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Japanese Journal of Clinical Oncology Pages 189-192

A Case of Liver Metastasis from Colon Cancer Masquerading as Focal Sparing in a Fatty Liver
Introduction
Case Report
Discussion
References

A Case of Liver Metastasis from Colon Cancer Masquerading as Focal Sparing in a Fatty Liver

A Case of Liver Metastasis from Colon Cancer Masquerading as Focal Sparing in a Fatty Liver Motohisa Kato1, Shigetoyo Saji1, Masayuki Kanematsu2, Daizo Fukada1, Kiichi Miya1, Takao Umemoto1, Katsuyuki Kunieda1, Yasuyuki Sugiyama1, Ikuhide Kuwahara1 and Kuniyasu Shimokawa3

1Second Department of Surgery, 2Department of Radiology and 3Department of Pathology, Gifu University School of Medicine, Gifu, Japan

Focal sparing in diffusely fatty liver is a well recognized entity. However, it occasionally creates some problems in the diagnosis of hepatic mass lesions. We recently experienced a case of liver metastasis from colon cancer which appeared as a wedge-shaped hyperdense area on non-enhanced CT (computed tomography). Other imaging techniques also demonstrated a wedge-shaped area which was difficult to distinguish from mere focal sparing in the fatty liver. CT arteriography and dynamic magnetic resonance images were useful for diagnosing this metastatic tumor. CT during arterial portography showed a wedge-shaped ischemic area in the anterior segment caused by intrahepatic portal vein blockade. The histological findings eventually revealed that the tumor, an adenocarcinoma, was surrounded by fibrotic tissue that mimicked focal sparing. We present the radiological features of this case and discuss how to arrive at a correct diagnosis.

Key words: liver - metastasis fatty infiltration - CT - MRI

INTRODUCTION

Diffuse fatty liver is a well recognized entity that is easily diagnosable by computed tomography (CT) or sonography. Fatty change frequently shows an irregular distribution, most likely reflecting regional differences in perfusion; in areas of decreased portal flow, less fat tends to accumulate than in better-perfused areas (1 ). This condition, called focal sparing, can occur in diverse patterns. Diagnosis of focal hepatic lesions is therefore often difficult in patients with fatty infiltration. We recently experienced a case of metastatic liver tumor masquerading as a wedge-shaped area of focal sparing in a fatty liver.

CASE REPORT

A 62-year-old, slightly obese man was referred to us on April 12, 1996 because of suspected liver metastasis. He had undergone sigmoidectomy for well differentiated adenocarcinoma of the sigmoid colon on September 2, 1993 in our department. Preoperative CT scan and magnetic resonance (MR) imaging in 1993 had shown a slightly fatty liver and no metastasis. According to histological examination of resected specimens of the colon, the tumor had invaded as far as the subserosal layer, and all of 24 extirpated lymph nodes were cancer-free. The patient had been followed up at another hospital, and was referred to us because of abnormal CT findings and elevation of the serum CEA level. On admission, his general condition was good. The heart and lungs were clear to auscultation and palpation of the liver revealed no abnormality. A full blood count on admission showed normal values. Serum electrolytes, blood urea nitrogen, creatinine, glucose, total bilirubin, alkaline phosphatase, aspartate aminotransferase (AST), alanine aminotransferase (ALT), leucine


Figure 1.Non-enhanced CT on admission in 1996, showing a wedge-shaped hyperdense area in the anterior segment of the right lobe.


Figure 2.Sonography shows an elliptical mass surrounded by a halo, indicated by the white wedges, in the anterior segment of the right lobe; its internal echogenicity is irregular.aminopeptidase (LAP) and gamma-glutamyltranspeptidase ([gamma]-GTP) were all within the normal ranges. The serum albumin level was 3.2 g/dl (normally 3.9-4.9 g/dl) and the cholinesterase level 108 IU/l (185-430 IU/l). The CEA level was 15.1 ng/ml and the cancer antigen 19-9 (CA19-9) level 167.4 U/ml. A chest X-ray on admission showed no abnormality.

Non-enhanced CT demonstrated a fatty liver associated with a wedge-shaped hyperdense area which occupied almost all of the anterior segment of the right lobe (Fig. 1 ); enhanced CT was not done. On sonography, the entire liver showed increased echogenicity, suggestive of fat deposition. An elliptical mass surrounded by a halo was seen in the anterior segment of the right lobe, and its internal echogenicity was irregular (Fig. 2 ). In terms of the abnormal finding in the anterior segment, non-enhanced CT suggested focal sparing and sonography suggested a metastatic tumor. Two further examinations were therefore performed to distinguish between these two types of lesion.


