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406 Chapter 11 Infectious Diseases and Tropical Medicine
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11.8
11.8
Ascariasis
Worms, also known as “helminthes,” are parasitic infections. Diagnosis is usually made by identifying the worm
eggs in the stool.
Ascariasis is a parasitic disease that arises due to
ingestion of food contaminated by the eggs of the roundworm (nematodes) Ascaris lumbricoides . Most patients
are children between 1–15 years of age. Consuming
uncooked vegetables and drinking polluted water from
wells are important sources of ascariasis infection.
After ingestion of the eggs, the larvae hatch from
the eggs before they reach the intestine, due to stimulation by gastric juices. The larvae penetrate the intestinal wall, enter the bloodstream, and travel via the
portal venous or the lymphatic systems to the liver and
then to the thoracic cavity. When they reach the lungs,
the larvae grow and mature within the lung alveoli.
When the worms are mature enough, they migrate
from the lungs into the bronchi and from the trachea to
the epiglottis, from where they are swallowed into the
intestine for the second time. The matured larvae grow
into adult worms in the intestine, especially the jejunum, and produce eggs that pass out in the feces. Up to
99% of ascarids are found in the jejunum and ileum.
Most patients are asymptomatic, although severe
ascariasis infection can cause abdominal cramps and
malnutrition. The worms may also invade the gallbladder, appendix, liver, or bile duct. Ileocecal intestinal
obstruction, ascending cholangitis, cholecystitis, appendicitis, and liver abscess are documented complications
of ascariasis.
Respiratory symptoms in the form of fever, hemoptysis, cough and pneumonia ( ascariasis pneumonia ) occur
5–26 days postinfection. The alveoli are fi lled with
eosinophils and white blood cells attacking the larvae.
Ascariasis is one of the most common causes of Loffl er’s
syndrome (fever, systemic eosinophilia, asthma, cough
with sputum, and signs of alveolar infi ltration on chest
radiograph). The adult worm can produce a neurotoxin
that can result in neurological manifestations ( ascariasis
encephalopathy ).
Diagnosis is made by identifying the ascaris eggs in
the feces, and pronounced eosinophilia on complete
blood count.
D i ff erential Diagnoses and Related Diseases
Visceral larva migrans ( VLM ) is a disease character-
ized by the invasion and residence of animal parasites
in human tissues for a long time. The disease is often
seen in children, and often caused by Toxocara canis
(from dogs) and Toxocara cati (from cats). Rarely,
VLM can be caused by pig’s roundworm, Ascaris
suum , which is closely related to human roundworm,
Ascaris lumbricoides .
Signs on Chest Radiograph
Signs of patchy alveolar infi ltration.
A pulmonary nodule can occur if the larvae form a granu-
lomatous lesion when they die.
Signs on Ultrasound
In the gallbladder, the ascaris worm is identifi ed as a tubular
structure with nondirectional movement causing a zig-zag
sign. The tubular structure has 3–4 parallel echogenic lines in
longitudinal axis and a target sign in transverse axis.
When the gallbladder is full of worms, echogenic, intralumi-
nal, and spaghetti-like structures are seen.
Signs on Barium enteroclysis
The ascarides are seen as long, tubular fi lling defects within
the intestinal lumen in the jejunum or the ileum (Fig. 11.8.1 ).
The worm may ingest the barium, which will cause its
gastrointestinal opacifi cation, resulting in double contrast
worm appearance around the barium (Fig. 11.8.1 ).
11. 8 A scari a sis 407
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Signs on CT
On bowel oral contrast-enhanced CT, the worm is seen as a
tubular fi lling defect within the bowel loops (Fig. 11.8.2 ).
A thin enhanced line within the tubular defect can be seen
representing contrast within the gastrointestinal tract of
the worm due to contrast ingestion.
In the gallbladder, the worms are seen as tubular, coiled
soft-tissue structures within the gallbladder with no
contrast enhancement. Speckles of curvilinear calcifi cations may be seen.
For Further Reading
Fig. 11.8.1. Barium enteroclysis radiograph of a patient with
ascariasis shows a long, tubular fi lling defect in the jejunum,
with a double contrast sign representing ascaris worm with barium ingestion ( arrowhead )
Fig. 11.8.2. Axial CT illustration demonstrates ascaris worms
within the intestinal bowel loops
1. Kakihara D et al Liver lesions of visceral larva migrans due
to Ascaris suum infection: CT fi ndings. Abdom Imaging.
