Dual-Energy CT in Enhancing Subdural Effusions that Masquerade as Subdural Hematomas: Diagnosis with Virtual High-Monochromatic (190-keV) Images

Abstract

Background and purpose: Extravasation of iodinated contrast into subdural space following contrast-enhanced radiographic studies results in hyperdense subdural effusions, which can be mistaken as acute subdural hematomas on follow-up noncontrast head CTs. Our aim was to identify the factors associated with contrast-enhancing subdural effusion, characterize diffusion and washout kinetics of iodine in enhancing subdural effusion, and assess the utility of dual-energy CT in differentiating enhancing subdural effusion from subdural hematoma.

Materials and methods: We retrospectively analyzed follow-up head dual-energy CT studies in 423 patients with polytrauma who had undergone contrast-enhanced whole-body CT. Twenty-four patients with enhancing subdural effusion composed the study group, and 24 randomly selected patients with subdural hematoma were enrolled in the comparison group. Postprocessing with syngo.via was performed to determine the diffusion and washout kinetics of iodine. The sensitivity and specificity of dual-energy CT for the diagnosis of enhancing subdural effusion were determined with 120-kV, virtual monochromatic energy (190-keV) and virtual noncontrast images.

Results: Patients with enhancing subdural effusion were significantly older (mean, 69 years; 95% CI, 60-78 years; P < .001) and had a higher incidence of intracranial hemorrhage (P = .001). Peak iodine concentration in enhancing subdural effusions was reached within the first 8 hours of contrast administration with a mean of 0.98 mg/mL (95% CI, 0.81-1.13 mg/mL), and complete washout was achieved at 38 hours. For the presence of a hyperdense subdural collection on 120-kV images with a loss of hyperattenuation on 190-keV and virtual noncontrast images, when considered as a true-positive for enhancing subdural effusion, the sensitivity was 100% (95% CI, 85.75%-100%) and the specificity was 91.67% (95% CI, 73%-99%).

Conclusions: Dual-energy CT has a high sensitivity and specificity in differentiating enhancing subdural effusion from subdural hematoma. Hence, dual-energy CT has a potential to obviate follow-up studies.

Fig 1.

Flowchart shows the patient-selection process. PTBI indicates penetrating traumatic brain injury.

Fig 2.

A 75-year-old woman who developed bilateral enhancing subdural effusion on a follow-up study obtained 11 hours after contrast infusion. Axial 120-kV image shows hyperdense subdural effusions (arrowheads, A) and right frontal subarachnoid hemorrhage (curved arrow, B). Iodine-overlay image shows contrast-stained subdural effusions (arrowheads). Virtual high-monochromatic (190-keV) (C) and virtual noncontrast (D) images show hypoattenuation (arrowheads) in the fluid.

Fig 3.

A 55-year-old man with left cerebral convexity and right occipital acute subdural hematomas with enhancement of a left subdural hematoma on a follow-up study obtained 6 hours after contrast infusion. Follow-up axial 120-kV (A) and iodine-overlay (B) images show hyperdense and contrast-stained subdural hematomas, respectively (arrowheads). Virtual high-monochromatic (190-keV) (C) and virtual noncontrast (D) images show hyperattenuation corresponding to the hematoma over the occipital lobes and left temporal lobe (arrowheads) and hypoattenuation corresponding to the enhancing component of hematoma over the left frontal lobe (curved arrow).

Fig 4.

Time-concentration curve. Spline graph using penalized B-spline shows iodine (milligrams/milliliter), attenuation (HU) related to contrast media (CM), and mixed 120-kV (Mixed 0.5) images versus hours (hrs) after contrast administration.