DOI:10.2214/AJR.07.2255
AJR 2007; 189:337-343
© American Roentgen Ray Society
Extrahepatic Abdominal Hydatid Disease Caused by Echinococcus granulosus: Imaging Findings
Ahmet Turan Ilica1,
Murat Kocaoglu2,
Nazif Zeybek3,
Suleyman Guven4,
Ibrahim Adaletli1,
Alin Basgul5,
Hidayet Coban6,
Aslan Bilici7 and
Yasar Bukte7
1 Clinic of Radiology, Diyarbakir Military Hospital, Diyarbakir, Turkey
21100.
2 Department of Radiology, Gulhane Military Medical Academy, Ankara,
Turkey.
3 Department of General Surgery, Gulhane Military Medical Academy, Ankara,
Turkey.
4 Clinic of Obstetrics and Gynecology, Diyarbakir Military Hospital, Diyarbakir,
Turkey.
5 Department of Obstetrics and Gynecology, School of Medicine of Marmara
University, Istanbul, Turkey.
6 Clinic of Urology, Diyarbakir Military Hospital, Diyarbakir, Turkey.
7 Department of Radiology, School of Medicine of Dicle University, Diyarbakir,
Turkey.
Received January 25, 2007;
accepted after revision April 18, 2007.
Address correspondence to A. T. Ilica
(aturca2002{at}yahoo.com).
Abstract
OBJECTIVE. The classical findings in hydatid disease caused by
Echinococcus granulosus with liver or lung involvement are well
known. However, diagnosing hydatid disease at unusual locations may be
challenging because of variable imaging appearances depending on the host
reaction. The purpose of this pictorial essay is to review the sonographic,
CT, and MRI features of extrahepatic abdominal hydatid disease including
intraperitoneum, retroperitoneum, diaphragma, bone, and soft tissue of the
abdomen.
CONCLUSION. Extrahepatic abdominal hydatid lesions have nearly
identical imaging features, including the presence of cyst wall calcification,
daughter cysts, and membrane detachment. The combinations of radiologic and
serologic tests especially in patients living in the endemic areas contribute
to the diagnosis. Despite their rarity, being familiar with the spectrum of
radiologic findings in these unusual sites is helpful to improve diagnostic
accuracy.
Keywords: abdominal imaging • CT • extrahepatic hydatid disease • MRI • sonography
Introduction
Hydatid disease (HD) is a zoonotic infection caused by
Echinococcus granulosus and rarely by Echinococcus
multilocularis. The disease is often manifested by slowly growing cystic
masses and continues to be a significant health problem in many sheep- and
cattle-raising areas [1].
Although the liver (75%) and lung (15%) are the most commonly involved organs,
the disease can be seen anywhere in the body (10%)
[2,
3].
Imaging findings range from purely cystic lesions to solid-appearing
masses. Ringlike or total calcification can be seen during the natural
evolution and is more common in the liver, spleen, and kidney
[1]. The endocyst may detach
from the pericyst causing "floating membranes" inside the cavity,
a finding that is highly specific for hydatid disease. The cyst may appear as
a well-defined fluid collection with a localized split in the wall. Complete
detachment of the membranes inside the cyst has been referred to as the
"water lily sign" on sonography
[4-6].
Multivesicular cysts manifest as well-defined fluid collections in a honeycomb
pattern, with multiple septa representing the walls of the daughter cysts.
When daughter cysts are separated by the hydatid matrix (a material with mixed
echogenicity), they show a "wheel spoke" pattern
[7].
Sonography is the most sensitive technique for the detection of membranes,
septa, and hydatid sand within the cyst. CT may display the same findings as
sonography and is best in showing cyst wall calcification, cyst infection, and
peritoneal seeding. MRI shows the characteristic low-signal-intensity rim of
the hydatid cyst on T2-weighted images
[8].
The aim of this study was to show the sonographic, CT, and MRI features of
surgically confirmed abdominal HD caused by E. granulosus at various
locations including the whole extrahepatic intraabdominal organs,
intraperitoneum, retroperitoneum, diaphragma, bone, and soft tissue in the
abdomen.
