AJR 2005; 184:1519-1523
© American Roentgen Ray Society
Tailgut Cyst: MRI Evaluation
Dal Mo Yang1,
Chul Hi Park1,
Wook Jin1,
Suk Ki Chang1,
Jee Eun Kim1,
Soo Jin Choi1 and
Dong Hae Jung2
1 Department of Radiology, Gachon Medical College Gil Medical Center, 1198,
Guwol-Dong, Namdong-Gu, Incheon 405–760, South Korea.
2 Department of Pathology, Gachon Medical College Gil Medical Center, Incheon
405–760, South Korea.
Received June 5, 2004;
accepted after revision August 26, 2004.
Address correspondence to D. M. Yang
(dmyang{at}ghil.com).
Abstract
OBJECTIVE. The purpose of our study was to evaluate the MRI features
of tailgut cysts in five patients.
CONCLUSION. Our results suggest that MRI may be useful in the
diagnosis of tailgut cyst. A multilocular cystic mass in the presacral space
is a characteristic MRI finding of tailgut cyst, which may also be revealed as
a cystic mass consisting of a large cyst accompanied by a small peripheral
cyst. However, further studies are necessary to establish the usefulness of
MRI for evaluating tailgut cysts.
Introduction
Tailgut cyst or retrorectal cystic hamartoma is a rare congenital lesion
thought to arise from vestiges of an embryonic hindgut and is found in the
retrorectal or presacral space
[1]. Although several reports
have described the pathologic features of tailgut cysts
[1–3],
a paucity of information regarding their imaging features is available
[4–8].
To our knowledge, the MRI features of tailgut cysts have been reported only in
case reports
[6–8].
Here, we describe the MRI findings of tailgut cyst.
Materials and Methods
We retrospectively reviewed the medical records and radiologic features of
tailgut cysts in five consecutive patients who presented between 1996 and
2003.
All five patients underwent MRI performed with a 1.5-T scanner (Magnetom
Vision, Siemens) using a surface coil. All patients underwent sagittal and
axial T1-weighted sequences with the following parameters: TR/TE, 600/14; 230
x 256 matrix; 2 excitations; 20-cm field of view; and 6-mm section
thickness with a 1.5-mm gap. All patients underwent sagittal and axial
T2-weighted imaging with the following parameters: 4,300/132; echo-train
length of 16; 240 x 256 matrix; 2 excitations; 20-cm field of view; and
6-mm section thickness with a 1.5-mm gap. Four patients also underwent CT. All
MR and CT images were reviewed retrospectively to determine the size,
appearance, and location of the lesions.
All five patients underwent complete surgical excision of the mass. The
pathology reports were reviewed, and the pathologic findings correlated with
the imaging findings. Each patient's clinical history was reviewed.
Results
The clinical, MRI, CT, and pathologic findings in patients with tailgut
cysts are summarized in Table
1. All patients were women, with an age range of 30–67 years
(mean, 44 years). Two of the five patients presented with constipation. Two
had right buttock pain and abdominal pain individually, and the remaining one
had the mass detected incidentally during workup for other medical
problems.
In three of five cases, MRI revealed multilocular cystic masses in the
presacral space (Fig. 1A,
1B,
1C). In the other two cases,
the mass consisted of a large cyst accompanied by a small, peripherally
located cyst, which were both located in the presacral space (Figs.
2A,
2B,
2C,
2D and
3A,
3B). The size of the tailgut
cysts ranged from 4.5 to 12 cm, with a mean of 7.6 cm. All the lesions were
hypointense on T1-weighted images, whereas on T2-weighted images, four of the
lesions showed high signal intensity (Figs.
1A,
1B,
1C,
2A,
2B,
2C,
2D,
3A,
3B) and one showed mixed high
and low signal intensity due to hemorrhage. In one of the five, there were
multiple small foci with low signal intensity within the mass on T2-weighted
images, which corresponded to aggregates of keratin (Fig.
2A,
2B,
2C,
2D). In two cases with a mass
consisting of a large cyst accompanied by a small peripheral cyst, the small
cyst was clearly identified on T2-weighted images. However, in one of the two
cases, a small cyst was not detected on the T1-weighted image (Fig.
3A,
3B).
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Fig. 2A. —45-year-old woman with history of constipation. Enhanced CT
scan shows well-defined hypodense mass (arrow) with thin wall in
presacral space. Rectum (arrowhead) is compressed and anteriorly
displaced.
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Fig. 2C. —45-year-old woman with history of constipation. On
T2-weighted image, mass (arrow) is hyperintense, and small-sized
hyperintense mass (arrowhead) is identified at posterior portion of
large mass.
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Fig. 3B. —31-year-old woman with right buttock pain. On T2-weighted
image, mass (arrow) is hyperintense, and small-sized hyperintense
mass (arrowhead) is identified at posterior portion of large
mass.
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In the four patients who underwent CT, the scans revealed discrete,
well-defined, hypodense, presacral masses with thin walls. These lesions were
unilocular (n = 1) and multilocular (n = 3) on CT.
On gross pathology, these masses were composed of variable-sized cysts
containing keratinous material or mucous fluid in four cases. In the other
case, the cyst contained hemorrhage. In all cases, microscopic examination
revealed fibrous tissue lined by squamous epithelium or a combination of
columnar, squamous, or transitional epithelium
(Fig. 2D).
