the hydatid cyst is a zoonosis caused by adult or larval stages of tapeworms belonging to the genus echinococcus granulosus .
the tapeworm stage is harbored in the intestine of carnivores such as dogs , which constitute the definitive host , and the eggs are passed in the feces of the infected carnivores and ingested by herbivores such as sheep , which comprise the intermediate host .
larvae emerge from the eggs in the intestine ; and after invasion to the blood vessels , they can migrate into almost every part of the body .
the usual destination is the liver via the portal tract , but sometimes the larvae pass through the liver barrier and reach the lungs and all the other viscera , where they transform into small cysts . 
 
echinococcosis / hydatidosis is one of the most important zoonotic diseases inasmuch as it occurs in different parts of iran .
adult worms have been recovered from dogs , jackals , and wolves , but human cases have been reported from hospital archives by pathological reports of surgically proven cases in different geographical areas of the country . in nearly all the previous reports , the liver was the most common location of the hydatid cyst , followed by the lung , with the approximate occurrence rates of 70% and 12% , respectively .
there is a small number of reports of higher incidence rates of lung involvement in iran , but such cases are very unusual .
the reported incidence in children has been a point of controversy in a few previous investigations , reporting incidence rates of 41 - 70% for the lung and 43 - 48% for the liver hydatid cyst . although most reported iranians with echinococcosis had cysts in their lungs and livers , more unusual cyst locations were also recorded . in a few previous reviews on hydatidosis form
iran , unusual body sites such as the heart , orbit , brain , muscle , salivary gland , bone , urinary tract , and pancreas were reported .
the aim of this paper is to provide an overview of the published cases of the hydatid cyst in unusual body sites from iran to delineate the most important demographic findings and locations of the disease in this hyperendemic country .
the published cases of the hydatid cyst in unusual body sites from iran were reviewed via a search in pubmed , scopus , google scholar , iranmedex , scientific information database ( sid ) , magiran , and irandoc ( 1990 - 2011 ) , using the keywords of  hydatid cyst and iran  and  echinococcus granulosus and iran  .
the following inclusion criteria were employed : 1 ) articles must be written in english and farsi ; 2 ) articles must have been published between 1990 and 2011 ; 3 ) studies must be from iran and contain case report(s ) , diagnosing the hydatid cyst in unusual locations ( i.e. other than the liver and lung ) ; and 4 ) cases must have been pathologically confirmed postoperatively .
in the last 20 years , about 463 cases of the hydatid cyst located in different parts of the body , excluding the liver and lung , have been published from iran .
the published cases of the hydatid cyst with unusual locations from iran the most common locations were the central nervous system ( brain , spinal cord , and orbit ) , musculoskeletal system , heart , and kidney , whereas some less common locations were the spleen , pancreas , appendix , thyroid , salivary gland , adrenal gland , breast , and ovary .
most of the published cases were reported from tehran ( as a referral center for the whole country ) ; nevertheless , other centers such as khorasan , azerbaijan , fars , isfahan , and yazd also reported unusual locations of the hydatid cyst . 

central nervous system 
  in the last 20 years , about 256 cases of the hydatid cyst in the brain , spinal cord , and orbit have been reported form different geographical areas of iran .
there are two reviews by abassioun et al . who reported 69 cases of the brain hydatid cyst .
these patients were 3 to 50 years of age , with a slight male preponderance . among these 69 reported cases , 5 cysts were in the posterior fossa , 2 in the cerebellum , one in the cp angle , one in the fourth ventricle , one in the pons , and 59 cases in the brain parenchyma .
the hydatid cyst of the orbit in the above - mentioned review was detected in 28 patients , with an age range of 5 to 54 years .
abassioun et al . also reported 36 cases of the spinal hydatid cyst , both intra and extradural , 20 of which were male and 16 cases were female patients .
apart from the above reviews , 105 other intracranial hydatid cysts were reported in 73 males and 32 females , with an age range of 5 to 60 years .
most of the intracranial hydatid cysts were within the brain hemisphere , and the most common presenting symptoms were headache and vomiting .
as a rule , the hydatid cyst of the brain tends to be solitary and spherical .
serologic tests are not diagnostic , and imaging studies such as computed tomography ( ct ) scan and magnetic resonance imaging ( mri ) are necessary for preoperative diagnosis . 
 
