Utility of the Midbrain Tegmentum Diameter in the Differential Diagnosis of Progressive Supranuclear Palsy from Idiopathic Parkinson's Disease

Abstract

Background and purpose: Various magnetic resonance (MR) measurements have been proposed to aid in differentiating between progressive supranuclear palsy (PSP) and idiopathic Parkinson's disease (IPD); however, these methods have not been compared directly. The aim of this study was to determine which measurement method exhibits the highest power to differentiate between PSP and IPD.

Methods: Brain MR images from 82 IPD and 29 PSP patients were analyzed retrospectively. T1-weighted 3D volumetric axial images, or sagittal images reconstructed from those axial images were examined. MR measurements included the length from the interpeduncular fossa to the center of the cerebral aqueduct at the mid-mammillary-body level, adjusted according to the anterior commissure-posterior commissure length (MB(Tegm)), the ratio of the midbrain area to the pons area (M/P ratio) as measured by both Oba's method (Oba M/P) and Cosottini's method (Cosottini M/P), and a modified MR parkinsonism index (mMRPI).

Results: Receiver operating characteristic (ROC) analysis indicated that the areas under the ROC curves (AUCs) exceeded 0.70, with a high intrarater reliability for all MR measurement methods. ROC analyses of four MR measurements yielded AUCs of 0.69-0.76. At the cutoff value with the highest Youden index, mMRPI had the highest sensitivity, while Oba M/P offered the highest specificity. A comparison of the ROC analyses revealed that MB(Tegm) was superior to mMRPI in differentiating PSP from IPD (p=0.049). There was no difference in discriminating power among Oba M/P, Cosottini M/P, and MB(Tegm).

Conclusions: Simple measurements of MB(Tegm) on axial MR images at the mid-mammillary-body level are comparable to measurements of the M/P ratio with regard to their ability to discriminate PSP from IPD.

Keywords: MRI; idiopathic Parkinson's disease; neuroimaging; progressive supranuclear palsy.

Fig. 1. Schematic diagrams of midsagittal (A and B) and axial (D) images of the brain and parasagittal and coronal (C) T1-weighted volumetric magnetic resonance (MR) images. A: The midbrain area (Oba M) and the pons area (Oba P) were measured using a standard line as described by Oba et al. B: The midbrain area (Cosottini M) and the pons area (Cosottini P) were measured using a standard line as described by Cosottini et al. C: The MR parkinsonism index (MRPI) was measured using a modified version of Quattrone's method (mMRPI). The middle cerebellar peduncle length measured in a parasagittal image is marked with an asterisk (*). Bilateral superior cerebellar peduncle lengths are marked by arrows (↓). D: The axial length of the midbrain tegmentum, adjusted according to the anterior commissure-posterior commissure length (MB^Tegm), was measured from the anterior interpeduncular fossa to the center of the cerebral aqueduct at the plane of the mid-mammillary body. Lines between the midbrain and the pons and between the pons and medulla oblongata represent the lower borders of the midbrain and pons areas, respectively.

Fig. 2. Receiver operating curve analyses of the brain structure measurements for differentiating progressive supranuclear palsy (PSP) from idiopathic Parkinson's disease (IPD). A: PSP vs. IPD, not age matched (n=111). B: PSP vs. IPD, age-matched. C: Probable PSP vs. IPD. Cosottini M/P: ratio of the midbrain area to the pons area in the midsagittal plane, measured by Cosottini's method, Oba M/P: ratio of the midbrain area to the pons area in the midsagittal plane, measured by Oba's method.