Spinal Hydatid as a Rare Cause of Posterior Mediastinal Lesion: Understanding Cervicothoracic Sign on Chest Radiography

Background: Location of an intrathoracic lesion on chest radiograph is facilitated by application of 'silhouette sign'. This helps narrow down the differential diagnoses. The list of probable diagnoses reduces further on determination of the density of the lesion. A spinal hydatid presents as a fluid-density posterior mediastinal lesion on chest radiograph with destruction of the vertebral body and preservation of the disc space. Spinal hydatid is, however, rare. Case Report: We describe a case of a 30-year-old female with gradual-onset paraperesis since six months. Chest radiograph was suggestive of a posterior mediastinal lesion with fluid density and destruction of D4 vertebra. MRI findings were consistent with spinal hydatid. The patient was started on perioperative benzimidazole therapy with resection of the hydatid cyst. The drug therapy was continued for six months post-operatively. Conclusions: A chest radiograph helps localise the site and possible contents of the lesion. It also guides further investigations. MRI is the imaging modality of choice for spinal pathologies causing cord compression including spinal hydatid. Echinococcal involvement of the spine is a rarity but needs to be considered in the differential diagnoses for spinal causes of gradual-onset paraperesis.