Detection of Coalescent Acute Mastoiditis on MRI in Comparison with CT

R Saat,A Laulajainen-Hongisto,A Markkola,J Jero,G Kurdo

doi:10.1007/s00062-020-00931-0

Abstract

PurposeCurrent imaging standard for acute mastoiditis (AM) is contrast-enhanced computed tomography (CT), revealing inflammation-induced bone destruction, whereas magnetic resonance imaging (MRI) outperforms CT in detecting intracranial infection. Our aim was to compare the diagnostic performance of MRI with CT in detecting coalescent AM and see to which extent MRI alone would suffice to diagnose or rule out this condition.MethodsThe MR images of 32 patients with AM were retrospectively analyzed. Bone destruction was evaluated from T2 turbo spin echo (TSE) and T1 Gd magnetization-prepared rapid acquisition with gradient echo (MPRAGE) images. Intramastoid enhancement and diffusion restriction were evaluated subjectively and intramastoid apparent diffusion coefficient (ADC) values were measured. The MRI findings were compared with contrast-enhanced CT findings of the same patients within 48 h of the MR scan.ResultsDepending on the anatomical subsite, MRI detected definite bone defects with a sensitivity of 100% and a specificity of 54–82%. Exception was the inner cortical table where sensitivity was only 14% and specificity was 76%. Sensitivity for general coalescent mastoiditis remained 100% due to multiple coexisting lesions. The absence of intense enhancement and non-restricted diffusion had a high negative predictive value for coalescent mastoiditis: an intramastoid ADC above 1.2 × 10−3 mm2/s excluded coalescent mastoiditis with a negative predictive value of 92%.ConclusionThe MRI did not miss coalescent mastoiditis but was inferior to CT in direct estimation of bone defects. When enhancement and diffusion characteristics are also considered, MRI enables dividing patients into low, intermediate and high-risk categories with respect to coalescent mastoiditis, where only the intermediate risk group is likely to benefit from additional CT.

Highlights

Despite the decreased incidence of acute mastoiditis (AM) in the antibiotic era, AM cases still occur and require prompt and effective treatment to avoid life-threatening complications [1, 2]
Infection was on the left in 14 (44%) and on the right side in 18 (56%) patients
ADC apparent diffusion coefficient, T2 TSE T2 turbo spin echo, 3D T1 MPRAGE Gd 3-dimensional isotropic T1 magnetization-prepared rapid acquisition with gradient echo with intravenous gadoterate meglumine ings are very unlikely to have coalescent AM and unlikely to benefit from additional computed tomography (CT)

Summary

Introduction

Despite the decreased incidence of acute mastoiditis (AM) in the antibiotic era, AM cases still occur and require prompt and effective treatment to avoid life-threatening complications [1, 2]. Diagnostic and treatment algorithms rely mostly on the clinical picture, imaging is required when complications such as coalescent AM (AM with inflammatory bone destruction) or intracranial spread are suspected. Imaging may support clinical decisions in equivocal situations, such as to estimate the need for surgery when the response to conservative treatment is suboptimal [3, 4]. Some authors recommend imaging all AM patients to exclude clinically silent complications [5,6,7]. The current standard for imaging AM is contrast-enhanced high-resolution CT, due to its ability to detect inflammation-induced bone destruction [8, 9].

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