Intraperitoneum and Retroperitoneum
Intraperitoneal HD accounts for 13% of all abdominal hydatidosis. The cysts
develop secondary to spontaneous or iatrogenic rupture of hepatic, splenic, or
mesenteric cysts and can be located anywhere in the peritoneum. Primary
peritoneal involvement is extremely rare
[7]. Single and unilocular
peritoneal hydatid cysts may not be distinguished from other peritoneal cysts
including mesenteric and duplication cysts on the basis of imaging findings
alone. Isolated retroperitoneal HD is also rare and usually secondary to the
involvement of liver [1] (Figs.
1A,
1B,
1C,
2,
3A,
3B,
4A,
4B,
4C,
4D,
5,
6A,
6B,
7).
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Fig. 1A —Intraperitoneal hydatid disease (HD) in 20-year-old woman with
history of liver HD. Axial sonogram of abdomen through level of gallbladder
shows cyst (arrow) compressing gallbladder (star). Cyst has
split wall in its posterior (arrowhead). This appearance is caused by
separation of laminated membrane from pericyst and is characteristic for
hydatid cysts.
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Fig. 1B —Intraperitoneal hydatid disease (HD) in 20-year-old woman with
history of liver HD. Axial T1-weighted MR image shows cyst near gallbladder
and double rim is seen on posterior surface, with hyperintense pericyst
located more externally (black arrow) and hypointense middle membrane
situated internally (white arrow).
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Fig. 1C —Intraperitoneal hydatid disease (HD) in 20-year-old woman with
history of liver HD. Axial T2-weighted MR image shows characteristic dark rim
of pericyst (arrowhead). Star = gallbladder.
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Fig. 2 —Rectovesical hydatid disease in 25-year-old woman complaining of
constipation. Contrast-enhanced CT image shows low-attenuation mass
(arrow) with radially oriented internal septae displacing rectum
(arrowhead).
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Fig. 3A —Disseminated intraperitoneal hydatid disease in 17-year-old girl who
presented with constipation and bilateral flank pain. Contrast-enhanced axial
CT image shows multiple intraperitoneal purely cystic masses (arrows)
and marked bilateral hydronephrosis (stars).
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Fig. 3B —Disseminated intraperitoneal hydatid disease in 17-year-old girl who
presented with constipation and bilateral flank pain. Sagittal reformatted CT
image reveals unilocular, thick-walled retrovesical cyst (arrowhead)
displacing distal ureter causing hydronephrosis.
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Fig. 4A —Intraperitoneal hydatid disease (HD) in 20-year-old man complaining
of epigastralgia. Axial sonogram of epigastrium shows large cystic lesion
(arrow) containing multiple peripheral rounded smaller cysts and
solid part (arrowhead), which settles in dependent part of cyst
pointing matrix or detached membrane, consistent with hydatid cyst
("wheel spoke" pattern).
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Fig. 4B —Intraperitoneal hydatid disease (HD) in 20-year-old man complaining
of epigastralgia. Axial T2-weighted MR image shows large epigastric hydatid
cyst (arrow) containing multiple daughter cysts displacing stomach
and liver HD (arrowhead). There is also heterogeneous hypointense
lesion in splenogastric space (star).
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Fig. 4C —Intraperitoneal hydatid disease (HD) in 20-year-old man complaining
of epigastralgia. Coronal contrast-enhanced CT image reveals rupture of
splenic hydatid cyst (arrow) into splenogastric space
(star). HD of liver (arrowhead) is also seen.
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Fig. 4D —Intraperitoneal hydatid disease (HD) in 20-year-old man complaining
of epigastralgia. Axial contrast-enhanced CT image above bladder shows another
cyst with enhancing pericystic wall and barely seen internal septa
(arrow).
