AJR 2003; 181:1349-1354
© American Roentgen Ray Society
Gastrointestinal and Genitourinary Smooth-Muscle Tumors
Margaret T. Betts1,
Eugene J. Huo and
Frank H. Miller
1 All authors: Department of Radiology, Northwestern University Medical School,
Ste. 800, 676 N St. Clair, Chicago, IL 60611.
Received December 2, 2002;
accepted after revision March 3, 2003.
Address correspondence to F. H. Miller
(fmiller{at}northwestern.edu).
Introduction
Leiomyomas are benign tumors of smooth muscle. They occur most commonly in
the uterus but may be found wherever there is smooth muscle. Differentiation
from their malignant counterpart, leiomyosarcomas, is difficult on both
imaging studies and histology. The presence of metastases is the only
definitive sign of malignancy. The terminology used for tumors arising from
smooth muscle of the gastrointestinal tract was recently reassessed. A
previously used term "gastrointestinal stromal tumor" or
"GIST" was used to denote any tumor arising in the stroma of the
gastrointestinal tract including leiomyoma or leiomyosarcoma. This term should
no longer be used as such. Because of recent advances in immunohistochemistry
and genetic markers, the term "GIST" should be reserved for only
those tumors expressing c-kit protooncogene and the CD34 antigen. The
smooth-muscle terminology of leiomyoma or leiomyosarcoma is still used in the
intestinal tract if there is clear evidence of this differentiation—for
example, in esophageal tumors
[1]. The purpose of this
pictorial essay is to review the imaging appearance of smooth-muscle tumors of
the gastrointestinal and genitourinary tracts and highlight the features that
are most helpful for diagnosis.
Esophagus
Smooth-muscle tumors of the esophagus occur with greatest frequency in the
middle and lower thirds of the esophagus
[2]. Leiomyomas generally occur
as intramural eccentric lesions. By contrast, leiomyosarcomas tend to grow
intraluminally. Because of their intramural location, leiomyomas produce
characteristic signs on barium swallow studies
(Fig. 1). Similar appearances
occur with other benign mesenchymal tumors such as schwannomas, neurofibromas,
and lipomas. CT is useful for establishing the intramural location of the
tumor and distinguishing it from a lipoma or extrinsic mass. A large (> 5
cm) heterogeneous mass suggests a leiomyosarcoma and, if ulcerated, may appear
indistinguishable from adenocarcinoma.
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Fig. 1. —40-year-old woman with esophageal leiomyoma. Esophagram shows
welldefined smooth filling defect (arrows). Note intact mucosa and
sharp angle tumor makes with adjacent esophageal wall, typical of submucosal
lesion.
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Stomach
Smooth-muscle tumors of the stomach are rare. Bleeding is the most common
presenting sign. On endoscopic sonography, these tumors can be identified as a
homogeneous hypoechoic mass in the muscularis mucosa or muscularis propria. On
CT, they are well-marginated homogeneous low-attenuation masses. They commonly
exhibit intraluminal growth (Fig.
2A). Calcification (Fig.
2B) and surface ulceration can occur. Early phase
contrast-enhanced CT may show the gastric mucosa enhancing to a greater degree
than the tumor, highlighting its submucosal origin (Fig.
3A,
3B,
3C). Malignant smooth-muscle
tumors tend to be large (> 5 cm) with a prominent exogastric component
(Fig. 4). They are
heterogeneous (Fig. 5) and are
frequently ulcerated. Central necrosis is common. Smooth-muscle tumors spread
by direct extension into adjacent organs, intraperitoneal seeding, or
hematogenous metastasis to the liver, lung, and bone
(Fig. 6). Leiomyosarcomas
infrequently metastasize to regional lymph nodes and can be confused with
metastatic adenocarcinoma or lymphoma
[3].
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Fig. 2B. —36-year-old man with leiomyoma of stomach. Axial CT scan
obtained with patient in prone position shows 6 x 4 cm intraluminal mass
(black arrow) with dense central calcification. Enlarged node
(white arrow) was removed and found to be benign.
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Fig. 3A. —44-year-old woman with gastric leiomyoma discovered
incidentally during investigation of three hepatic hemangiomas. Arterial phase
contrast-enhanced CT scan shows homogeneous low-density 1.5-cm mass in wall of
stomach (solid straight arrow). Note greater enhancement of stomach
mucosa (open arrow) in contrast to mass. This feature helps to
identify submucosal location of tumor. Two hepatic hemangiomas (curved
arrows) are also seen on this image.
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Fig. 3B. —44-year-old woman with gastric leiomyoma discovered
incidentally during investigation of three hepatic hemangiomas. Axial
T2-weighted HASTE image (TR/TE, 1,000/60; flip angle, 150°) shows tumor
(white arrow) to be isointense to stomach wall. This contrasts with
high signal intensity of hemangiomas (black arrows).
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Fig. 3C. —44-year-old woman with gastric leiomyoma discovered
incidentally during investigation of three hepatic hemangiomas. Axial
contrast-enhanced fat-suppressed T1-weighted image (165/2.3; flip angle,
70°) shows well-defined, smooth, uniformly enhancing lesion
(arrow) arising from stomach wall. Note nodular peripheral
enhancement of hepatic hemangiomas.
