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Institute of Clinical Medicine University of Tsukuba Tsukuba, 305-8575, Japan
The University of California San Francisco pediatric radiology group showed that focal fatty infiltration of the liver was less frequently encountered in children and young adults and that occurrence of this condition increased significantly with age [1]. The authors defined focal fatty infiltration on CT as a hypoattenuating geometric or ovoid (the latter word erroneously omitted in the "Materials and Methods" section) lesion adjacent to the falciform ligament, gallbladder fossa, or porta hepatis.
Shortly after the histopathologic description of focal fatty change in 1980, radiologists continued to report focal fatty infiltration and irregular fatty infiltration as potentially malignant hepatic pseudolesions. As radiologists have learned more, the distribution, relative incidence, etiology, and morphology of solitary focal fatty infiltration mimicking a tumor have been clarified to a considerable degree. This entity is frequently adjacent to the falciform ligament and is caused by systemic venous supply to the liver parenchyma through physiologic communication of a systemic vein, such as the inferior vein of Sappey, with the intrahepatic portal vein [2,3,4]. It sometimes occurs around the hepatic hilum (caused by the parabiliary venous system or aberrant gastric venous drainage carrying abundant hormones—mainly insulin) [5]. Rarely, for unknown cause, this entity occurs elsewhere; it could even be apart from the hepatic capsule, in striking contrast with the former two locations.
However, to my knowledge, no articles have pointed out that focal fatty infiltration often occurs around the gallbladder (with the exception of the gallbladder neck [3]). All focal fatty infiltration in the patients studied by Kammen et al. [1] was localized adjacent to the falciform ligament. Fortunately for the authors, no patients had a solitary metastatic lesion adjacent to the gallbladder.
In the "Discussion" section of their article, Kammen et al. [1] described etiology that applies not to focal fatty infiltration but to diffuse fatty infiltration, according to current knowledge. Potential predisposing conditions were described in seven of 20 patients; however, I wonder what differences in underlying diseases may exist between patients with focal fatty infiltration and those without. The authors hypothesized without any data that a higher percentage of body fat is related to focal fatty infiltration. If they could not the obtain body weight and height of patients, they still could considerably evaluate this factor on the basis of CT findings of subcutaneous and intraabdominal fat. I think their hypothesis may be correct, not because of a relationship to obesity—as is the case with diffuse fatty infiltration—but probably because of increased venous supply to the liver caused by an increased systemic venous pressure associated with obesity.
Kammen et al. [1] described the characteristic CT appearance of focal fatty infiltration of the liver as vessel penetration and lack of mass effects. However, this is true in large lesions; such findings are rarely found in small lesions, especially those adjacent to the falciform ligament. Color Doppler sonography detects a vein running into focal fatty infiltration occasionally around the hepatic hilum [6] or often into focal spared area around the gallbladder and hepatic hilum [7, 8] but rarely in the area adjacent to falciform ligament. I think that xenon-133 scanning and other scintigraphy would not have been useful in imaging the smaller lesions Kammen et al. encountered (0.4-2.2 cm, with a mean diameter of 1.3 cm).
The authors successfully showed that the incidence of focal fatty infiltration adjacent to the ligament falciform in children and young adults increases with age [1]. However, on the basis of recent academic achievement in imaging and other fields, the authors should have more logically defined the location of focal fatty infiltration (fortunately no ill effect resulted) and made their discussion more practically useful by focusing on the small lesions they encountered.
References
University of California San Francisco San Francisco, CA 94143 Children's Hospital Research Center at Oakland Oakland, CA 94609
My colleagues and I thank Dr. Itai for the letter regarding our article [1]. The primary motivation for our work was to familiarize radiologists with the incidence and appearance of focal fatty infiltration of the liver in children. We found that in children older than 5 years, the incidence of focal fatty infiltration of the liver increases with age and should be taken into consideration when evaluating the liver for possible disease. In younger children, focal fatty liver is extremely uncommon and should be a diagnosis of exclusion.
Our article [1] discussed the cause of fatty infiltration of the liver, but Itai is correct in stating that focal fatty infiltration adjacent to the falciform ligament has also been shown to be related to aberrant right gastric drainage to this site [2,3,4]. In children, we have observed focal fatty infiltration of the liver only adjacent to the falciform ligament. In adults, we have seen focal fatty infiltration of the liver adjacent to the falciform ligament, porta hepatis, and gallbladder fossa.
In our retrospective analysis, we looked at possible causes for fatty infiltration of the liver and found potential predisposing conditions in seven of 20 patients. However, we did not evaluate for these conditions in our control group. Because the incidence of focal fatty infiltration increases with age, we postulated that this might be related to an increased ratio of body fat to total weight. A prospective study controlling for age, weight, and percentage of body fat could potentially answer these questions.
In general, focal fatty infiltration of the liver in children is a low-density geometric lesion adjacent to the falciform ligament. A helpful feature to distinguish focal fatty infiltration (if the lesion is large enough) from other liver abnormalities is the presence of a nondisplaced vessel coursing through it. Many of the lesions are too small for this helpful feature to be recognized. Suspicious liver lesions should be further investigated, and if the diagnosis of focal fat is suggested, a lipid-sensitive MR imaging sequence can reliably establish the diagnosis.
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