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Fig. 5 —Disseminated abdominal hydatid disease in 17-year-old girl with
abdominal pain. Axial contrast-enhanced CT image shows intraperitoneal
uniloculated and multiloculated cysts (black arrowheads) and multiple
liver (white arrowheads) and spleen (thick white arrows)
cysts. Pancreas (thin white arrows) has thickened and heterogeneous
appearance as consequence of hydatid involvement.
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Fig. 7 —Retroperitoneal hydatid disease in 25-year-old woman with right
flank pain. Axial contrast-enhanced CT image shows cystic mass
(arrow) extending to right lumbar region with barely seen central
hydatid matrix (star) in right posterior pararenal region. Large
hydatid cyst is also seen in liver (arrowhead).
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Spleen
Involvement of the spleen is relatively rare and is the third most common
site after the liver and lungs. The incidence of splenic involvement has been
reported to be from 0.9% to 8%
[1]. Primary splenic
hydatidosis is quite rare and accounts for less than 2%
[9]. It develops secondary to
systemic dissemination or intraperitoneal spread from ruptured liver hydatid
cysts. Splenic and hepatic cysts are commonly solitary and show the classical
radiologic appearance of HD (Figs.
8A,
8B,
9,
10,
11A,
11B,
11C). The differential
diagnosis of splenic hydatidosis includes epidermoid cysts, pseudocysts,
abscess, hematoma, and neoplasms
[9].
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Fig. 8B —Involvement of spleen in 20-year-old man with liver and peritoneal
hydatid disease (HD). Contrast-enhanced axial CT shows hypoattenuating lesion
(black arrow) in spleen with speck of calcification (black
arrowhead) on lateral wall and epigastric (white arrow) and
liver HD (white arrowhead).
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Fig. 9 —Isolated hydatid disease (HD) of spleen in 50-year-old woman who
presented with painful mass in left upper quadrant. Axial contrast-enhanced CT
image shows multiloculated cystic mass with multiple peripheral daughter cysts
and dense matrix in center (arrow), typical of HD.
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Fig. 10 —93-year-old woman with spleen lesion incidentally discovered on CT
during investigation for urinary stone disease. Axial contrast-enhanced CT
image shows heavily calcified mass that contains detached membranes
(arrow).
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Pancreas
Primary pancreatic involvement is very rare (0.25% of the cases), and it is
often associated with hepatic disease
[10]. The diagnosis of a
hydatid cyst in the pancreas is extremely difficult on the basis of imaging
findings without a high index of suspicion. The cyst may easily be confused
with a pseudocyst of the pancreas. However, the presence of a thickened and
more laminated wall than a simple cyst and a thin layer of calcification
within the lesion associated with liver HD may suggest a hydatid cyst
(Fig. 12). The differential
diagnosis includes pseudocyst, serous cystadenoma, and mucinous cystic
neoplasm [10].
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Fig. 12 —Hydatid disease of pancreas in 42-year-old woman with 6-month
history of epigastric pain. Axial contrast-enhanced CT image shows
uniloculated cystic mass (arrow). Diagnosis was only made by means of
positive serology and was confirmed by surgery.
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Genitourinary Tract
Involvement of kidney is rare (3%)
[1]. Cysts are usually
unilateral and located in the upper or lower pole. Eighteen percent of renal
hydatid cysts have been reported to rupture into the collecting system,
leading to acute colic and hydatiduria. However, primary HD of these
structures is extremely rare
[1]. Imaging findings consist
of a polar-located unilocular or multiloculated cyst usually with a daughter
cyst showing lower attenuation on CT (Fig.
13). Mural calcification may also be present. The differential
diagnosis of renal hydatidosis includes simple or infected renal cyst,
abscess, and necrotic neoplasm
[2].
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Fig. 13 —Primary hydatid disease of kidney in 21-year-old man who presented
with flank pain. Axial unenhanced CT image through upper pole of right kidney
shows large cyst (arrow) with daughter cyst (arrowhead) in
its periphery, which has typically lower attenuation than mother cyst.
