Reversible MR changes in the cat brain after cerebral fat embolism induced by triolein emulsion

Abstract

Background and purpose: Clinical cerebral-fat embolism shows both reversible and irreversible changes. We used MR imaging to investigate the reversibility of embolized lesions induced with a fat-emulsion technique and to evaluate the histologic findings.

Methods: A fat emulsion was made with 0.05 mL of triolein and 20 mL of normal saline and vigorous to-and-fro movement through a three-way stopcock. In 50 cats, the internal carotid artery was infused with the fat emulsion. Cats were divided into six groups on the basis of time delay after embolization: 1 hour; 1 and 4 days; and 1, 2, and 3 weeks. MR imaging and histologic examination were performed at these times.

Results: Embolized lesions were hyperintense on T2-weighted images, isointense or mildly hyperintense on diffusion-weighted images, isointense on apparent diffusion coefficient maps, and enhancing on gadolinium-enhanced T1-weighted images at 1 hour. These MR imaging findings were less evident at day 1 and reverted to normal after day 4 (isointense on all images). Electron microscopy showed minimal findings in the cortical lesion in groups 1 and 2 (group 1 at 1 hour and group 2 at 1 hour and 1 day). Light microscopic findings revealed evidence of necrosis-small focal gliosis and demyelination in the periventricular white matter-in only one cat. The number of intravascular fat globules was not significantly different between groups, as visualized by oil red O staining.

Conclusion: Cerebral-fat embolism induced by a triolein emulsion revealed reversible MR findings and minimal histologic findings.

Fig 1.

Fat globules. A, Photomicrograph of the fat emulsion. The fat globules are of variable size, mostly less than two times the size of red blood cells (arrow, original magnification ×40). B, An intravascular fat globule is pinkish-red on oil red O staining (original magnification ×200).

Fig 2.

Images obtained in a cat in group 4: A indicates T2WIs; B, Gd-enhanced T1WIs; C, DWIs; D, ADC maps; E, light photomicrograph; F, electron photomicrograph. 1 indicates 1 hour after embolization; 2, 1 day; and 3, 7 days. At 1 hour, the embolized lesion in the left hemisphere appears hyperintense in A1, enhanced in B1, mildly hyperintense in C1, and isointense in D1. At 1 day, T2WI hyperintensity (A2) and contrast enhancement (B2) are substantially decreased and not evident at day 7 (A3, B3). After day 1, DWIs (C2, C3) and ADC maps (D2, D3) reveal isointensity of the lesion. In E, Light microscopy of the gray matter (top) and white matter (bottom) shows no evidence of demyelination (Luxol fast blue stain, original magnification ×100). In F, Electron microscopy of the gray matter shows no evidence of neuropil or interstitial swelling (original magnification ×3000).