2004;29:598–602
2 . Robbani I et al Worms in liver abscess: extensive hepatobil-
iary ascariasis. Dig Liver Dis. 2008;40(12):962. doi: 10.1016/j.
dld.2008.03.008
3. Ochoa B. Surgical complications of ascariasis. World J Surg.
1991;15:222–7
4. Maheshwari PR. Gall bladder ascariasis. Clin Radiol Extra.
2004;59:8–10
5. Sherman SC et al The CT diagnosis of ascariasis. J Emerg
Med. 2005;28(4):471–2
6. Slesak G et al Obstructive biliary ascariasis with cholangi-
tis and hepatic abscess in Laos: a case report with gall bladder ultrasound video. J Infect. 2007;54:e233–5
7. Reeder MM. The radiological and ultrasound evaluation of
ascariasis of the gastrointestinal, biliary, and respiratory
tracts. Semin Roentgenol. 1998;33(1):57–78
8. Hayashi K et al Hepatic imaging studies on patients with
visceral larva migrans due to probable Ascaris suum infec-
tions. Abdom Imaging. 1999;24:465–9
408 Chapter 11 Infectious Diseases and Tropical Medicine
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11.9
11.9
Guinea Worm Disease (Dracunculiasis)
Dracunculiasis is an infection of the body by Dracunculus
medinensis , a tissue-invasive round worm (nematode).
The name “Medinensis” is derived from the frequency of human guinea worm infestation near Medina,
a city in Saudi Arabia. It is a disease that is seen in the
Middle East, Asia, and Africa.
The parasite enters the body through drinking water
infected with the larvae, which penetrate the intestine
and enter the blood stream to lie deep within the subcutaneous tissues. The worm can grow under the skin up to
100 cm, and usually exposes its uterus out of the host
body through the skin to release its larvae into the water.
Patients infected with D. medinensis often present
with allergic symptoms, nausea, and vomiting. Patients
also present with skin blisters, sterile abscess, and
(uncommonly) septic arthritis. The worm can be sensed
under the skin within the abscess.
D. medinensis tends to migrate into the lower
extremities, breast, and scrotum. Other sites in the body
might be affected as well. It rarely affects the viscera.
The adult worm can directly invade any joint, resulting in monoarthritis. The knee is the most common joint
involved, resulting in an intense destructive arthropathy ( Ibadan knee ). Other manifestations include sterile
monoarthritis due to immune complexes, also commonly affecting the knee.
The worm is often removed from the skin by driving a small stick under the part of the worm that is
looped out of the skin, and the worm is slowly twisted
to pull it out of the subcutaneous tissues (Fig. 11.9.1 ).
Signs on Radiograph
When the female worm dies, it will calcify, giving an intact, long,
curvilinear, and beaded radio-opaque shadow in the radiograph,
and this is diagnostic. No other parasite condition simulates this
long, beaded full worm calcifi cation within the muscles or the
soft tissues in the body (Figs. 11.9.2 and 11.9.3 ).
Fig. 11.9.2. Anteroposterior plain radiograph of the thoracic
spine shows linear, beaded, radio-opaque shadow in the left
paraspinal region in a patient with dracunculiasis, representing a
dead worm ( arrowheads )
Fig. 11.9.1. An illustration demonstrates the classical method of
extracting the guinea worm from the body. The worm is wrapped
around a stick and slowly pulled out. The worm can be very
long, and the process of pulling the worm out may take days
Fig. 11.9.3. Plain radiograph of the soft tissue of the posterior
thigh in the same patient shows multiple linear and rounded calcifi ed lesions, representing dead intramuscular worms
11.9 Guinea Worm Disease (Dracunculiasis) 409
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For Further Reading
1. Iriemenam NC et al Dracunculiasis – the saddle is virtually
ended. Parasitol Res. 2008;102:343–7
2. Legmann P et al Epidural dracunculiasis. A rare cause of
spinal cord compression. Neuroradiology. 1980;20:43–5
3. Watts S. An ancient scourge: the end of dracunculiasis in
Egypt. Soc Sci Med. 1998;46(7):811–9
4. Muller R. Dracunculiasis medinensis: diagnosis by indirect
fl uorescent antibody technique. Exp Parasitol. 1970;27:
357–61
5. Peng SL. Rheumatic manifestations of parasitic diseases.
Semin Arthritis Rheum. 2002;31:228–47
410 Chapter 11 Infectious Diseases and Tropical Medicine
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11.10
Hydatid Cyst (Echinococcosis)
11.10
Echinococcosis is a disease caused through infection
from the human tapeworms Echinococcus granulo-
sus and Echinococcus multilocularis . Each infection
behaves in a different manner within the human body.