Figure 3.(a) T1-weighted MR images show a wedge-shaped hypointense area, as seen on non-enhanced CT (TR = 316, TE = 11). (b) T2-weighted MR images show an irregularly shaped hypointense area in the anterior segment (TR = 2000, TE = 80). (c) Opposed-phase MR images show a hyperintense area in the entirely hypointense liver (TR = 120, TE = 2.1). (d) In-phase MR images show a hypointense area in the entirely hyperintense liver ( TR = 120, TE = 4.2).

On MR imaging, T1-weighted images (Fig. 3 ) showed a wedge- shaped hypointense area, as seen on non-enhanced CT, and T2-weighted images (Fig. 3 ) showed an irregularly shaped hypointense area in the anterior segment. Opposed-phase images showed a hyperintense area in the entirely hypointense liver (Fig. 3 ). In contrast, in-phase images showed a hypointense area in the entirely hyperintense liver (Fig. 3 ). Although these four sequences suggested focal sparing, dynamic MR images clearly showed irregular enhancement in the abnormal area of the anterior segment, suggesting a metastatic tumor (image not shown). Normal vessel-like structures were not observed in this abnormal area.


Figure 4. (a) CT arteriogrphy discloses irregular enhancement in the anterior segment, as seen on dynamic MR imaging. (b) CT during arterial portography clearly shows a wedge-shaped hypointese area in the anterior segment, indicating ischemia, due to intrahepatic portal vein blockade.

CT arteriogrphy (CTA) (Fig. 4 ) disclosed irregular enhancement in the anterior segment, as seen on dynamic MR images. CT during arterial portography (CTAP) (Fig. 4 ) clearly showed a wedge-shaped hypointese area in the anterior segment, suggesting ischemia in this area.

Based on these findings, this lesion was strongly suspected of being a metastatic tumor associated with focal sparing, and a fine-needle biopsy was performed under sonographic guidance on May 22, 1996. This proved that the lesion was an adenocarcinoma and right hepatectomy was performed on July 4, 1996. At surgery, the tumor was found to be exposed on the surface of the anterior segment, adjoining not the middle hepatic vein but the right hepatic vein. Macroscopic observation of the sliced resected specimen showed that the tumor was elliptic and not encapsulated, measuring 6.0 * 5.5 * 5.0 cm. Histological examination revealed that the tumor, a well differentiated adenocarcinoma, was surrounded by fibrotic tissue, and that this fibrotic tissue contained fewer fat vacuoles than the rest of the liver parenchyma (Fig. 5 ).

After the operation, the patient suffered from severe jaundice and hyperammonemia. Moreover, his temperature rose to 39oC on the 5th postoperative day, and methicillin-resistant Staphylococcus aureus (MRSA) was detected in his blood. The serum total bilirubin level rose to 19.9 mg/dl on the 11th postoperative day. Postoperative liver insufficiency and sepsis were diagnosed and intensive care including plasma exchange and administration of vancomycin was performed. The serum bilirubin and ammonia levels had recovered almost to normal by about five weeks after the operation and the patient was discharged on the 74th post- operative day.


Figure 5.Histopathology of the resected liver tumor. The liver tissue containes an abnormal number of fat vacuoles (upper left), while the fibrotic liver tissue adjacent to the well differentiated adenocarcinoma contains fewer fat vacuoles than the rest of the liver parenchyma.

DISCUSSION

Detection of a mass within a fatty liver can be difficult by CT. Irregular fatty infiltration can show a roundish or well circumscribed appearance, and may be solitary or multiple, simulating hepatic masses (2 -5 ). On the other hand, focal sparing in a diffusely fatty liver can be observed most frequently around the gallbladder bed, and its most common shape resembles a spot, band or ring (6 ). However, it can occur in other parts of the liver and show various shapes including a wedge, as was seen in the present case (7 ). Such atypical cases may simulate neoplasms on CT scans (1 ,8 -10 ). Conversely, some cases of true hepatic masses have been reported to mimic fatty infiltration (11 ) or focal sparing (12 ).

Focal fatty infiltration increases the echogenicity of the liver on US images and produces low attenuation on CT images. Focal sparing shows oppsite patterns on US and CT: decreased echogenicity on US images and high attenuation on CT images. On MR images, the fatty area is hyperintense on T1- and T2-weighted images (not heavily on the latter). Although standard MR sequences are less helpful for visualization and characterization of fatty infiltration, chemical shift images (opposed- and in-phase images) are quite useful for depicting fat distribution and assist the diagnosis of focal fatty infiltration or sparing (7 ). Onaya et al. (12 ) reported that the basic points suggesting the presence of fatty infiltration are: 1, the abnormal area does not show an overall mass effect; 2, the vessels are normally distributed and are evident in the abnormal area.

