Midbrain area and the hummingbird sign from brain MRI in progressive supranuclear palsy and idiopathic normal pressure hydrocephalus

Abstract

Background and Purpose:The main radiological finding in progressive supranuclear palsy (PSP) is reduced midbrain volume. Both qualitative (e.g., hummingbird sign) and quantitative (e.g., area measurements) markers have been noted. Recent studies have shown a similar reduction also in idiopathic normal pressure hydrocephalus (iNPH). The purpose was to investigate the reliability and accuracy of these markers in discriminating PSP from iNPH and controls. Methods: Eight neuroradiologists viewed sagittal MR images of the midbrain from 104 subjects: 26 PSP patients, 40 iNPH patients, and 38 healthy controls. They visually assessed whether the hummingbird sign was present or not, grading their confidence from 1 to 5. Assessments were translated into a score between +5 and -5: from maximum confidence of presence to maximum confidence of absence. A positive median score was considered to indicate hummingbird sign. Sagittal midbrain area was manually measured in each subject.Results: Seventy-seven percent of PSP patients, 65% of iNPH, and 3% of controls were visually assessed as having the hummingbird sign. Manually measured midbrain area also showed overlap between PSP and iNPH. Regarding discrimination of PSP patients, midbrain area measurements, using a cutoff of 90 mm 2 , yielded a higher area under the curve (AUC = 0.86) than visual assessment scores (AUC = 0.83), and higher reliability. Conclusions:Measuring sagittal midbrain area is more accurate and reliable than visual assessment. Due to significant overlap in appearance, a midbrain with a hummingbird sign or reduced sagittal area should raise the suspicion of PSP only after other signs of iNPH have been considered.

Higher prevalence of idiopathic normal pressure hydrocephalus‐like MRI features in progressive supranuclear palsy: An imaging reminder of atypical parkinsonism

“…Traditionally, NPH and PSP are classified as two distinct diseases and should be thoroughly distinguished to avoid futile treatment. Several researchers tried to find additional MRI indexes differentiating one from the other, such as Magnetic Resonance Parkinsonism Index, Magnetic Resonance Hydrocephalic Index, interpeduncular angle, midbrain area, and cortical thickness (Bianco et al, 2022;Ohara et al, 2020;Quattrone et al, 2020;Ugga et al, 2020;Virhammar et al, 2022). In our opinion, a portion of the two entities does overlap and share similar features, implying the transitory role of NPH mimics in the clinical course of PSP.…”

Imaging Markers for Normal Pressure Hydrocephalus: An Overview

“…Hummingbird sign, an imaging sign of PSP reflecting midbrain atrophy with sparing of pons, could also been found in a great percentage of iNPH patients. Thus, when this sign is present, the other iNPH imaging signs should be evaluated before PSP suspicion is risen [77]. According to another study, the combination of EI and CA markers helped to discriminate PSP patients with marked ventricular dilatation from patients with iNPH, which could benefit from shunt surgery [78].…”

Automatic assessment of disproportionately enlarged subarachnoid-space hydrocephalus from 3D MRI using two deep learning models

“…The main reason for missed detection or misdiagnosis of Hakim disease, even when advanced imaging technologies are widely available, is that Hakim disease is often less prominent with ventricular dilatation (VD) and more prominent with Sylvian fissure dilation (SFD), which is also caused by medial temporal lobe atrophy, a wellknown imaging feature specific to Alzheimer's disease and mild cognitive impairment (Coupe et al, 2019;Wang et al, 2022). Consequently, VD and SFD are easily misinterpreted as brain atrophy related to neurodegenerative diseases including Alzheimer's disease (McCarty et al, 2019;Virhammar et al, 2021). To distinguish Hakim disease from focal cerebral atrophy, disproportionately enlarged subarachnoid space hydrocephalus (DESH) (Hashimoto et al, 2010;Shinoda et al, 2017;Gunter et al, 2019;McCarty et al, 2019;Virhammar et al, 2021), including tightened sulci in the high convexities (THC) (Sasaki et al, 2008;Ishikawa et al, 2010;Narita et al, 2016;Yamada et al, 2016aYamada et al, , 2021bYamada et al, , 2023aYamada and Mase, 2023), have recently been noted as the most important imaging features specific to Hakim disease.…”