Detection of Coalescent Acute Mastoiditis on MRI in Comparison with CT

Abstract

Purpose Current 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. Methods The 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. Results Depending 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%. Conclusion The 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.

Differences in mastoid and middle-ear cavity opacification in CT between intensive care patients and patients with acute mastoiditis requiring surgical treatment

“…We analyzed a monocentric cohort of 24 AM patients which might seem rather small. Nevertheless, the size of our cohort is in line with or exceeds prior studies [ 4 , 5 , 16 ]. Vassbotn et al enrolled 57 patients in a 20 years retrospective study but only approximately 5 patients were older than 10 years of age [ 5 ].…”

“…Of note, in our cohort these signs were only rarely seen and may be interpreted to inherit a low sensitivity. Mastoid air cells can be heterogeneously configurated and a bone pseudodehiscence might erroneously be reported as AM-associated bone erosion [ 16 ]. The reporting of bone erosion is known to be challenging [ [15] , [16] , [17] ].…”

“…Mastoid air cells can be heterogeneously configurated and a bone pseudodehiscence might erroneously be reported as AM-associated bone erosion [ 16 ]. The reporting of bone erosion is known to be challenging [ [15] , [16] , [17] ]. Moreover, the extend of mastoid and paramastoid bone ossification is a dynamic process in an aging person [ 10 ].…”

“…Moreover, the extend of mastoid and paramastoid bone ossification is a dynamic process in an aging person [ 10 ]. Mild permeative changes may resemble a variant extent of ossification [ 10 , 16 ]. In adults, retroauricular swelling is only rarely seen which is in line with our data [ 4 ].…”

“…Vassbotn et al enrolled 57 patients in a 20 years retrospective study but only approximately 5 patients were older than 10 years of age [ 5 ]. Saat et al analyzed 32 patients of whom 23 were adults in their retrospective comparison of MRI versus CT examination to detect coalescent AM [ 16 ]. In a 19-year retrospective study from Palma et al in total 62 adult patients were enrolled but only 18 were treated surgically [ 4 ].…”