A New Classification System is Helpful in Diagnosing Intracranial Complications of Acute Mastoiditis in CT

To assess the usefulness of the new computed tomography (CT) classification criteria proposed by Horowitz et al. and their effect on inter-observer agreement when estimating intracranial complications of acute mastoiditis.

In this study 53 contrast-enhanced CT scans of patients with acute mastoiditis were each retrospectively reviewed by two radiologists, using two different assessment criteria for intracranial complications. According to the new criteria, intracranial CT findings in the perisinuous area were graded into four classes (I normal, II linear halo, III nodular halo ≤4 mm thick and IV nodular halo >4 mm thick), where classes III and IV indicate a high risk for epidural abscesses. Inter-reader agreement was estimated by weighted kappa analysis for both methods.

With the old method, epidural abscesses were suspected in six and venous sinus thrombosis in five patients. With the new method, high-risk perisinuous lesions (classes III or IV) were detected in 11 patients, and sinus thrombosis outside the perisinuous area in 3 patients. All epidural abscesses were in the perisinuous area. Of the patients four, in whom intracranial pathology was not suspected with the old method, fell into the high-risk group (class III) according to the new method. All class IV lesions were also determined to be pathological with the old method. The inter-observer agreement (weighted kappa) rose from 0.21 (old method) to 0.80 (new method) when assessing epidural abscesses and from 0.44 (old method) to 0.85 (new method) when assessing sinus thrombosis.

The new assessment method raised the inter-observer agreement for detection of intracranial acute mastoiditis complications, namely epidural abscesses and venous sinus thrombosis.