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Fig. 4. —67-year-old man with gastric leiomyosarcoma. Axial
contrast-enhanced CT scan shows large exophytic mass arising from stomach wall
(arrow). Its large size, prominent exogastric growth, and lobulated
margins are features suggestive of malignancy.
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Fig. 5. —50-year-old man with gastric leiomyosarcoma. Axial
contrast-enhanced CT scan shows exophytic mass arising from stomach wall
(straight arrow). Note heterogeneity of tumor with areas of higher
density representing hemorrhage (curved arrow).
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Fig. 6. —68-year-old man with recurrent leiomyosarcoma of gastric
antrum with metastases. Axial contrast-enhanced CT scan obtained 9 months
after resection shows 5-cm perihepatic mass (black arrow) along with
multiple high-density intraperitoneal implants (white arrows).
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Small Intestine
Stromal tumors may be located throughout the small intestine. These tumors
are highly vascular, and bleeding is the most common single presenting sign
[4]. On barium examinations,
they appear as smooth intraluminal masses
(Fig. 7A). The overlying
mucosa may be effaced or ulcerated. On CT, leiomyomas appear as round sharply
defined masses of homogeneous soft-tissue attenuation and show uniform
enhancement. Leiomyosarcomas of the small intestine are similar in appearance
to their gastric counterparts: typically large extraluminal heterogeneous
masses, often with central necrosis or cystic degeneration. Despite the large
size of the masses (Fig. 7B),
these tumors may not cause obstruction, which is similar to small-bowel
lymphoma and unlike adenocarcinoma.
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Fig. 7A. —71-year-old man with leiomyosarcoma of ileum. Small-bowel
barium study shows large polypoid mass with intraluminal component
(arrows) that was found to be nonobstructive despite its large
size.
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Kidney
Renal leiomyomas have been categorized into three types: small subcortical
lesions, which are the most common and incidentally detected at autopsy or
surgery; large solitary masses originating in the renal vessels or capsule,
usually causing clinical symptoms; and those arising from the renal pelvis.
Renal leiomyomas are indistinguishable from leiomyosarcomas. Their imaging
appearances are extremely variable
[5]. They may be purely cystic,
purely solid, or have mixed components. On CT, large lesions tend to be
heterogeneous in both attenuation and enhancement
(Fig. 8A). On MRI, the tumors
are isointense with muscle on T1-weighted images and of heterogeneous signal
intensity on T2-weighted images. Tumors arising from the capsule or cortex are
indistinguishable from renal cell carcinoma. Tumors arising from the renal
pelvis are rare but may mimic a transitional cell carcinoma
(Fig. 8B).
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Fig. 8B. —53-year-old man with leiomyosarcoma of renal pelvis. Coronal
contrast-enhanced fat-suppressed T1-weighted image (TR/TE, 107/2.0; flip
angle, 60°) shows tumor arising from renal pelvis. It enhances
heterogeneously and to a lesser degree than renal cortex (arrow).
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Bladder
Leiomyoma, although rare overall, is the most common benign neoplasm of the
bladder (Fig. 9A,
9B,
9C). Tumor growth is most
commonly intravesical (63%), is often extravesical (30%), and only
occasionally intramural (7%)
[6]. On excretory urography or
cystography, the intravesical component is seen as a well-defined smooth
intraluminal mass forming sharp angles of interface with the bladder wall. On
MRI, leiomyomas are typically isointense to the bladder wall. They show a
variable pattern of enhancement, with some enhancing homogeneously and others
with little or only peripheral enhancement. Identification of its submucosal
location and smooth margins helps to distinguish leiomyomas from transitional
cell carcinomas. Leiomyomas and leiomyosarcomas cannot be consistently
differentiated. However, large size, heterogeneity, and irregular margins are
features of leiomyosarcoma.
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Fig. 9A. —46-year-old man with leiomyoma of bladder. Axial T1-weighted
fat-suppressed image (TR/TE, 195/2.0; flip angle, 70°) shows 6 x 4
cm mass (arrows) with both intra- and extravesical components. Tumor
has signal intensity similar to that of bladder wall.
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Vulva
Smooth-muscle tumors of the vulva are rare. Leiomyomas are almost
impossible to distinguish from leiomyosarcomas. A large tumor with
infiltrative margins is more likely to be malignant
[7]. To our knowledge, the MRI
appearances have not been reported, but in our experience, they are
well-defined, homogeneous, and isointense to muscle and enhance vividly after
contrast administration (Fig.
10A,
10B,
10C).
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Fig. 10A. —34-year-old woman with leiomyoma of vulva. Axial T1-weighted
image (TR/TE, 691/15; flip angle, 90°) shows well-defined homogeneous 4
x 3 cm tumor (arrow), which is isointense to muscle.
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Fig. 10C. —34-year-old woman with leiomyoma of vulva. Sagittal
contrast-enhanced fat-suppressed T1-weighted image (183/2.6; flip angle,
70°) more clearly depicts vulvar origin of tumor (arrows) than
A and B.
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Conclusion
Smooth-muscle tumors can occur throughout the body but are rare outside the
uterus. Regardless of site of the smooth-muscle tumor, differentiation of
benign tumors from their malignant counterparts is difficult on imaging.
Imaging studies are useful not only to identify the exact origin of the tumor,
but also to assess its margins and involvement of adjacent organs and to
identify metastases.
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