Fig. 4.

Histological appearance of a representative motion segment with vertical presentation of ectopic mineralization associated with DISH. Images correspond to the specimen shown in Fig. 1a, T4–5. a Digital radiograph of the intact tissue prior to decalcification showing the localization of ectopic mineral within the motion segment (contoured by dotted yellow line). VB vertebral bone, IVD intervertebral disc. b Representative section stained with hematoxylin and eosin demonstrating the appearance of the intact section; scale bar represents 10 mm. The yellow box corresponds to the region within the fibrocartilage of the IVD with a discrete amorphous calcification imaged with a 20× objective (c–e). The white box corresponds to a region of heterotopic ossification along the anterior aspect of the IVD imaged with a 20× objective (f–h). The black box corresponds to the discrete calcification within the anterior longitudinal ligament imaged with 4× and 20× objectives (i–k). c, f, i Stained with hematoxylin and eosin; d, g, j stained with Masson’s trichrome; and e, h, k the hematoxylin and eosin stained sections visualized with polarized light. Scale bars for c–k represent 100 µm. c–e Highlight an amorphous region of dystrophic calcification localized within the annulus fibrosus (asterisk) and characterized by a granular appearance and variable eosinophilic staining. f–h A region of heterotopic ossification marked by organized osteons (black arrowheads). i–k Reveal an area of dystrophic calcification (black arrows) localized within the anterior longitudinal ligament (contoured by black dotted lines). k Corresponds to the dotted outline in j. All images are oriented as shown in a