Echinococcus granulosus produces cystic lesions within
the body, while Echinococcus multilocularis produces
tumor-like lesions.
Echinococcus granulosus Disease
Fig. 11.10.1. An illustration shows the gross pathological appearance of hydatid cysts
Infection with E. granulosus is found in the Middle
East, Africa, Mediterranean countries, and Eastern
Europe. The defi nitive hosts for the parasite are dogs
and sheep. Humans are intermediate hosts who are
infected with the parasite by ingesting food contaminated by the defi nitive hosts’ feces or by direct contact
with the defi nitive hosts.
After the parasite is ingested, the eggs hatch, and
the embryos penetrate the intestinal mucosa, enter the
portal circulation, and are carried to various organs.
Any organ can be infected by E. granulosus , but the
liver (75%) and lungs are considered the most common areas for hydatid cyst disease. The original cyst
grows 2–3 cm per year; as the cyst enlarges, it starts to
form internal daughter cysts (Fig. 11.10.1 ).
Patients with E. granulosus infection are often
asymptomatic, unless a cyst is ruptured. A ruptured
cyst usually results in fever, pruritus, eosinophilia, and
fatal anaphylactic shock.
Grading of the Liver Lesions by E. granulosus
On the different radiological imaging modalities, different shapes of the hydatid cyst may be encountered.
This is due to the fact that the cysts undergo different
stages of life and death during the course of the disease
(Fig. 11.10.2 ).
The hydatid cyst walls are composed of three layers. The fi rst layer (pericyst) is made up of compressed
host tissue and infl ammatory cells. The second and the
third walls are the true cyst walls. The second wall is
an outer acellular layer (ectocyst), and the third is an
inner cellular wall (endocyst). The daughter cysts arise
from the endocyst wall.
Grade 1 lesion (purely cystic lesions): This grade is
seen on ultrasound, CT, or MRI as a pure cyst without internal inhomogeneities. This grade is explained
by intact endocysts, and patients with grade 1 lesions
benefi t from percutaneous aspiration and scolecidal
injection therapy.
Signs on Chest Radiograph
Hydatid cyst lesions are seen as a well-circumscribed, round
mass, with no internal texture (Figs. 11.10.2 and 11.10.3 ). It
mimics a solid pulmonary mass, and may lead to a false diagnosis
of pulmonary tumor. Absence of symptoms and presence of other
cystic lesions within the liver are important clues.
Signs on US
On ultrasound, the hydatid cyst shows a double wall ( double-line
sign ). This is an important sign that diff erentiates a grade 1
hydatid cyst from a simple hepatic cyst, which shows a thin
single wall.
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Fig. 11.10.2. An illustration
shows the different stages
of hydatid cysts that may
be encountered during CT
examination: ( a ) pure cystic
form, ( b ) a cyst with multiple
hypodense lesions within
it, ( c ) a cyst with internal
septations, ( d ) fl oating water
lily sign, ( e ) ball of wool
sign, and ( f ) calcifi ed
cystic wall
Fig. 11.10.3. Posteroanterior plain chest radiograph shows two
large masses located at the right middle and lower lung fi elds in
a patient with hydatid liver disease. The masses represent intact
hydatid cysts within the lung
Signs on CT
The cyst appears as a simple cyst with no internal
septations, densities, or contrast enhancement
(Fig. 11.10.4 ).
Grade 2 lesions (lesions with complex morphology
with or without biliary dilatation around the lesion):
This grade is characterized by the appearance of different intracystic textures. These textures arise due
to previous rupture of an endocyst, with hydatid
fl uid leakage into the potential space between the
endocysts and the pericyst. Later, this fl uid causes
different intracystic textures seen on ultrasound, CT,
or MRI.
