Asian Cardiovasc Thorac Ann 2007;15:e60-e62
© 2007 Asia Publishing EXchange Ltd
Primary Hydatid Cyst of the Posterior Mediastinum
El Hassane Kabiri, MD,
Abdelfettah Zidane, MD,
Fouad Atoini, MD,
Adil Arsalane, MD,
Hicham Bellamari, MD1
Department of Thoracic Surgery
1 Department of Anesthesiology, Mohamed V Military University Hospital, Rabat, Morocco
For reprint information contact: El Hassane Kabiri, MD, Tel: 212 6181 8545, Fax: 212 3756 3432, Email: hassankabiri{at}yahoo.com, Immeuble 29 Appt 7, Résidence Mes Ellil, Secteur 23, Riad 10100, Rabat, Morocco.
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ABSTRACT
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Hydatid cystic disease is still a health problem in Morocco. Mediastinal localization is very rare. We report the case of a 24-year-old man who presented with right chest pain and dyspnea. Chest X-Ray and computed tomography showed a mediastinal mass. The diagnosis was confirmed perioperatively by macroscopic and histologic investigations. Resection of the cyst was performed, and a small part intimately adherent to the inferior vena cava and oesophagus was left in place. There were no complications or recurrence.
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INTRODUCTION
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Hydatid cystic disease is a parasitosis caused by Echinococcus granulosus larvae. Cysts can be found anywhere in the body, especially in the liver and lungs. An intrathoracic but extrapulmonary location is very rare and represents less than 0.1% of all localizations. A mediastinal site is exceptional. The clinical problem of this latter localization is to differentiate it from other causes of mediastinal cysts. Surgery is the optimal treatment but must be complemented with concomitant medical treatment when there is a risk of dissemination.
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CASE REPORT
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A 24-year-old man was admitted to our department with right chest pain, chronic cough, and dyspnea. The postero-anterior chest X-Ray revealed inferior mediastinal opacity (Figure 1
). The patient was in good general state, his blood pressure was 120/90 mm Hg, body temperature was 37.2°C rectally, and his respiratory rate was 16 breaths·min–1. All other clinical systemic examinations were normal. Laboratory findings and bronchoscopy were normal. Thoracic computed tomography revealed a cystic postero-inferior mediastinal mass located between the inferior vena cava, the esophagus, and the thoracic aorta (Figure 2). The mass measured 5.2 cm x 7.5 cm on water density assessment. Serological hydatid tests (indirect hemagglutination, immuno-electrophoresis and ELISA) were negative.
The lesion was approached through a posterolateral thoracotomy. Inspection revealed a mass in contact with the lower pulmonary lobe, inferior vena cava, and esophagus. The cyst was isolated and protected with soaked sponges of scoliocidal agent (H2O2). A needle was used to aspirate the fluid, followed by resection of the hydatid membrane. During excision of the residual cavity, a small part of the cystic wall was left in place as it was intimately adherent to the inferior vena cava and esophagus. The diagnosis was confirmed perioperatively macroscopically, and in histological studies.
There were no intraoperative or postoperative complications. The mean hospital stay was 5 days. On follow-up there was no evidence of recurrence on regular chest X-Ray.
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DISCUSSION
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Mediastinal hydatid cysts are very rare, representing less than 0.1% of all localizations and less than 1% in the thorax.1 Mediastinal hydatid cysts occur more frequently in the posterior mediastinum. Compared with intrapulmonary cysts, calcifications are more frequently found in mediastinal cysts. An explanation for this has been proposed as an absence of ventilation in the mediastinal lesion.1
Mediastinal hydatid cysts are usually isolated and primitive. The parasite localizes in the region after passing the hepatic and pulmonary filter, probably via an arterial branch of the thoracic aorta or via lymphatics. While there are no specific symptoms, patients may present with chest pain, cough, and dyspnea. In addition, hemoptysis when the cyst involves the pulmonary parenchyma, superior vena cava syndrome when the cyst is large,2 intrathoracic phrenic or laryngeal recurrent neurological symptoms,1 vertebral destruction,3 and possible Bernard-Horner’s syndrome1,4,5 have been reported. Most patients are asymptomatic; the lesion being discovered incidentally on a routine chest X-Ray.1,6
Radiological imaging consists of a chest X-Ray and thoracic computed tomography (CT) facilitating diagnosis of a cystic mass. However, it is very difficult to confirm the hydatid nature of the cyst as the lesion is rarely round. If the cyst presents with calcifications, one should be very suspicious of a hydatid cyst. A multivesicular cyst is also suggestive of the diagnosis. While a CT scan is very useful and instructive to the surgeon to reveal the different anatomical relations of the cyst, there are no pathognomonic signs of hydatid cystic disease.1,6 Magnetic resonance imaging (MRI) can be of more assistance than a CT scan in the case of posterior localization for diagnosis of spinal involvement, and in some cases when neurologic signs are evident.3 Systematic abdominal ultrasound should be performed in all cases, considering that the liver is the primary organ for hydatid disease.1
Serological tests are often negative when the cyst is intact and uncomplicated. Fine needle CT guided aspiration is still considered dangerous however it can be useful for diagnosis despite the risk of dissemination and anaphylactic shock.7 An attempt to perform this technique is made in cases where CT confirms the water density of the intra-thoracic mass.
The differential diagnoses of mediastinal cysts are still numerous even after CT scan. Several conditions must be considered according to the location of the lesion. In posterior mediastinal localization the following diagnoses must be ruled out:1,6
- bronchogenic cyst: the lesion is located beside or in contact with the bronchus and/or trachea and there are no changes after contrast infusion,
- enteric cyst: right side location essentially and an association with vertebral abnormalities,
- cystic lymphangioma: usually the lesion is cervical, and occasionally presents with mediastinal extension,
- neurogenic tumors,
- paravertebral masses.
Complications of mediastinal hydatid cyst can be very serious and include:
- rupture into the mediastinum, pleural cavity, and right ventricle,
- cysto-aortic fistula with the possibilities of multiple systemic embolizations, multi-organ failure, and death,8
- infection,
- compression of vital structures1,5 and life-threatening pulmonary embolism in case of rupture into the right ventricle.
For these reasons, surgical intervention for mediastinal cysts is indicated.
The aim of surgical treatment for hydatid cysts of the mediastinum is to eradicate the parasites, to prevent intrathoracic rupture, and to excise the residual cavity.1,6 The procedure is usually best performed through a posterolateral or anterolateral thoracotomy. Despite maximal precautions, there is always a risk of perforation during the procedure, with resultant risk of dissemination. Even if it is still not well proven, it is our policy if dissemination occurs to give adjuvant medical treatment.1,6 Medical treatment of hydatid disease with oral albendazole or mebendazole is recommended when there is a risk of dissemination. The regimen is 10 to 15 mg·kg–1·day–1 for 3 to 6 months with regular assessment of hepatic function before commencing therapy, and at least monthly thereafter. However, this treatment is generally not considered a reliable way of eradicating the parasite, as it is a long process and efficacy has not been demonstrated.1
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CONCLUSION
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Although rare, hydatid cysts should always be considered in the differential diagnosis of mediastinal cystic lesions particularly in endemic areas. Preoperative diagnosis is suspected on epidemiological data, clinical findings, serologic and radiological investigations but can only be definitively confirmed perioperatively. Many procedures can be used to eradicate this parasitosis but the optimal approach remains prevention.
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REFERENCES
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ABSTRACT
INTRODUCTION
