[A rare cause of posterior mediastinal tumors: mediastinal hydatid cyst]. / Une cause rare des tumeurs du médiastin postérieur: le kyste hydatique médiastinal.

Mediastinal hydatid cyst is extremely rare even in endemic areas, representing 0-4% of all hydatid cyst locations. We report the case of a 50-year old patient admitted to our Department with a mass in the left dorsal paraspinal region; chest X-ray showed posterior left basal opacity. Chest CT scan showed posterior mediastinal mass located in the left costovertebral gutter extending from D9 to D11. MRI confirmed the existence of a posterior mediastinal mass with endocanalar extension and spinal cord compression, first evoking cystic schwannoma. These radioclinical data were consistent with a neoplastic origin; a transparietal biopsy was performed which showed a paucicellular specimen composed of translucent eosinophilic material with appearance just barely compatible with hydatid cyst. Hydatic serology was positive. The diagnosis of hydatid cyst was retained and the patient underwent thoracotomy which revealed mediastinal hydatid cyst, confirmed by histologic examination. The postoperative course was uneventful. Mediastinal location of hydatid cyst is very rare and poses a problem in differential diagnosis with other mediastinal tumors.