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11.10
Fig. 11.10.5. Coronal abdominal CT image in a patient with
hepatic and splenic hydatid cyst shows hepatic hydatid cyst with
internal hypodense lesions ( arrowheads ) and splenic hydatid
cyst with calcifi ed wall ( arrow )
Fig. 11.10.4. Axial abdominal CT images show a very large hydatid
cyst that occupies almost the entire right lobe of the liver ( a ), and
the cyst appearance after aspiration of the cyst contents ( b )
Signs on US, CT, and MRI
Internal septations with honeycomb-like appearance can be
seen on ultrasound, CT, and MRI. (Fig. 11.10.2 )
Small internal echoes may be seen on ultrasound, refl ecting
fl oating protoscoleces ( snow fl akes sign ).
The daughter cysts may be seen as multiple hypodense
lesions, compared to the density of the original cyst on CT
(Figs. 11.10.5 and 11.10.2 ).
Grade 3 lesions (lesions with intrabiliary rupture):
Because the cyst is originally formed within the liver
tissue, which in turn contains biliary canaliculi,
cysto-biliary communication may occur as an uncommon complication. This grade is characterized by
intrahepatic biliary dilatation with hydatid vesicle
escape from the mother cyst into the biliary radicals,
causing regional biliary obstruction (Fig. 11.10.6 ).
Fig. 11.10.6. Axial CT illustration demonstrates grade 3 hydatid
cyst disease. Notice the right lobe cyst with dilated biliary radicals around it, with an intrabiliary daughter cyst ( arrow )
Grade 4 lesions : This grade is characterized by
rupture of the pericyst and the endocysts, with
spillage of the cyst content into the neighboring
organs or spaces. Leakages of the hydatid fl uid
into the peritoneum causes severe irritation andperitonitis. Later, peritoneal calcifi cation arises
(Fig. 11.10.7 ).
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This sign is known as the “ fl oating water lily sign ”
(Figs. 11.10.8 and 11.10.2 ). Degeneration of cysts is
seen as multiple, solid-like lesions within the mother
cyst, resulting in a pseudotumor appearance on ultrasound or CT, known as the “ ball of wool sign ”
(Figs. 11.10.9 and 11.10.2 ). Finally, circular or curvi-
linear calcifi cation of the hydatid cyst wall is a sign
of inactive disease (Figs. 11.10.10 and 11.10.2 ).
Fig. 11.10.7. Plain abdominal radiograph in a patient with previous intraperitoneal ruptured hydatid cyst shows multiple calcifi cations involving the mesentery and the intraperitoneal structures
Grade 5 lesions : This grade is characterized by death
of the cyst (inactive disease). It is seen as collapse of
the hydatid membrane (pericyst) over the residual
endocysts. This is seen on plain radiographs, CT, and
MRI as a thick wall plus an irregular, wavy, waterfl uid level fl oating on top of the residual hydatid fl uid.
Fig. 11.10.9. Ultrasound image of a liver hydatid cyst shows internal, multiple, solid-like lesions within the cyst (ball of wool sign)
Fig. 11.10.8. Posteroanterior plain chest radiograph shows ruptured hydatid cyst with fl oating water lily sign ( arrowheads ).
Notice the cystic wall mimicking a cavity ( arrow )
Fig. 11.10.10. Lateral plain radiograph of the thoracic spine
shows a calcifi ed hydatid cyst in the paraspinal region
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11.10
D i ff erential Diagnoses and Related Diseases
Hepatic atrophy–hypertrophy complex (HAHC) : obstruc-
tion of a major hepatic or portal vein or biliary tree
branch results in atrophy of the hepatic segment supplied by this vein or biliary branch. As the liver has
the ability to regenerate, compensatory hypertrophy
of the liver is usually seen when a large segment of the
liver parenchyma is atrophied. This phenomenon is
known as the HAHC. HAHC may occur uncommonly
as a complication of hydatid cyst disease, especially
when the cyst occupies a large area within the right
lobe of the liver. It is important for HAHC to be documented by the radiologist, because it informs the surgeon that the cyst is tightly involved with one or more
of the portal triad structures or a major hepatic vein
(Fig. 11.10.11 ).