there were 11 cases of the spinal hydatid cyst ; they were all adults above 20 years of age and presented with signs and symptoms related to cord compression such as low back pain , radicular pain , and paraparesis .
the majority of the spinal hydatid cysts were extradural , and primary intradural hydatid cysts were very rare . aside from the aforementioned review ,
the orbital hydatid cyst was rarely reported form iran : there were only 8 cases , all presenting in childhood .
the reported symptoms were visual impairment and proptosis , and anatomically most of the orbital cysts were in the intraconal space because most branches of the ophthalmic artery supply the intraconal space . 
 musculoskeletal system 
  in the last 20 years
, the skeletal hydatid cyst has been reported in 44 patients , comprised of 28 males and 16 females with an age range of 5 - 71 years ( mean age=41.5 years ) .
the locations of the skeletal hydatid cysts were varied such as the maxillary sinus , mandible , knee , long bones , and ilium .
the clinical manifestations of the osseous hydatid cyst may take a long time to become obvious , and that is when the cyst is detected by swelling , pathologic fracture , and secondary infection .
the bone hydatid cyst is polycystic in contrast to other non - osseous locations , which is because of the absence of adventitia around the cyst .
the diagnosis of the osseous hydatid cyst is based on imaging modalities such as ct scan .
the hydatid cyst involvement of the skeletal muscle is even less common than that of the bone . in our review of iranian cases
, we found 11 reported patients , 8 males and 3 females with an age range of 22 - 80 years ( mean age=29 years ) , with the hydatid cyst of the skeletal muscle .
the reported locations were in the latissmus dorsi , gluteal muscle , cervical muscles of the paraspinal area , and thigh .
the most common presenting symptoms were painless swelling , causing symptoms secondary to the compression effect on the adjacent organs .
radiological studies , including mri , are the mainstay of the preoperative diagnosis of the skeletal muscle hydatid cyst . 

cardiovascular system 
  the third most common unusual location of the hydatid cyst reported from iran is the cardiovascular system , with 42 cases having been reported in the last 20 years .
the cases comprised 25 males and 17 females with an age range of 8 to 73 years ( mean age=29.5 years ) .
most of the cardiac hydatid cysts were located in the ventricular wall , and the most common presenting symptoms were angina , dyspnea , and palpitation , in consequence of the pressure effects of the cyst on the coronary and conducting system .
likewise , only 2 cases of the intrapericardial , and endocardial , hydatid cysts were reported from iran .
the vascular hydatid cyst in the aorta and superior vena cava with invasion to the myocardium was reported in a study from iran .
there were reports of very infrequent asymptomatic cases of the hydatid cyst of the heart detected during ekg evaluations for another surgery .
serologic tests are positive in about 50% of the patients , but transesophageal echocardiography ( tee ) is known as the imaging procedure of choice for the diagnosis of the cardiovascular hydatid cyst . 

