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Temple University Hospital Philadelphia, PA 19140
We read with interest the article entitled "Subarachnoid Gadolinium Enhancement Mimicking Subarachnoid Hemorrhage on FLAIR MR Images" by Lev and Schafer [1], which dealt with the leakage of contrast material into the subarachnoid space detected on fluid-attenuated inversion recovery (FLAIR) MR imaging. We report our observation of gadolinium leakage into the subdural space detected on FLAIR MR images in patients with subdural hemorrhage.
FLAIR MR imaging is an inversion recovery pulse sequence that produces a cerebrospinal fluid-nulled heavily T2-weighted image. Also, FLAIR has mild T1-weighting, so paramagnetic contrast material appears hyperintense.
Prompt identification of subdural hemorrhage is important for proper treatment of patients. Although a large acute subdural hemorrhage can be recognized on FLAIR or conventional T1- and T2-weighted MR images, a smaller or thinner (usually <3-4 mm) hemorrhage could be missed because the blood is isointense to the adjacent brain parenchyma or skull (Fig. 2A).
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Two patients with acute (< 48 hr duration and containing oxyhemoglobin) and five patients with chronic (> 14 days duration) subdural hemorrhage were examined. The chronic subural hemorrhage appeared isointense to the cerebrospinal fluid on the unenhanced T1- and T2-weighted sequences. After administering a standard dose of 0.1 mmol per kg of body weight of IV gadolinium, we first obtained T1-weighted images and then fast-FLAIR images.
FLAIR MR images obtained with gadolinium revealed a characteristic intense dural and subdural enhancement in all seven patients with subdural hemorrhage, both acute and chronic (Figs. 2B and 3B). In addition, the extent of the acute subdural hemorrhage was best visualized on gadolinium FLAIR images compared with the conventional T1- or T2-weighted or unenhanced FLAIR images. Gadolinium-enhanced T1-weighted spin-echo images showed dural enhancement in one of the patients with acute hemorrhage and in all of the patients with chronic hemorrhage (Fig. 3A); however, the enhancement was much more intense on the gadolinium-enhanced FLAIR images.
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The increased conspicuity of subdural hemorrhage on the gadolinium FLAIR images appears to be related to the diffusion of contrast material into the subdural space. The diffusion of gadolinium is likely due to the increased membrane permeability and neovascularization related to trauma and associated inflammation. The mechanism for better visualization of gadolinium-induced hyperintensity on FLAIR MR images is probably related to a combination of the presence of a lower concentration of gadolinium within the subdural space because of the diluting effect of blood and the effect of T1-weighting on the FLAIR images [2].
For the larger clinically significant subdural hemorrhage in adults, the conventional T1- and T2-weighted MR sequences are probably adequate; however, when the subdural hemorrhage is small and thin, gadolinium-enhanced FLAIR MR imaging appears to be the best sequence for detection and visualization of the full extent of the subdural hemorrhage. This finding could be important in proper treatment of infants and children in whom thin (3-4 mm) subdural hemorrhage could be clinically significant [3]. Similarly, subdural hemorrhage in the posterior fossa often tends to be thin and would probably be best revealed by gadolinium-enhanced FLAIR MR imaging. Lastly, we believe that there is a role for gadolinium-enhanced FLAIR MR imaging in the assessment of suspected intracranial injury caused by child abuse; subdural hemorrhage is the most frequent form of intracranial abnormality found in these patients.
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This article has been cited by other articles:
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  J.M. Morris and G.M. Miller Increased Signal in the Subarachnoid Space on Fluid-Attenuated Inversion Recovery Imaging Associated with the Clearance Dynamics of Gadolinium Chelate: A Potential Diagnostic Pitfall AJNR Am. J. Neuroradiol., November 1, 2007; 28(10): 1964 - 1967. [Abstract] [Full Text] [PDF]
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