Hydatid disease caused by E. granulosus and E. multilocularis commonly presents with pulmonary and hepatic cysts. Primary paraspinal muscle cysts are a rare presentation. Here we report a case of paraspinal muscular hydatid cyst presented with cervical mass and associated pain. Hydatid disease serologic test was negative besides of any identifiable hepatic or pulmonary cystic lesions. Radiographic findings were unspecific for hydatid cysts. With primarily diagnosis of muscular cystic neoplasm, surgical resection was planned. Cyst contained ac lear liquid. Cyst wall was excised and surgical field was irrigated with hypertonic solution. The patient's symptoms resolved by discharge day. Postoperative pathological examinations revealed a muscular hydatid cyst.
Hydatid cystic disease is endemic in many parts of the world specially in mediteranian countries (1). Echinococcus granulosus and less commonly Echinococcus multilocularis are primary species responsible for hydatid cysts in humans (2,3). Its cycle consists of humans as intermediate host and dog as final and definitive host (4). The larvae phase of Echinococcus penetrates intestinal wall and commonly being transferred to liver via portal circulation (5). As a result hepatic hydatid cyst is the most common. Primary soft tissue hydatosis without hepatic or pulmonary involvement is a rare entity in hydatid disease. Specially paraspinal muscular involvement occurs very rarely and it's been reported in limited number of cases in available literature (6).
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Here we report a case of cervical paraspinal muscular hydatid cyst without identifiable hepatic or pulmonary hydatid involvement.
ÙŽA 33 years old man presented with complaint of pain and mass in posterior part of his neck since 2 weeks earlier. His pain was aggravated with motion and changing position. In physical examinations a 4-3-3 cm mass was revealed in left posterior cervical region which was cystic in consistency without tenderness or erythema of overlying skin. All neurologic examinations was normal. CXR and liver profile was normal. Serologic test for hydatid disease was negative. The MRI scan demonstrates a well-defined cystic lesion in muscular compartment of neck in left posterior aspect. No relation to thecal sac or posterior fossa was revealed (Figure 1). With primary diagnosis of cervical neoplastic muscular cyst the patient underwent a surgical intervention. During surgery cyst was entered which contained clear liquid. Cyst wall was excised completely and sent to pathological laboratory. Because of high prevalence of hydatid cysts in Iran, one of the rare differential diagnoses was paraspinal hydatid cyst. Therefore the surgical field was irrigated with hypertonic solution to deal with spillage of cyst contents.
Microscopic pathological examination revealed laminated histology consistent with muscular hydatid cyst.
The patient was discharged with good general condition without complaining of previous symptoms.
Primary hydatid cyst in soft tissue and muscles without hepatic or pulmonary cysts is extremely rare (7).A proposed explanation for this observation is effective filtering effects of hepatic and pulmonary circulation which trap the echinococcal larvaes (8). Although in 10-15 % of cases larvaes can escape from this filtering effect and form hydatid cysts in other organs (9).
Sener et al provided an alternative mechanism for bypassing hepatic and pulmonary circulation in formation of primary widespread spinal and paraspinal hydatid cysts (10).
Based on presence of portosystematic anastomoses in various anatomic locations, they proposed that the larvae penetrate the intestinal muscle and may directly enter to the inferior vena cava system through small venous connections at the intestinal walls instead of entering the portal circulation.
A palpable slow growing mass is the most constant clinical finding in soft tissue hydatid disease. Symptoms related to their compressive effects on adjacent organs are another common finding (9). Our patient's main complaint is consistent with described findings in literature (11). Rupture or intraoperative spillage of cyst contents may present as anaphylactic shock or cyst recurrence (8).
The muscular hydatid disease may mimic congenital cysts, psudocysts, cystic tumors, abscess and hematomas. Therefore their preoperative diagnosis imposes a clinical challenge (7).
Radiographic tools are the mainstay of preoperative diagnosis of soft tissue cysts (12).
The MRI scan of the present case demonstrates a regular thin walled cystic lesion without septation and enhancement resembling simple muscle cyst.
The multilocular lesion with several daughter cysts inside mother cyst is considered characteristic although endovesicolar daughter cysts are regarded as unusual in muscular hydatid cysts by some authors(12).
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Some features are suggested to be helpful in diagnosis. The Rim Sign in the MRI images appears as low signal intensity surrounding the cyst and can be helpful to distinguish hydatid cyst from other pathologies.(13)
A characteristic appearance resembling to a bunch of grasp is described by Mirhoseini et al. In their case, cyst wall was hypointense in both T1 and T 2 weighted images and were thin walled nonseptated cysts without enhancement.(14)
Although detachment of germinative layer from pericyst ( water lily sign ) is considered to be pathogonomic but it's rare in musculoskeletal hydatid cysts(9).
In our case serologic tests before surgery was negative.
Serologic tests like hemmaglutinin, complement fixation and ELISA may aid in diagnosis but are not positive in all cases of muscular hydatid cyst (7). Although immunologic tests are valuable in the diagnosis of hydatid cysts, only a positive test is helpful (15). Therefore complete reliance on serology for definitive diagnosis is not recommended (16). Hydatid cyst capsule may play a role in false negative results in serologic tests because of isolation of parasite from the host immune system by cyst capsule (15).Other proposed explanation is inadequate Th-2 cell activation and cytokine production that is implicated in immunoglobulin expression in cystic echinococcus (15).
Different treatment modalities have been proposed for treatment of hepatic and extrahepatic hydatid cysts.
Therapy for extra hepatic echinococcal disease is dependent on size, location and clinical presentation of the cyst besides of general health status of the patient (6).
Small cysts can be managed with anti-helmitic drugs (6). For muscular hydatid cyst surgery with broad safe margin is considered as the best treatment (11). García-Alvarez et al reported that cysts that are not amenable to radical resection failed to heal and had to be operated again regardless of chemotherapy (13). Adjuvant administration of Benzimidazole derivatives pre and post operatively is advocated by some authors (13). Because of difficulties in definitive preoperative diagnosis of muscular paraspinal hydatid cyst and possible morbidities of radical en block resection of the cyst, percutaneous drainage techniques have been developed.
Conventional simple percutaneous drainage in hepatic cysts was not used routinely because of dissemination risk. PAIR as a new version of percutaneous techniques with concurrent chemotherapy is used for hepatic cysts with promising results. It has been shown to be effective with low morbidity and recurrence (17, 18).
Recently Biljic et al reported the first case of para spinal muscular hydatid cyst treated with PAIR technique with subsequent albendazole. In that case, they performed percutaneous drainage, 95% ethanol injection and reaspiration. No procedure related complication nor recurrence was reported in 26 months of follow-up (16). However, efficacy and potential complications of this technique is not determined in larger groups of patients and it seems that more experience is needed before advocating PAIR as an alternative therapy for surgery.
Although ideal is to excise the cyst intact, but it's not possible in every case. To dealing with spillage of cyst contents and preventing formation of new cysts, methods of formalin or aqueous iodine, silver nitrate or hypertonic saline irrigation have been suggested in previous studies (14).
In present case, based on radiographic and serologic appearance, simple muscle cyst was more likely. Therefore, cyst was opened and cyst wall was excised completely. Because hydatid cyst is known to be endemic in Iran (14), we considered the rare possibility of hydatid cyst. So the surgical field was irrigated with hypertonic solution in order to prevent dissemination of possible hydatid cyst.
Based on Findings of the presented case, we emphasize considering hydatid disease in differential diagnosis of paraspinal muscular cysts, especially in endemic areas.