosis are present
[2].
MRI has been considered the most accurate preoperative technique for
classification of fistula in ano and useful for evaluation of the primary
track and extensions and for distinction from pilonidal sinus disease
[3-5].
To our knowledge, only two cases of mucinous adenocarcinomas arising from
fistula in ano detected by MRI are described in the literature
[6,
7]. The purpose of this study
was to describe the MRI findings in patients with mucinous adenocarcinomas
arising from fistula in ano.
Materials and Methods
Patients
Between June 1996 and November 2004, 1,802 consecutive patients with
long-standing chronic fistula in ano underwent MRI before surgery or biopsy in
our hospital. A retrospective review of the pathology reports of these
patients identified 11 patients (0.61%) with mucinous adenocarcinoma arising
from fistula in ano (10 men, 1 woman; median age, 53 years; age range, 38-79
years). All 11 patients with mucinous adenocarcinoma complained of the passage
of pus, sometimes with blood, from an opening near the anus. Three patients
complained of increasing pain over a period of a few days. The patients had a
fistula in ano for 2-11 years (median, 5 years). Our institutional review
board did not require its approval for this retrospective analysis, but
patient consent was obtained in conformity with criteria of the ethics
committee.
Imaging
MRI was performed either with a 1.0-T system (Magnetom Impact, Siemens
Medical Solutions) (n = 3) or a 1.5-T system (Magnetom Vision,
Siemens Medical Solutions) (n = 8). All patients were examined using
a phased-array pelvic coil. Imaging was supervised by an attending
radiologist. The long axis of the anal canal was identified by using a midline
sagittal localized image. By using this image for guidance, axial, sagittal,
and coronal T2-weighted fast spin-echo images were aligned with the
longitudinal axis of the anal canal and were obtained using the following
parameters: TR range/effective TE range, 3,883-5,000/99-120; echo-train
length, 15; 350-mm field of view; 256 x 256-512 matrix; 6-mm section
thickness; and 0.6-mm intersection gap for the 1.0-T system; and
3,950-5,760/90-120; echo-train length, 15; 200-350 x 320-350 mm field of
view; 240-512 x 256-512 matrix; 6- to 9-mm section thickness; and 0.6-
to 1.8-mm intersection gap for the 1.5-T system. Axial T1-weighted spin-echo
MRI was performed with the following parameters: TR range/TE range,
500-660/15-17; 300-350 x 320-350 mm field of view; 160-256 x
256-512 matrix; 6- to 10-mm section thickness; and 0.7- to 2-mm intersection
gap for the 1.0-T system; and 437-760/10-17; 180-330 x 330-350 mm field
of view; 128-512 x 256-512 matrix; 6- to 10-mm section thickness; and
0.6- to 2-mm intersection gap for the 1.5-T system. Coronal and sagittal
T1-weighted spin-echo MR images with fat suppression were obtained immediately
after IV bolus injection of 0.1 mmol of gadopentetate dimeglumine (Magnevist,
Schering) per kilogram of body weight. The following parameters were used:
450-931/15-17; 210-350 x 330-380 mm field of view; 160-224 x
256-512 matrix; 5- to 6-mm section thickness; and 0.5- to 0.6-mm intersection
gap for the 1.0-T system; and 570-1,120/8-17; 180-350 x 30-350 mm field
of view; 128-512 x 256-512 matrix; 4- to 8-mm section thickness; and
0.4- to 1.6-mm intersection gap for the 1.5-T system. Axial images were added
when needed.
Image Review
All images were reviewed by two board-certified radiologists (with 7 and 20
years of experience, respectively). One reviewer was involved in previous
reading of the MR images; the other was not. Image review was performed on
hard copies. The two reviewers evaluated MR images independently and reached a
consensus. They were aware of the pathologic reports; however, images from
these 11 patients with mucinous adenocarcinoma were reviewed at the same
session but in a randomized order. Two patients did not undergo
contrast-enhanced studies.
MRI-based classification of fistula in ano was defined by using established
MRI criteria [8]. Features
evaluated on MRI included masses filled with markedly hyperintense content on
T2-weighted fast spinecho images, enhancing solid components, meshlike
internal enhancement, a fistula between the mass and the anus, fluid
collections without a thick fibrous capsule, contrast enhancement of
peripheral structures or peritumoral areas, and regional areas of lymph node
enlargement. These features were selected from the previous case reports and
our personal experience [6,
7].
