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Original Report |
1
Department of Medical Diagnostic Sciences and Special Therapies, University of
Padua, Via Giustiniani 2, 35128 Padua, Italy.
2
Department of Radiology, Cittadella Hospital, 35013 Cittadella (PD),
Italy.
3
Department of Surgery, University of Padua, 35128 Padua, Italy.
Received May 4, 2001;
accepted after revision July 10, 2001.
Address correspondence to L. Rubaltelli.
Abstract
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CONCLUSION. Although representing a frequent pattern in metastases and mycotic abscesses, a central hyperechoic core encircled by a hypoechoic halo has not yet been reported in relation to pseudotumors. Whereas multifocal target lesions in the liver suggest metastases or mycotic abscesses, an isolated target lesion in the fourth hepatic segment requires a differential diagnostic approach and a pseudotumor should be suspected because of its clinical relevance.
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We describe seven cases of targetlike pseudotumors located in the medial segment of the left lobe of patients affected by hepatic steatosis. Although central hyperechogenicity and peripheral hypoechogenicity represent a frequently seen pattern in metastases and mycotic abscesses [9], such findings have not yet been reported in relation to pseudotumors.
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The seven patients ranged in age from 39 to 75 years; six were men. In two patients, a sonographic examination was performed to stage an adenocarcinoma of the colon; in five patients, scans were obtained because the patients had upper abdominal pain. Laboratory tests showed normal hepatic function in six of the patients and a slight increase in transaminase in one.
All sonography was performed using a 3.5- to 5.0- MHz convex transducer; color Doppler and power Doppler sonographic examinations were performed (AU4 Idea, Esaote, Genoa, Italy; and Logic 500, General Electric Medical Systems, Milwaukee, WI). In all patients, scans were photographed to allow a prospective evaluation of the size and shape of the lesions.
Each patient underwent follow-up sonographic examinations for 4-12 months (mean, 8 months), and each was examined with CT that always included both unenhanced and enhanced scans. The two patients with adenocarcinoma of the large bowel were operated on and underwent intraoperative sonography and sonographically guided biopsy during surgery.
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CT in comparison with the sonographic targetlike image revealed an area of hyperattenuation in three patients; in one patient, hyperattenuation with a small central zone that was less dense was seen (Fig. 3A,3B,3C). CT did not reveal focal changes of hepatic density in the remaining three patients. Although hyperattenuation was particularly evident on the unenhanced scans, scans with contrast enhancement were never suggestive of malignancy.
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In all patients, both sonographic examination and CT revealed the presence of fatty liver. The two patients with tumors of the colon underwent intraoperative sonography and the preoperative diagnosis of the target lesion anterior to the portal vein was confirmed. Sonographically guided biopsy performed at the time detected hepatic fatty infiltration; no malignant cells were evident at histology.
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Arterial portographic CT is also able to detect portal hypoperfusion of the fourth segment, which is similar in shape to the sonographically observed spared areas [6, 7]. More recently, Itai and Matsui [11], in correlating CT, MR imaging, and sonography, have distinguished the various aspects of " `nonportal' splanchnic venous supply to the liver" in focal sparing of fatty liver, focal fat deposit, and focal enhanced area. Moreover, hyperechoic pseudotumors, likewise situated immediately anterior to the portal vein, have been reported in otherwise normal livers and interpreted as atypically located areas of focal steatosis [8].
The features of the pseudolesions reported in this study resemble a target, a central hyperechoic core being encircled by a hypoechoic halo. All the observed foci were located at the dorsal part of the fourth segment of fatty livers, a characteristic but nonpathognomic site of pseudotumors. Targetlike liver images are almost always caused by metastases (Fig. 2B), especially from large-bowel tumors, or by mycotic abscesses. A localized lymphomatosis or a hepatocellular carcinoma should also be considered in the differential diagnosis [9]. Whereas multifocal target lesions suggest a malignant disease or mycotic abscesses, a unifocal target lesion is nonspecific and requires a differential diagnosis.
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The diagnosis of pseudotumor in our study is based on sonographic follow-up, CT, and the absence of clinical symptoms or notable alterations of biochemical data. In two patients, the diagnosis of pseudolesion was confirmed by intraoperative biopsy that revealed hepatic steatosis.
A spared (hypoechoic) area with a steatotic central (hyperechoic) zone is the most probable hypothesis explaining these targetlike features which, although rare, can lead to erroneous diagnosis and therapy. Therefore, the dorsal part of the fourth segment, in addition to hypoechoic pseudotumors (Fig. 1B), readily distinguishable by their site and their morphologic characteristics, can also contain rarer hyperechoic pseudonodular (Fig. 1C) or targetlike images (Figs. 1A, 2A, and 3A).
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It can be affirmed that hypoechoic lesions in steatotic livers, located typically immediately anterior to the vena porta, can be interpreted as pseudolesions and that, in the absence of risk factors, an echographic follow-up may be a sufficient recommendation. On the contrary, targetlike images are suggestive of a malignant lesion that must be excluded by means of CT, MR imaging, or biopsy before the hypothesis of a rarer, although possible, atypical pseudolesion can be advanced.
In conclusion, sonographic targetlike findings on sonography, including isolated images, must be characterized with CT, MR imaging, or biopsy, because a differential diagnosis includes various conditions—first of all, a malignancy. Therefore, diagnosis of a targetlike pseudolesion at segment IV of the liver must rely on exclusion criteria. Although exceedingly rare, a pseudolesion should always be considered in differential diagnosis, because of its clinical relevance.
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