hydatid disease ( hd ) , also known as cystic echinococcosis , is caused by infection with the larval stage of echinococcus granulosus . the disease has the highest incidence in countries where sheep are raised with the help of dogs . in endemic regions , human incidence rates for hd can reach > 50/100,000 person - years , and prevalence levels as high as 5%10% may occur in parts of east africa , central asia china , argentina , and peru . the adult tapeworm , which inhabits the small intestine of dogs , produces eggs which contain the larval tapeworm ( oncosphere ) . intermediate hosts ( sheeps and humans ) become infected by accidental consumption of water or food that has been contaminated . oncospheres penetrate the intestine and are carried through bloodstream where they are filtered out in various organs . the most common hydatid cyst sites in humans are the hepatic filter , 60%70% of cases , followed by lung and brain . bone hydatid cyst presentation without hepatic affectation is infrequent and occurs in 0,5 - 2% of cases , half of which infest the spine . primary involvement of the sacral spine , as in the current case , is very rare . the first case was described in 1951 . since then , few cases have been reported in literature [ table 1 ] . as a result , sacral hydatid cyst ( shc ) we document diagnosis and treatment of a patient with a primary shc and is compared with other cases published in literature . a 48-year - old woman from south mediterranean region was admitted at our center because of low back pain radiating to the left buttock . she had no improvement with analgesia and physiotherapy for a year . neurological examination showed no motor , sensory , patellar , or achilleian reflexes deficits , and no bladder disorders . the magnetic resonance ( mr ) revealed a cystic lesion with cerebrospinal fluid - like signal in contact with left sacral roots extending through sacral holes reaching iliac muscle [ figure 1 ] . the mr image suggested , as the first option , a neurogenic tumor ( sacral neurofibroma or schwannoma ) , as the second , giant cell tumor ( gct ) or chordoma . after consultation with radiologists and pathologists , a computed tomography - guided biopsy was performed with an 11-gauge bone access needle . during biopsy , a greenish - yellow aspirate was obtained . pathological study revealed hydatid cysts presence , with an inner germinal layer , surrounded by an outer layer of chitin [ figure 2 ] . specific enzyme - linked immunosorbent assay ( elisa ) serological tests proved negative . before surgery , treatment with oral albendazole ( 400 mg/12 h ) and praziquantel ( 100 mg/8 h ) for 2 months was given to the patient . magnetic resonance t2-short - tau inversion recovery . cystic lesion with cerebrospinal fluid - like signal in contact with left sacral roots extending through sacral holes reaching iliac muscle hydatid cyst ( cyst wall , inner germinal layer ) ( h and e , 200 ) surgical treatment was performed using a dual approach to the lumbosacral spine . first stage : ilium anterior approach , dissecting external oblique , internal oblique , and transversus abdominis . the cyst extended to the psoas muscle and left sacral foramens [ figure 3 ] . during dissection of the cyst , the wall was broken and the operating field was irrigated with hypertonic saline ( 7.2% nacl ) . ilium anterior approach , dissecting external oblique , internal oblique , and transversus abdominis after which the hydatid cyst was found after the anterior approach , the patient was prepared for the second posterior spine approach to remove the sacral root origin of the sacral cyst [ figure 4 ] . lumbopelvic instrumentation and bone grafting ( femoral head ) to fill the bone defect in the sacrum were added [ figure 5 ] . ( a ) hydatid cyst ( highlighted in blue ) on top of the dural sac . ( b ) first and second left sacral roots , after removing the hydatid cyst ( highlighted in black ) lumbopelvic instrumentation and bone grafting ( femoral head ) to fill the bone defect in the sacrum ( highlighted with black arrows ) the patient continued treatment with albendazole ( 400 mg / two times a day ) and praziquantel ( 40 mg / kg day ) 3 months after surgery . at 12 months after surgery , the patient is free of symptoms and is complete autonomous for performing the basic activities of daily living . misdiagnosis of sacral echinococcosis in mr is common [ table 1 ] . in the present case , neurofibromas , or schwannomas , can grow through the neural foramens outward from the sacral canal , and a giant mass may form anterior to the sacrum . reported a presacral schwannoma with purely cystic form with similar mr characteristics to a shc . on mr , benign schwannomas have smooth tumoral margins and are isointense with muscle on t1-weighted images and hyperintense on t2-weighted images . in shc , mr shows a cystic lesion with similar characteristics to cerebrospinal fluid with a thin peripheral enhancement after contrast administration . the sacral hydatid cyst ( shc ) capsule is best seen on t2- and proton density - weighted images . anterior sacral meningocele is a protrusion of the meninges through a defect in the anterior aspect of the sacrum into the retroperitoneal space . this lesion is seen with equal signal intensities of cerebrospinal fluid on all mr sequences and is usually unilocular . the most common gcts site is distal femur and proximal tibia in 50%65% , but can affect sacrum in 4%9% of cases . the mr t2-weighted images show a heterogeneous high signal with areas of low - signal intensity ( variable ) due to hemosiderin or fibrosis . the sacrum is the most common location , accounting for approximately 30%50% of all chordomas . because chordomas lie in bone , they are usually extradural and induce bone destruction . in the mr , destructive lytic lesion with expansile soft - tissue mass can help distinguish chordoma from shc . puncture of the cyst could cause the migration of parasites to the bloodstream causing an anaphylactic shock ; hence , the assistance of an anesthesiologist during biopsy is recommended . the indirect hemagglutination test and the elisa serology is 80%100% sensitive and 88%96% specific for liver cyst infection , but less sensitive for lung involvement ( 50%56% ) or other organs ( 25%56% ) . in the present case , other tests , such as immunodiffusion and immunoelectrophoresis , provide specific confirmation after a positive elisa serology , and they were not used in this patient . although medical treatment can decrease the size of cysts , the definitive treatment is complete surgical removal of the cyst . there are several antiparasitic treatment alternatives ; however , the most effective therapy appears to be the combination of albendazole + praziquantel rather than albendazole alone . in patients originating from endemic areas of hd , with chronic low back pain and an sacral mr suggestive of neurogenic tumor , meningocele , chordoma , or gct , sacral spinal hd should be considered in the differential diagnosis .
hydatid disease is caused by infection of echinococcus granulosus . 
 bone hydatid cyst presentation without hepatic affectation is infrequent and occurs in 0,5 - 2% of cases . 
 this rare condition makes clinicians not always aware of the disease , and as a result , misdiagnosis of spinal echinococcosis is common . 
 we present a case of a 48-year - old female patient with primary sacral hydatidosis . 
 chronic low back pain radiating to the left buttock was the only symptom . 
 the magnetic resonance imaging ( mri ) suggested a neurogenic tumor versus giant cell tumor . 
 biopsy and pathological study revealed a hydatid cyst . 
 anthelmintic and surgical treatment was performed . at 12 months after surgery , 
 the patient is free of recurrence . in patients with chronic low back pain and a mr suggestive of neurogenic tumor , spinal hydatid cyst 
 should be considered in the differential diagnosis . 
 it is recommended the assistance of an anesthesiologist during biopsy to avoid an anaphylactic shock .