Markedly hyperintense content was defined as signal intensity similar to or
brighter than perirectal fat on T2-weighted fast spin-echo images
[9]. If the amounts of the
high-signal-intensity fluid occupied more than 50% of the tumoral area as
determined from the available T2-weighted fast spin-echo images, we finally
judged it as a tumor filled with markedly hyperintense content
[10]. Enhancing solid
components were defined as areas with a major axis at least 5 mm long located
in the fluid or mucin pool and with contrast enhancement after IV
administration of gadolinium chelate. Fistula between the mass and the anus
was defined as a high-signal-intensity communication between the mass and the
anus assessed on T2-weighted images. Fluid collections were detected on both
T1-weighted and T2-weighted images. If a thick fibrous capsule was not
observed as a low-signal-intensity area on both T1-weighted and T2-weighted
images, we judged it as a fluid collection without a thick fibrous capsule.
Contrast enhancement of peripheral structures or peritumoral areas was
assessed on the fat-suppressed contrast-enhanced T1-weighted images. Regional
lymphadenopathy was defined as perirectal and internal iliac lymph nodes
greater than 10 mm in the short axis and inguinal lymph nodes greater than 15
mm in the short axis.
Results
Table 1 summarizes the MRI
findings of mucinous adenocarcinomas arising from fistula in ano. The major
axis of the lesions ranged from 1.8 to 17.5 cm (median, 6.3 cm) on T2-weighted
MR images. All 11 patients with mucinous adenocarcinoma had tumors filled with
markedly hyperintense content on T2-weighted fast spin-echo images
(Fig. 1A). All nine patients
receiving contrast material for MRI studies had enhancing solid components
within the mass (Fig. 1B). A
fistula between the mass and the anus was detected in all 11 patients. A mucin
pool without a thick fibrous capsule (Fig.
2) was noted in 8 (73%) of 11 mucinous adenocarcinoma patients.
Contrast enhancement of the peritumoral areas was noted in eight (89%) of nine
patients (Fig. 3). All nine
patients receiving contrast material for MRI studies had a meshlike internal
contrast enhancement pattern (Fig.
1C). Regional areas of lymph node enlargement were noted in five
(45%) of 11 patients with mucinous adenocarcinomas
(Fig. 1C). Regional lymph node
metastasis was detected in all five patients with mucinous adenocarcinomas,
two patients by surgical resection and three patients on follow-up
evaluation.
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Fig. 1A —51-year-old man with mucinous adenocarcinoma arising from
fistula in ano. Sagittal T2-weighted fast spin-echo MR image (TR/TE,
4,020/118; echo-train length, 15; 300 x 300 mm field of view; 512
x 512 matrix; 8-mm section thickness; 1.6-mm intersection gap) shows
markedly hyperintense heterogeneous content (arrows) within mass.
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Fig. 1B —51-year-old man with mucinous adenocarcinoma arising from
fistula in ano. Sagittal fat-suppressed contrast-enhanced T1-weighted MR image
(873/8.4; 300 x 300 mm field of view; 512 x 512 matrix; 6.5-mm
section thickness; 1.3-mm intersection gap) shows several enhancing solid
components (white arrows) and linear and papillary meshlike enhancing
areas (arrowheads).
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Fig. 2 —67-year-old man with mucinous adenocarcinoma arising from
fistula in ano. Axial T2-weighted fast spin-echo MR image (TR/TE, 5,760/106;
echo-train length, 15; 330 x 330 mm field of view; 512 x 512
matrix; 7-mm section thickness; 1.4-mm intersection gap) shows markedly
hyperintense mucin pool (arrow) without thick fibrous capsule. Thick
fibrous capsule of fistula in ano (arrowhead) can be identified where
there is no carcinoma.
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Fig. 3 —55-year-old man with mucinous adenocarcinoma arising from
fistula in ano. Coronal fat-suppressed contrast-enhanced T1-weighted MR image
(TR/TE, 930/10; 350 x 350 mm field of view; 256 x 256 matrix; 7-mm
section thickness; 1.4-mm intersection gap) shows contrast enhancement of
peritumoral adipose tissues (arrows).
