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Reply

The University of Texas M. D. Anderson Cancer Center Houston, TX 77030

WEB—This is a Web exclusive article.

We appreciate the opportunity to respond to the letter from Reeder et al. [1]. The authors draw attention to the important point that there are differences in the quantitation of CT density (attenuation values) among CT scanners from different manufacturers and, indeed, among scanners. We would also add that calibration of scanners is important. Nevertheless, the errors induced by these factors exceed the inherent variability of liver parenchyma and geographic variability of steatosis throughout the liver. The size of the region of interest (ROI) in our study was chosen as a compromise to allow measurement in regions where only a small area was amenable to evaluation. The issue of the "best" ROI size and configuration is open to debate.

We agree that nonalcoholic steatohepatitis is of significant clinical importance because we have been at the forefront in bringing this issue to light specifically with regard to chemotherapy for colorectal liver metastases [2]. However, as we and others [3] have stressed, clinically important steatohepatitis can be associated with as little as 5% steatosis. No reliable radiographic method to detect steatohepatitis has yet been developed. Only vague correlates (greater liver span and increased caudate-to-right-lobe ratio than simple steatosis) have been described [4]. The aim of our work was to take the first step to define a simple, reproducible method to assess steatosis. Subsequent steps in clinical management can be guided by radiographic findings (careful choice of chemotherapeutic regimens known to be associated with development of steatohepatitis, use of percutaneous biopsy, or laparoscopy before other surgical interventions as clinically indicated). Finally, hepatic parenchymal abnormalities are defined along a spectrum from mild to severe, including steatosis, steatohepatitis, fibrosis, and sinusoidal abnormalities to name a few. Imaging alone may not adequately quantify each different disease but may provide information that guides clinical management of patients with specific radiographic findings.

The authors indicate that CT and MRI costs at their institution are similar [1]. Given the widespread use of CT and its utility for imaging liver and extrahepatic organs including peritoneum, bowel, and lymph nodes, the potential utility of unenhanced CT is appealing. The addition of MRI solely for characterizing steatosis may not be practical in all cases. We use MRI in a more selective way to specifically characterize certain abnormalities in the liver. These factors and the topic of steatohepatitis remain under active study. In our experience, the cost of MRI exceeds that of CT in most situations, particularly unenhanced abdominal CT.

We provide a simple, reproducible, and reasonably cost-effective tool to estimate hepatic steatosis. As with every test, limitations exist; however, unenhanced CT can be readily performed at the time of CT for the abdomen and pelvis, and the results can be interpreted and clinical management tailored to the individual patient by a multidisciplinary team including radiologists and clinicians.

References

1. Reeder SB, Ranallo F, Taylor AJ. CT and MRI for determining hepatic fat content. (letter) AJR 2008;190 : [web]W167
2. Vauthey JN, Pawlik TM, Ribero D, et al. Chemotherapy regimen predicts steatohepatitis and an increase in 90-day mortality after surgery for hepatic colorectal metastases. J Clin Oncol2006; 24:2065 –2072[Abstract/Free Full Text]
3. Kleiner DE, Brunt EM, Van Natta M, et al. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology 2005;41 :1313 –1321[CrossRef][Medline]
4. Oliva MR, Mortele KJ, Segatto E, et al. Computed tomography features of nonalcoholic steatohepatitis with histopathologic correlation. J Comput Assist Tomogr 2006;30 : 37–43[CrossRef][Medline]

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This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ng, C. S. Articles by Vauthey, J. N. Search for Related Content PubMed Articles by Ng, C. S. Articles by Vauthey, J. N. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?