2017, Volume 33, Number 1, Page(s) 030-036
Review of Hydatid Cyst with Focus on Cases with Unusual Locations
Sevinç HALLAÇ KESER1, Ayşegül SELEK1, Dilek ECE1, Cem Cahit BARIŞIK2, Sibel ŞENSU3, Gonca Gül GEÇMEN1, Selma ŞENGİZ ERHAN4, Şermin ÇOBAN KÖKTEN1, Nagehan ÖZDEMİR BARIŞIK1, Aylin EGE GÜL1
1Department of Pathology, Dr. Lütfi Kırdar Kartal Educational and Research Hospital, İstanbul, Turkey
22epartment of Radiology Medipol University, İstanbul, Turkey
33Agonist Health Care, İstanbul, Turkey, 4Department of Pathology, Okmeydanı Educational and Research Hospital, İstanbul, Turkey
Keywords: Hydatid cyst, Echinococcosis granulosis, Unusual locations, Fine needle aspiration
This study has been conducted so as to contribute to health statistics of hydatid cyst by the data obtained from our clinic, and to
discuss hydatid cysts in unusual locations.
Material and Method: Cases diagnosed as hydatid cyst at Dr. Lutfi Kirdar Kartal Research and Education Hospital Pathology Clinic between
2007 and 2015 have been evaluated based on criteria such as age, sex and location.
Results: A total of 364 cases, 209 females and 155 males, have been included in the study. The subjects in the cases are aged between 4 and 81
(mean: 38.84). Regarding the sites, 254 (69.8%) of the cases are located in liver, and 53 (14.6%) in the lung. Fifty-seven cases (15.6%) have been
detected in unusual sites other than the lung or liver. The rate of isolated organ involvement, other than the lung and liver, has been found to be
Conclusion: Since hydatid cyst can be found in all the body sites, it should be taken into account in the differential diagnosis of all cystic lesions.
Hydatid cyst (HC), cystic echinococcosis (CE), hydatid
disease (HD), is a zoonotic parasitic disease caused by
Echinococcus granulosus (EG). It threatens human health
and leads to huge economical loss both in our country
and around the world1
. The prevalence of HC shows
regional differences and ranges between 0-79 per 100.000
. Its prevalence amounts to 50-400/100,000,
and its incidence is 3.4/100,000 in Turkey3
EG is a 5 mm long hermaphroditic tapeworm4,5. Dogs
or other carnivores are considered as definitive hosts, while
sheep or other ruminants, as intermediate hosts. After
ingestion of food or water that has been contaminated by
dog feces containing parasite eggs, most of embryos die
in the hepatic capilleries but some of them turn into cysts
and even move to lungs and/or other organs.6-8. While
parasitic larvae develop, cysts are seen in organs, giving the
disease its name, CE or HC8,9. Parasites may settle in
almost every site of the body forming primary HC10.
Liver and lung are reported as the most frequent locations,
yet unusual sites such as peritoneum, retroperitoneum,
spleen, kidney, heart, pelvic, urinary tract, bladder, bone, soft tissue, pancreas, gallbladder, inguinal, supraclavicular,
cerebral, spinal cord, and abdominal wall have also been
described4,6,7,11-29. Secondary HC mostly occurs after
spontaneous or travmatic rupture of a cyst in abdominal
cavity when free protoscolices and/or tiny cysts develop to
become larger cysts10.
During the diagnosis, lung X-ray, ultrasound (USG),
computerized tomography (CT), and magnetic resonance
(MR) were used to locate lesions30,31. Histopathological
examination and detection of three cyst layers that are
the outer layer (pericyst), the middle layer and the inner
germinal (or germinative) layer play a significant role in HC
diagnosis6. Fine neddle aspiration cytology (FNAC) has
lately been introduced for the diagnosis of HC. Laminated
membrane, scolex and hooks can be found in cyst fluid32,33.
HC cases may be seen in many locations of the body; and
when it is localized in unusual regions, this could lead to
certain difficulties with regard to diagnosis. We have aimed
to contribute to health statistics by presenting HC data of
our clinic while discussing HCs with unusual locations.
In the study, 364 cases of HC, diagnosed between June
2007 and June 2015 in our clinic, were included. Based
on the archival records, cases were reviewed for age, sex,
and locations. Histology slides were re-evaluated by two
pathologists (SHK, AS), and patients were grouped based
on their sex, age and the location of HCs. Five groups
were formed based on age. Patients, 0-14 yrs of age was
considered Group 1; those aged 15-29 were in Group 2;
those aged 30-44 yrs in Group 3; 45-59 yrs in Group 4, and
those above the age of 60 were included in Group 5. All
the cases were classified based on the locations, number of
lesions or other organ involvements.