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Fig. 1C —51-year-old man with mucinous adenocarcinoma arising from
fistula in ano. Coronal fat-suppressed contrast-enhanced T1-weighted MR image
(930/10; 350 x 350 mm field of view; 256 x 256 matrix; 7-mm
section thickness; 1.4-mm intersection gap) shows meshlike enhancing areas
(arrowheads) and lymphadenopathy of left internal iliac node
(white arrow). Severe stenosis of rectum (black arrow) is
evident.
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Discussion
MRI accurately shows the perianal anatomy and has had a major impact on the
preoperative assessment of fistula in ano
[8]. It has been suggested that
markedly hyperintense content on T2-weighted fast spin-echo images reflects
the mucin pool of mucinous adenocarcinomas
[9]. We hypothesized that the
mucin produced by a mucinous adenocarcinoma would not be localized within the
fistula or abscess cavity because of the invasive nature of cancer cells,
whereas the mucin secreted by the anal gland would be localized within the
fistula or abscess cavity. Mucin pools without thick fibrous capsules may
reflect the invasiveness of the mucinous adenocarcinoma. That is, cancer cells
having invaded the perirectal or perianal tissues may have produced mucin
pools before the fibrotic reaction. Radiological and pathologic correlation
studies could not be performed because all the specimens were made into a
permanent preparation.
The contrast enhancement pattern was internally heterogeneous and meshlike,
and enhancing structures or enhancing solid components were depicted centrally
in parts of the tumors that may contain predominantly extra-cellular mucin.
Extracellular mucin is contained within a meshlike internal structure formed
by cells, cords, and vessels
[11-13].
Administration of gadolinium chelate may enhance the meshlike internal
structure. This enhancement may distinguish mucinous adenocarcinomas from
abscesses and more complicated types of fistula in ano.
Contrast enhancement of peripheral structures or peritumoral areas may also
be a reliable finding reflecting the invasion of cancer cells. However, active
inflammation within the fistula in ano or abscess similarly enhances the
contrast material in peripheral structures or peritumoral areas, regardless of
the presence or absence of mucinous adenocarcinomas. Thus, MRI might be
beneficial after inflammation subsides.
Regional lymphadenopathy is a nonspecific finding; however, correlation
with any of the associated MRI findings and clinical data seems to be helpful
in narrowing the range of diagnostic possibilities. Lymph node metastasis was
diagnosed in all five patients showing regional lymphadenopathy. Thus, the
finding of regional lymphadenopathy may be a helpful sign of locally advanced
mucinous adenocarcinoma arising from fistula in ano and lymph node
metastasis.
A previous report suggested that a fistula between the mass and the anus is
a characteristic finding of mucinous adenocarcinoma arising from fistula in
ano [7]. Our results supported
the previous suggestion because all 11 patients with mucinous adenocarcinoma
showed a fistula between the mass and the anus. However, most MR studies were
performed preoperatively to depict the fistula tract. Thus, the majority of
patients had clinically apparent fistula in ano, which often had direct
continuity between the mass and the anus regardless of whether they had
mucinous adenocarcinomas. But this finding may be useful to distinguish
mucinous adenocarcinoma arising from fistula in ano from malignant
transformation of a tailgut cyst, teratoma, or dermoid cyst
[14]. The mucinous
adenocarcinoma shown in Figure
1A mimics malignant transformation of a tailgut cyst; however, the
history of long-standing chronic fistula in ano and the previous MR and CT
findings could easily exclude the presence of a tailgut cyst.
This study had several limitations. First, the reviewers knew the
pathologic diagnosis before the images were evaluated. However, the reviewers
did not know each specific diagnosis and location of mucinous adenocarcinoma
per case. Second, this was a retrospective study of patients from a single
institution. Third, mucinous adenocarcinoma arising from fistula in ano is an
uncommon diagnosis, and the number of cases was small. Fourth, the pool of MR
images was heterogeneous, with different imaging techniques spanning 8 years
between June 1996 and November 2004 during which the technology was
changing.
In conclusion, a single retrospective study cannot be generalized to others
without additional scientific verification. However, MRI provides good detail
and important diagnostic information on patients with long-standing chronic
fistula in ano. Several characteristic MRI findings may help diagnose mucinous
adenocarcinomas arising from fistula in ano.
Acknowledgments
We acknowledge and appreciate the support and assistance provided by
Shigeru Kosuda and Yutaka Sakurai, National Defense Medical College, Japan;
and Murali Cherukuri Krishna, Radiation Biology Branch, National Cancer
Institute, National Institutes of Health (NIH), Bethesda, MD.
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Abstract
Introduction