kidney and urinary tract 
  our investigation yielded 31 published cases , 23 males and 8 females with an age range of 9 to 73 years ( mean age=44 years ) , of the hydatid cyst of the kidney and urinary tract . among these cases , 29 patients had the renal hydatid cyst and 2 had the bladder wall hydatid cyst .
there is no serologic and immunological test pathognomonic for the diagnosis of the renal hydatid cyst , but ultrasonography and , in particular , ct scan can be of great help .
there were 20 cases of the splenic hydatid cyst from iran in 13 males and 7 females with the reported age ranging from childhood to 75 years .
the splenic hydatid cyst exhibits a variety of clinical features , requiring a high index of suspicion for diagnosis .
uterus , ovary , and fallopian tube 
  there were 9 published cases , with a mean age of 50 years ( mean age=34 - 84 years ) , of the ovarian hydatid cyst from iran .
the uterine hydatid cyst is extremely rare , and only one case was reported from iran with the accompanied involvement of the fallopian tube in a 25-year - old female , who presented with lower abdominal pain .
the diagnosis was made after laparotomy for the evaluation of the cause of the symptoms .
the most popular methods of diagnosis are ultrasonography , ct scan , and mri , all of which are much more sensitive than immunologic tests . in the last 20 years
, 6 patients , 4 males and 2 females with a mean age of 34.5 years , have been reported with the pancreatic hydatid cyst .
this cyst usually manifests as an epigastric mass , recurrent acute pancreatitis , chronic pancreatitis , and obstructive jaundice .
complications of the pancreatic hydatid cyst depend on the relationship between the cyst and the pancreatic duct .
the methods of choice for the diagnosis of the pancreatic hydatid cyst are ct scan and mri .
there were 9 published cases , 4 males and 5 females with a mean age of 16.5 years , of the hydatid cyst of the salivary gland : 7 in the parotid gland and 2 in the submandibular gland .
eight cases of the breast hydatid cyst were published from iran , all in the female breast with a median age of 40.7 years .
the most common presenting symptom was a well - defined palpable breast mass , which can be confirmed by mammography and ultrasonography . in the last 20 years
, only 4 cases of the thyroid hydatid cyst have been reported from iran , all in females between 17 and 35 years of age ( mean age=14.3 years ) .
the patients with the thyroid hydatid cyst presented with pressure symptoms and signs of dyspnea , hoarseness , goiter , and dysphagia .
clinically , the thyroid hydatid cyst presents with a solitary mass , mimicking a thyroid cystic nodule .
the diagnosis can be made by fine needle aspiration ( fna ) and isotope scanning .
the adrenal hydatid cyst in iran was reported in only 2 cases : a 49-year - old female and a 42-year - old male .
the adrenal hydatid cyst is mostly asymptomatic and is incidentally found by imaging ; on rare occasions , however , it can cause hypertension .
another case was reported , presenting with vague flank pain with a primary diagnosis of a renal tumor , for which surgery was undertaken .
there was only one reported case of the appendiceal hydatid cyst from iran , diagnosed after laparotomy in a 47-year - old male worker presenting with vague abdominal pain .
seven cases , 5 males and 2 females with a mean age of 28.7 years , of the mediastinal hydatid cyst were reported from iran .
omentum and retroperitoneum 
  seven cases of the mesenteric , diaphragmatic , omental , pelvic , and retroperitoneal hydatid cyst have been reported from iran in the last 20 years .
these cases may remain asymptomatic until reaching a large size , and the clinical signs vary according to the site . the parapharyngeal hydatid cyst in a 41-year - old female , and the nasolabial hydatid cyst in an 11-year - old adolescent , were the last two extremely rare case reports in this review from iran .
hydatid disease is a unique parasitic disease that is endemic in many parts of the world .
this parasitic disease is a significant public health concern in iran , as an endemic country , rendering a review of the published cases of hydatid disease from this hyperendemic country vitally important .   in hydatid disease ,
the liver and lung are the most common involved organs , but the disease can be seen in any organ of the body .
the rates of the localization of hydatid disease in different body organs vary in the literature .
all the published cases in iran included in this review are based on hospital experiences proven postoperatively by pathological examination .
our results demonstrated that the most common locations of the hydatid cyst , after the lung and liver , were the central nervous system , orbit , musculoskeletal system , cardiovascular system , kidney , and urinary tract .
there were also reports of the spleen , uterus , ovary , pancreas , salivary gland , breast , adrenal , appendix , mediastinum , omentum , and retroperitoneum hydatid cysts .
the clinical manifestations in the hydatid cyst of most parts of the body are too nonspecific to make a diagnosis based on the signs and symptoms before surgery . in all of the previous reports from iran and all around the world
, it has been shown that serologic tests have many false - negative results , but imaging modalities such as ultrasonography , ct scan , and mri have been the methods of choice , especially the latter , which has been the diagnostic method of choice for the preoperative diagnosis of the hydatid cyst in most unusual locations . 
  the best treatment for the hydatid cyst is surgical excision , accompanied by postoperative medical therapy .
the next part of this review presents the salient points of each unusual site of the hydatid cyst extracted from the most recently published literature . 

central nervous system , spinal cord , and orbit 
  the cerebral and spinal cord hydatid cysts are very rare .
indeed , the existing literature contains about 300 articles , accounting for 2 - 3% of all the cases of hydatidosis . 
 
the most common location is the intraparenchymal supratentorial , and the most common presenting symptoms are headache and weakness in the previous reports from other parts of the world , which is very similar to the cases published from iran . in the last 20 years , 256 cases of the central nervous system hydatid cyst have been published from iran .
this cyst site accounted for the third common site of the hydatid cyst after the lung and liver .
according to the recent literature , this cyst accounts for about 1% of all the cases of the hydatid cyst . in this location ,
the intravertebral discs are usually preserved because the disease tends to progress beneath the periosteum and ligaments .
the orbital hydatid cyst accounts for about 1 - 2% of the cases in the previous literature and is most commonly detected in childhood .
musculoskeletal system 
  osseous hydatid disease and muscular hydatidosis are uncommon and account for 0.5 - 4% and 0.5 - 2.5% of all hydatidosis cases , respectively ( in endemic areas ) .
the most common locations of the osseous hydatid cyst are the vertebra , pelvis , and long bones in the previous records from other parts of the world . however ,
in the published cases form iran , there were 55 cases with variable locations such as the long bone , mandible , maxilla , and pelvis .
muscle involvement of the hydatid cyst is reported as an uncommon location , because of high lactic acid , which is not a suitable environment for the parasite . 

