PMC10270697_01
Scout film showing a well-defined homogenous opacity in left hilum with hilar overlay sign and indistinct descending aorta localizing the lesion in posterior mediastinum. Increased density of the left side chest wall with asymmetry is noted (white star) (A). Axial pre- and post-contrast chest CT image in the Mediastinal window at T5 level shows a large (> 10 cm), non-enhancing, low density (HU values on CT show low density (mean HU +- SD = - 1 +- 10)) cyst with lytic lesion of adjacent vertebral body and rib seen (B and C). Areas of calcification are seen in the cyst wall and superior part of the cyst (white arrow) (D).
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Localized regions of calcification were present in the inferior portion and lateral wall of the cyst (Figures 1 and 2).  
Coronal image reconstruction shows the close relationship between the cyst and descending aorta (black arrow) (A). Axial, post-contrast CT images at T5 level show chest wall asymmetry with multiple cystic lesions, with minimal wall enhancement (white arrow) (B). Axial Mediastinal window and sagittal bone window reconstruction show lytic lesions of posterior vertebral body, left pedicle and transverse process with adjacent ribs seen (short black arrow). There is widened left side neural foramen and perineural fatty effacement (white arrow) (C and D).
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Localized regions of calcification were present in the inferior portion and lateral wall of the cyst (Figures 1 and 2).  
H and E stained histologic sections from chest wall biopsy 10x (A) and 20x (B) show multiple fragments of acellular laminated fibrous tissue with intense foreign body-type giant cell granuloma accompanied by a few small mature lymphocytes, predominant chronic mononuclear inflammatory cells on satellite granular necrotic debris background.
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These were predominantly mixed chronic mononuclear inflammatory cells on a satellite granular necrosis debris background, which are consistent with a hydatid cyst (Figure 3). 