Total biopsies (n=250041) were investigated for an 8-year
period. The annual incidence rate of HC was 5.4%. As
for the cases, 209 individuals were female and 155 were
male. The ages of the individuals varied between 4-81 years (mean:38.84). The distribution of the cases based
on the age is presented in Figure 1
. When the cases were
classified by their sites, 254 cases (69.8%) were located
in the liver, and 53 cases (14.6%) in the lung. Besides, 57
cases (15.6%) were detected in unusual sites, other than
the lung or liver. Clinical features of 57 unusual cases were
investigated, and 27 cases revealed a previous diagnosis of
liver HC. Distribution of cases based on involvement sites is
presented in Table I
. To reach a diagnosis, lung X-ray, USG,
CT and MR examinations have been used based on the
features of the cases (Figure 2A,B
). In the histopathological
examination of all cases, we have searched structures
in conjunction with HC to be able to come up with a
definite diagnosis (Figure 3A,B
). In three of our cases, HC
was diagnosed solely with FNAC. In one case, structures
resembling HC were seen in bronchial lavage. In 40 of the
cases, both biopsy and cytology materials revealed findings
in conjunction with HC. No reaction or complication was
recorded after FNAC (Figure 4A-D
Click Here to Zoom
|Figure 2: A) MR image of
hydatid cysts that include
multiple daughter cysts
and semisolid areas in liver
and spleen. B) MR image
of hydatid cyst in the lower
pole of the right kidney.
Click Here to Zoom
|Figure 3: A) Pericyst and membrane structures in
hydatid cyst localized in the bladder. B) Acellular
eosinophilic laminated membranous structures and
scoleces (H&E; x20).
Click Here to Zoom
|Figure 4: A) Hook structure in cyst fluid (May Grunwald Giemsa, x10). B) Degenerated membrane structures in cyst fluid (May
Grunwald Giemsa, x20). C-D) Degenerated scolex in cyst fluid C) PAP; x100, D) May Grunwald Giemsa, x100).
Incidence of HC, which is one of the most important
zoonotic disases worldwide and in our country, is
approximately 5.7/100.000 per year9,
and it has a high
prevalance in Central Anatolia, Eastern Anatolia and
. In our study of 8-year period,
364 cases of HC were included. Our clinic has a large number
of HC cases that might be due to the high immigration rate
in our region, and also to ovine-cattle breeding still being
practiced in places close to urban areas.
Although found in all ages, HC is frequently observed in
adulthood10. In the national studies, cases were detected between the ages o f 4 and 79 years; mean age ranges between 28.2 and 35.9 years for females, and 25.3 and 41.6 years
for males10. HC was mostly seen among women both
in the world and in our country1, and it is considered
to be due to domestic pet care and food preparation in
houses by women34. Ages of our cases, similar to the
literature, were between 4 and 81years while the mean age
was 40.55±1.066 (5-80) for women and 36.55±1.325 (4-81) for men. Our patients were mostly females (57.4% female,
and 42.6% male) as well.
In the previous national studies, liver (66.4-89.3%), and
lung (7.1-21.6%) were the mostly reported locations of HCs9. Likewise, 69.8% of our cases were in liver, and 14.6%
were in the lung.
In one study, the rate of involvement of more than one organ
was reported as 6.7%7 and in the same study, liver and
lung were both involved in 2.2% of the cases7. Our results
were similar to that study: the rate of cases with a history of
liver HC in the clinical history was found to be 7.5 % and 2.2
% of these cases had involvement of liver and lung.
The rate of the cases located in unusual sites in our study
amounts to 15.6%. 5.3 % of these cases had a liver HC history
as well. In the literature, the rate of organ involvement other
than lung or liver was reported between 5.7-13.9%4,7,
and our result was similar (10.3%). In several studies, HCs
of unusual locations were seen mostly in adults (7-13%)
and in children the rate amounts to 7%7. In our study,
cases with unusual locations were all seen in adults but not
in children. In the group with individuals aged 0-14, the
most frequent involvement was seen in the lung (n:8) and
then in the liver (n:4).