The present case revealed a wedge-shaped area with an almost linear boundary and did not show a mass effect in the non-enhanced CT and MR sequence, including chemical shift images. The dynamic contrast enhancement techniques, CTA and dynamic MR imaging, showed irregular enhancement in the abnormal area, which indicated disappearance of the normal vessel structure and was quite useful for diagnosing the metastatic tumor. CTAP showed a wedge-shaped ischemic area. It was suggested that the tumor caused this ischemia due to intrahepatic portal vein blockade. Pathological examination revealed fibrotic liver tissue adjacent to the tumor; this fibrotic tissue contained fewer fat vacuoles than the rest of the liver parenchyma. It was suggested that this fibrotic liver tissue corresponded to the area of focal sparing seen on CT and MR images. In conclusion, the present case was difficult to diagnose because the tumor was hidden within the area of focal sparing, and dynamic contrast enhancement techniques, including CTA, CTAP and dynamic MRI, were useful for diagnosis.

References

1. Arai K, Matsui O, Takashima T, Ida M, Nishida Y. Focal spared areas in fatty liver caused by regional decreased portal flow. Amer J Roentgenol 1988;151:300-2.

2. Baker ME, Silverman PM. Nodular focal fatty infiltration of the liver: CT appearance. Amer J Roentgenol 1985;145:79-80.

3. Kashihara T, Murata K, Tsubakimoto K, Ogawa R, Kashihara T, Murata K et al. Multifocal fatty infiltration of the liver: report of six cases. Nippon Igaku Hoshasen Gakkai Zasshi 1990;50:1063-7 (in Japanese).

4. Nishimoto H, Ohara S, Morita O, Kamiike O, Nishioka M, Yoshida S et al. A case of focal fatty liver difficult to distinguish from the liver metastasis of rectal cancer on CT. Jpn J Clin Radiol 1989;34:367-70. MEDLINE Abstract

5. Ortega M, Zambrano I, Jimenez M, Rios JJ. Fatty liver with malignant features. J R Soc Med 1990;83:805-6. MEDLINE Abstract

6. Chen K, Hirayama Y, Yunoki M, Hirano Y. Focal sparing around the gallbladder in fatty liver: a useful sign for the diagnosis of borderline cases by CT. Nippon Igaku Hoshasen Gakkai Zasshi 1989;49:146-52 (in Japanese). MEDLINE Abstract

7. Mitchell DG. Focal manifestations of diffuse liver disease at MR imaging. Radiology 1992;185:1-11. MEDLINE Abstract

8. Newman JS, Oates E, Arora S, Kaplan M. Focal spared area in fatty liver simulaing a mass: Scintigraphic evaluation. Dig Dis Sci 1991;36:1019-22. MEDLINE Abstract

9. Kissin CM, Bellamy EA, Cosgrove DO, Slack MSN, Husband JE. Focal sparing in fatty infiltration of the liver. Br J Radiol 1986;59:25-8. MEDLINE Abstract

10. McKenzie A, Gill G, McIntosh R, Hennessy O. Computed tomographic and ultrasound appearances of focal spared areas in fatty infiltration of the liver. Australas Radiol 1991;35:166-8. MEDLINE Abstract

11. Leifer DM, Chan TW. Liver metastases from ovarian cystadenocarcinoma masquarading on CT as lobar fatty infiltration. J Comput Assist Tomogr 1993;17:816-8. MEDLINE Abstract

12. Onaya H, Itai Y, Kurosaki Y, Saida Y, Ebihara R, Kuramoto K. Metastatic tumors in irregular fatty liver mimicking focal sparing. Rad Med 1994;12:69-73.

Received October 11, 1996; accepted January 10, 1997
For reprints and all correspondence: Motohisa Kato , Second Department of Surgery, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500 , Japan
Abbreviations: CT, computed tomography; MR, magnetic resonance; AST, aspartate aminotransferase; ALT, alanine aminotransferase; LAP, leucine aminopeptidase; [gamma]-GTP, gamma-glutamyltranspeptidase; CA19-9, cancer antigen 19-9; CTA, CT arteriogrphy; CTAP, CT during arterial portography; MRSA, methicillin-resistant Staphylococcus aureus.

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Copyright© Japanese Journal of Clinical Oncology, 1997.
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