Spinal Dural Ossifications Are Hyperintense on T1-Weighted Sequence and May Mimic Dural Lesions

Spinal dural ossifications (SDOs) are bone plaques on the dura mater surface. They are usually incidental findings in humans and dogs, and rarely can cause clinical signs. The authors noticed that SDOs on magnetic resonance imaging (MRI) may appear hyperintense on a pre-contrast T1-weighted (T1W) sequence. This study aimed to assess the MRI signal of SDOs in dogs. For this retrospective descriptive study, the hospital archive was searched for dogs that underwent both a pre-contrast computed tomography (CT) study and at least one pre-contrast T1W MRI sequence, from January 2020 to April 2024. CT images were evaluated for the presence of SDOs, and the MRI signal of the lesions was assessed at the same level by one first-year diagnostic imaging resident and three board-certified radiologists. Dogs' breed, gender, and age were recorded. Ten dogs were included. Adult dogs (median = 10.5 years) and large breed dogs (median = 31 kg) were overrepresented. On CT, all SDOs appeared as punctiform or linear mineral-attenuating structures on the dura mater. SDOs were predominantly hyperintense on T1W and hypointense on T2-weighted (T2W) images. When fluid attenuating inversion recovery (FLAIR), short tau inversion recovery (STIR), and T2*W sequences were available, SDOs were hyperintense, iso-/hypointense, and presented signal void, respectively. This study confirms SDOs are commonly T1 hyperintense. This signal likely depends on the architecture of microcalcifications: calcium traps water protons, slowing their rotation to near Larmor frequency, and shortening T1 recovery times. Pre-contrast T1W sequences should be carefully evaluated to avoid misinterpreting SDOs for contrast-enhancing dural pathologies (such as plaque-like neoplastic dural lesions) or punctiform hemorrhage.