How does one differentiate between ruptured hydatid
cyst and acute abscess?
The wall of the abscess is enhanced after contrast
injection on CT, while the hydatid cyst wall will not
enhance.
The air-fl uid level surface is straight in the abscess,
while in the hydatid cyst it has a wavy water surface due to the collapsed pericyst (fl oating water
lily sign).
Echinococcus alveolaris Disease
Infection with E. multilocularis is found in the United
States, Canada, Japan, and Central and Northern
Eurasia. The defi nitive hosts for E. multilocularis are
foxes and rodents. Like E. granulosus , humans are
intermediate hosts who are infected via ingesting food
or water contaminated with the eggs or by direct contact with the defi nitive hosts.
In contrast to E. granulosus , E. multilocularis cysts
are not confi ned within a pericyst layer, and grow by
external vesiculation. The cyst is small (1–10 mm in
diameter), and forms multilocular alveolar cysts that
resemble lung alveoli, hence the name alveolaris . The
external parasitic proliferation initiates a fi broinfl ammatory response of the host within the affected organ,
commonly the liver. This will later result in a fi brous,
tumor-like lesion composed of E. multilocularis embed-
ded in a keloid scar and necrotic liver tissue. Stenosis
of the porta hepatic with the hepatic veins within the
lesion is commonly found. When the lesion heals,
multiple, punctuate calcifi cations arise within the
lesion, which makes the lesion increasingly resemble a
malignant hepatocellular carcinoma (HCC) or metastasis of the liver.
Fig. 11.10.11. Axial CT illustration shows the hepatic atrophy–
hypertrophy complex. Notice the large hydatid cyst occupying a
large portion of the right lobe of the liver ( arrowhead ), with
compensatory hypertrophy of the left liver lobe ( arrow )
Signs on US
In the liver, there are multiple echogenic nodules embedded
within irregular and indistinct margins from the normal hepatic
parenchyma ( hailstorm sign ).
Signs on CT
The liver often shows a hypodense mass with a “geographic
map” appearance and inhomogeneous internal texture
(Fig. 11.10.12 ).
Areas of punctuate calcifi cations within the lesions are very
common in healed lesions (90% of cases). (Fig. 11.10.12 )
Unlike HCC, the lesion shows no enhancement or mild
enhancement in the portal venous phase because of the
fi brous stroma within the mass (characteristic and diagnostic).
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Areas of central liquefaction may be seen.
There are no signs of retroperitoneal lymphadenopathy
(another diff erentiating point from HCC).
Signs on MRI
The scan shows an inhomogeneous mass with geographic
margins and characteristically low T1 and low T2 signal
intensities, with no enhancement or mild enhancement after
contrast enhancement in the portal venous phase (Fig. 11.10.13 ).
Fig. 11.10.12. Axial nonenhanced abdominal CT in a patient
with Echinococcus alveolaris disease affecting the left lobe of
the liver shows liver mass with geographic edges ( arrowheads )
and internal punctuated calcifi cations
For Further Reading
1. Czermak BV et al Echinococcosis of the liver. Abdom
Imaging. 2008;33:133–4
2. Etlik Ö et al Contrast-enhanced CT and MRI fi ndings of
atypical hepatic Echinococcus alveolaris infestation. Pediatr
Radiol. 2005;35:546–9
3. Rozanes I et al Grading of liver lesions caused by Echinococcus
granulosus . Eur Radiol. 1993;3:429–33
4. Karabulut K et al Hepat ic atrophy-hypertrophy complex due to
Echinococcus granulosus . J Gastrointest Surg. 2006;10:407–12
5. Katranci N et al Correlation CT, MRI and histological fi nd-
ings of hepatic Echinococcus alveolaris : a case report.
Comput Med Imaging Graph. 1999;23:155–9
6. Sasaki F et al Alveolar echinococcosis of the liver in chil-
dren. Pediatr Surg Int. 1994;9:32–4
Fig. 11.10.13. Axial T1W ( a ) and T2W ( b ) nonenhanced MR
images in a patient with Echinococcus alveolaris disease show a
mass that resembles HCC ( arrowheads ), with multiple cystic
lesions within the mass. Notice that the mass bulk is hypointense
on T2W image ( b ) due to the fi brous (keloid) nature of the lesion
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