cardiovascular system 
  the heart and large blood vessels also have been reported as the common unusual body sites of the hydatid cyst in endemic areas of the world , accounting for 0.5 - 2% of all the reported cases .
the diagnostic method unique for this part of the body is echocardiography , which has been claimed as the method of choice for the diagnosis of the cardiac hydatid cyst . nonetheless , ct scan and mri are also helpful in other parts of the body . 
 kidney and urinary tract 
  the kidney is the most common location in the urinary tract and has been reported in about 2 - 3% of all cases of the hydatid cyst . in many of the previous reports from other parts of the globe ,
the kidney is reported as the third common site of the hydatid cyst after the liver and lung . in our survey of the published cases from iran , however , the renal hydatid cyst was the fourth most common location of the hydatid cyst .
the clinical symptoms are nonspecific , and the only interesting and diagnostic symptom reported is hydatiduria .
the hydatid cyst of the urinary bladder is even less common , and only 2 cases were published from iran .
this cyst can also present with hydatiduria and is , otherwise , extremely difficult to diagnose before surgery .
less than 2 - 5% of the cases of the hydatid cyst have been reported from the spleen .
many of the reported splenic hydatid cysts worldwide are asymptomatic , and a very small number of patients show nonspecific left upper quadrant pain . 

uterus , ovary , and fallopian tube 
  the ovary is the most common site of hydatidosis in the female genital tract , but overall it is extremely uncommon ( less than 1% ) .
the clinical presentations are very nonspecific , and making a correct preoperative diagnosis is very difficult . there were only 9 cases of the ovarian hydatid cyst published from iran .
the uterine hydatid cyst is even less common than ovarian hydatidosis , and its occurrence is exceptional .
the clinical presentation of this cyst is also very nonspecific , and it is difficult to diagnose the cyst before surgery . only one case of the uterine hydatid cyst was reported from iran .
the hydatid cyst of the fallopian tube is most often accompanied by the ovary hydatid cyst and can cause infertility and spontaneous rupture of the tube .
the pancreatic hydatid cyst is very uncommon and accounts for less than 1% of the cases .
there are reports from iran and other parts of the world about the diagnosis of the salivary gland hydatid cyst via fna cytology .
this cyst is reported to be capable of causing anaphylaxis and dissemination , but there are increasing numbers of reports on the diagnosis of the salivary gland hydatid cyst via fna , without any complications .
the breast involvement of the hydatid cyst is rare , with a reported incidence of 0.27% .
mammography , ct scan , and mri can help to diagnose the breast hydatid cyst before surgery .
however , there are rare case reports of preoperative diagnosis by fna cytology without complications .
the hydatid cyst of the thyroid is very rare and clinically presents like a simple colloidal cyst .
for all the reports of the role of fna in the diagnosis of the thyroid hydatid cyst , as is the case in the salivary gland and breast , its application is controversial .
the adrenal hydatid cyst is most often asymptomatic , but reports of hypertension are also available . in our survey ,
only 2 cases of the adrenal hydatid cyst were reported from iran ; both patients underwent surgery with the impression of the adrenal cyst .
the hydatid cyst of the appendix is exceptional , and fewer than 10 cases have been reported worldwide .
the mediastinal hydatid cyst is uncommon but it should be included in the differential diagnosis of the mediastinal cyst in endemic parts of the world .
our findings yielded 7 cases from iran , presenting with cardiac or respiratory problems . 

omentum and retroperitoneum 
  the omental and retroperitoneal hydatid cysts are very uncommon , but these cysts can become huge in size .
the hydatid cyst can present in any part of the body and no site is immune .
these unusual locations often produce nonspecific symptoms ; consequently , it is advisable that the hydatid cyst be considered in the differential diagnosis of all cysts of the body , especially in endemic countries such as iran .
 hydatid disease is caused by echinococcus granulosus and is endemic in many parts of the world , including iran . 
 this parasitic tapeworm can produce cysts in almost every organ of the body , with the liver and lung being the most frequently targeted organs . 
 however , the cyst tends to appear in different and sometimes unusual body sites in various geographical areas of the world.this review provides information on the reported cases of the unusual body sites of the hydatid cyst from iran in the last 20 years . 
 a literature search was performed through pubmed , scopus , google scholar , iranmedex , society information display ( sid ) , magiran , and irandoc using the keywords of  hydatid cyst and iran  and  echinococcus granulosus and iran  , and 463 published cases of the hydatid cyst in unusual body sites from iran were reviewed , evaluated , and discussed . 
 the most common locations were the central nervous system ( brain , spinal cord , and orbit ) , musculoskeletal system , heart , and kidney , while some less common locations were the spleen , pancreas , appendix , thyroid , salivary gland , adrenal gland , breast , and ovary . 