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J Thorac Cardiovasc Surg 1995;109:814-815
© 1995 Mosby, Inc.
LETTERS TO THE EDITOR |
Professor of Radiology
Thomas Jefferson University Hospital
Jefferson Medical College
132 South 10th St.
196 Main Building
Philadelphia, PA 19107
To the Editor:
I appreciate the recent effort by Burt and associates 
1 to address the ability of magnetic resonance imaging (MRI) to distinguish between benign and malignant adrenal masses in patients with non-small-cell lung cancer. Unfortunately, their methods preclude adequate evaluation.
Burt and associates do not describe their MRI technique adequately A simple label of "T2-weighted" is not sufficient. A wide variety of parameters, such as repetition time (TR) and echo time (TE), can affect image contrast on "T2-weighted" images. The limitations of this study, however, extend beyond this omission.
In their introduction, the authors refer to early studies using midfield (035 to 0.5 T) MRI instruments in which adrenal adenomas were found to have signal intensity similar to that of liver. The authors then refer to two more recent studies using higher field strength instruments (1.5 T) which "tried to develop MRI criteria to predict whether an adrenal mass is benign or malignant." 2,3 In particular, these authors found that at 1.5 T, the liver is not a suitable standard for visual comparison to adrenal glands and that T2 ratios were far more useful. Unfortunately, Burt and colleagues have attempted to discriminate between benign and malignant adrenal masses at 1.5 T using the already discredited technique of visual comparison to liver.
Simple comparison of signal intensities on T2-weighted images cannot distinguish accurately between adrenal adenomas and metastases because lipid (abundant in adrenal adenomas) and neoplastic tissue both have high signal intensity on most T2-weighted images. A more direct method for distinguishing between benign and malignant adrenal masses, based on specific histologic differences between these entities, was suggested by Leroy-Willig and coworkers 4 in 1987. In this in vitro pilot study, these authors successfully used chemical-shift (spectroscopic) magnetic resonance techniques for reliable identification of small quantities of lipid within benign adrenal masses. In a subsequent study in 1989, they 5 confirmed these principles in vivo using techniques not available at most MRI centers. Subsequently in 1992, my colleagues and I 6 published our results with chemical-shift MRI techniques that were commercially available on many MRI systems, including the system as used by Burt and associates. This chemical-shift MRI technique has subsequently been confirmed by other authors as highly accurate for distinguishing benign from malignant adrenal masses. 7 Thus we currently recommend chemical-shift MRI as a reliable and practical method for distinguishing between benign and malignant adrenal masses. Burt and coworkers in fact refer to our 1992 article and acknowledge that chemical-shift MRI might be more effective than the methods they used. They did not, as they state, use the "best currently available MRI scanning techniques" for their 1994 publication.
I hope that Burt and associates and other thoracic and cardiovascular surgeons maintain their interest in the potential impact of MRI on presurgical diagnosis. Well-designed studies on this subject would be of benefit to the surgical and radiologic literature alike.
References
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