Extrapleural fat is a benign condition and refers to the relative diffuse deposition of fat outside the parietal pleura with a typical appearance on CT images. In plain x-ray, the resulting soft-tissue shadow produced can be confused with pleural thickening or plaques.

In this case, although the placement and expansion of fat tissue at the base of the left hemithorax are more suggestive of extrapleural fat and the defect in the posterior part of the left hemidiaphragm could be an accompanying finding, according to the history of chest pain and CT scan findings in the prone position the extrapleural fat ruled out, and herniation of fat tissue through Bochdalek hernia is a definite and final diagnosis that can also explain the patient's symptoms.