Although a few unusual cases of primary peritoneal
involvement have been described, peritoneal HCs are almost
always secondary to hepatic involvement6. The overall
prevalence of peritoneal involvement in cases of abdominal
HD is approximately 13%6. Isolated retroperitoneal HCs
are also rare, and secondary to the involvement of other
organs, especially liver, or in cases where there is a history
of surgery6,11. It has to be differentiated from mesenteric
cyst and intestinal duplication cyst6. Our cases with
peritoneal involvement ranked in 3rd place regarding
frequency (3%), and all of our cases had a history of liver
HC. However, our retroperitoneal case was a secondary HC
located on the left adrenal lodge.
The involvement of spleen in HC is rare. It is the 3rd most
common site and the prevalence of splenic involvement
ranges between 0.9% and 8%1,7,9. Splenic HC
generally develops by means of systemic dissemination or intraperitoneal spread from a ruptured liver cyst.
Isolated splenic involvement is very infrequent6 and
splenic HCs are generally solitary6. Splenic hydatidosis
should be differentiated from other splenic cystic lesions,
such as epidermoid cyst, abcess, hematoma, posttraumatic
pseudocyst, neoplasms like lymphangioma
and haemangioma12,13. We had 7 cases with splenic
involvement (on 4th place), two cases were primary HC, and
five had a previous HC.
Renal involvement is rare (1-4%)6,7, and the frequency
was found to be only 0.4% in one study4. It is reported as
the common site following liver and lung in several articles14. They are mostly solitary and located at upper pole or
cortex6. Multilocular HCs can be misdiagnosed as simple
renal cysts, cystic nephroma, and cystic variants of renal
cell carcinoma6 and infected HCs can be misdiagnosed
as renal abcess6. In our study, the renal involvement rate
was 1.6%. One of our six cases was located at the right lower
pole; two at the left lower pole; and two at the right upper
pole. Location of one case was reported as the ‘left kidney’.
Heart HC is very rare (0.02-2% of cases) and may occur
owing to hematogenous spread or rupture of a lung HC6.
The cyst grows very slowly and the disease is diagnosed
long after the infection15. Diagnosis is made through
echocardiography14. The most commonly affected
cardiac chambers (in decreasing order of frequency) are the
left ventricle (50-60% of cases), interventricular septum (10-
20%), the right ventricle (5-15%), pericardium (10-15%),
and the right or left atrium (5-8%) (6,11). Nevertheless, CT
scan and MR are also helpful in other parts of the body14.
We have observed six cases. All of these cases had isolated
heart involvement. One case was located in the right atrium,
one case in the right ventricle, and one in the myocardium.
Three cases were reported as ‘located in the heart’. One case
(0.3%) was reported to be adjacent to the right ventricle.
Primary involvement of the pelvic cavity is very rare and
patients usually manifest pressure symptoms that affect
the adjacent organs16. Commonly, cysts are detected in
other parts of the body, mostly in the liver16. Only a few
cases of primary pelvic HC have been reported and primary
pelvic involvement is very unusual16. We have diagnosed
6 cases; one located at the stump line of a patient with a
history of total abdominal hysterectomy with bilateral
salpingo-oophorectomy. In the history of another case, the
lesion was located adjacent to the urinary bladder, and the
patient had operations in liver, kidney and urinary bladder
with HC described. One case was at perirectal area and
one was placed in the left iliac wing deviating surrounding tissues to the right. The other three cases were reported as
‘located in pelvic region’.
Urinary tract and bladder involvement can occur secondary
to kidney HCs6. Primary HCs of these structures are
extremely rare6. It is observed approximately in 0.2-0.5%
of the cases17. There have been certain reports in the
literature of retrovesical HC causing urinary retention6.
The rate of our urinary bladder cases was 0.8%. All of the
three cases were primary ones that were located at posterior
wall of urinary bladder.
Bone involvement is also rare (0.5-2.4% of cases)6,18,
and diagnosing osseous hydatidosis takes more time
compared to that of other sites19. The most commonly
involved bone structures are spine (35% of cases), pelvis
(21%), femur (16%), tibia (10%), ribs (6%), skull (4%),
scapula (4%), humerus (2%) and fibula (2%)6. Pericyst
formation does not occur in bone, and the cyst has a much
thinner wall6. In the spine, HC bears a resemblance
to tuberculosis spondylitis or chronic osteomyelitis6,
fibrous dysplasia of bone, osteosarcoma, benign cystic
lesion of bone, Brown tumor (hyperparathyroidism), and
various other neoplastic lesions20. We found three cases,
one with bone involvement at the right humeral shaft,
and another at the right femur. The case with sacral bone
involvement had a history of three operations due to spinal
Soft-tissue HC occurs in 0.5-4.7% of patients living in
endemic areas (6,18). The growth of the cyst within a muscle
is difficult due to the contractility of muscles and presence
of lactic acid6,7. HC has an affinity for muscles of the
neck, trunk and limbs because of increased vascularity and
decreased activity of these muscle groups6,7. Soft tissue
HCs are often confused with benign soft tissue tumors7.
