TO THE EDITOR: We read with great interest the article by Zamora and Lin5 (Zamora CA, Lin DD: Enhancing subdural effusions mimicking acute subdural hematomas following angiography and endovascular procedures: report of 2 cases. J Neurosurg 123:1184–1187, November 2015). The authors reported 2 interesting cases of iodine contrast extravasation into the sudural space mimicking acute subdural hematoma after intracranial neuroendovascular procedures. We applaud the authors for bringing attention to this important phenomenon and appreciate their literature review to help readers better understand the pathophysiology of contrast extravasation.
We have encountered similar cases and found that dual-energy CT (DECT) has significant diagnostic value in differentiating between contrast and blood in the subdural space.3 Dual-energy CT is a relatively new imaging technology that first became commercially available in 2006. It is based on the principle that materials have different attenuations at varying energy levels, which means that materials with similar Hounsfield units at one energy level will have different Hounsfield units at another energy level. Given this intrinsic property of materials, CT images obtained at 80 and 140 kV can be processed by computer algorithms, and each voxel can be separated into brain parenchyma, iodine, and hemorrhage components.1 Given these components for each voxel, computer software can then generate a set of images including a single-source image (equivalent to conventional CT), a virtual nonenhanced image, and an iodine overlay image. Hemorrhage would only appear hyperdense on a virtual nonenhanced image, while contrast extravasation would only appear hyperdense on an iodine overlay image (Table 1). Multiple recent studies have demonstrated that DECT can readily differentiate hematoma from contrast extravasation with high sensitivity, specificity, and positive predictive value.1,2,4
Appearance of contrast extravasation versus hemorrhage on DECT
| Diagnosis | Conventional CT | Virtual Nonenhanced Image | Iodine Overlay Image |
|---|---|---|---|
| Hemorrhage | Hyperdense | Hyperdense | Nonhyperdense |
| Contrast extravasation | Hyperdense | Nonhyperdense | Hyperdense |
| Mixed hemorrhage/contrast extravasation | Hyperdense | Hyperdense | Hyperdense |
We recently encountered a case that illustrates this point nicely. Our patient presented with subarachnoid hemorrhage and had external ventricular drain placement for hydrocephalus. Subsequently, the patient underwent endovascular treatment of a left posterior communicating artery aneurysm, and postoperative CT demonstrated a left-sided hyperdense mass in the subdural space concerning for subdural hematoma (Fig. 1A). However, the subdural collection appeared hyperdense on an iodine overlay image (Fig. 1B) and was not hyperdense on a virtual nonenhanced image (Fig. 1C). Given these imaging characteristics on DECT, the diagnosis of contrast extravasation was made. Indeed, a follow-up CT scan the next day showed near-complete washout of the contrast material (Fig. 1D).
A: Postoperative CT demonstrating a left-sided hyperdense subdural space concerning for subdural hematoma. B: Iodine overlay image from DECT demonstrating hyperdense signal suggesting contrast extravasation. C: Virtual nonenhanced image from DECT did not show hyperdense signal from the subdural collection, suggesting the absence of hematoma. D: Follow-up CT scan obtained the next day, demonstrating near-complete washout of the contrast material. Figure is available in color online only.
Dual-energy CT is an important tool in distinguishing intracranial hemorrhage from contrast extravasation, and it can help clinicians quickly reach the correct diagnosis and avoid potentially unnecessary surgical intervention.
References
- 1↑
Gupta R, , Phan CM, , Leidecker C, , Brady TJ, , Hirsch JA, & Nogueira RG, et al.: Evaluation of dual-energy CT for differentiating intracerebral hemorrhage from iodinated contrast material staining. Radiology 257:205–211, 2010
- 2↑
Phan CM, , Yoo AJ, , Hirsch JA, , Nogueira RG, & Gupta R: Differentiation of hemorrhage from iodinated contrast in different intracranial compartments using dual-energy head CT. AJNR Am J Neuroradiol 33:1088–1094, 2012
- 3↑
Postma AA, , Das M, , Stadler AAR, & Wildberger JE: Dualenergy CT: what the neuroradiologist should know. Curr Radiol Rep 3:16, 2015
- 4↑
Tijssen MPM, , Hofman PAM, , Stadler AAR, , van Zwam W, , de Graaf R, & van Oostenbrugge RJ, et al.: The role of dual energy CT in differentiating between brain haemorrhage and contrast medium after mechanical revascularisation in acute ischaemic stroke. Eur Radiol 24:834–840, 2014
- 5↑
Zamora CA, & Lin DD: Enhancing subdural effusions mimicking acute subdural hematomas following angiography and endovascular procedures: report of 2 cases. J Neurosurg 123:1184–1187, 2015