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Hydatid cysts of the adrenal gland are also rare, with an incidence at
autopsy of 0.06-0.18% [11]. HD
accounts for only 6-7% of all adrenal cysts and is usually secondary to
generalized HD. Rarely, the echinococcal infection is limited to an adrenal
gland. Early lesions appear as simple cysts. After some modifications in the
cysts, daughter cysts and floating membranes in the lumen or calcification may
be seen (Fig. 14). The
differential diagnosis of adrenal hydatidosis includes endothelial cysts,
lymphangiomatous and angiomatous cysts, pseudocysts, cystic degeneration of
benign or malignant adrenal neoplasms, and epithelial cysts
[11].
HD of the female genital tract is extremely rare. In the majority of
reported cases, hydatid cysts were either found at multiple sites in the
abdomen and pelvis or had developed after rupture or surgery for primary
disease of the abdominal organs
[12]. The ovaries are the
leading site of involvement in such cases. In the involvement of the uterus,
which is extremely rare, hydatid vesicles may be found in the vagina during
the examination. There are many similarities between the hydatid cyst and
other pelvic malignant diseases on the basis of imaging findings. Daughter
cysts may resemble septal structures and mimic complicated ovarian cysts and
even ovarian malignancy (Figs.
15 and
16A,
16B). HD should be considered
in the differential diagnosis of cystic pelvic masses, especially in endemic
areas [13].
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Fig. 15 —Hydatid disease (HD) of uterus in 72-year-old woman who presented
with pelvic pain. Axial contrast-enhanced CT image shows cystic mass
(arrow) in uterus associated with liver HD (not shown).
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Diaphragma
Diaphragmatic localization is very rare, with an incidence of 1%, and most
of these are generally associated with liver disease
[14]. Multiplanar
thoracoabdominal MRI or reformatted CT scans may help to show its
topographical relationships and pulmonary and hepatic involvement. The CT
findings consist of thickened and lobulated diaphragma with unilocular or
multilocular cysts. Cysts may split the leaves of the diaphragma. CT is
valuable for visualizing transdiaphragmatic migration of hydatid disease and
evaluating the thoracic component (Fig.
17).
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Fig. 17 —Involvement of diaphragma in 21-year-old woman with known liver
hydatid disease. Contrast-enhanced CT shows marked thickening of diaphragm
(arrows), which contains small daughter cysts
(arrowheads).
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Abdominal Bone and Soft Tissues
Primary soft-tissue involvement by HD is uncommon even in endemic areas and
represents 0.5-4.7% of patients
[3]. Primary focus within
muscle in the absence of pulmonary or hepatic involvement is very unusual.
Imaging findings are variable and nonspecific including unilocular cyst,
multilocular cyst, and complex solid lesion. The frequency of osseous
involvement in HD is 1-2.4%
[15]. It is most commonly seen
in the spine and pelvis. Imaging findings include a well-defined, typically
multiloculated, osteolytic lesion with expansion of the bone, thinning of the
cortex, and extension into the adjacent soft tissue. The extraosseous
component may calcify, but the intraosseous component rarely shows
calcification [1] (Figs.
18 and
19).
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Fig. 18 —Hydatid disease (HD) of abdominal wall (arrowhead) in
10-year-old girl who presented with painful mass. Axial unenhanced CT image
shows simple cyst of lateral abdominal wall. Associated liver HD made
diagnosis easier in this patient.
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Fig. 19 —Musculoskeletal involvement of left sacroiliac region in 59-year-old
man who presented with left lower extremity pain and diminished arterial
pulses. Axial contrast-enhanced CT image shows cystic masses involving left
psoas muscle (arrow), sacrum, ileum (black arrowhead), and
gluteus muscles (white arrowhead). (Reprinted with permission from
[15] Kizilkaya E, Silit E,
Basekim C, Karsli AF. Hepatic, extrahepatic soft tissue and bone involvement
in hydatid disease. Turk J Diagn Intervent Radiol 2002;
8:101-104)
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Abstract
Introduction