We had a case located in the left psoas muscle (0.3%). Our
right paravertebral HC was at the T12 level, not related with
muscles but in the neighborhood of the ribs.
Pancreas HCs cause diagnostic and therapeutic problems7. Primary HC of the pancreas is uncommon, with
a reported prevalence of 0.25-2%4,6,7. Among the
pancreas HCs, the head of the pancreas is more frequently
involved (57%), followed by the body (24%) and the tail
(19%)21,22. It has also been reported that 9.3% of these
lesions perforate in a spontaneous way or rupture into
the peritoneal space23. In the differential diagnosis,
it is important that pancreatic pseudocysts and cystic
malignancies of the pancreas are kept in mind23. Both of
our cases were primary HCs located in the distal pancreas.
Primary HC of the gallbladder is highly uncommon, and
the incidence is 0.4%4,24. Cysts can be located either in
the lumen of the gallbladder or on its external surface24.
It is important that the gallbladder HCs are differentiated
from the liver HCs and other extrahepatic cystic lesions25. Liver hydatidosis shows a long asymptomatic period
of cystic growth, whereas in primary gallbladder HC,
symptoms begin at an earlier phrase, and the diagnostic
imaging shows smaller cysts with deformation of the
gallbladder25. We diagnosed only one gallbladder HC
case (0.3%) which coexisted with a hepatic HC.
Diagraphmatic and subdiaphragmatic locations are seldom
(1%) involved, and they are mostly associated with liver
disease18,26. The diagnosis of the diaphragmatic location
is frequently incidental, particularly when the cyst is small
and isolated26. Differential diagnoses include adrenal
tumor, cystic lymphangioma and splenic exophytic HC26. Our singular case (0.3%) was a primary HC located
at subdiaphragmatic area, between the liver, spleen and
A literature review has revealed that less than five cases of
HC were in the inguinal canal in adults and only one case
in a child27. These cases manifest themselves mostly with
swelling and the differential diagnosis of swelling includes
inguinal hernia, encysted hydrocele of the cord and lipoma
of the cord27. Our case was a 30-year-old primary HC,
operated due to a mass lesion at the left inguinal area.
Only a few case reports are found in the literature28,
including secondary cases as well. The most common
differential diagnosis in neck swelling includes masses of
thyroid, salivary gland and lymph node, all of which may be
inflammatory, noninflammatory and malignant. Soft tissue
sarcomas, especially the ones with rhabdomyomatous
differentiation, may manifest themselves as neck swelling28. We recognized two cases, one at the left supraclavicular
area and the other at the incisura jugularis.
Incidence of cerebral HC is 0.8-4%1,10 and 50-75% of
them are at the pediatric age7,11. Cysts are often solitary,
supratentorial and intraparenchymal7. The parietal lobe
is the most frequently involved location6,11. Our case
was an adult with a HC located at occipital lobe.
Spinal HCs account for less than 1% of all HCs6. The
thoracic spine is the most frequently involved (50% of cases),
followed by the lumbar (20%), sacral (20%), and cervical
(10%) spine6. Spinal HC is clustered into five groups,
which are intramedullary, intradural extramedullary,
extradural intraspinal, vertebral, and paravertebral6.
The first three groups of HC are uncommon6. HCs are typically multiple when they are located in the spinal cord6. In our study, the spinal HC rate was 0.5% (2 cases), one
of which was located in thoracic intramedullary extradural,
and the other in the thoracic intradural extramedullary
Solitary abdominal parietal wall HC is a finding that is rare,
with only 5 cases reported. All of the cases in literature
had HC located either in the right iliac region or right
paraumblical region29. We also observed a case with a
primary HC found at the abdominal left lateral wall.
In conclusion, the distribution of our HCs as well as our
unusually located cases has been presented in this study.
The results establish that HC that can be found in all parts
of the body and this should always be taken into account in
the differential diagnosis of cystic lesions.
CONFLICT OF INTEREST
The authors have no conflict of interest to declare.
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