Discussion
The tailgut or postanal gut is the most caudal part of the hindgut, distal
to the future anus. It normally involutes by the eighth week of embryonic
development. If a tailgut remnant persists, it may give rise to a tailgut cyst
[1]. Tailgut cyst is more
common in women and usually presents in middle age, but it can be discovered
at any age [4,
5]. It is usually detected as
an asymptomatic mass but may be found in patients with abdominal pain or
constipation [4]. Rarely,
malignant transformation of the tailgut cyst has been reported, in which case
adenocarcinoma, carcinoid, neuroendocrine carcinoma, and sarcoma arise within
the cyst
[8–10].
Grossly, tailgut cyst is a multiloculated, cystic mass with a thin wall and
glistening lining and is filled with a mucoid material
[1,
2]. It usually measures several
centimeters in diameter. Infection or inflammation may cause fibrosis of the
cyst wall and breakdown of the cyst lining.
Microscopically, it is characterized by the presence of a cyst lined with
multiple, varying types of epithelium; columnar, mucinsecreting epithelium
predominates, while other areas of squamous and transitional epithelium often
coexist [1].
The radiologic findings on sonography, CT, and MRI have been described.
Sonography shows a multilocular, retrorectal cystic mass. Internal echoes may
be found within the cyst. They are due to the multicystic nature of the mass
and the presence of gelatinous material or inflammatory debris within the cyst
[4]. CT shows a discrete,
well-marginated, presacral mass with water or soft-tissue density, depending
on the contents of the cyst [4,
5]. Calcifications may be seen
in the cyst wall [6]. When the
mass is large, the rectum is displaced by the mass
[6]. If concurrent infection or
malignant transformation occurs, CT may reveal loss of discrete margins and
involvement of contiguous structures
[4].
On MRI, tailgut cyst usually has low signal intensity on T1-weighted images
and high signal intensity on T2-weighted images
[6–8].
However, it may have high signal intensity on T1-weighted images due to
presence of mucinous materials, high protein content, or hemorrhage in the
cyst [7,
9]. In addition, a malignant
change or fibrous tissue within the cyst may show as irregular wall thickening
or a polypoid mass with intermediate signal intensity on both T1- and
T2-weighted images with enhancement after the IV administration of
paramagnetic contrast material
[8,
9]. In most of our cases,
tailgut cysts were hypointense on T1-weighted images and hyperintense on
T2-weighted images. However, one of the five cysts appeared as low signal
intensity on T2-weighted images. This finding correlated with that of
pathology because hemorrhage contributed to the finding.
On MRI, tailgut cyst has been reported with a unilocular or multilocular
cystic appearance
[6–8].
However, Kim et al. [7]
reported that a multilocular appearance with internal septa on T2-weighted
images is a finding unique to tailgut cyst. In our study, three of five cases
had multilocular cystic masses. Interestingly, we observed that the other two
of our five cases had a large cyst accompanied by a small peripheral cyst. In
addition, the multilocular appearance of these cystic masses was more clearly
visualized on MRI than on CT. In one of the four patients who underwent CT,
the cyst appeared unilocular on CT. However, a small cyst was identified at
the peripheral portion of the large cyst on MRI. In addition, the small cyst
was clearly identified on T2-weighted rather than on T1-weighted images.
Therefore, we believe that T2-weighted MR images offer clearer delineation of
the multilocular appearance of the cystic masses and may be useful for the
detection of a small cyst. Kim et al.
[7] asserted that for the
evaluation of a presacral mass, MRI has the advantage over CT of being able to
offer multiplanar capabilities and good tissue contrast. In addition, we
believe that sagittal MRI can be used to assess the relationship of the mass
with the surrounding rectum and boney structures, and MRI may be helpful for
surgical planning of the mass.
Many differential diagnoses should be considered when a presacral cystic
mass is discovered, including epidermoid cyst, dermoid cyst, rectal
duplication cyst, anal gland cyst, cystic lymphangioma, and anterior
meningocele
[11–13].
Distinction of tailgut cyst and other presacral cysts is important because of
the malignant potential of a tailgut cyst
[8]. However, because
substantial overlap exists in the imaging findings of the presacral cysts, it
is difficult to distinguish the imaging appearance of tailgut cyst from that
of many other presacral cysts. Therefore, histologic analysis is essential to
establish a definitive diagnosis of tailgut cyst.
However, in the differential diagnosis of presacral cystic masses, we
believe that the unilocular or multilocular characteristic is also important.
Among the presacral cystic masses, epidermoid cyst, dermoid cyst, rectal
duplication cyst, and anterior meningocele are usually unilocular
[11–13].
In contrast, tailgut cyst and cystic lymphangioma are usually multicystic
[11]. Therefore, careful
analysis is required to determine whether the cystic mass is unilocular or
multilocular. We believe that MRI may be useful for the differentiation of
unilocular and multilocular masses and especially for the detection of a small
peripheral cyst.
Our study was limited by being a retrospective and single-institution
study. In addition, it was limited by the small sample size. Thus, further
study will be necessary to examine more fully the MRI findings of tailgut cyst
and the differentiation of tailgut cysts and other presacral cystic
masses.
Despite its rarity, tailgut cyst should be considered when a multicystic
mass, or one accompanied by a small peripheral cyst, is present in the
presacral space on MRI. Knowledge of these characteristic findings can be
helpful in the distinction of presacral cysts.
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Abstract
Introduction
