**5. Radiographic characteristics**

Radiographically, non-demonstrable evidence of a fracture in consecutive studies supports the diagnosis of KD [14]. However, it is important to perform the differential diagnosis between KD and nontraumatic or spontaneous vertebral ON associated with osteoporosis. Clinically, it should be emphasized that osteoporotic compression fractures are not associated with neurological symptomatology. On the other hand, chronic radiographic osteoporotic fractures are not associated with changes in signal intensity on MRI [35]. This contrasts with the variability in signal characteristics on MRI in KD [6, 98]. Usually, these appear with an increase in the signal on T1-weighted images and reduced signal on T2-weighted images. However, in both KD and spontaneous vertebral ON, a hyperintense linear area on MRI can be observed. This pattern of signal change has been referred "double line sign" and corresponds to the phenomenon of IVC. This describes the accumulation of gas in the vertebral body observed in X-ray studies (**Figure 1**). This sign has also been observed associated with malignancy and intraosseous disc herniation, so it should not be considered as pathognomonic of ON.

Another radiological sign associated with ON is the intravertebral fluid of the vertebral body. This appears as a well-circumscribed area of low signal intensity on T1-weighted MRI and high signal intensity on T2-weighted images [39, 99]. This characteristic is known as a sign of fluid. In this regard, it was reported the coexistence of air and fluid in the same vertebral body in 21.5% of the cases. It was observed a more severe vertebral collapse in those cases with only intravertebral air than in those with fluid with or without air [100].
